volume 21, issue 6 | november 2017 - j-igu.in 21-6 (web)/igu 21-6 issue.pdf · basin, east godavari...

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Volume 21, Issue 6 | NoVemBeR 2017

Journal of Indian Geophysical UnionEditorial Board

Indian Geophysical Union Executive Council

Chief Editor P.R. Reddy (Geosciences), Hyderabad

PresidentProf. Shailesh Nayak, Distinguished Scientist, MoES, New Delhi

Associate EditorsB.V.S. Murthy (Exploration Geophysics), Hyderabad

D. Srinagesh (Seismology), Hyderabad

Nandini Nagarajan (Geomagnetism & MT), Hyderabad

M.R.K. Prabhakara Rao (Ground Water Geophysics), Hyderabad

Vice-PresidentsDr. Satheesh C. Shenoi, Director, INCOIS, Hyderabad

Prof. Talat Ahmad, VC, JMI, New Delhi

Dr. V.M. Tiwari, Director, CSIR-NGRI, Hyderabad

Dr. Sunil K. Singh, Director, CSIR-NIO, Goa

Editorial Team

Solid Earth Geosciences:Vineet Gahlaut (Seismology), New DelhiB. Venkateswara Rao (Water resources Management), HyderabadN.V. Chalapathi Rao (Geology, Geochemistry & Geochronology), VaranasiV.V. Sesha Sai (Geology & Geochemistry), Hyderabad

Marine Geosciences:K.S.R. Murthy (Marine Geophysics), VisakhapatnamM.V. Ramana (Marine Geophysics), GoaRajiv Nigam (Marine Geology), Goa

Atmospheric and Space Sciences:Ajit Tyagi (Atmospheric Technology), New DelhiUmesh Kulshrestha (Atmospheric Sciences), New DelhiP. Sanjeeva Rao (Agrometeorology & Climatoplogy), New DelhiU.S. De (Meteorology), PuneArchana Bhattacharya (Space Sciences), Mumbai

Editorial Advisory Committee:Walter D Mooney (Seismology & Natural Hazards), USAManik Talwani (Marine Geosciences), USAT.M. Mahadevan (Deep Continental Studies & Mineral Exploration), ErnakulumD.N. Avasthi (Petroleum Geophysics), New DelhiLarry D Brown (Atmospheric Sciences & Seismology), USA Alfred Kroener (Geochronology & Geology), GermanyIrina Artemieva (Lithospheric Structure), DenmarkR.N. Singh (Theoretical& Environmental Geophysics), AhmedabadRufus D Catchings (Near Surface Geophysics), USASurjalal Sharma (Atmospheric Sciences), USAH.J. Kumpel (Geosciences, App.Geophyscis, Theory of Poroelasticity), GermanySaulwood Lin (Oceanography), TaiwanJong-Hwa Chun (Petroleum Geosciences), South KoreaXiujuan Wang (Marine Geology & Environment), ChinaJiro Nagao (Marine Energy and Environment), Japan

Information & Communication:B.M. Khanna (Library Sciences), Hyderabad

Hon. SecretaryDr. Kalachand Sain, CSIR-NGRI, Hyderabad

Joint SecretaryDr. O.P. Mishra, MoES, New Delhi

Org. SecretaryDr. ASSSRS Prasad, CSIR-NGRI, Hyderabad

TreasurerMd. Rafique Attar, CSIR-NGRI, Hyderabad

MembersProf. Rima Chatterjee, ISM, Dhanbad

Prof. P. Rama Rao, Andhra Univ., Visakhapatnam

Prof. S.S. Teotia, Kurukshetra Univ., Kurukshetra

Mr. V. Rama Murty, GSI, Hyderabad

Prof. B. Madhusudan Rao, Osmania Univ., Hyderabad

Prof. R.K. Mall, BHU, Varanasi Dr. A.K. Chaturvedi, AMD, Hyderabad

Mr. Sanjay Jha, Omni Info, NOIDA

Mr. P.H. Mane, ONGC, Mumbai

Dr. Rahul Dasgupta, OIL, NOIDA Dr. M. Ravi Kumar, ISR, Gujarat

Prof. Surjalal Sharma, Univ. of Maryland, USA

Dr. P. Sanjeeva Rao, Advisor, SERB, DST, New Delhi

Dr. N. Satyavani, CSIR-NGRI, Hyderabad

Prof. Devesh Walia, North Eastern Hills Univ., Shillong

EDITORIAL OFFICEIndian Geophysical Union, NGRI Campus, Uppal Road, Hyderabad- 500 007

Telephone: +91 -40-27012799; 27012734; Telefax:+91-04-27171564E. mail: [email protected], website: www.j-igu.in

The Open Access Journal with six issues in a year publishes articles covering Solid Earth Geosciences; Marine Geosciences; and Atmospheric, Space and Planetary Sciences.

Annual SubscriptionIndividual ` 1000 per issue and Institutional ` 5000 for six issues

Payments should be sent by DD drawn in favour of “The Treasurer, Indian Geophysical Union”, payable at Hyderabad, Money Transfer/NEFT/RTGS (Inter-Bank Transfer), Treasurer, Indian Geophysical Union, State Bank of India, Habsiguda Branch, Habsiguda, Uppal Road, Hyderabad- 500 007A/C: 52191021424, IFSC Code: SBIN0020087, MICR Code: 500002318, SWIFT Code: SBININBBHO9.

For correspondence, please contact, Hon. Secretary, Indian Geophysical Union, NGRI Campus, Uppal Road, Hyderabad - 500 007, India; Email: [email protected]; Ph: 040 27012799, 272012734

CONTENTS

Editorial

S.No. Title Authors Pg.No.

1 Geophysical attributes to evaluate subsurface structural features using ground magnetic data in parts of Karimnagar district, Telangana

M. Laxminarayana, Ram Raj Mathur and S.P. Anand

457

2 Delineation of groundwater potential zones using geo-electrical surveys in SSW part of Yeleru river basin, East Godavari District, Andhra Pradesh

M. Subrahmanyam and P. Venkateswara Rao

465

3 An appraisal of the plate tectonic forces: Role of Gravitational Potential Energy (GPE) in the deformation of Indo-Eurasia collision zone

C.D. Reddy and Mahesh N. Shrivastava

474

4 Tsunami forces acting on ocean structures: A synthetic study

Mounica Jakkula, Harini Guruhappa, Manaswini Ganjam and Kirti Srivastava

482

5 Study of Effects of Basin Shape, Shape-Ratio and Angle of Incidence of SH-Wave on Ground Motion Characteristics and Aggravation Factors

Kamal and Komal Rani 490

6 Interpretation of Seismic data for thrust/fault identification using variance and inverse of variance attribute analysis

Mausam Gogoi and G.K. Ghosh

500

7 Analysis of Tectonically controlled Valley Floor morphology of the Central Segment of Sabarmati River Basin: An Integral approach using satellite images and GIS Techniques

Nisarg H. Bhatt and R.D. Shah

507

8 Paleoproterozoic magmatism in the Cuddapah basin, India; role of continental arc extensional tectonics in initiation and evolution of basins Paleoproterozoic segment

V. V. Sesha Sai, Vikash Tripathy, Santanu Bhattacharjee and Tarun C. Khanna

516

9 Dust storms and their influence on optical and chemical properties of aerosols along north-western Indo-Gangetic Plains

Disha Sharma and Umesh Kulshrestha

526

10 Types of Irrigation and Historical development-a comprehensive compilation

P.R.Reddy 535

News at a Glance 543

Technical News Raja Acharya 549

This is an open access Journal. One can freely DOWNLOAD contents from:

Website: www.j-igu.in

ISSN: 0257-7968 (Clarivate Analytics) ISSN: 0971-9709 (NISCAIR)

Approved as bimonthly ESCI journal by Clarivate Analytics Cited in Indian Citation Index (ICI), New Delhi

Recognized by UGC Evaluated by NISCAIR, New Delhi

Monsoon fluctuations

Mysterious Intraseasonal Oscillations in Monsoons India’s summer monsoon is a major event. The monsoon has long been studied by meteorologists, climatologists, and oceanographers hoping to understand and forecast its behaviour. One phenomenon in particular, the monsoon intra-seasonal oscillations (MISOs), has captured scientists’ interest. MISOs are alternating periods of heavy and minimal rainfall, each lasting for about a month or so and tending to follow a cyclical, northward shifting pattern from the equator to southern Asia. Although they were once believed to be a function of the tropical atmosphere, more recent studies have suggested that MISOs come from some kind of powerful atmosphere-ocean interaction. Li et al. examined the pathways of MISOs travelling across the Bay of Bengal, a region where the monsoon undergoes changes in intensity and frequency. They addressed the contribution from two variables: the depth of the mixed layer, which lies just below the sea surface, and the thickness of the barrier layer, which forms the bottom of the mixed layer. Using an ocean model with data from 2000 to 2014, the researchers investigated how these upper ocean processes affect sea surface temperature (and how variations in sea surface temperature, in turn, affect rain formation in the MISOs). An influx of freshwater from the monsoon, the researchers found, creates a shallow mixed layer and a thick barrier layer, causing dramatic fluctuations in sea surface temperature over the course of the season. What’s more, these air-sea interactions lead to the highly irregular rainfall patterns seen as the MISOs reach Asia. Using advanced models and checking them against satellite data allowed the researchers to pinpoint these driving forces behind MISOs with more precision. Their efforts promise to improve the accuracy of future simulations and forecasts of the MISOs that occur during India’s summer monsoon. (Source: Journal of Geophysical Research: Oceans, https://doi.org/10.1002/2017JC012692, 2017)

“Our earth is very old, an old warrior that has lived through many battles. Nevertheless, the face of it is still changing, and science sees no certain limit of time for its stately evolution. Our solid earth, apparently so stable, inert, changing and mobile is still evolving. Its major quakings are largely the echoes of that divine far-off event, the building of our noble mountains. The lava floods and intriguing volcanoes tell us of the plasticity, mobility, of the deep interior of the globe. The slow coming and going of ancient shallow seas on the continental plateaus tell us of the rhythmic distortion of the deep interior-deep-seated flow and changes of volume. Mountain chains prove the earth’s solid crust itself to be mobile in high degree. And the secret of it all—the secret of the earthquake, the secret of the “temple of fire,” the secret of the ocean basin, the secret of the highland—is in the heart of the earth, forever invisible to human eyes”.

- Reginald Aldworth Daly (1871 –1957) was a Canadian geologist.

Since Thomson Reuters (present Clarivate Analytics) intimated in 2014 that it would re evaluate performance of JIGU in 2017 to take a decision regarding granting SCOPUS accreditation, I have decided to bring out the soft copy of November issue before time so that all the six issues of volume 21 will be available for timely initiation of JIGU impact factor evaluation. To my request letter communicated to customer service wing of Clarivate Analytics about up gradation of JIGU as an SCI journal, I have received a detailed mail in third week of August from the concerned officer of customer service wing(Customer Support Representative, Customer Care - Asia Pacific, Clarivate Analytics).She has intimated that SCOPUS accreditation is no longer connected with Clarivate Analytics and JIGU performance evaluation would be taken up after completion of two years as ESCI journal. It is intimated by the Customer Support Representative ….. “with respect to your question about moving the journal to SCI, a journal selected for the WoS Core Collection’s ESCI (http://wokinfo.com/products_tools/multidisciplinary/esci/) will remain there for at least two years, before being considered for a potential move, out of ESCI, to one or more of our flagship citation indexes -- AHCI, SCIE, SSCI, SCI. This period of time allows us to, in part, monitor the journal’s citation activity and track timely delivery of content. In the meantime, inclusion in ESCI is a very important first step in the rigorous selection process required of the Collection’s principal citation indexes. A journal in ESCI is discoverable, citable, and indexed with the same detail as any other journal in WoS.” This development has added a new dimension to our efforts to get full fledged SCI status. Since the last 12 to 15 months interaction with Thomson Reuters/ Clarivate Analytics is being solely carried out by me with the assistance from the Organising Secretary of IGU. Because of this, there is a possibility that any change ( as desired earlier by me ) in the journal`s management at this juncture may affect JIGU up gradation plans. To avoid such a possibility I wish to continue till 31st March, 2018 (end of present editorial board two year term).I have requested Clarivate Analytics to take up evaluation of JIGU quality and performance in January, 2018 (2 year term of JIGU as ESCI journal will be completed by 31st, December, 2017). I sent above details to President of IGU and sought his permission to continue as Chief Editor of JIGU till 31st March, 2018. Few days before release of soft copy President agreed to my proposal. Since soft copy of November issue will be released in the first week of October and uploaded on to JIGU website before end of October, Clarivate Analytics can objectively evaluate JIGU performance during the last 4 years ( including 2 years as ESCI journal), without any hindrance. Even though I will

be constantly in touch with Clarivate Analytics I earnestly request help and support from IGU management to ensure success of our initiative. While the evaluation result will take some time, it is my duty to let our readers know about a positive and encouraging development. Indian Citation Index (ICI), a full-fledged accreditation channel recognised by University Grants Commission (UGC) has intimated us that JIGU is recognised by UGC as one of the quality journals published from India and papers published in it entail authors in meeting stipulated norms in submitting Ph.D, getting scholarships and recruitments. I do hope this positive development would help our young researchers.

In 2017 the long stretch of heat wave during April, May and first quarter of June sapped my energies considerably and troubled me very much in meeting my obligations to JIGU. Like me many ailing senior citizens suffered a lot. It is projected by number of research groups, from different parts of the earth that the heat wave trend noticed this year will become a regular feature from now onwards, with intensity increasing year after year. To bring in to light some useful information I give below details of some recent studies. It is time the vulnerable segments of our population (children and senior citizens) plan from now onwards to face next year heat wave.

More Intense, More Frequent, and Longer Lasting Heat Waves

A global coupled climate model, prepared by two US scientists, shows that there is a distinct geographic pattern to future changes in heat waves. The researchers examined future behaviour of heat waves in a global coupled climate model, the Parallel Climate Model (PCM). This model has a latitude-longitude resolution of about 2.8° in the atmosphere and a latitude-longitude resolution of less than 1° in the ocean, and it contains interacting components of atmosphere, ocean, land surface, and sea ice. The PCM has been used extensively to simulate climate variability and climate change in a variety of applications for 20th- and 21st century climate. Model results for areas of Europe and North America, associated with the severe heat waves in Chicago in 1995 and Paris in 2003, show that future heat waves in these areas will become more intense, more frequent, and longer lasting in the second half of the 21st century. Observations and the model show that present-day heat waves over Europe and North America coincide with a specific atmospheric circulation pattern that is intensified by ongoing increases in greenhouse gases, indicating that it will produce more severe heat waves in those regions in the future. Heat waves are generally associated with

Editorial

specific atmospheric circulation patterns represented by semi stationary 500-hPa positive height anomalies that dynamically produce subsidence, clear skies, light winds, warm-air advection, and prolonged hot conditions at the surface (P.S: Geopotential height is a vertical coordinate referenced to Earth’s mean sea level — an adjustment to geometric height (elevation above mean sea level) using the variation of gravity with latitude and elevation. Thus it can be considered a “gravity-adjusted height”. One usually speaks of the geopotential height of a certain pressure level, which would correspond to the geopotential height at which that pressure occurs. “500 hPa” tells us that the height map is at the 500 hectoPascal pressure level. hPa is the International standard unit).

The 500-hPa height anomalies are most strongly related to positive warm season precipitation anomalies over the Indian monsoon region and associated positive convective heating anomalies that drive mid-latitude teleconnection patterns in response to anomalous tropical convective heating in future climate. Thus, areas already experiencing strong heat waves could experience even more intense heat waves in the future. But other areas could see increases of heat wave intensity that could have more serious impacts because these areas are not currently as well adapted to heat waves.

(Source: Gerald A. Meehl and Claudia Tebaldi. REPORTS 996 13 AUGUST 2004 VOL 305 SCIENCE; www.sciencemag.org/cgi/content/full/305/5686/994/DC1)

A scientific observation reveals human being’s role in record heat waves in China. A new study suggests that even hotter events will follow unless greenhouse gases emissions are reduced considerably. Details are given below.

Are Humans to Blame for Worsening Heat Waves in China?

At least 40 people died during China’s record-breaking 2013 heat wave, when temperatures spiked to more than 105°F. The deadly event was just one of a string of intensifying heat waves that have hit the country over the past 50 years, and a new study finds that these events can be attributed in part to human-made climate change. Under business-as-usual carbon emissions, such extreme temperatures will become the new normal across roughly 50% of China’s landmass, the authors warn.

Sun et al. investigated heat waves across China from 1961 to 2015 using daily temperature and precipitation data from more than 2400 monitoring stations across the country. Then, the researchers used computer models to assess past and future changes in heat waves. In some simulations, they included only natural drivers of heat

waves and drought, including climatic oscillations such as El Niño, and volcanic eruptions. In other simulations, they included known human contributions to heat waves, through warming caused by greenhouse gas emissions. The simulations that most closely resembled China’s real heat wave history were those that included the human influences, showing that natural causes alone were not enough to explain the country’s observed heat waves. In fact, including factors such as rising greenhouse gas emissions from burning fossil fuels led to more than a tenfold increase in the likelihood of the most intense heat waves occurring again in the future, the scientists found.

Under even a “moderate” future emissions scenario, the Intergovernmental Panel on Climate Change’s Representative Concentration Pathway 4.5, these once unusual heat waves will occur more frequently, last longer, reach higher temperatures, and occur in more regions of China, the authors expect. (Source: Geophysical Research Letters, https://doi.org/10.1002/2017GL073531, 2017).

Compared to China we are in no way better, as per a recent study.

Indian Scenario:

The mean temperature across India has risen by 0.5 degree C during the period 1960 and 2009 and this has led to a significant increase in heat waves in the country. Based on modelling studies, researchers from Indian Institute of Technology (IIT) Bombay, Indian Institute of Technology (IIT) Delhi and the University of California, Irvine have found that when the summer mean temperature during this period increased from 27 to 27.5 degree C, the probability of a heat wave killing in excess of 100 people shot up from 13% to 32% — an increase of 146%. For instance, there were only 43 and 34 heat-related fatalities in 1975 and 1976 respectively when the mean summer temperature was about 27.4 degrees C. But in 1998, at least 1,600 people died due to heat wave when the mean summer temperature was more than 28 degrees C. Similarly, when the average number of heat wave days in the country increased from six to eight, the probability of heat wave-related deaths increased from 46% to 82% — a 78% increase. The average number of heat wave days between 1960 and 2009 was 7.3 per year. In the last four years (2014-2017), India has witnessed as many as 4,620 deaths caused by heat wave, out of which 4,246 people died in Andhra Pradesh and Telangana alone. The figures according to the Ministry of Earth Sciences paint a grim picture for the future.

With more than 2000 dead in a year in extremely hot weather across India, a recent Indian Institute of Technology-Bombay study predicts more intense and longer

heat waves, more often and earlier in the year in future. In a changing climate, newer areas, including large swathes of southern India and both coasts – hitherto unaffected – will be severely hit, resulting in more heat stress and deaths (as per the publication in the journal Regional Environmental Change-2013). From climate model projections, researchers have pointed out that there is a possibility of high occurrences of heat waves in South India in future (which is already witnessing higher temperatures). Such a forecast is in line with global and Indian studies. Other recent assessments have predicted that intense heat waves will grow with rising global temperatures, up by 0.9°C since the start of the 20th century. The Intergovernmental Panel on Climate Change records that from 1906 to 2005, the mean annual global surface-air temperature increased by about 0.74°C (land-surface air temperature increases more than sea-surface temperature). As a result, there will be significant changes in the frequency and intensity of extreme weather events, including heat waves, as IPCC’s 2014 report warns. Even though it is difficult to directly link present single-year high heat-wave occurrence to climate change, however, there is a good possibility that such heat waves may indicate the adverse impacts of global warming. A rise in the frequency and intensity of heat waves would increase the risk of heat stroke and heat exhaustion, and even deaths from hot weather, the IIT-B team predicted, echoing concerns raised by IPCC scientists. With a large proportion of people without sufficient access to water, electricity and primary healthcare facilities, India could be very vulnerable to heat waves, the study noted. Heat waves are an important class of climate hazard that may have serious consequences on health and ecosystem, keeping existing vulnerabilities of population in mind. The study highlights the need to better understand the direct temperature-related consequences in order to develop better adaptation strategies. The IIT-B study is important because it is particularly exhaustive. The team projected intensity, duration and frequency of severe heat waves for low, middle and high range rates of climate change as shown in long-term projections called representative concentration pathways( RCPs).

As per the study Future heat zones will be South India and both coasts. Under the most probable-case and the worst-case scenarios, 2070 onward, there could be an increase in intensity, duration and frequency of severe heat waves. In particular, a large part of southern India, east and west coasts, which have been unaffected by heat waves, are projected to be severely affected after 2070. Severe heat waves are expected to appear early in future years, starting in early April, under the worst-case scenario. A sizeable

part of India is also projected to be exposed to extreme heat-stress conditions, intensification of heat wave and heat-stress leading to increased mortality. Heat-stress is a condition in which the body cannot cool off to maintain a healthy temperature–resulting in rashes, cramps, dizziness or fainting, exhaustion, heat stroke, and a worsening of existing medical conditions (P.S: during mid April to first quarter of June I suffered due to all these ill effects). (Source: https://www.civil.iitb.ac.in/~subimal/&https://journosdiary.com/2017/06/10/heat-waves-deaths-india/) Study by the Long Range Forecasting division at the National Climate Centre in Pune, at the India Meteorological Department, has shown a noticeable increase in the heat wave and severe heat-wave days over the country during 2001-2010– the warmest decade recorded – compared to the previous four decades. The IMD team used heat-wave information from 103 stations on the Indian mainland during the hot-weather season of March to July over the past 50 years (1961-2010). They examined various statistical aspects of heat waves and severe heat waves, such as long-term climatology, decadal variation, and long-term trends.IMD team also found heat waves linked with El Niño-Southern Oscillation, denoting fluctuating ocean temperatures in the equatorial Pacific, known for its global impact. The study indicates the complexity of future weather predictions. They found that heat waves of eight or more days peak a year after the El Nino (warm) phase of this cycle and are at a minimum a year after the La Nina (cool) phase. (Source: D. S. Pai et al (2013), http://www.scidev.net/filemanager/root/site_assets/sa/long_term_climatology_and_trends_of_heat_waves_over_india_during_the_recent_50_years_1961-2010_.pdf)

I have specifically selected this topic to advocate the necessity to safeguard the interests of all those senior citizens who are beyond 65 years of age. Youngsters, especially those who are physically capable should show needed empathy towards this segment of our population, who have served our country in a significant way when they were young and energetic.

In this Issue

In the sixth and last issue of 2017 (Volume 21), there are 10 research articles, an “editorial”, a “News at a Glance” and one Technical News.

Hope you would enjoy the contents and suggest ways and means to enhance quality of the manuscripts. While expressing my sincere thanks to one and all I solicit your continued support to JIGU.

P.R.Reddy

Quotes on Heat wave “Nothing is sudden in nature: whereas the slightest storms are forecasted several days in advance, the destruction of the world must have been announced several years beforehand by heat waves, by winds, by meteorites, in short, by infinity of phenomena”.

- Nicolas Antoine Boulanger (1722 – 1759) was a French philosopher ***

“Our analysis shows that, for the extreme hot weather of the recent past, there is virtually no explanation other than climate change. The odds that natural variability created the extremes are minuscule, vanishingly small. To count on those odds would be like quitting your job and playing the lottery every morning to pay the bills”.

-James Hansen (1941--) is an American adjunct professor at Columbia University.***

“Major heat wave in India - 122 degrees . It was so hot people in India were sweating like Americans waiting to hear if their job is being outsourced to India”.

- Jay Leno (1950--) is an American comedian and television host. ***

“Climate change is a global problem. The planet is warming because of the growing level of greenhouse gas emissions from human activity. If this trend continues, truly catastrophic consequences are likely to ensue from rising sea levels, to reduced water availability, to more heat waves and fires”.

- Malcolm Turnbull (1954--) the former Prime Minister of Australia ***

“For the sake of our children and our future, we must do more to combat climate change. Now, it’s true that no single event makes a trend. But the fact is the 12 hottest years on record have all come in the last 15. Heat waves, droughts, wildfires, floods-all are now more frequent and more intense. We can choose to believe in the overwhelming judgment of science-and act before it’s too late”.

- Barack Obama (1961--) 44th President of USA

Geophysical attributes to evaluate subsurface structural features using ground magnetic data in parts of Karimnagar district, Telangana

457

Geophysical attributes to evaluate subsurface structural features using ground magnetic data in parts of Karimnagar district,

TelanganaM. Laxminarayana1, Ram Raj Mathur*2 and S.P. Anand1

1Indian Institute of Geomagnetism, New Panvel (W), Navi Mumbai 4102182Center for Exploration Geophysics, Osmania University, Hyderabad 500007

*Corresponding Author: [email protected]

ABSTRACTTo decipher both the shallow and deeper features related to Godavari and Kaddam Rivers and the lineaments present in the eastern margin of Deccan Volcanic Province (DVP) in the Indian Precambrian shield, a total field ground magnetic survey was carried out around Jagtial town, Karimnagar district, Telangana. The total field anomaly map based on 653 magnetic observations acquired at 300 m station interval reveals a combination of NE-SW, NNE-SSW and NW-SE trends, which coincide with the trends in the earlier observed aeromagnetic anomaly map of the region. The Reduction-to-pole (RTP) map also reveals lineaments that trend in the NW–SE and NE–SW with varying wavelength and amplitude. From the analysis of magnetic data we have mapped the north-west extension of the Kinnerasani Godavari Fault (KGF). From our observations the Kaddam Lineament Zone (KLZ) has been deciphered to be bounded by the Kaddam Lineament to the north and Kinnerasani Godavari Fault (KGF) to the south forming a small linear basin. Both the Kaddam Lineament and the KGF appear to be deep seated lineaments/faults. Also, the north-west extension of charnockites within the KLZ, which form the basement for the deposition of Proterozoic sediments, have been delineated. Results of the present study detailed in this paper may help to understand better some of the structural features in this region, which had not been ascertained in earlier studies.

Key words: Eastern Dharwar Craton, Geophysical attributes, Total Magnetic Field, Ground magnetic data, Kaddam Lineament, Kinnerasani Godavari Fault, Karimnagar Granulite Belt, Deccan Volcanic Province (DVP).

INTRODUCTION

Peninsular India comprises several cratons surrounded by mobile belts whose geological history dates backs to almost three billion years. The major cratons include the Dharwar and Singhbhum cratons separated from the Bastar craton, respectively by the Godavari and Mahanadi grabens. The NW-SE trending Pranhita-Godavari Gondwana graben marks a zone of recurrent rifting. A belt of high grade granulitic rocks were delineated along the northern and southern shoulders of the Pranhita-Godavari Gondwana graben of which the southern granulitic belt was termed Karimnagar Granulite Belt (KGB) (Rajesham et al., 1993; Acharyya, 1997; Anand and Rajaram, 2003). The Karimnagar Granulite Belt, northern part of the Eastern Dharwar craton, extends for about 150km with an approximate width of 20km. In addition the southern shoulder of the Godavari Graben is also traversed by several NW-SE and NE-SW trending lineaments that may be associated with different tectonic regimes. Among these the ~300km long Kaddam mega lineament (GSI, 2000), which runs NW-SE from Narmada-Tapti up to the Godavari graben is the most prominent. Much of the studies of the KGB and the lineaments, including the Kaddam lineament, are based on surface geology, geochronology and remote

sensing data, which provided a fairly good picture of the surface and near surface terrain characterization.

To determine trends, extents, and geometries of structural features magnetic data has successfully been used to interpret the subsurface geology. Earlier studies have attributed various deep crustal anomalies and the asymmetric nature of the geophysical anomalies in the Godavari graben from gravity, magnetic, magnetotelluric and DSS observations (Kaila et al., 1990; Mishra et al., 1987; 1989; Mishra, 2011; Murthy and Babu, 2009; Gokarn et al., 2001; Sarma and Krishna Rao, 2005; Chakravarti et al., 2007; Naganjeneyulu et al., 2010). From the gravity data of the Godavari-Pranahita sub-basin Mishra et al., (1989) opined that the main fault in the northeastern margin of the rift valley stretched up to Bhadrachalam as a sharp gradient has signature in the Bouguer anomaly. From the joint inversion of gravity and magnetic data across the Godavari Basin, Sarma and Kirshna Rao (2005) suggested that the main graben formation is Post-Proterozoic with a maximum thickness of the sediments to be around 7 km. However, the relation of Kaddam fault with the Godavari graben is not ascertained in earlier studies and requires further investigations (Sangode et al., 2013). In the present paper an attempt is made to understand the subsurface continuation and lateral extension of the lineaments in the

J. Ind. Geophys. Union ( November 2017 )v.21, no.6, pp: 457-464


458

region and to extract subsurface lithological information, using magnetic data.

Geological Set-Up

The area under investigation is located at the boundary of Adilabad and Karimnagar Districts, Telangana State. This area lies in the Eastern Dharwar Craton bordering the Godavari Graben. Figure 1 shows a generalized geologic and tectonic map of the study region (after Som et al., 2010; GSI, 2000; Bhuvan, ISRO/NRSC, 2014). Major part of the region is occupied by Tonalite/Granodiorite suite of acidic rocks belonging to the Proteozoic age. These rocks at places contain enclaves of Archean metasediments represented by Banded Hematite Quartzite (BHQ) (Kameswara Rao, 1989). These metasedimentary enclaves have either a sharp or diffusive boundary with the enveloping granitic (Som et al., 2010) country rock. Arkose and limestones are found along a narrow patch running in a NW-SE direction. The region of study falls under the KGB (Rajesham et al., 1993, Anand and Rajaram, 2003; Rajaram et at, 2000) with the most predominant rock being coarse grained unfoliated charnockites (Santosh et al., 2004).

The KGB rocks are remnants of an Archaean supracrustal granite association, which underwent granulite grade metamorphism around 2.5 Ga. Highly exposed granite-gneisses, charnockites, banded magnetite, quartzite and dolerite dykes, gneisses and basic granulites occupy the eastern sector of the study region (Prakash, 2013). Two major fracture/lineament trends viz. NW-SE and NE-SW are visible in the region. Among these the major NW-SE lineament is the Kaddam Lineament. Sangode et al., (2013)

reported that the Kaddam mega-lineament along with its associated structural features caused the Godavari River to change its direction into four sharp bends and finally connecting with the Kaddam River along the Kaddam fault. The Kaddam mega-lineament extending northwest up to the junction of seismically active region of Tapi and Purna faults and to the seismically active region of Bhadrachalam towards the south, is considered to be a neotectonic fault (GSI, 2000). Several NW-SE and NE-SW trending doleritic dykes intrude the area. The area is drained mainly by the Godavari River and its tributaries of which the Peddavagu River flows in the western part of the study region.

METHODOLOGY

The study area lies between 18º52’ to 19º06’ N latitudes and 78º46’ to 79º06’ E longitudes. The total magnetic field (F) was measured at 653 observation points with an average interval of 300 m (Figure 2) using a Proton Precession Magnetometer of resolution 0.1 nT. Figure 2 is a histogram equalized total intensity (F) crustal anomaly map prepared after removing the main and external fields from the observed magnetic data. IGRF-2015 was utilized to account for the main field at each observation point. For the representation of the external field variations, the magnetograms corresponding to survey period (i.e., date and time) were utilized from the Magnetic Observatory data of IIG, Nagpur.

The analysis of total field magnetic anomalies is complicated as the ambient field direction changes with location and the magnetic anomalies may not directly be placed over the causative bodies (Blakely, 1995). Hence,

Figure 1. Geology and tectonic map in the Godavari Sub-Basin (after Bhuvan, ISRO/NRSC, 2014; http://bhuvan.nrsc.gov.in/gis/thematic/index.php).


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Reduction-To-Pole (RTP) of the magnetic data was carried out to circumvent the bipolar nature of the anomalies such that the anomalies are placed directly over the source (Silva, 1986). The study area being in low magnetic latitudes, the pseudo-inclination method (MacLeod et. al., 1993; Xiong Li, 2008) has been applied, wherein a pseudo-inclination higher than the actual inclination is specified to suppress the amplitude of the noise along the direction of declination. Since the airborne magnetic data was collected in the entire study region to understand the distribution of magnetic sources in the study region the analytic signal map of airborne data was also utilized.

RESULTS AND DISCUSSIONS

The magnetic anomaly map shows a combination of varying amplitudes and trends suggesting differing lithologies at varying depths. Based on this different lineaments in NNW-SSE and NW-SE directions with few lineaments trending in NE-SW have been marked in Figure 3. One major lineament (AA’) trending NW-SE, restricting the north-eastern continuation of several minor lineaments, presumably depicts the regional attribute of the Kaddam lineament/fault. Another NW-SE trend BB’ can also be delineated from the anomaly map. A small NS trending

Figure 2. Total Magnetic Field Anomaly Map showing the observation locations in the area.

Figure 3. Total Magnetic Field Anomaly Map showing the regional attributes in the prominent NW-SE trend and the NS trend.


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anomaly (CC’) is observed parallel to River Peddavagu. Several high magnetic closures observed throughout the study area could be due to charnockite/pyroxinite/sillimanite gneisses.

As the study area is covered by reserved forest, hills and inaccessible terrain, several data gaps of more than few kilometres exist in the ground magnetic coverage. The aeromagnetic data (Figure 4) (GSI, 1995, Rajaram et al., 2006) acquired at 1500 m altitude and with a line spacing of 4km has been utilized to obtain a regional picture of the distribution of the magnetic sources and the lineaments. The total field anomaly map generated after applying necessary corrections is shown in Figure 4 as a histogram equalized colour image. Butterworth low pass filter with cut-off wavelength of 2km is used for removing some high frequency noise in the data. Much of the long wavelength

anomalies seen in the ground magnetic anomaly map are reflected in the aeromagnetic data. The lineaments delineated from ground magnetic anomaly map (Figure 3) on aeromagnetic data are also observed. It can be seen that the major lineaments like Kaddam lineament (AA’ and BB’) are well reflected and its continuation from northwest to southeast can be clearly traced in the aeromagnetic map. The ground magnetic data (Figure 3), gives an impression that two NE-SW minor lineaments are restricting the southward extension of the Kaddam lineament. Its extension is visible in the aeromagnetic map suggesting that the minor lineaments are at relatively shallow depth levels. In addition to the lineaments, the aeromagnetic map depicts a high amplitude bipolar anomaly towards the north-central part, which can possibly represent an iron ore body (GSI, 2010).

Figure 4. Aeromagnetic map of the study area in the Godavari Graben (after GSI, 1995).

Figure 5. RTP Map of (a) ground magnetic data (b) aeromagnetic data.


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The anomalies in the RTP maps (computed from ground magnetic data and aeromagnetic data (Figure 5), using respective inclination and declination of the ambient field depending on the epoch during which data is collected) reveal a combination of NW–SE and NE–SW trends with varying wavelength and amplitude signifying different levels of occurrence of the sources.

A slight shift in the location of anomalies as compared to total field anomaly map can be observed in the RTP map. From Figure 3 the NW-SE trend of Kaddam lineament (AA’) and BB’ is clearly evident as in the RTP map of both ground data and aeromagnetic data. Some of the high frequency closures seen in the ground magnetic RTP map (Figure 5a) may not be visible in the aeromagnetic RTP map (Figure 5b) as the aeromagnetic data was collected at a higher altitude

and hence these might have been filtered. The magnetic lows in the RTP map overlie the sedimentary belt of Arkose and Limestone formations. In the RTP map of the ground magnetic data, this low is divided into two distinguished lows but the same appears as single low in the aeromagnetic RTP map. This suggests the possibility of a fault/lithological contact at the shallow level while in the deep it appears as single unit. A bipolar anomaly seen in the central part of the RTP aeromagnetic anomaly map (Figure 5b) depicts the location of mapped magnetite ore (GSI, 2010), as a single magnetic high located over the source.

As the RTP map constitutes anomalies ranging in amplitude as well as wavelength, it is possible to separate out the magnetic anomalies arising from different depth levels. To have an understanding of the deeper sources, the RTP

Figure 6. Upward Continued Magnetic Map for 3 km of (a) ground magnetic data (b) aeromagnetic data.

Figure 7. (a) Distribution of (a) magnetic sources (b) major lineaments and rock types.KLn – Kaddam Lineament; KGLn – Kinnersani Godavari Lineament; C – Charnokites; Ir – Iron ore


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of ground and airborne magnetic data is upward continued to 3km (Figure 6) (Telford et al., 1993). Continuation maps generated can be qualitatively used to construct a structural model of the region. Several high frequency and high amplitude anomalies representing charnockite/pyroxinite/sillimanite gneisses evident in the anomaly map (Figure 3) are absent in this RTP map suggesting they are at shallow depths. As the level of upward continuation increased, the NW-SE trends including the Kaddam lineament, is more prominent suggesting that the basic Precambrian structure in the region under study trends NW-SE representing the regional Dharwar-Bastar-Godavari Graben trends. We have not reproduced the downward continued anomaly maps, as in the study region much of the sources responsible for the magnetic signatures are either exposed or at very shallow levels so that the downward continued maps just reflect high amplitude closures. The analytic signal map of aeromagnetic data (Figure 6a) shows the distribution of magnetic sources in the study region.

It can be seen that most of the sources are either to the south or north of the Kaddam lineament. Higher amplitude maxima suggest strong magnetic carriers in the subsurface.

The NW-SE trend, in accordance with the trend of the Godavari graben and the Dharawar craton, appears to be the dominant trend in the study area as these lineaments are seen at all levels of upward continuation. Minor NE-SW trends can be attributed to faults associated with river (for eg. Peddavagu) and these trends appear to be at shallow levels owing to their absence in the upward continued maps.

From a combination of the anomaly map and its transformation, we have generated an interpreted map showing the delineated lineaments/faults and also the distribution of magnetic sources in the study region (Figure 7), which shows two NW-SE trending lineaments of which the northern one is the Kaddam Fault/Lineament (GSI, 2000). From the present study we have delineated another NW-SE lineament (BB’) south of the mapped Kaddam lineament. The sismo-tectonic map of the Godavari graben and adjoining regions (GSI, 2000) shows a NW-SE fault termed Kinnerasani Godavari Fault (KGF), south of the Kaddam Fault, which lies towards the southeast of the study region. Hence, we conclude that the delineated NW-SE lineament (BB’) is the northwest continuation of the KGF. On comparison with the geology map, it can be seen that all sedimentary rocks including Arkose and limestones are constrained to lie between these two lineaments/faults. We have assigned the nomenclature for this region bounded by Kaddam Lineament and KGF as Kaddam Lineament Zone (KLZ), which probably represents the northward extension of the Pakhal sedimentation. Sangode et al., (2013) extensively studied the Precambrian terrain of Adilabad and Karimnagar districts about the Quaternary reactivation of old fracture system associated with the

Kaddam lineament /fault by field studies. Further, the northern and southern extension of the Kaddam lineament is associated with seismically active regions supporting the active tectonic role of the Kaddam Lineament.

From Figure 7b it is clear that the major part of the KLZ is occupied by highly magnetic sources. Charnockite exposures are seen towards the southeast end of the KLF (Figure1). Previous studies including magnetic anomaly interpretation and susceptibility measurements (Ramachandran, 1990, Murthy and Rao, 2001) have shown that Charnockites are highly magnetic. Hence, we infer that the magnetic sources occurring within the Kaddam Lineament Zone is the subsurface continuation of charnockites. It was previously inferred that the linear belt of magnetic sources along the shoulders of the GG, from south of Adilabad to Khammam are exposed and buried charnockites (Anand and Rajaram, 2003) probably forming the basement for the deposition of Proterozoic sediments. From this detailed study, it can be further confirmed and refined that high grade granulitic rocks (Charnockites) occur in patches along the shoulder of Godavari Graben, even though it appears as a continuous belt when the area is looked from a regional perspective. Studies by England and Thompson (1984) have suggested that high-grade metamorphism is related to crustal thickening during a compressive regime. Hence, it appears that a compressive scenario between the Dharwar and Bastar cratons existed in the Precambrain (?) times, which resulted in the exhumation of these high grade granulitic rocks that usually form at high temperature and relatively higher pressure. Laboratory studies (Ramachandran, 1990) revealed that charnockites have undergone retrograde metamorphism and depleted magnetite content. These alterations tend to show low susceptibilities compared to charnockites that have undergone prograde metamorphism. During prograde metamorphism Fe-Ti oxides are produced at the expense of silicate assemblages. Rajaram and Anand (2014) have shown that charnockites that have been affected by intrusives during a later period show up as magnetic sources while those not associated do not show considerable magnetic anomalies. This is due to the fact that magnetic mineralogy (magnetite content) of the protolith that has undergone tectono-thermal alteration due to sporadic younger intrusive tends to increase the magnetite content of the protolith due to prograde metamorphism, thereby increasing the magnetization that can be easily mapped using the aeromagnetic data. There are several intrusives in the form of doleritie dykes, gabbro plutons etc., reported from the study area (Rajesham et al., 1993). Due to these instrusions the high grade metamorphic rocks might have undergone prograde metamorphism in the later periods thereby increasing the magnetite content and susceptibility which are being mapped by the ground and aeromagnetic surveys.


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CONCLUSIONS

Ground magnetic surveys were conducted in the Jagital and Karimnagar Districts, Telangana. These studies have helped to delineate several major and minor faults in the region of which the NW-SE tending Kaddam fault/ lineament is prominent. The north-westward extension of the Kinnerasani Godavari Fault (GSI, 2000) was mapped. From our studies the area bounded by the Kaddam Lineament to the north and Kinnerasani Godavari Fault (KGF) to the south, termed as the Kaddam Lineament Zone (KLZ), is attributed to a small linear basin facilitating deposition of the Proterozoic sediments. The subsurface, north west extension of charnokites within the KLZ forming the basement for the deposition has been marked. Both the Kaddam Lineament and the KGF appear to be deep seated faults. Further, the recent earthquakes in the Bhadrachalam region provide evidence of the seismic activity in this region, suggesting the necessity to monitor the weaker tectonic boundaries in this region.

ACKNOWLEDGEMENTS

The authors are deeply indebted to Prof. D.S Ramesh, Director IIG, for taking personal interest and granting permission to publish this work. Fruitful discussion with Dr. Gautam Gupta, IIG is thankfully acknowledged. Thanks are due to Dr. M.R.K.Prabhakara Rao for reviewing the manuscript and useful suggestions. The authors wish to thank Prof. B.V.S. Murty, for his patient reading of the manuscript, objective evaluation and useful suggestions to enhance the quality of the presentation. Dr. P. R. Reddy, Chief Editor of JIGU, deserves special thanks for his guidance in finalizing the paper and apt handling of editing. Thanks are due to Shri B.I. Panchal, IIG for drafting the figures.

Compliance with Ethical Standards

The authors declare that they have no conflict of interest and adhere to copyright norms.

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“The mineral world is a much more supple and mobile world than could be imagined by the science of the ancients. Vaguely analogous to the metamorphoses of living creatures, there occurs in the most solid rocks, as we now know, perpetual transformation of a mineral species”.

- Pierre Teilhard de Chardin (1881 – 1955) a French idealist philosopher and Jesuit priest ***“Exploration is really the essence of the human spirit”.

- Frank Borman (1928--) is a retired United States Air Force pilot and NASA astronaut ***“If you go to work on your goals, your goals will go to work on you. If you go to work on your plan, your plan will go to work on you. Whatever good things we build end up building us”.

- Jim Rohn (1930 – 2009) an American entrepreneur, author and motivational speaker ***“Exploration is the engine that drives innovation. Innovation drives economic growth. So let’s all go exploring”.

Edith Widder (1951--) is an American oceanographer and marine biologist, ***

“I’m a storyteller; that’s what exploration really is all about. Going to places where others haven’t been and returning to tell a story they haven’t heard before”.

- James Cameron (1954--) is a Canadian filmmaker, engineer and philanthropist ***“There’s a constant tension in climbing, and really all exploration, between pushing yourself into the unknown but trying not to push too far. The best any of us can do is to tread that line carefully”.

- Alex Honnold (1985--) is an American rock climber

Delineation of groundwater potential zones using geo-electrical surveys in SSW part of Yeleru river basin, East Godavari District, Andhra Pradesh

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Delineation of groundwater potential zones using geo-electrical surveys in SSW part of Yeleru river basin, East Godavari District,

Andhra PradeshM. Subrahmanyam* and P. Venkateswara Rao

Department of Geophysics, Andhra University, Visakhapatnam *Corresponding Author: [email protected]

ABSTRACTData of 40 Vertical Electrical Resistivity soundings covering an area of about 144 square kms located in SSW part of Yeleru river basin, East Godavari district provided by Andhra Pradesh state Ground Water department was analyzed to delineate potential sources of ground water, its extent and depth of water table. The study revealed mainly a three layer subsurface with top layer consisting of clay/lateritic gravel, followed by the sandstones. The general geology of the study area is Rajahmundry sandstone. Saturated sandstone with a resistivity range of 10-50 Ωm extending to a maximum depth of approximately 135 m forms the major aquifer, while layers with less than 10 Ωm may be possibly due to high clay content and hence poor aquifers. The fence diagrams and geoelectric sections reveal potential aquifers in the northern part of the region dominated by a thickness of 21-50m with a small patch showing a thickness above 50m and clay dominated zones in the southern part of the region, which are unevenly distributed. Thus, the study provides vital clues on the distribution and thickness of the aquifer, which helps to decide the type of well to be built (dug well, bore well) in future groundwater exploration/ exploitation programs.

Key words: Yeleru river basin, Vertical Electrical Soundings, Groundwater potential zones, Fence diagram, geo electric sections.

INTRODUCTION

Yeleru River is one of the major streams in East Godavari district. The basin area covers different geological formations like Flood plains, Rajahmundry sandstones, Tirupati sandstones, Charnockites and Migmatite group of rocks including Deccan traps. The present study is confined to the Rajahmundry sandstone formations in the basin area. This study area located between 17.000 to 17.130 N

latitudes and 82.000 to 82.170 E longitudes spread over an area of 144.224sq.km (Figure 1) covers the villages around Peddapuram mandal, which is an irrigation command area. The major crops in the area are Tapioca, Rice and Sugar cane (Groundwater Brochure, 2013). The topography of the area varies from 33 to 81m above mean sea level. The average annual rainfall of the district is about 1280 mm (East Godavari district web portal), of which more than half contributed by South-West monsoon. Figure 2 shows the total annual rainfall during six years (2009-2014). This chart also indicates total maximum rainfall of 1909 mm during the year 2010 (much above annual average of 1280 mm), which decreased from 2012 onwards touching a low of 632 mm in 2014. This has resulted in decline in groundwater levels in all the three study blocks with maximum difference in Ramesampeta from 5.29m in the year 2013 to 12.62m in 2014. Due to the heavy demand of water for irrigation, people looked for deeper groundwater to meet their requirements.

Among all the geophysical methods the resistivity techniques especially the Vertical Electrical Sounding (VES) method is widely used for investigating subsurface layer parameters and groundwater potential (Jagadeswara Rao, 2003; Hardianshah and Abdul Rahim, 2013). This method was found suitable for hydro-geological surveys in sedimentary rocks (Kelly and Stanislav, 1993; Hadi, 2009). In sedimentary rocks, the resistivities of the interstitial fluid are probably more important than that of the host rock. Resistivity for sandy material is about 100Ωm and decreases with increasing clay content to about 40Ωm and the values decrease further to 1-10Ωm for those more typical of clay (Reynolds, 1987a; Majumdar and Das, 2011). In the present study, a detailed investigation has been made to identify the ground water potential zones in the study area using electrical resistivity sounding data.

Hydrogeology of the Study Area:

Groundwater in the study area occurs under phreatic and semi confined conditions and the hydro geological regime of the area is influenced by the Yeleru River. There are three observation wells, which have been monitored for six years from 2009 to 2014 during both pre monsoon and post monsoon. These three open wells show depths of water level of 24m at Peddapuram, 16m at Ramesampeta and 8m at Katravulapalli. As the infiltration rate is high in sandstone formations, the depth to water level has been



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raising abruptly during post monsoon in all wells (Figure 3). Very Shallow water levels were clearly observed during post

monsoon of 2010, 2012 and 2013 wherein the water levels in these three years were much deeper during pre-monsoon.

Figure 1. Location map of the study area.

Figure 2. Actual annual rainfall of the district (2009-2014).


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Figure 4. Vertical Electrical Sounding curves (40 nos.) of the study area.

Figure 3. Depth to water levels in dug wells during the period 2009-2014 (Pre and Post monsoons) at three locations Peddapuram, Katravulapalli

and Ramesampeta.


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Table 1. Interpreted Results of the vertical electrical soundings.

Code Longitude Latitude Elevation Resistivity (Ωm) Thickness (m) Total Thickness(m)

1st Layer

2nd Layer

3rd Layer

4th Layer

5th Layer

1st Layer

2nd Layer

3rd Layer

4th Layer

DH-19 82.136 17.0757 41 17.7 10.2 4.6 18.9 0.9 50.8 31.9 83.6

DH-80 82.1517 17.0674 41 279.5 34.3 8 71.6 12.1 1.4 19.7 14.9 30.6 66.6

DH-86 82.0908 17.0678 54 102.9 249.8 42.3 8.4 1.5 3.7 36.5 41.7

DH-87 82.089 17.066 56 66.1 204.2 41.2 8.2 0.6 5.2 37.2 43

DH-88 82.0473 17.0571 60 72 16 25 8 30 1 10 15 30 56

DH-106 82.1235 17.0673 53 55 19 26 10 1 10 40 51

DH-111 82.104 17.045 40 142.2 34.1 10.9 2.1 41.8 43.9

DH-114 82.1103 17.0778 45 89.3 70.4 20.5 39.4 1 10.5 111.6 123.1

DH-120 82.0471 17.0477 58 39.9 11.1 15.3 8.7 1.5 11.7 39.4 52.6

DH-121 82.0414 17.0551 65 645.8 80.3 46.6 1.8 26.7 28.5

DH-122 82.055 17.06 66 76.4 26.5 7 1.3 77.8 79.1

DH-123 82.0336 17.0609 64 147 26 100 24 13 1.4 5.5 4 45 55.9

DH-124 82.026 17.068 72 27 20 11 2 42 44

DH-128 82.0482 17.0476 56 470 38.5 19 9.1 1.2 3 75.4 79.6

DH-129 82.0427 17.0717 77 142 21.2 4 20 0.8 37.4 44.9 83.1

DH-140 82.0897 17.0628 54 82 261.1 26.7 12.1 1 2.3 39.8 43.1

DH-141 82.044 17.0634 67 30 13 35 7 1.5 3 50 54.5

DH-142 82.042 17.061 67 200 50 23 10 2 8 60 70

DH-145 82.1208 17.0865 45 12 35 10 25 10 1 1.5 5.5 15 23

DH-147 82.0903 17.0266 33 21.8 32.4 6.3 40.9 2 14.1 21 37.1

DH-185 82.1107 17.0919 53 83 23 20 10 1 12 123 136

DH-221 82.0438 17.0481 63 411.2 39.1 18.6 7 1 10.4 120.8 132.2

DH-222 82.0974 17.0422 46 128.8 17.1 9 1.2 46.5 47.7

DH-226 82.0558 17.0513 60 57.5 9.3 13.9 7 1 5.6 60.6 67.2

DH-231 82.0947 17.0332 35 151.5 61.1 3.8 102.3 15.1 0.5 5.1 11.4 50.9 67.9

DH-233 82.052 17.075 77 396.9 19.3 2.5 0.9 88.7 89.6

DH-234 82.05 17.074 77 27.6 14.5 4.9 1.5 54.7 56.2

DH-236 82.0469 17.0412 61 38.5 21.4 9.7 6.8 0.5 9.3 44.3 54.1

DH-237 82.034 17.07 80 48.7 21.7 14.4 6.9 0.5 15.1 26.6 42.2

DH-238 82.0385 17.0714 81 368.9 40.3 16.8 5 0.9 3.8 45.3 50

DH-239 82.0997 17.0489 43 60 22 10 1.5 20 21.5

DH-240 82.103 17.049 41 251.7 62.8 26.7 1.6 17.7 19.3

DH-257 82.0999 17.0695 42 9.3 6.6 13.7 6.2 29.6 1.4 4 21 103.1 129.5

DH-258 82.099 17.066 43 8.4 1.7 16.9 4.8 0.8 1.7 28.1 30.6

DH-259 82.135 17.085 35 1547.3 99.3 23.1 1.7 22.5 24.2

DH-260 82.144 17.069 46 377.5 36.3 4.9 2.9 114.1 117

DH-261 82.1372 17.0673 55 391.9 727.9 95.8 39.8 0.8 3.3 19.7 23.8

DH-21 82.0857 17.125 44 47.2 16.6 5.4 20 1 24 84.7 109.7

DH-118 82.0938 17.1255 42 79.6 29.3 6.8 1 38.5 39.5

DH-119 82.093 17.128 39 30 18 32 8.5 1 6 23 30


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METHODOLOGY

Electrical resistivity data of 40 Vertical Electrical Soundings (VES) using Schlumberger array with maximum of half- current electrode spacing varying between 100-250 m are initially interpreted with theoretical curves prepared by Orellana and Mooney (1966) for having preliminary understanding of the true resistivities and thicknesses of the subsurface layers of different composition. The shapes of the curves indicate 3-5 layer subsurface patterns

corresponding to Q, HK, KH, QH, KQ, QQ, HKH, QHK, HKQ and KHK (Figure 4). These curves have been interpreted with the inversion technique using RESIST program (Vander Velpen and Sporry, 1993) based on the criteria of flexibility and user friendliness to process the data with Wenner, Schlumberger and Dipole-Dipole arrays. The results obtained from partial curve matching technique were given as inputs for RESIST program. The inversion of the resistivity data is based on the Marquardt-Levenberg technique. The layers resistivity and thicknesses of all the

Table 2. Resistivity ranges of Sandstones.

S.No. Resistivity in Ωm Formation

1. <10 Saturated Clay

2. 10-50 Unconsolidated/Saturated Sandstones

3. 51-250 Top soil/Dry sands/Consolidated sandstones

4. 251-1550 Lateritic gravel

Figure 5. Top figure is the fence diagram for region-I, Bottom two figures are the lithologies along the geo-electric section AA` and BB` of Figure 1.


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sounding curves determined with RESIST program are given in table-1.

Sub Surface Lithology:

Based on the interpreted resistivity values, geology of the area and lithology of the three observation wells, the subsurface lithology is classified broadly into clay, consolidated and unconsolidated sandstones and gravel (Reynolds, 1997; Hasan et al., 2013). The resistivity ranges of these formations are shown in table 2. In some pockets of the study area, dry sand is observed in the top layer. Most of the curves initially show descending trend with an exception of a very few curves with a high second layer resistivity. Such a trend could probably be due to dry sandy/lateritic gravel layer followed by a steep fall in the third layer resistivity (~41-42Ωm) with a larger thickness of approximately 36-37m (DH86 and DH87), which could be a potential zone of groundwater. The top layer consists of sand/sandy loam/dry soils/lateritic gravel with a thickness of 0.5 to 2.9m with an average thickness of 1.7m underlain by saturated sandstones at many places. In addition to this, clay formations (very low resistive less than 10 Ωm) were

identified at a few locations in deeper layers. Sounding data inferred the thickness of saturated sandstones varying between 10 – 135m (maximum at DH-185).

The study area is divided into three regions (I, II & III in Figure 1) and fence diagrams have been generated based on the lithology of the observation wells and resistivity values (table 2) for each region separately, for better view of the lithology. Fence diagrams for regions-I, II and III are drawn based on 17, 6 and 14 soundings, respectively. For each region, soundings located along straight lines are connected for drawing geoelectric sections (AA`, BB`, CC`, DD`, EE`, FF`), based on the resistivity values. All these fence diagrams and sections are shown in Figures 5, 6 and 7.

Discussion of Region-I: Fence diagram for this region (top of Figure 5) covering an area of about 17.4 square km is drawn on the basis of layer resistivities and thicknesses of 17 VES data. By looking at this figure, one can easily infer that bed rock is not reached at any of the sounding points in spite of the sounding spread extending to 250m (AB/2). Saturated sands of Rajahmundry sandstones, which form a major aquifer (resistivity range 10-50 Ωm) occupy maximum area of the region and extend to a maximum depth of 50m below

Figure 6. Top figure is the fence diagram for region-II, Bottom figure is the lithology along the geo-electric section CC` of Figure 1.


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mean sea level (DH-221). Open well dug at Ramesampeta in this region up to a depth of 16m also shows sandstone.

Bottom diagrams of Figure 5 are lithological sections along profiles AA’ and BB’ of region-I (Figure 1).

Figure 7. Top figure is the fence diagram for region-III, Bottom three figures are the lithologies along the geo-electric section DD`, EE` and FF` of Figure 1.


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Section AA`: The topography of this section varies between 72 and 77m above mean sea level (amsl) along W-E direction. Two major formations viz. saturated sandstones followed by saturated clay have been inferred along this section. The thickness of the clay zone ( <10 Ωm ) varies in the range of 10–50m, found at depth of 40m below ground level (bgl) with 10m thickness at a distance of 600m from A (West) and increasing towards A`(East) with maximum thickness at distance of 2 km from A. Above this zone, saturated sand (10-50 Ωm) is encountered with an average thickness of approximately 30-40m, over a length of 3km along AA`.

Section BB`: The length of this section is 3.6km and runs along N-S direction with surface topography decreasing from 80 m amsl on the northern side (B) and 60m amsl on the southern side (B`). Saturated sandstone is inferred at most of the locations with few locations revealing dry sand as top layer at 2 km from B (DH121) and clay zone with a thickness of 50m at a depth of 10 m bgl located on southern most part of the section (DH236). The thickness of aquifer (saturated sandstone) is about 60m extending to a distance of about 1 km (DH142) towards south from B (DH238). The depth to this aquifer is approximately 1 m bgl.

Discussion of Region-II: The fence diagram of this region (top of Figure 6) covering an area of about 5.34 square km is based on the resistivity and thickness values of the different layers of the subsurface from 6 VES data. It can be inferred from this fence diagram that two thirds of the fence area is occupied by saturated sandstones, while one third is covered by consolidated sandstones (high resistive).

Section CC`: This section of 2.9 km (bottom of Figure 6) revealed aquifer (saturated sandstone) along a length of about 800-900m having thickness of 30- 40m. This unconfined aquifer is located from a distance of 1.4 km from the point C (DH147) and at the sounding point DH222. The region occupied by consolidated sandstones

and clay (from Point C to approximately 1.4 km) in some parts of this section is not suitable for ground water exploitation.

Discussion of Region-III: 14 electrical resistivity soundings (VES) were carried out in this region covering an area of about 31.91 square km. The maximum surface elevation from the mean sea level is approximately 50m. The subsurface lithology is depicted in the fence diagram (Figure 7 top) based on the lithology of the well near DH19 (Peddapuram). Entire region is covered by saturated sandstones as can easily be observed from the fence diagram, with an exception at few locations where clay and consolidated sandstones are revealed.

Section DD`: The length of this section (bottom of Figure 7) is about 4.3 km. Dominant formation along this section is saturated sandstone covering the entire length of the section with the exception at DH257, where the thickness of this formation is very less. This is underlain by a thick clay zone. The sandstone (saturated) is a good aquifer with thickness varying from 20m at DH257 to a maximum thickness of 90m at DH114 along length of approximately 2.8 km from D along this section.

Section EE`: The distance between E and E` is 5.3 km (bottom of Figure 7). Most of the region is characterized by saturated sandstones, with an average thickness of around 40m. At few locations, clay deposits (10-20m thick) embedded into this formation (DH145, DH19 and DH80). Clay zone of 20m underlain by the same thickness of consolidated sandstones (high resistive) is observed in between the sounding locations DH260 and DH80, extending over a length of 800 m at a depth of 20 m bgl.

Section FF`: This sections runs to about 7.0 km in the W-E direction in which saturated sandstones with an average thickness of 50m over a length of 6.0 km are the major formation along this section. At some locations, this formation is exposed onto the surface (DH87 and DH106) and at other locations (DH261) it is overlain by

Figure 8. Spatial distribution of the saturated sandstone (10-50 Ωm) of varying thicknesses.


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dry sand of 20m in thickness over a length of 800m and top soil of 10 m thick at DH258. Thus, this sandstone aquifer of 50m thick is undulating over a length of 6.0 km with patches of clay pockets at a few locations (DH258 and DH106) at a depth of 40 m bgl. The presence of clay may play a big role in the yield of the wells. However, at the end of the section (DH260 - DH80) clay and consolidated sandstone together with a thickness of 40m is delineated. EE` and FF` join at this point. Along this section ground water potential is revealed in the region from DH87 and DH260.

Summary

The three fence diagrams and the lithology along the six geoelectric sections reveal the geometry, thickness, spatial and depth extent of sandstone aquifer. In addition to aquifer, zones of clay and consolidated sandstone are also inferred from these geoelectric sections. The aquifer thickness map based on the thicknesses of the saturated sandstone (figure 8), inferred poor aquifers in the southern most parts of the study area as revealed by smaller thickness, whereas, towards northern and central parts, the thickness of the aquifer is around 50 m and could yield good amount of water. The major aquifers are delineated along the sections AA`, DD` and FF`. Along DD` the layer with maximum thicknesses of 90m extending over a length of 1.4 km may be due to a very good source of groundwater. Thus, the study plays a key role in delineating the aquifer and clay zones, which helps to decide the type of well and depth to be drilled in future groundwater exploration/exploitation programs.

ACKNOWLEDGEMENTS

We express sincere thanks to Andhra Pradesh Ground Water Board for providing geophysical and geo hydrological data of the study area. The second author acknowledges the financial support from UGC through Rajiv Gandhi National Fellowship, New Delhi. The authors express their sincere gratitude to Dr. M.R.K. Prabhakara Rao, whose comments/suggestions helped in revising the paper. Thanks are due to Chief Editor for his encouragement and final editing.



REFRENCES

Groundwater brochure of East Godavari district, Andhra Pradesh,

2013. Central ground water board, Ministry of water

resources, Government of India, Southern Region, Hyderabed.

East Godavari district official web portal link “http://

eastgodavari.nic.in/districtprofile/Climate.aspx”.

Hadi Tahmasbi Nejad, 2009. Geoelectrict Investigation of the

Aquifer Characteristic and Groundwater Potential in

Behbahan Azad University Farm, Khuzestan Province, Iran.

Journal of Applied Science, v.9, no.20, pp: 3691-3698.

Hardianshah Saleh, and Abdul Rahim Samsudin, 2013. Geo-

Electrical Resistivity Characterization of Sedimentary rocks

in Dent Peninsular, Lahad Datu, Sabah. Borneo Science 32:

March, 2013.

Hasan Imam, Md., Delwar Hossain and Woobaid Ullah A.S.M.,

2013. Geoelectrical Resistivity Survey for the Evaluation

of Hydrogeological Condition of Bagerhat and Adjascent

Areas,Bangladesh. Journal of Geological Society of India,

v.82, pp: 290-294.

Jagadeeswara Rao, P., Suryaprakasa Rao, B., Jagannadha Rao, M.,

and Harikrishna, P., 2003. Geo-Electrical data analysis to

demarcate groundwater potential zones in Champavathi

River basin, Vizianagaram District, Andhra Pradesh. J. Ind.

Geophys. Union. v.7, no.2, pp: 105-113.

Kelly, W.E., and Stanislav, M., 1993. Applied Geophysics in

Hydrogeological and Engineering Practice, Developments in

Water Science Series,. Elsevier, Princeton, N.Y., ISBN: 0-44-

889936-1., v.44.

Majumdad, R.K., and Das, D., 2011. Hydrological Characterization

and Estimation of Aquifer Properties from Electrical Sounding

Data in Sagar Island Region, South 24 Parganas, West Bengal,

India. Asian Journal of Earth Sciences, v.4, no.2, pp: 60-74

Orellana, E., and Mooney, H.M., 1966. Master tables and curves

for vertical electrical sounding Over layered structures.

Interciencia, Madrid, Spain, p: 150.

Reynolds, J.M., 1987a. The role of surface geophysics in the

assessment of regional groundwater potential in northern

Nigeria. In: Cuishaw, M.G., Bell, F.G., Cripps, J.e. and

O’Hara, M. (cds), Planning and Engineering Geology,

Geological Society Engineering Group Special Publication

no.4, pp: 185-190.

Reynolds, J.M., 1997. An Introduction to Applied and Environmental

Geophysics. Reynolds Geo-Sciences Ltd, UK, Published by

John Wiley & Sons Ltd., p: 422

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691-703.

Received on: 28.6.17; Revised on: 19.7.17; Re-revised on: 21.7.17; Accepted on: 2.8.17


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An Appraisal of the Plate Tectonic Forces: Role of Gravitational Potential Energy (GPE) in the Deformation of Indo-Eurasian

Collision ZoneC.D. Reddy*1 and Mahesh N. Shrivastava2,3

1Indian Institute of Geomagnetism, Navi Mumbai, 410218, India2Universidad Católica del Norte, Antofagasta, Chile

3National Research Center for Integrated Natural Disaster Management, Santiago, Chile*Corresponding Author: [email protected]

ABSTRACTConcording with the plate tectonic theory, lithosphere consists of several tectonic plates moving in different directions and stimulating various tectonic processes and consequencing mountains, earthquakes, volcanoes, mid-oceanic ridges and oceanic trenches. It is excogitated that three main plate tectonics driving forces viz. ridge push, slab pull and trench suction together with resistance force viz. collisional resistance, basal drag etc. maneuvering deformation in Indo-Eurasian collision region. But these forces acting in tandem are not sufficient in explaining the discrepancies in regional surficial lithospheric deformation pattern explicitly. Hence, we invoke Gravitation Potential Energy (GPE) derived deviotoric stress in explaining the deformation pattern of Indo-Eurasian collision region. We also provide explanation for the occurrence of Mw 7.3 aftershock following the 2015 Mw 7.9 Nepal earthquake construing the GPE as an important proxy to the deviatoric stress field.

Key words: Tectonic forces,Topography,GPE, Indo-Eurasian, Himalaya, deformation.

INTRODUCTION

Wegener, (1912), by compiling and analyzing large amount of data from various disciplines (viz. fossil, meteorological similarities in the America, Africa and parts of Northern Europe), proposed the theory of continental drift. He had surmised that the continental drift was powered by the centripetal force pertinent to rotation of the earth. However, it was soon realized that this force was too small to drive the continental movement. Later on, it was suggested that the driving mechanism for these plate motions is linked to mantle convection, i.e. convective motion in the asthenosphere that exert a drag to the over lying lithosphere there by driving plate motion, and mantle convection in turn is powered by the heat in the interior of the earth generated by radioactive decay (Holmes, 1928). During 1950s and 1960s, new geological and geophysical techniques viz. radiometric dating, bathymetric mapping of the seafloor produced a wealth of new data, which led to the development of the theory of plate tectonics (tectonic is derived from τεχτονικη, which designated in ancient Greek the art of building) (e.g. Dietz, 1961; Hess, 1962). As per the plate tectonic theory, the earth’s outer shell called lithosphere consists of several plates moving in different directions and stimulating various tectonic processes, manifesting as earthquakes, mountain building etc., and providing explanations for various geological observations.The theory of plate tectonics revolutionized the perception of

geophysicists and geologists on the geodynamics of the earth. It should be noted that like any scientific theory, the theory of plate tectonics has its own limitations and cannot account for all the observable facts.

What forces drive the plates remain enigmatic and one of the intriguing problems in the theory of plate tectonics. Though, it is proposed that mantle convection drives movement in the interior but is not the major driving mechanism to move the plates. Forsyth and Uyeda, (1975), Solomon et al., (1975) and Chapple and Tullis, (1977) proposed that the plates are driven by forces that are applied at plate boundaries. The main driving forces were thought to be the slab-pull force (Cloos, 1993), where the slabs would pull the trailing subducting plates to which they are attached towards the trench, and the ridge push force (Lister, 1975; Meijer and Wortel, 1992), where the plates on either side of a spreading ridge are pushed away from these ridges. A third force, the trench suction force, was also proposed, which resulted from slab sinking and would drive overriding plates towards the subduction zone (Lithgow-Bertelloni and Guynn, 2004). On the other hand, the main resisting forces are collision resistance, basal shear/ drag. As all these forces collectively are not able to explain the deformation pattern in Himalaya collision region, it is proposed that the GPE (Bucher, 1956; England and Molnar, 2005; Flesch et al., 2001) induced force arising due to lateral density variations along with the topography playing significant role. All these aspects are discussed in the context of Indian subcontinent/ Himalaya regions.


An Appraisal of the Plate TectonicForces: Role of Gravitational Potential Energy (GPE) in the Deformation of Indo-Eurasian Collision Zone

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Tectonic Forces

Theory of plate tectonics revolutionized our understanding of earth science, in particular provided a unified explanation for the processes of earthquakes, volcanoes, and mountain building. The forces capable of deforming the lithosphere have three possible sources: (i) mantle convection, (ii) plate tectonic processes, and (iii) lateral variations in GPE. Mantle convection: In the mantle convection process, the tectonics plates are driven by the internal heat energy within the earth. This comprises the heat left over from the initial formation of the earth and heat from the radioactive decay of the minerals inside the earth. Heat from the earth’s lower mantle rises as plumes towards the upper mantle

where cooling occurs. The plumes spread out, then sink back into the interior, known as mantle convection. These convection currents seem to propel the motion of plates.Plate tectonic processes: Plate tectonic processes are responsible for most geographical and geological features of the earth, in particular, those that are associated with natural hazards such as volcanoes and seismic zones. The tectonic forces arising from various tectonic processes (as discussed below) can be further divided as plate driving forces (e.g. ridge push, slab pull, slab suction, plume push) and plate resistance forces (e.g. collisional resistance, basal drag). These aspects are explained below in detail. GPE: Potential Gravity Theory (PGT) studies show that surface topography and lateral variations in crustal

Figure 1. Indo-Eurasian collision and adjacent regions with important tectonic features superposed on topography. The red star indicates Mount Everest.

Figure 2. Forces acting upon a plate. F denotes a driving force, whereas R denotes a resisting force (Bott, 1982). Ridge push (FRP), Slab pull (FSP), Negative Buyant force, (FNB), Collisional Resistance (FCR), Bending Resistance (RB), Slab Resisntace (RS), Over riding place Resistance (RO), Ridge Resistance (RR), Trench Suction (FSU), Basal Drag (RDO).


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thickness and composition may lead to significant gravity-induced horizontal stresses (e.g., England and Molnar, 2005; Flesch et al., 2001). Pressure variations associated with topography and Moho undulations may reach 10–75 MPa (e.g. 1000 m of local topography or 5000 m of Moho depression produce 20–30 MPa pressure difference) (Tesauro et al., 2011). Stress changes associated with surface elevation as well as sub-surface density distribution are referred to as topographic deviatoric stress or more simply the GPE (Bucher, 1956). The gravitational collapse leads to reduction of lateral differences in GPE causing the neighboring lithospheric columns to undergo compression or extension (e.g., Artyushkov, 1973; Fleitout and Froidevaux, 1982). Thus, the variation in GPE is an important proxy to the deviatoric stress field and is estimated in Himalaya collision region (Figure 1).

Plate Driving Forces

Stress field in Indo-Eurasian collision region is sensitive to various tectonic forces, boundary conditions, geophysical parameters and lithosperic rheology. In particular, the driving mechanism for the Indian plate has been a source of controversy since the advent of the plate tectonics theory (Ghosh et al., 2006). Below, we address some of the major tectonic (plate driving and resistive) forces that are operative in Indian subcontinent and Himalaya region. Figure 2 gives all these forces. It should be noted that plate tectonics is a thermodynamic engine and can be calculated as such (Swedan, 2015).

Ridge Push

Ridge push results from the elevated position of the oceanic ridge, which causes slabs of lithosphere to slide down the flanks of ridge and acts perpendicular to the ridge axis. Here, we address the ridge push force FRP acting along the Central Indian ridge between the borders of Somalia and Indian plate. The expression for the ridge push is given by the relation (Turcotte and Schubert, 2002) as

where ρm is density of the mantle (3300 kg/m3 ), g is the acceleration due to gravity (9.8 m/s2), αv is the thermal expansion coefficient (3 x 10-5 /K), (Tm - T0), the temperature difference between mantle and surface (1200 K), ρw is the density of water (1000 kg/m3), thermal diffusivity (kd) can be taken as 1 mm2/s and t is the age of lithosphere in seconds. The magnitude of this force is calculated based on the mean age of 20 Ma for this oceanic lithosphere. This force is applied as pressure of magnitude 7.5 x 1012

N/m distributed along the entire oceanic lithosphere and acts normal to the strike of the ridge.

Slab Pull

The slab-pull force results from the negative buoyancy of the subducting slab compared with the surrounding sub-lithospheric mantle. Slabs are negatively buoyant due to their higher average density compared to the ambient mantle (∼80 kg/m3 for 80 Ma oceanic lithosphere; Cloos, 1993) and hence sink like a rock. As these slabs sink into the asthenosphere, they pull the trailing plate along. The slab pull force is proportional to the excess mass of the cold slab in relation to the mass of the warmer displaced mantle. The force contribution can be given by the relationship (Turcotte and Schubert, 2002):

where b = slab length, λ = 4000 km, u0= 50 mm/yr, ϒ = 4 MPa/K, and Δρos = 270 kg/m3, with the remaining parameters identical to those in the equation used for ridge push. For example, a 700 km long, 100 km thick 80 Ma slab (with density contrast Δρ= 80 kg/m3) has a negative buoyancy force of 5.5 × 1013 N per meter trench length. However, most of the negative buoyancy is thought to be absorbed by shear forces and slab-normal forces in the mantle resisting subduction and sinking of the slab (Forsyth and Uyeda, 1975).

For fast moving plates (5–10 cm/yr) the subducting slab attains a ‘terminal velocity’ where forces related to the negative buoyancy of the slab are balanced by viscous drag forces acting on the slab as it enters the mantle and the net force experienced by the horizontal plate is quite small (Forsyth and Uyeda, 1975). The amount of net force actually transferred to the horizontal plate, however, is still quite controversial. Schellart, (2004) suggests that as little as 8%–12% of slab pull force is transferred to the horizontal plate while Conrad and Lithgow-Bertelloni, (2002) suggest that as much as 70%–100% may be transmitted.

Slab Suction

Slab pull occurs when detached slabs that descend into the mantle, excite viscous flow that might exert traction on the base of the lithosphere, thereby sucking plates along. Attached slabs also create suction. Slab suction forces are one of the major plate tectonic driving forces. This driving force is important when the slabs (or portions thereof) are not strongly attached to the rest of their respective tectonic plates. They cause both the subducting and overriding plate to move in the direction of the subduction zone.

Slab suction is the weakest of the three major forces involved in plate motion, the others being slab pull (the strongest) and ridge push (Conrad and Lithgow-Bertelloni, 2002). They further suggest that slab-pull forces account


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for around half of the driving force of plate tectonics, with a nearly equal contribution from subduction suction induced by subducting slabs. However, both attached and detached portions of lithosphere that descend beneath the 660 km deep mantle transition zone probably do not transmit stresses into higher-level slabs, and only their suction effect adds to plate motions.

Plume Push

Plume push force is pertinent to non-tectonic plumes. Plume rises through the mantle from well beneath the lithosphere, and consequently, logically can expect a vertically upwards force, while the ridge push, slab pull, slab suction cause horizontal movement of the plates. Based on modeling of the geophysical data from the Indian Ocean, Müller, (2011) suggested that a mantle-plume head might have coupled the motions of the Indian and African tectonic plates, and determined their velocities. While the Indian plate was accelerated, African plate was slowed, which is explained by a push exerted in the same direction of Indian plate motion (i.e. in NE direction) while it opposed the African plate motion moving in same direction. Thus, it became clear that the motion of the Indian and African plates were synchronized and the Réunion hotspot was the common source of force.

The enigmatic question is how did a mantle plume exert such a force ?. It may be (i) because plume push caused a local bulge from which the plates slid, or (ii) the mantle motion associated with the mushroom-like structure of the horizontally growing plume head might exert viscous drag on the overlying plates (Müller, 2011). Cande and Stegman, (2011) further provided the evidence that such mantle plume “hot spots”, which can last for tens of millions of years and are active today at locations such as Hawaii, Iceland and the Galapagos, may work as an additional tectonic driver, along with ridge push and slab pull forces.

Plate Resistance Forces

Collisional ResistanceCollisional resistance arises when a plate collides with another plate boundary (as is the case with Indian and Eurasian plates). It directly resists all the driving forces associated with plate tectonics. It is observed that at the collision boundary along Himalayas, the Indian plate converges at an average rate of 50 mm/yr (Bilham et al., 1998). The resistance arising along the Himalayan pate boundary where the Indian plate converges under Eurasian is referred to as the continental collision force Fcc. Coblentz et al., (1998) estimated a force of 2 x 1012 N/m for the Himalayas and hence applied as pressure along this boundary. In spite of high velocities, the collision

forces in Himalayas are lower than the slab pull force in the subduction zone.

Basal Shear/ Drag ForceBasal shear stresses, the second major class of stresses are those applied at the base of the lithosphere. The drag force operates on almost all parts of a moving lithospheric plate. This force was initially considered to be the main reason why Wegner’s theory of continental drift was discarded, i.e. the forces required to force a continent around the globe was simply too large. As seen, this is not true considering the large shear zone created by the asthenosphere that allows lithospheric plates to slide around the earth. However, the basal drag force still acts to resist plate motion at the interface between the lithosphere and upper mantle.

Among all the above driving forces, it is observed that only ridge push is a numerically well-known force that depends on the age of the lithosphere. However, the estimates of slab pull and collision forces are subjected to large number of uncertainties in the subduction zones (Scholz and Campos, 1995).

Theoretic Background of GPE and Deviatoric Stress

Lithosphere is considered to be composed of the elastic part of the crust and the viscous part of the upper mantle. Here we consider the entire lithosphere as a fluid, which is floating on the asthenosphere and obeying Navier–Stokes equation, which is consequence of Newton’s second law of motion.

where , p is the pressure,T is the stress tensor, f = rg is the downward force per unit volume and v is the flow velocity.Assuming a specific viscous rheology and steady state, the above equation can be re-written as

(1)where is the unit vector in vertical direction, σij is the total stress and xj is the jth coordinate direction. In the above equation summation notation is used, where i is given values of x, y, and z and the repeated index j is used to represent the summation over x, y, and z.

Equation (1) can take the form

2(i)

2(ii)

2(iii)


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If the horizontal gradients in shear traction τxy and τyz are small compared to ρg i.e.

then above equation can be expressed as

(3)The vertically averaged equations 2(i) and 2(ii) from the surface at z= -h to the base of the lithosphere at uniform depth z=L, where h is the surface elevation and L is the base of the lithosphere

where τxz(L) and τyz(L) are the traction applied to the base of the lithosphere that fall out the vertical integrals (τxz(-h) and τyz(-h) are zero).

The vertically averaged stresses τij and σzz obtained by dividing the corresponding depth integrals by reference lithosphere thickness L are defined as

(4)

(5)The vertically averaged vertical stress defined in

equation (5) is equivalent to 1/L times the GPE per unit area defined by the reference level at the base of the lithosphere at depth L. The GPE per unit area of a column of material U above a given depth z is given by the integral of the vertical stress σzz from the L to the surface h (Molnar and Lyon-Caen, 1988)

(6)where ρ(z) is the density, L is the depth of the lithosphere, h is the topography elevation and g is the acceleration due to gravity. The horizontal stresses can be directly related to the vertical density distribution (Dahlen,1981).

(7)where σ¯xx is the horizontal stresses averaged over the thickness of the lithosphere, relative to a reference state against which the Δρ is measured. Using the definition of GPE in equation (6) the horizontal stress can be expressed in terms of the potential energies

(8)

where ΔU is the difference between the potential energy of the lithosphere column Ul and the potential energy of some others reference column Ur DU = Ul – Ur (9)

Estimation of GPE for Indo-Eurasian Collision Region

Himalayas, the most active seismo-tectonic collision orogeny belt in the world, resulted from collision of the Indian plate ~50 Ma ago and characterized by large mountain ranges. Schellart and Rawlinson, (2010) detail convergent plate margin dynamics from structural geology, geophysics and geodynamic modeling perspective.The deformation and stress field in Himalaya collision zone is difficult to explain using the plate boundary driving/ resistive forces previously explained. Speculating that the GPE derived forces significantly affect the stress field/strain rate in the lithosphere (although other local stress sources may also be an important factor in explaining the observed stress field in this region), we attempted to estimate GPE in Himalaya collision region.

In this study, we considered the Indo-Eurasian collision region confined by 60o-110o E and 20o -50o N, the Mount Everest and Eastern Himalaya Syntaxis (EHS) with adjacent regions. Laterally heterogeneous lithosphere has been assigned a uniform thickness of 100 km, since beyond this depth there exists almost uniform density. The GPE difference is estimated considering satellite altimetry data ETOPO5 and crustal thickness model CRUST2.0 (Laske et al., 2001). The seismic crustal thickness considered here is more accurate representation of the GPE as it is constrained by seismic data set (Bassin et al., 2000; Mooney etal., 1998). Assuming constant crustal and mantle densities of 2750 kg/m3 and 3300 kg/m3 respectively and assuming the lithosphere to be in Airy isostatic compensation, we calculated GPE (Figure 3) and its associated deviatoric stress field at each grid point (5’x5’grid spacing) using the formulation described above. Thus estimated GPE and deviatoric stress distribution are shown in Figures 3 and 4 respectively.

DISCUSSION

The acting forces on the lithospheric plate have three possible sources: (i) mantle convection, (ii) plate tectonic processes e.g. ridge push, slab pull, and (iii) lateral variations in GPE. The state of dynamic equilibrium of the plate can be mathematically defined as

(10)where σ is the stress tensor and f denotes the body force, ρ is the density of the plate, c is the coefficient of damping, and are the plate accelerations and velocities (Jayalakshmi and Raghukanth, 2017). In the equation (10), the terms on the RHS represent the forces due to inertia and damping. Presently, Indian plate decelerates


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at very slow rate of few millimeters per year (Harada and Hamano, 2000; Bowin, 2010), the first term on RHS can be neglected. The damping force is the resistance induced by the plate due to mantle drag force (shown in Figure 2), which is caused by the viscous couplings between the plate and the mantle beneath.

The total stress tensor at any point in the lithosphere can be considered to be composed of isotropic part and the anisotropic “deviatoric” part. The isotropic part of the stress tensor is an invariant quantity corresponding to the mean normal pressure of magnitudes of the order of 20-40 MPa averaged over a 100 km thick lithosphere (e.g. Batchelor, 1967; Jaeger, 1979; Coblentz et al., 1998), whereas an anisotropic “deviatoric” part is dynamic part causing deformation and changes in shape. The present study concerns estimation of “deviatoric” stresses within the lithosphere that are associated with GPE differences. It should be noted that the parts of lithosphere whose vertically-averaged strength exceeds the

stresses generated by gravity acting on density differences behave as rigid blocks, where as weaker lithosphere deforms pervasively (Coblentz et al., 1998).

The deviatoric stresses associated with GPE in combination with plate boundary forces are the powerful tools to trace and explain the first order deformation patterns in active collision/subduction zones (Flesch et al., 2007; Liu et al., 2002; Ghosh et al., 2006; Fleschet al., 2001). Though the Indo-Eurasian collision took place ~65–50 Ma ago, the convergence still continues. However, slab pull as the driving force may be minimal. Further, as the basal tractions discussed previously are not intrinsic to lithosphere, hence this component can also be ignored. Thus, the deviatoric stress pattern derived here from inversion of GPE fields calculated using topography and available knowledge of crustal structure and density variation should be sensitive pointer and thus could be used to trace present day pictures of deformation in Indo-

Figure 3. GPE per unit area distribution in the Himalaya collision and contiguous region. The rectangles 1,2 and 3 represent high GPE gradients in Indo-Gangetic Plains (IGP) (Shrivastava et al., 2013).

Figure 4.Vertically averaged horizontal deviatoric stresses derived from the GPE distribution shown in figure 3 superposed on the topography. The star indicates the location of the Mount Everest (Shrivastava et al., 2013).


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Eurasian collision zone. The estimated GPE values are found to vary in the range 1.4 -1.6 x 1014 N/m, where the maximum value 1.6 x 1014 N/m corresponds to the Mount Everest (~8850 m high, see Figure 1). In the calculation of GPE stress in Indo-Eurasian collision region, we have not considered dynamic topography and some plate boundary forces. Nevertheless, it is interesting to note that the estimated deviatoric stresses are corroborated well with that of stress and strain rates obtained by inverting the focal mechanism solutions of large earthquakes and GPS derived plate motions. It should be noted that the GPS estimated strain rates are sensitive to near-surface deformation, where as the GPE derived deviatoric stresses provide depth integrated value for the full thickness of the lithosphere (Hsu et al., 2009). This aspect is clearly observed in much smaller region i.e. in Shillong plateau region of EHS (Baruah et al., 2016). They noted that due to higher topography and density heterogeneities, the western edge of the Shillong plateau shows a dissimilar GPE variation with respect to that in the eastern edge. The strain rate measured by the GPS measurements has not shown any EW disparity in stress pattern.

Another interesting aspect of GPE derived stress pertains to 2015 Mw 7.9 Nepal earthquake. It is surmised that the large aftershock Mw 7.3 on May 12, 2015 following the April 25, 2015 Nepal earthquake seems to have occurred due to imploding stress due to very high topography of the Mount Everest. It should be noted that, as a balancing act, the GPE produced stress is countered by the stress in the adjoining region. In the event of this stress being weakened by the after shock activity as is the case consequent to Mw 7.9 earthquake, the imploding stress field can bring the fault regions that are criticality stressed, to rupture. This may be the reason why Mw 7.3 after shock occurred at the outer periphery of the after shock clustered region (Shrivastava et al., 2017).

CONCLUSIONS

In this study, we have provided description of various tectonic driving and resistance forces and GPE and deviatoric stress estimation. These tectonic forces are of the order: ridge push force 7.5 x 1012 N/m, slab pull 5.5 × 1013 N/m, collisional resistance 2.1 x 1012 N/m, GPE derived stress 12 x1012 N/m2. We must note that these estimates are subjected to large number of uncertainties. These forces generate first-order stress fields inflicting lithospheric perturbations on the scales of more than 500 km, nevertheless, failing to explain the deformation in Himalaya collision region. The deviatoric stress field associated with GPE explicates this discrepancy, and explained satisfactorily (i) the stess distribution in Indo-Eurasian collision region, and (ii) the occurance of Mw. 7.3 after shock following the 2015 Mw 7.9 Nepal earthquake.

ACKNOWLEDGEMENTS

Dr. C.D. Reddy thanks Prof. D.S. Ramesh, Director, IIG for the offer of Visiting Scientist post that facilitated completion of this piece of research work. Authors are thankful to Dr. P.R. Reddy, Chief Editor of JIGU for inviting to write this article and for carrying out final editing. Dr. B. K. Rastogi has critically reviewed the manuscript and provided valuable inputs. Research funding for Mahesh N. Shrivastava was provided by the FONDECYT 3160773 grant. Figures have been prepared by using GMT package.



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Tsunami forces acting on ocean structures: A synthetic studyMounica Jakkula*1,2, Harini Guruhappa2, Manaswini Ganjam2 and Kirti Srivastava1,2

1Academy of Scientific and Innovative Research (AcSIR), 2CSIR- National Geophysical 2Research Institute (CSIR-NGRI), Hyderabad, 500007, India.


ABSTRACTAndaman-Sumatra subduction zone had produced several large and great earthquakes in the past, some of which have generated destructive tsunamis. Tsunami forecast model is used to provide an estimate of wave arrival time, wave height, and inundation area immediately after a tsunami event. Forces caused due to a tsunami on different structures also play an important role. Considerable amount of research has been done on shape, size and strength of near-coastal structures. But, the impact on the ocean structures (like Oil Rigs) has not been addressed. In this paper, the lateral forces due to tsunami acting on a vertical hypothetical wall constructed in an ocean or sea are calculated. The location of the wall is taken in between India and Sri-Lanka due to the large scale destruction of structures on land and in the ocean caused by 2004 tsunami. To address the problem in an organized way, firstly, a hypothetical wall divided into 6 sections has been selected. Secondly, the wave heights are calculated for each section using TUNAMI N2 model. Thirdly, calculation of forces using the wave heights are made separately for each section for a better understanding of forces acting. And lastly, change in forces with time is calculated to bring out varied nature of forces with time. The acquired information is then plotted to explicitly show the changes. Results reveal that the hydrostatic forces acting on the wall structure in the ocean or the sea shall not pose a great threat to the structure. Also, due to the presence of such barriers the tsunami wave energy would get dissipated and less damage would happen to the adjoining coastal region. We have also followed the same approach to calculate the changes in tsunami forces with time on the Oil Rigs in the Ravva Offshore field.

Key words: Tsunami, Hydrostatic force, Wave heights, Vertical hypothetical wall, TUNAMI N2 model, Andaman-Sumatra subduction zone.

INTRODUCTION

A tsunami is a series of water waves caused by the displacement of a large volume of a body of water. Tsunamis have been causing drastic damage to the coastal areas. Their effects on man-made structures are the reasons for a large amount of economic losses. Earlier, the study on Tsunami induced forces was not given significance due to the less frequency of tsunamis. After viewing the destructed buildings and many other damaged structures due to 2004 Sumatra-Andaman & 2011 Tohoku tsunamis, these forces are being given importance and considered in engineering constructions along tsunami prone areas.

Extensive research has been conducted on the impact of hydrodynamic forces on classical coastal protection works (breakwaters, seawalls, reefs, etc.). Mizutani and Imamura (2001) measured the wave force of tsunamis acting on prevention structures along the coast such as seawalls and breakwaters. Kumaraguru et al., (2005) dealt with the impact of the tsunami on coral reefs. Such research studies help in measuring the reduction in tsunami impact while building preventive structural models (Kunkel et al., 2006). But, there is a very limited research on tsunami impact on structures such as buildings and bridges located inland. One such work by Azadbakht and Yim (2014) calculated tsunami loads on bridges using

simulations separately with initial impact and impact at full inundation. Failure analysis of several buildings is another effective approach to evaluate design equations for hydrodynamic loading conditions. This approach was adopted by Chock et al., (2011) in his Tohoku Tsunami-induced building damage analysis.

The devastation brought by the 26 December 2004 Indian Ocean Tsunami on coastal communities in Indonesia, India, Sri Lanka, Thailand, and other countries outlined the urgent need for research on the evaluation of structural resilience of infrastructure located in tsunami-prone areas. Nistor et al., (2009) worked on forces generated by tsunami-induced hydraulic bores, including debris impact. Further, he presented the sample calculations of tsunami loading on a prototype structure.

Experimental investigations have been done in the estimation of tsunami-induced hydrodynamic forces on infrastructure located in the vicinity of the shoreline. One such work by Suzuki et al., (2014) has specifically considered the Tohoku-Pacific Ocean Earthquake that occurred in 2011, which has caused a great damage to the bridges in the submerged area. In conventional designs, however, it was not assumed that those bridge girders or other bridge elements would be carried away by tsunami wave forces. Estimation of tsunami wave force was difficult because no load calculations or design methods had been


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established. Hence, hydraulic model experiments and numerical simulations in 2D and 3D have been carried out to understand the behavior of tsunami waves and the impact of tsunami wave forces acting on the bridge.

All these studies consider coastal or near-coastal structures. Though we have incorporated calculation of tsunami forces in engineering of coastal structures, no such study is available while engineering the structures in the ocean (like Kalpasar dam). In this paper, we have take up a case study of 2004 Indian Ocean tsunami caused by the Sumatra earthquake and specifically evaluated the different types of forces acting on a hypothetical wall in the Indian Ocean due to the tsunami waves. Also the same approach has been followed in calculating the tsunami wave impact on the Ravva field oil rigs located offshore near East Godavari district, Andhra Pradesh, India.

Mathematical Formulation

Theory of tsunami waves has been discussed by several researchers (Imamura, 1996; Imamura et al., 2006; Yalciner et al., 2005). To obtain the initial surface wave specific details of the initial sea bottom deformation is necessary. Mansinha and Smylie method (Mansinha and Smylie, 1971) has given a complete set of closed-form analytical expressions to obtain the internal as well as surface deformation. To obtain this one needs the information pertaining to the earthquake source parameters such as fault length, width of the fault, focal depth, angle between N & fault axis, dip angle, slip angle and displacement. Once the initial wave is generated one of the wave fronts would start moving towards the deep ocean and another towards the nearest local shoreline.

Since the vertical acceleration associated with tsunami waves is small compared with the gravity acceleration, tsunamis waves are usually resolved using 2D hydrostatic models (Imamura et al., 2006) and mathematically it is expressed as

(1)

(2)

(3)In the above equation M and N are expressed as

(4)where D is the total water depth given by h+η, t is time, h(x, y) is unperturbed depth, g is the gravitational acceleration, u and v are components of the horizontal velocities, M and N are the discharge fluxes in the x- and y- directions.

Imamura et al., (2006) used a finite difference technique based on Leap-Frog scheme to develop a code

to solve the tsunami wave propagation i.e. TUNAMI-N2. The formulation uses the central difference method with a second order truncation error. The deformation at the sea bottom gives the initial condition, which is computed using Mansinha and Smylie method (Mansinha and Smylie, 1971). This gives rise to the initial wave. The boundary conditions are free transmission in the open sea and the perfect reflector on land is assumed (Imamura et al., 2006).

Waves break at a depth ranging from about 0.8 to 1.4 times their height, depending on their steepness and seabed slope. If the structure is located in this range of water depth then it would be subjected to the action of breaking wave forces. On the contrary, if it is installed in depth deeper than this range, it would be subjected to non-breaking wave forces. Finally, structures in shallower depths would be influenced by broken water action. While non-breaking wave forces are static in nature, the remaining two (Breaking and Broken wave forces) are dynamic or time-varying (Deo, 2013)

Non-breaking wave forces:

On a smooth faced vertical wall, the incident wave would undergo pure reflection and standing waves will be formed. Assuming linear theory to be valid the subsurface pressure at depth ‘z’ is given by (Sainflou, 1928)

Where γz is static and γH costkx coswt is dynamic part.Choosing x = 0, cos(kx) =1.

Let ρ be the density of water, g be the acceleration due to gravity, d be the depth of water below mean sea level, b be the length of the section of the dam, ν be the velocity of the incoming wave and h be the wave height above mean sea level.Here γ=ρg, H is the vertical distance between the maximum crest and maximum trough, k is the wave number of the tsunami wave, w=2π/T, T is the time period of the wave.Force is calculated by integrating wave pressure on the entire area of cross-section.

CASE STUDY

A Hypothetical Wall

To demonstrate the methodology we have taken a tsunamigenic source in the Andaman-Sumatra subduction zone.

The 26th December 2004 Sumatra earthquake of Mw 9.3 along the subduction zone between Indian plate and Burmese plate triggered a tsunami causing large-scale devastation in the coastal cities across the Indian Ocean. Due to the occurrence of aftershocks, a large


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amount of stress was released causing rupture of 1200-1300 km northward from its epicenter up to Andaman region (Swaroopa et al., 2011). The Sumatra earthquake zone has been divided into five segments by Ioualalen et

al., (2007) to model the 26th December 2004 tsunami and the initial deformation at the five segments is computed based on the deformation parameters given in table 1.

Figure 1. Directivity map of 2004 Sumatra tsunami and the hypothetical location of the wall structure.

Table 1. Earthquake source parameters.

Watts et al, 2007 Segment-1 Segment-2 Segment-3 Segment-4 Segment-5

Coordinates 94.57oE to 3.83oN 93.90oE to 5.22oN 93.21oE to 7.41oN 92.60oE to 9.70oN 92.87oE to 11.70oN

Length (km) 220 150 390 150 350

Width (km) 130 130 120 95 95

Depth(km) 25 25 25 25 25

Dip (degrees) 12 12 12 12 12

Strike (degrees) 323 348 338 356 10

Rake(degrees) 90 90 90 90 90

Slip(m) 18 23 12 12 12

Figure 2. Water depths along different sections of the wall structure.


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In the present study, the Sumatra tsunami has been simulated to assess the impact of forces on the given wall structure. The TUNAMI N2 code is extensively used in quantifying the tsunami propagation, arrival times, run up and inundation extents. This code is being used by several researchers to simulate the Pacific, Indian and Atlantic tsunamis. Tsunami directivity is computed and is shown

in Figure 1. A two-dimensional wall structure is assumed between Kodiyakarai (India) and Illavalai (SriLanka) (Figure 1). The wall is divided into 6 sections along the length (Figure 2) and forces on each section are calculated based on the height of tsunami waves in that section. Tsunami arrival time, wave heights and the arrival time of the maximum wave are all plotted in Figure 3 and the results tabulated in table 2.

Figure 3. Tsunami wave height versus time at different locations along the wall structure.

Figure 4. Sum of hydrostatic force and the non-breaking wave forces versus at different locations along the wall structure.


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Taking into consideration the maximum wave heights and comparing the water depth in each section we clearly know that the wave breaking criteria is not satisfied. So, we calculate the non-breaking wave forces for each section using Equation 5 (where h, k and w are calculated from the wave data generated by TUNAMI N2).

To compute the forces on the wall structure we take the values b=30km, g =9.8m/s2,ρ=103kg/m3. Here we have taken the total forces to be the summation of hydrostatic force and the non-breaking wave forces. Figure 4 shows the plot of forces versus time at different locations near and around the hypothetical wall structure.

Application: Offshore Ravva Field Oil Rigs

The Ravva field is one of the most efficient fields in the world and has maintained its low-cost operating base by focusing on oil field life-cycle planning, continuous monitoring of operational costs and the innovative application of operating technologies. The Ravva oil field platforms (RA to RH) are located offshore about 4.1km from the coast. The oil and gas production has declined over the years due to the aging of the oil field. Figure 5 shows the locations of the oil rigs. We have applied the same method in calculating tsunami forces on the oil rigs

Table 2. Depths and maximum wave heights at different locations.

Locations Depth(m) Wave heights(m)

Nagapattinam -11 5.0634

cuddalore -11 7.1271

Chennai -7 5.9341

Pallepalam -10 3.3129

Kodiyakadu -7 4.3078

Aluvai -7 3.673

Wall1 -2 4.4368

Wall2 -10 5.2228

W1 -8 5.8136

W2 -5 4.5563

W3 -9 4.0815

W4 -8 3.1891

Figure 5. Locations of the Oil Rigs.


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Figure 6. Wave herights and Wave forces per unit width versus at different Oil Rigs.


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mentioned in Table 3. The 2004 Indian Ocean tsunami, which has been discussed earlier is applied and the tsunami wave heights at different rig locations are computed.

From the Table 3 we understand that the wave breaking criteria is not satisfied. So we calculate the non-breaking wave forces for each location using Equation 5 (where h, k and w are calculated from the wave data generated by TUNAMI N2). The maximum wave height at each rig location is computed and tabulated in Table 3.

Taking g =9.8m/s2and ρ=103kg/m3 we obtained the forces per unit width at each location. Here we are calculating the forces per unit width, as the width of the rigs is not known. However, the width could be of the order of 100m, which implies that the forces could be of the order of 105N. The tsunami wave heights and forces are plotted in Figure 6.

CONCLUSION

Great earthquakes in the sea have often generated the devastating tsunami waves. Tsunami is a very complex natural phenomenon to understand, and its complexity lies in all its stages, i.e., generation, propagation, run up and inundation. Assessment of tsunami hazard along a particular coast is the focus in this study. A study is made for understanding the impact of tsunami forces on the ocean structures. We can see that a large amount of the force acting on the wall is due to the hydrostatic force, which will be surely considered during the wall construction. Due to its proximity to the source one expects to observe a major impact on the wall, yet the forces are much lesser compared to the cyclone-induced wave. Cyclone induced wave forces are almost 2-5 times more than the tsunami induced forces. Since the sizing of the wall protection in such locations will be made depending on the wave conditions exerted during the cyclone action, we opine that the tsunami would not pose any threat to the wall structure. The study on the oil rigs in the ocean shows that tsunami wave forces did not cause any damage to the rigs due to their location in the deep ocean.

ACKNOWLEDGEMENTS

We acknowledge AcSIR, CSIR-NGRI and UGC for making this work possible. We thank CGIAR-CSI for the SRTM data. We thank the Chief Editor for his continued support, guidance, encouragement and precise reviewing and editing.



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Table 3. Depths and maximum wave heights at Oil Rigs.

Locations Depth(m) Wave heights(m)

RA -13 1.932

RB -9 1.7791

RC -13 1.9193

RD -12 2.2708

RE -10 2.0983

RF -9 1.5971

RG -10 1.4198

RH -9 2.9295


489

Kunkel, C.M., Hallberg, R.W., and Oppenheimer, M.,

2006. Coral reefs reduce tsunami impact in model

simulations. Geophysical Research Letters, v.33, no.23.

Mansinha, L., and Smylie, D.E., 1971. The displacement fields

of inclined faults. Bulletin of the Seismological Society of

America, v.6, no.5, pp: 1433-1440.

Mizutani, S., and Imamura, F., 2001. Dynamic wave force of

tsunamis acting on a structure. In Proc. of the International

Tsunami Symposium, pp: 7-28.

Nistor, I., Palermo, D., Nouri, Y., Murty, T., and Saatcioglu, M.,

2009. Tsunami-induced forces on structures. Handbook of

coastal and ocean engineering, pp: 261-286.

Sainflou, G., 1928. Essai sur les digues maritimes verticales. École

nationale des Ponts et Chaussées.

Suzuki, T., Shijo, R., Yokoyama, K., Ikesue, S., Yamasaki, H.,

And Motoyama, J., 2014. Clarification of Behavior of Huge

Tsunami Action on Bridges-Hydraulic Model Experiment

and Simulation Technology. Mitsubishi Heavy Industries

Technical Review, v.51, no.3, p: 21.

Swaroopa Rani, V., Kirti Srivastava and Dimri, V.P., 2011.

Tsunami Propagation and Inundation Due to Tsunamigenic

Earthquakes in the Sumatra-Andaman Subduction

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Received on: 15.3.17; Revised on: 19.5.17, Re-revised on: 25.7.17, Accepted on: 2.8.17

“The sea loved the moon When she was supposed to love the shore.

The moon knew And hence made his intentions known.

That she should love the shore Who was destined for her.

Yet his protests seemed weak. And even when he pushed her towards the shore-

She always retreated back.

To want, to need, to love the moon For all she’s worth.

Everyone said, it wasn’t meant to happen. Yet, the Tsunami rose that night for their union.”

― Saiber - an young Indian story teller by choice and a poet by heart

Kamal and Komal Rani

490

Study of Effects of Basin Shape, Shape-Ratio and Angle of Incidence of SH-Wave on Ground Motion Characteristics and

Aggravation FactorsKamal*1 and Komal Rani2

1Department of Geophysics, Kurukshetra University Kurukshetra, Haryana2B.A.R. Janta College, Kaul, Kaithal, Haryana


ABSTRACTThis paper presents the effects of basin-shape, shape-ratio, impedance contrast (IC), sediment-damping and angle of incidence of SH-waves on the ground motion characteristics and associated spatial variations of average spectral amplification (ASA) and average aggravation factor (AAF) in the basins. Seismic responses of basin models were simulated using a SH wave fourth-order spatial accurate time-domain finite-difference algorithm based on staggered-grid approximation of viscoelastic velocity-stress wave equations. The obtained ASA and AAF were largest in the semi-circular basin and least in the trapezoidal basin for the considered model parameters. On an average, an increase of ASA and AAF were obtained with an increase of IC, sediment quality factor and the basin shape-ratio (in the shape-ratio range 0.03 - 0.16). An increase of ASA and AAF with the increase of angle of incidence of SH-wave was inferred.

Key words: Basin effects, basin-generated Love waves, aggravation factor and finite difference simulation.

INTRODUCTION

Seismic microzonation of an area is very much essential for the minimization of the impact of the earthquake hazard and prediction of seismic risk as well as developing cost effective earthquake resistant design of structures. A highly variable damage patterns have been reported in a particular basin due to the physical phenomenon like double-resonance (Dobry and Vacetic, 1987; Narayan et al., 2002), basin generated surface waves (Bard and Bouchon, 1980; Kawase, 1996; Hatyama et al., 1995; Pitarka et al., 1998; Graves et al., 1998; Narayan 2005; Narayan and Singh, 2006; Kamal and Narayan, 2014; 2015), basement focusing effects (Gao et al., 1996; Booth et al., 2004; Narayan and Kumar, 2013; 2014) and site effects and attenuation characteristics (Joshi et al., 2012; Kumar et al., 2013; 2014; 2015; Kumar et al., 2016) etc. Basin generated surface waves were confirmed based on the recorded ground motion in the Santa Monica and Kobe basins, theoretical studies and the observed damages during the 1994 Northridge earthquake and 1995 Kobe, Japan earthquake (Kawase, 1996; Graves et al., 1998; Pitarka et al., 1998). There are other numerous consistent macro-seismic observations showing a significant increase in damage severity in narrow zones located near the basin-edge (Poceski, 1969; Yuan and Huang, 1992). A significant number of scientists have studied the effects of soil layering on the characteristics of edge generated surface waves (Semblat et al., 2005; Narayan and Singh, 2006). Bard and Bouchon (1980) reported

preferential surface wave generation in case of larger angle of incidence of body wave at the basin edge.

The current practice of seismic microzonation in many countries is to transfer the bedrock motion to the surface using the 1D SH-wave response of a soil column. Based on the theoretical studies, it was inferred that the 1D response was inadequate to explain the observed damages in Santa Monica during the 1994 Northridge earthquake (Graves et al., 1998) and in Kobe basin during the 1995 Kobe, Japan earthquake (Pitarka et al., 1998). To incorporate the 2D/3D complex site effects in seismic microzonation, Chavez-Garcia and Faccioli (2000) have proposed the term aggravation factor (aggravation factor is simply the extra spectral amplification due to the complex 2D/3D site effects over the 1D response of the soil column). In the basins, as mentioned above, an important cause for the spatial variation of the seismic ground motions is the basin generated sur face wave.

In this paper, a detailed study of effects of basin-shape, shape-ratio, impedance contrast (IC), sediment-damping and angle of incidence of SH-waves on the ground motion characteristics and associated spatial variations of average spectral amplification (ASA) and average aggravation factor (AAF) in the basins are documented. Seismic responses of basin models were simulated using a SH wave fourth-order spatial accurate time-domain finite-difference (FD) algorithm based on staggered-grid approximation of viscoelastic velocity-stress wave equations. Snapshots have also been computed for inferring the development


Study of Effects of Basin Shape, Shape-Ratio and Angle of Incidence of SH-Wave on Ground Motion Characteristics and Aggravation Factors

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of basin generated surface waves and their back and forth propagation in the basin.

Salient Features of the Used SH Wave FD Program

A computer program developed by Narayan and Kumar (2013),which is based on the staggered grid (2,4) finite-difference approximation of the viscoelastic SH wave equation for the heterogeneous anelastic medium is used. The frequency-dependent damping in the time-domain FD simulations is incorporated based on the GMB-EK rheological model (Emmerich and Korn, 1987; Kristek and Moczo, 2003). A material independent anelastic function developed by Kristek and Moczo (2003) was used since it is preferable in case of material discontinuities in the FD grid (Narayan and Kumar, 2013; 2014). Both the sponge boundary (Israeli and Orszag, 1981) and A1 absorbing boundary (Clayton and Engquist, 1977) conditions were implemented on the model edges to avoid the edge reflections (Kumar and Narayan, 2008). In order to avoid the thickness discrepancy of the first sediment layer, which causes an increase of value of the numerically computed

fundamental frequency, VGR-stress imaging technique proposed by Narayan and Kumar (2008) is used.

Effects of Basin Shape

To study the effects of shape of basin on the ground motion characteristics, four basin models, namely, semi-circular (CRBM), rectangular (REBM), triangular (TRBM) and trapezoidal (TPBM) basins have been considered. The remaining geometrical parameters like width, maximum depth of sediment and inelastic parameters of the sediment and rock are the same for all the four considered basin models. The north-south cross sections of the CRBM, REBM, TRBM and TPBM basin models are shown in figure 1a-d, respectively. The width and maximum depth of all the basins are 3000 m and 200 m, respectively. All the distances are measured with respect to the centre of basins. A horizontal plane wave front has been generated at a depth of 300 m using various point sources. The point source has been generated in the form of Ricker wavelet. The dominant frequency in the considered Ricker wavelet was 4.0 Hz and frequency bandwidth 0-10 Hz. Seismic responses have been computed at 41 equidistant (100 m

Figure 1a-d. shows the considered semi-circular (CRBM), rectangular (REBM), triangular (TRBM) and trapezoidal (TPBM) basin models, respectively.

Table 1. The velocities and quality factors, density and unrelaxed moduli for the sediment and rock.

Model Vs(m/s)

Density(g/cc)

QS Unrelaxed Moduli (GPa)

Sediment 650 2.00 65 0.8707

Rock 2000 2.40 200 9.6938


492

apart) receiver points, extending 2000 m south to 2000 m north of centre of the basins. The velocities and quality factors for the P- and S-waves at a reference frequency 1.0 Hz (Fr=1.0 Hz), density and unrelaxed moduli µ (modulus of rigidity), K (bulk modulus), and λ (Lame’s parameter) for the sediment and rock are given in table 1. Four relaxation frequencies as 0.02 Hz, 0.2 Hz, 2.0 Hz and 20.0 Hz were used for the computations of the unrelaxed moduli. To reduce the requirement of computational time and memory, the basin models have been discretized with a continuous variable grid size (Narayan and Kumar, 2008). The vertical grid size was 5 m from free surface to a depth of 265 m and 15 m thereafter. Similarly, in the horizontal direction, the grid size is 5 m from 2100 m south to 2100 m north of centre of basins and 15 m thereafter. The time step is chosen to be 0.001 second to avoid stability problem. The seismic response of the model with no sediment is also computed for the quantification of spectral amplifications.

Figure 2a-d shows the seismic responses of CRBM, REBM, TRBM and TPBM basin models, respectively. The incident SH-wave, its multiple and basin-generated Love waves and multiples of the basin-generated Love waves are the first, second, third and fourth arrivals in a chronological order. Based on the analysis of figure 2, the fundamental and first modes of Love waves can be inferred in the basins. But, their characteristics are highly variable with basin-shape. Very large amplitude at the centre of basin may be due to the constructive interference of the Love waves generated at the left and right edges of the basin. A leakage of the Love wave energy in the rock can be inferred at each reflection of Love waves at the basin-edge. Further, it appears that the

Love waves are highly dispersive in nature depending on the basin-shape. The basin generated Love waves can be inferred in all the basins but their characteristics are highly variable from basin to basin. So, it may be concluded that basin-shape plays an important role in amplification of incident SH-waves and the basin generated Love waves.

Snapshots

In order to further infer the development of Love waves in the basins, snapshots in a rectangular area in the CRBM basin have been computed at different moments. Snapshots were computed in a rectangular area extending 2000 m south to 2000 m north of centre of basin and from free surface to a depth of 360 m. Figures 3 shows the snapshots at different times. The snapshots at times 0.45s to 1.35s depict that the incident plane wave front of SH-wave, it’s multiple and generation and propagation of Love waves towards the centre of basin. Similarly, snapshots at times 1.65s to 3.45s depict the propagation of Love waves in the basin.

Average spectral amplification

The spectral amplifications were computed just by taking the ratio of spectra of responses with and without basin in the model. The spectral ratio has been used to compute the average spectral amplification (ASA) at a particular location. Figure 4a illustrates the comparison of spatial variation of ASA in different basins. An analysis of this figure reveals that the largest and lowest ASA are obtained in the CRBM and TPBM basins, respectively. Further,

Figure 2a-d. The seismic responses of the CRBM, REBM, TRBM and TPBM basins, respectively.


493

Figure 3. Snapshots of response of the CRBM basin at different moments.

largest ASA in the CRBM and TRBM basins are occurring at the centre of basin.

Average aggravation factor

In order to study the effects of shape of basins on the spatial variation of average aggravation factor (AAF), spectral

aggravation factors were computed just by taking the spectral ratio of 2D response with the 1D response of the model at a particular location. Then spectral aggravation factors were used to find out the AAF at different locations in the basins. Figure 4b shows the comparison of spatial variation of AAF caused by mainly Love waves. Analysis of this figure depicts that the trends of spatial variation of AAF is almost the same

Figure 4a-b. Spatial variation of ASA and AAF, respectively in the CRBM, REBM, TRBM and TPBM basins.


494

Figure 6. Spatial variations of ASA and AAF, respectively in the CRDM-CRDM4 basins.

as that of the ASA in different basins. The largest AAF of the order of 1.6 was obtained at the centre of the CRBM basin. The cause of increase of AAF towards the centre of basins may be the constructive interference of the surface waves moving from opposite direction. So, it can be inferred that very large damage may occur in the central part of the basins, particularly TRBM and CRBM basins.

Effects of Shape Ratio of Basin

The shape-ratio of basin is defined as the ratio of maximum depth of basin with the half-width of basin. The shape-ratio of basin has been changed by changing the depth as well as width of the basin. The effects of shape-ratio for both the cases have been studied. First, seismic responses of four basin CRDM1-CRDM4 models with maximum depth of sediment as 200 m, 150 m, 100 m and 50 m and a fixed width as 3000 m with shape-ratios as 0.13, 0.10, 0.06 and 0.03, respectively have been computed. The seismic

responses of another four basin CRWM1-CRWM4 models with width as 3500 m, 3000 m, 2500 m and 2000 m and a fixed maximum depth as 200 m with shape-ratios as 0.11, 0.13, 0.16 and 0.20, respectively have also been computed. So, finally the range of basin-shape-ratio is 0.03-0.2. Figure 5a-d shows the seismic responses of the CRDM1-CRDM4 models, respectively. The characteristics of the SH-wave multiples and the basin generated surface waves are highly variable with the change of shape-ratio. A comparison of spatial variations of ASA and AAF in the CRMD1-CRDM4 basins are given in figure 6. On an average an increase of ASA/AAF with an increase of shape-ratio can be inferred for the considered model parameters and frequency bandwidth. Similarly, Figure 7a-d shows the seismic responses of the CRDM1-CRDM4 models, respectively. The characteristics of the SH-wave multiples and the basin generated surface waves are highly variable with the change of shape-ratio. Similarly, a comparison of spatial variation of ASA and AAF in the CRWD1-CRWM4 basins are given in figure 8.

Figure 5. The seismic responses of the CRDM1-CRDM4 basins, respectively.


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Figure 7. The seismic responses of the CRWM1-CRWM4 basins, respectively.

On an average an increase of ASA/AAF with an increase of shape-ratio can be inferred. So, it may be concluded that AAF/ASA increases with the increase of shape-ratio of basin, if shape-ratio is less than 0.20.

Effects of Impedance Contrast and Sediment-Damping

In this sub-section, the effects of impedance contrast (IC) and sediment-damping on the ground motion

characteristics in the basin are documented. In order to find out the effects of IC on the AAF, seismic responses of 1D basin models at different locations in the basin were also computed for different IC and sediment-damping. The velocities and quality factors at reference frequency, density and un-relaxed moduli for the different ICM1-ICM4 basin models are given in table 2. The width and maximum depth of the semi-circular ICM1-ICM4 basins were taken as 3000 m and 200 m, respectively. Figure 9a-b shows the spatial variation of ASA and AAF. An increase of ASA

Figure 8. Spatial variations of ASA and AAF, respectively in the CRWM1-CRWM4 basins.

Figure 9. Spatial variations of ASA and AAF, respectively in the ICM1-ICM4 basins.


496

and AAF with an increase of IC can be inferred. Further, the ups and downs are increasing with an increase of IC due to the development of more and more low frequency surface waves. The interference of these lower frequency surfaces is responsible for the large ASA/AAF at the centre of basin with a large IC.

To study the effects of sediment-damping on the ground motion characteristics, seismic responses of four semi-circular BDM1-BDM4 basin models were computed for different-sediment damping. The velocities at reference frequency and density are the same as given in table 1. The quality factors at reference frequency and unrelaxed moduli for the different BDM1-BDM4 basin models are given in table 3. The width and maximum depth of the semi-circular BDM1-BDM4 basins were also taken as 3000 m and 200 m, respectively. Figure 10a-b shows the spatial variation of ASA and AAF. An increase of ASA and AAF with an increase of quality factor can be inferred. The larger increase of AAF towards the centre of basin as compared to near the basin-edge with increase of quality factor, reflects the effects of sediment-damping on the basin-generated Love waves.

Effects of Angle of Incidence of SH-Wave

To quantify the effects of angle of incidence of SH-waves on ground motion characteristics in the basin, seismic responses of the ICM1 basin model have also been computed for 200, 450 and 600 angles of incidence of SH-waves. The angles of incidence of SH-wave in CRAM2, CRAM3 and CRAM4 models are 200, 450 and 600, respectively (Figure 11). The remaining parameters for the CRAM2, CRAM3 and CRAM4 models are same. The CRAM1 model corresponds to the ICM1 model where angle of incidence of SH-wave is 00. Figure 12a&b show the seismic responses of the CRAM2 basin model without and with basin in model, respectively. Similarly, figures 12c&d and 12e&f show the seismic responses of the CRAM3 and CRAM4 basin model without and with basin in model, respectively. An analysis of figure 12a reflects that the inclined linear wave source (200) has generated SH-wave. Further, these waves have generated Love waves in the basin. Similarly, an analysis of figure 11c reflects the inclined linear SH-wave source (450) generation. Because of large angle of incidence of SH-wave, it appears

Table 2. The velocities and quality factors, density, IC and unrelaxed moduli for the ICM1-ICM4 basin models.

Model Vs(m/s)

Density(g/cc)

IC QS Unrelaxed Moduli (GPa)

ICM1 650 2.00 3.69 65 0.8707ICM2 800 2.05 2.92 80 1.3443ICM3 950 2.10 2.40 95 1.9345ICM4 1100 2.15 2.02 110 2.6479Rock 2000 2.40 --- 200 9.6938

Table 3. The quality factors and unrelaxed moduli for the BDM1-BDM4 basin models.

Parameters BDM1 BDM2 BDM3 BDM4QS 32.50 48.75 65.00 81.25

Unrelaxed Moduli

0.8974 0.8795 0.8707 0.8655

Figure 10. Spatial variations of ASA and AAF, respectively in the BDM1-BDM4 basins.


497

that the SH-wave has also caused Love wave at the point where the SH-wave front interacted with the free surface with considerable amplitude. An increase of amplitude of basin-generated love wave in basin can be inferred. This was also observed by Narayan (2012) and Narayan and Kumar (2013). Further, incident SH-wave has generated Love waves in the basin. So, in the CRAM3 and CRAM4 basin models, we have both the basin-generated and basin-induced Love waves (Figure 12d & 12f). A complex mode

conversion of basin induced Love wave at the basin edge can also be inferred (Narayan, 2012).

Figure 13a-b depicts the comparison of spatial variations of ASA and AAF for the CRAM1-CRAM4 basin models, respectively. Analysis of figure 13 depicts that in case of angle of incidence as 200, 450 and 600, the amplification is largest towards the left edge of basin, in case of CRAM3 and CRAM4 models. On the other hand, the amplification is symmetrical around the centre of the

Figure 11. CRBM basin model and the incident plane wave fronts with different angle of incidence at the free surface.

Figure 12a-f. The seismic responses of the CRAM2, CRAM3 and CRAM4 models without and with basins, respectively.


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basin in CRAM1/ICM1 basin model. This is due to the normal incidence of the SH-waves. It can also be inferred that the level of AAF is larger in CRAM2, CRAM3 and CRAM4 models as compared to the CRAM1/ICM1 model. Further, the level of AAF is larger in CRAM4 model as compared to the CRAM3 model. So, it may be concluded that amplification of ground motion increases with the increase of angle of incidence of SH-waves.

CONCLUSIONS

Based on the analysis of seismic responses of various basin models and the computed snapshots, it is inferred that the incident SH-wave generates Love wave in the basin. The analysis of simulated responses of basins having different shapes revealed that the ground motion in the basin is highly dependent not only on the shape of basin but also on the width and largest depth of basin, while other parameters are the same. Almost, all the factors like ASA and AAF were largest in the semi-circular basin and least in the trapezoidal basin for the considered model parameters. The obtained largest AAF level near the edge of rectangular basin was also reported by Moczo and Bard (1993) and intense damage during past earthquakes (Poceski, 1969; Yuan and Huang, 1992).

On an average, an increase of ASA/AAF was obtained with an increase of IC, sediment quality factor and the basin shape-ratio (in the range 0.03 - 0.20). Furthermore, an increase of ground motion amplification towards the centre of basin with the decrease of sediment-damping reflects the effects of damping mainly on the basin-generated surface waves. The percentage increase of ground motion amplification is more than the percentage increase of IC across the basement. This may be due to the increased duration and trapping of surface waves in the basin due to an increase of IC. Based on the analysis of responses of basins for the different angles of incidence of SH-waves, it may be concluded that amplification of ground motion increases with the increase of angle of incidence of SH-waves in the basin. For example, the largest AAF was

of the order of 1.63 and 1.69 for angle of incidence of 450

and 600, respectively.

ACKNOWLEDGMENTS

The research study presented in this paper has been carried out under the Dr. D.S. Kothari Postdoctoral Fellowship (DSKPDF) scheme. This study is financially supported by UGC research grant DSKPDF (F.4-2/2006(BSR)/ES/15-16/0037).The authors are grateful to an anonymous reviewer for objective evaluation and useful suggestions. They also express their thanks to Chief Editor of JIGU for apt editing.


The authors declare that they have no conflict of Interest and adhere to copyright norms.

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motion characteristics using 2.5-D modeling”, PAGEOPH,

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the characteristics of basin-edge induced surface waves and

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contrast on the characteristics of basin transduced Rayleigh

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finite-difference program for the simulation of SH-wave

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Received on: 25.4.17; Revised on: 11.5.17; Re-Revised on: 27.7.17; Accepted on: 1.8.17


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Interpretation of Seismic data for thrust/fault identification using variance and inverse of variance attribute analysis

Mausam Gogoi*1 and G.K. Ghosh2

1Dibrugarh University, Assam2Oil India Limited, Assam


ABSTRACTSeismic attribute is classically defined as a component extracted from seismic data that can be analyzed in order to enhance the hidden information used to identify a better geological or geophysical prospect in certain depositional environment. Seismic attributes are the components of the seismic data which are obtained by measurement, computation, and by logical or experience based reasoning. It is well established by seismic experts that seismic attributes help visual enhancement or quality of the features of interpretation interest. They became a valid analytical tool for lithology prediction and reservoir characterization. A good seismic attribute is either directly sensitive to the desired geological features or reservoir properties of interest. In this study, variance and inverse of variance attribute analysis has been carried out first for the synthetic data and thereafter applied to the real field seismic data for automatic fault /thrust identification. Synthetic seismic traces are generalized and data has been digitized to calculate the variance on the said seismogram. With the help of MS excel sheet, theoretical formulation has been carried out to study, variance and inverse of variance of different traces using three point window in the excel sheet. After studying the variance and inverse of variance attribute, it is noted that these attributes can provide better identification for fault/thrust and edge detection. The variance and inverse of variance attribute analysis applied to the real field seismic data for automatic interpretation for thrust/fault identification, has helped in clearly distinguishing the fault locations.

Key words: Seismic data, attribute analysis, three point window, variance and inverse of variance, attribute analysis.

INTRODUCTION

The interactive interpretation of seismic data and attribute analysis can help evaluation of fault pattern and fault location along with the continuity and discontinuity of the traces in seismic sections. In order to bring out meaningful subsurface images the seismic attribute analysis (Chopra and Marfurt, 2007; 2009) with integrated approach of geo-scientific data can play an important role for understanding the subsurface features.

In this study, attribute analysis has been carried out in the Dibrugarh area falling in the Assam-Arakan basin of north-eastern part of India (Samik, 2003). Various attribute studies have been carried out such as- dip deviation, sweetness, local structural dip, local structural azimuth, variance and inverse of variance to study the images and proper structural lineaments of the subsurface. From this analysis it is suggested that the variance and inverse of variance attribute jointly can give the proper picture of the fault and structural edge location.

A theoretical study has been carried out using variance attribute analysis applicable to the synthetic data set. Further, this approach has been applied to the real field seismic data for automatic fault identification. With the help of MS excel sheet, theoretical formulation has been

carried out to study mean, variance and inverse of variance for each sample data using a windows shift of 3 data point.

This attribute analysis can be applicable for automatic thrust/fault identification. It has been observed that the fault locations are clearly distinguished through variance and inverse of variance analysis.

METHODOLOGY AND THEORY

The role of variance and inverse of variance play an important role for mapping the thrust and fault identification. As variance is the opposite of coherency it can be calculated through trace to trace variability in a certain sample interval using seismic traces. This produces an interpretable lateral changes in acoustic impedance and leads to low variance coefficients. While in the other case, higher variance coefficients signify higher discontinuities in the case of inverse variance. Thus by studying low variance coefficients and high variance coefficients in seismic signature, one can identify/detect the thrust and fault location.

Initially, we have selected a synthetic seismic dataset having thrust and fault demarcation. This data containing all relevant information has been digitized. In this study, we have selected 10 seismic traces of 500 ms length (2800ms



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to 3300 ms). The data has been digitized for all the seismic traces for the calculation of variance and inverse of variance attribute analysis. Using MS excel sheet, we have calculated the mean and standard deviation. This has been followed by calculation of variance and inverse of variance for each trace. The output has been plotted in the MS excel sheet.

Variance Attribute

Variance is statistically defined as the square of the standard deviation (Fisher, 1918 and Fisher (1925). Mathematically, standard deviation (SD=σ) can be expressed as mentioned in equation (1)

(1)The Arithmetic Mean (AM) of a series is obtained by

adding the values of the series and dividing the number of items.If x1, x2, x3, ………… xn, are the values of the variable x. AM denoted by x is given by equation (2),

(2)In the case of grouped data, let x1, x2, x3, ………… xn,

are the values of the variable x with frequency f1, f2……….fn, then, AM denoted by x and f as given in equation (3).

(3)

Where N = Sf = Total frequency.In case of continuous frequency distribution x is taken

as midpoint of class interval. Variance is the average of the squared differences from the mean as given in equation (4).

(4)Where: n= no. of observations fi= frequency xi= variable xm= mean of xi (average)

Inverse of Variance Attribute

Inverse of variance attribute analysis is the reciprocal of variance attribute and mathematically can be expressed as in equation (5) (Sańchez-Meca and Marıń-Martıńez, 1998).Inverse of variance attribute = (1/ σ2) (5)

Substituting the value of variance (from equation 4) in equation (5), this can be simplified as shown equation (6)

(6)Calculation of the detailed mathematical derivations

for the variance and inverse of variance, for the theoretical data, has been explained by Gogoi and Ghosh (2015).

CASE STUDY – FOR SYNTHETIC DATA

A particular window of a seismic section is considered where a faulted zone is focused. With the help of Microsoft Excel, each trace of that window, Mean, Variance and Inverse of Variance are calculated. The curves are plotted simultaneously in the graph and interpreted. A theoretical calculation for a sample dataset (Figure 1) is used with

Figure 1. The window of a seismic section of the fault zone from where the data of the traces are taken for various attribute calculations.


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averaging 3 point dataset for calculating the mean, which is explained in Table 1. The same procedure is applied for calculating the other formulation for variance and for the inverse of variance analysis simultaneously (Table 2).

It is significantly observed that the variance and inverse of variance are well correlated for delineating the thrust/fault location in the test data set. The amplitudes for the variance and inverse of variance are opposite in nature. Here, we have attempted to plot the test data for three different interpretations. Figure 2 shows the trace calculations for the cross line. Figure 3 shows the test section of the seismic data of a fault section. Figure 4 shows the variance of the seismic data and Figure 5 shows the inverse of the variance of the seismic data simultaneously.

CASE STUDY- REAL FIELD DATA

We have selected the field data, which is located in Dibrugarh area, a part of Assam-Arakan basin in the northeastern India. Few in-lines and cross-lines sections of this 3D volume are selected for attribute analysis. We have also carried out attribute analysis for Structural dip, Local structural azimuth, Structural Smoothing, Sweetness, Instantaneous Phase, Dip Deviation, Variance etc. The various attributes are shown in Figure 6 (a to h)

We have noticed that in a trace of inverse of variance the low amplitude and in variance the high amplitude indicate presence of the fault. Finally the outcome of the attribute in time slice of basal section gives proper picture of the fault as shown in Figure 7.

Table 1. Seismic dataset has been used after 3 data point window for calculating variance and inverse of variance.

Table 2. Some examples of the synthetic dataset for calculation of variance and inverse of variance.


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Figure 2. Traces calculation for the Cross line-520 and the corresponding plots of (a)test raw data, (b)Mean data, (c)Variance, and (d)Inverse of Variance are shown.

Figure 3. Test seismic data for the calculation of variance and inverse of variance indicated a fault section.


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Figure 4. Map shows the variance of the seismic data with Positive filled.

Figure 5. Map shows the inverse of variance of the seismic data with Positive filled.


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Figure 6. Types of Attributes namely (a) Curvature, (b) Dip Deviation, (c) Instantaneous Phase, (d) Local Structural Dip, (e) Sweetness, (f) Structural Smoothing, (g) Variance, and (h) Inverse of Variance respectively.

Figure 7. One of the time sections of 3D window showing fault.


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CONCLUSIONS

It has been found that the variance and inverse of variance attribute analysis has significantly helped the fault identification in comparison to other attributes.

It is noted that in variance attribute, significant high amplitudes are observed. However, in the case of inverse of variance attribute, the low amplitudes are indicated. By joint inspection with the help of variance and inverse of variance attribute, it is possible to mark and identify the thrust/fault locations reasonably good, and are not visible from the raw seismic section.

ACKNOWLEDGEMENTS

We express our sincere thanks to Oil India Limited, Duliajan, Assam for providing us with the requisite data and extending facilities to work with the software. We are grateful to OIL for the permission to publish the paper. Dr. B. K. Rastogi carried out reviewing and suggested useful changes to enhance the quality of the manuscript. We gratefully thank Chief Editor for helping in restructuring the revised version and final editing.



Received on: 16.3.17; Revised on: 9.6.17; Re-revised on: 28.7.17; Accepted on: 1.8.17

REFERENCES

Chopra, S., and Marfurt, Kurt J., 2009. “Seismic Attribute- A

Historical perspective”. Geophysics, doi: 10.1190/1.2098670.,

v.70, no.5, pp: 35O-285O.

Chopra, S., and Marfurt, Kurt J., 2007. “Seismic Attributes for

Prospect Identification and Reservoir Characterization”.

Geophysics, pp: 34-45.

Samik K. Kanjilal, 2003. “Assam and Assam Arakan Basin its

overview.” pp: 435-670.

Fisher, R.A., 1918. “The correlation between relatives on the

supposition of Mendelian inheritance”. Transction of the

Royal Society of Edinburgh, v.52, pp: 399-433.

Fisher, R.A., 1922. “On the mathematical foundations of

theoretical statistics”. The Philosophical Transactions of

the Royal Society, A, ccxxii. 309-68.

Sańchez-Meca, J., and Marıń-Martıńez, F., 1998. “Weighting

by inverse variance or by sample size in meta-analysis:

A simulation study. Educational and Psychological

Measurement” v.58, pp: 211-220.

Gogoi, M., and Ghosh, G.K., 2015. “Structural interpretation of

Seismic data for fault identification using attribute analysis”.

M.Tech. Exploration Geophysics Dissertation. Department

of Applied Geology, Dibrugarh University. (Unpublished

report), pp: 48.

• Views expressed in this text are that of authors only and may not

necessarily be of Dibrugarh University or Oil India Limited.

“Try to forget what objects you have before you - a tree, a house, a field, or whatever. Merely think, ‘Here is a little square of blue, here an oblong of pink, here a streak of yellow,’ and paint it just as it looks to you, the exact color and shape, until it gives you your own impression of the scene before you”.

- Claude Monet (1840 –1926) was a founder of French Impressionist painting

***

“Geometric shapes hold an energy pattern, and scientists did some experiments which say certain geometric shapes can affect matter around them. It’s simply because when a human looks at a shape, they instantly receive energy from their brain”.

- Tom DeLonge (1975--) is an American musician and film producer.

Analysis of Tectonically controlled Valley Floor morphology of the Central Segment of Sabarmati River Basin: An Integral approach using satellite images and GIS Techniques

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Analysis of Tectonically controlled Valley Floor morphology of the Central Segment of Sabarmati River Basin: An Integral approach

using satellite images and GIS TechniquesNisarg H. Bhatt*and R.D. Shah

M.G. Science Institute, Navarangpura, Ahmedabad, 380007, Gujarat*Corresponding Author: [email protected]

ABSTRACTPresent paper deals with the integrated study of satellite and field investigation in the central segment of Sabarmati River basin that covers ~ 20,000 km2 area along Cambay fault system. The valley floor morphology within the central segment of the Sabarmati River basin is controlled by several NNW-SSE, NW-SE, and NE-SW trending faults of Cambay basin. The sequential reactivation of these faults gives rise to morphological changes in the river system, leading to incision and widening of valley floor, favorable sites for deposition of Quaternary sediments. The consequence of sequential reactivation and deposition of sediments is reflected in the form of tectonic geomorphology in the area. Several geomorphic markers, such as paleochannels, wind gap, uplifted strath terraces, incised ravine surfaces, compressed meandering, and offset of drainage pattern associated with tectonic activity have been identified in the region.

Key words: Sabarmati River, Morphotectonics, Neotectonics, GIS, Geomorphology

INTRODUCTION

Morphotectonic studies can be defined as the study of different types of landforms produced by tectonic processes, or application of geomorphology to solve tectonics problems (Keller and Pinter, 1986). The tectonic landforms analysis has been done using high-resolution Landsat 8 optical images and CARTOSAT digital elevation models (DEM). In tectonically active regions, evolution of landforms depend upon the interactions between surface processes and tectonic deformation. (Kothyari et al., 2016; Graveleau et al., 2015). The detailed geomorphological and morphotectonic interpretation of drainage system can provide the information about the neotectonic activity in the area (Prakash et al., 2016). The Sabarmati River basin is controlled by rocky Aravallis to the north and the Gulf of Khambhat (GOK) in the south (Merh and Chamyal, 1997; Raj, 2012). The river flows across the southwest inclined topographic slope and crosses the alluvial plains in the central portion of the basin and finally disappears into the GOK, covering approximately 20,000 km2area. In the central portion, the river flows parallel to the peri cratonic Cambay basin (Biswas, 1987). It is mostly occupied by Gujarat alluvium plains (Figure 1). Further, based on satellite data investigation Sareen et al., (1993) and Zeuner (1950) identified several NE-SW to NNE-SSW oriented linear features controlling the hydrological network. These studies revealed that the Quaternary landforms within the Gujarat alluvial plain are controlled by active tectonic activity (Chamyal et al., 2003; Jain et al., 2004). In the present study, ~90 km long stretch of Sabarmati River

basin has been investigated to evaluate tectonic activity in the central portion of the basin. In the present study, we have used high-resolution satellite imageries to identify tectonic signatures from the central portion of Sabarmati basin. In addition to tectonic signatures major tectonic boundaries have also been demarcated.

Methodology

The methodology involves the visual and digital analysis of the satellite remote sensing data as well as field work for ground truth (Joshi et al., 2013). The database was generated using Landsat 8 ETM FCC data. Digital elevation model (DEM) was generated using the Shuttle Radar Topography Mission (SRTM) data downloaded from CIAT SRTM website (http://srtm.csi.cgiar.org) and CARTOSAT-1 data downloaded from Bhuvan website (http://bhuvan.nrsc.gov.in). Various thematic layers comprising river channel with water, bank line of the river, floodplain, fluvial terraces, sandbars/channel bars, point bars, palaeo-meanders/cut-off meander loops, paleochannels, and ox-bow lakes have been generated using onscreen analysis of satellite data in GIS platform. These layers were compiled to form a fluvial geomorphological map (Figure 11). Ground truth data collection was carried out in pre-monsoon season during April 2016. The ground control points and the field photographs were collected at certain places. For detailed geomorphic analysis, the entire study area has been divided into three major zones; zone of compressed meandering represented by zone-1, ravine surfaces marked as zone-2, and the upper hilly regions marked as zone-3.



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ObservationsBased on tonal and textural variation we identified different levels of fluvial terraces and scroll plains near Mahudi (23°30’18.62”N latitude and 72°47’52.74”E longitude) (Figure 2a). The incision of first order drainage pattern (ravine surfaces) is clearly visible in DEM data (Figure 2a). Several traces of NE-SW, NW-SE, and N-S oriented faults have been identified using the satellite data with the help of DEM observation. It is inferred that the leading side of river terraces are truncated by faults (Figures 2 b and c). A trace of paleo river course has also been identified near Mahudi using DEM analysis (Figure 3).

Near Mahudi (23°30’18.62”N lat i tude and 72°47’52.74”E longitude) approximately 40 m thick two levels of starth terraces are well preserved at the west bank of River (Figure 2c). The T1 terrace is around 29 m thick, whereas the T2 terrace is ~11m thick and resting over the two thick conglomeratic bedrock (Figure 2d). The elevation difference of each terrace has been estimated from Cartosat DEM data. The lower fluvial sequence is

formed by hard and compact fine to medium sand. In T2 terrace the stabilized dunes are found on the top of the fluvial sequence. The upper sequence comprises 7.5m of grayish yellow fine sand to medium sand and silty clay with an erosion contact. It is succeeded by the 2 m thick Aeolian deposit. The presence of an archaeological site on the top level of terrace indicates that the site was occupied by humans around 1600 AD (Tandon et al., 1999). Due to subsidence of land with the impact of tectonic activity forced the humans to settle down at this place. The previous study shows that the aggradation of oldest terraces T1 was started around 55ka (Srivastava et al., 2001) and continued till 12 ka. The incision pattern and presence of conglomerate bed indicate that these terraces are uplifted after deposition of the T2 surface befor 12ka (Srivastava et al., 2001). A Paleochannel and N-S trending fault is observed near Prantij (23° 24’ 52” N 70° 50’ 53” E) with the help of Cartosat ortho and DEM data (Figure 3). The presence of cutoff meander events is a key component in the complex dynamics of meandering rivers (Camporeale et al.,

Figure 1. Location and drainage map of Sabarmati River basin (Note: the study area is highlighted by a black rectangle).


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2008). Such a cutoff meander is observed at Checkhlapagi village (23°19’14.10”N 72°50’56.09”E) along the faults trending NW-SE. it is also inferred that the N-S oriented Bok Fault is left laterally displaced near Chekhlapagi along NW-SE fault (Figures 4 a and b).

Field Evidences

A large amount of evidence of geomorphic expressions associated with tectonic activity has been documented within the Sabarmati river basin. These geomorphic

Figure 2. (a) Landsat image superimposed on DEM, (b) Geomorphic map of Mahudi area (c) River Section Near Mahudi showing two major divisions of formation (Aeolian and Fluvial) with two levels of terraces. (d) section found in the same area showing Displacement and Exposure of Conglomerate Bed.

Figure 3. Cartosat Satellite data and Geomorphic Map of Bok Paleochannel with Bok Fault near Prantij.


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expressions are the development of river terraces, incision of the channel, offset by river channel, development of deep gullies and ravine surfaces, uplifted scroll plains, compressed meandering, and fault scarp. River terraces and incised ravine surfaces are the most remarkable geomorphic expressions. They are associated with tectonic activity. Maurya et al., (2000) suggested that the ravines, drainage asymmetry, alleys valleys, and entrenched meanders are indicative of Holocene tectonic uplift.

Fluvial Terraces

At a place Oran (Lat: 23°24’16.3”N, Long: 72°47’25.”E) 22m thick two river levels of Strath terraces are well preserved (Figure 5). The T1 terrace is around 32 m thick. T1 terrace is composed of the 9m thick basal conglomerate. T2 terrace is preserved by the fluvial sequence (10m) and the Aeolian Deposit (3m).The fluvial sequence comprises fine to medium sand. The Aeolian deposit comprises

Figure 4. (a) Geomorphic map showing Major Geomorphic Features, lineaments near Chekhlapagi Village (b) Field photo of fault scarp and incised terraces near Chekhlapagi Village.

Figure 5. Two levels 22m high fluvial terraces near Oran Village.


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Figure 6. Different Types of Fluvial Terraces and their Field Evidence showing unpaired terraces (a) and (b): Two levels of unpaired terraces In Meshwo River near Krishnanagar, The most remarkable feature is ponding of river. (c) and (d): Two level of Terraces Rest upon conglomerate near Pimplaj village.

stabilized dunes. Near Krishnanagar (23° 4’ 34” N latitude and 72° 50’ 1” E longitude) two levels of unpaired terraces are well preserved along Meshwa River (Figures 6 a and b). These terraces are developed within the contraction band with NNW-SSE and NE-SW oriented faults. The river Meshwo has incised within the contraction zone. Near Pimplaj village (23° 14’ 26” N 72° 57’ 35” E) unpaired fluvial terraces are present. A prominent offset of Meshwo joining streams is also seen (Figures 6c and d). One can also see the offset of the stream along the fault and development of Ravines and gullies towards the upthrown block. Here compression of meandering is caused by relative motion along the fault, as the river crosses fault segments that became incised. The fault is oriented towards NW-SE. Here two-levels of surface terraces are found that can be described as T1 and T2. These terraces are resting over ~2 m thick conglomerate unit.

Wine Glass Valley

Wine glass valleys are conventionally associated with head ward erosion towards the up-thrown block of a normal oblique fault (Graveleau et al., 2015). In the present study, the wine glass Valley is associated with an NNW-SSE oriented fault near Mahudi. The tectonic uplift along this fault has not only developed wine glass Valley but several other geomorphic expressions, which are also observed along the surface trace of the fault. Fault scarps may be modified by head ward erosion. The trunk Stream of Sabarmati River flowing from hanging wall of the fault, incised and formed a deeply- V-shaped valley within the fault zone (Wine glass structure) (Figures 7 a and b).

Near Mahudi Presence of Scroll plains are observed (Figure 7 c). There are three generations of scroll plains. The scroll plain 1 is the oldest and the last one, the scroll plain3, is the youngest. (Srivastava et al., 2001). The presence of three scroll plains suggests the tectonically active nature of Sabarmati river basin. The presence of ingrown meander morphology and vertical offset, which distinct each scroll plain, suggests tectonically active nature. It represents the distinct tectonic events that are responsible for the formation of the scroll plains. As such, it can be said that the river had passed through two major tectonic activity events.

Offsets in Drainage

The offset of drainage pattern is one of the common geomorphic expressions of tectonically active areas. In the present study, several offsets have been documented along the NNW-SSE and NW-SE oriented faults. A prominent 3 km long offset of Sabarmati River has been observed along a NNW-SSE oriented fault, passing through the Mahudi. Another offset is found near the Oran village. At this place the offset of the river is around 2.80 km. Similar offsets with same trends are observed in Khari and Meshwo Rivers at 1.4 and 2.5km, respectively. Figure 8 depicts the satellite view of offset pattern observed along the Sabarmati river basin.

Ravine Surfaces

Ravines are first order geomorphic expressions of active movement. Within the Sabarmati river basin, the ravine surfaces are mainly associated with intrabasinal Cambay


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faults and subordinate climatic effect. These ravine surfaces are oriented along NW-SE direction, as illustrated in Figure 9. In the present study area, these ravines are developed along the first order streams. Development of ravines and associated incision in this region is correlated with

tectonic movement along these faults. Ravines are formed by the action of the stream that erodes the land. The directional analysis of ravine orientations shows that the ravine trends are related to neotectonic activity along older structural trends during Quaternary. In the central portion

Figure 8. Offset in Major Drainage Pattern (a) and (b) Sabarmati River showing offsets and Lineaments, (c) Khari River showing offset and Lineament (d, e, and f) and Meshwo River Showing offsets and Lineaments.

Figure 7. (a) Schematic block model of Mahudi area shows incision of fluvial terraces and development of wineglass Valley and Scroll plains toward the uplifted block (b) field photograph shows wineglass valley near Mahudi(c) 3 Level of scroll plains in Sabarmati River near Mahudi.


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of Sabarmati river basin these ravine surfaces are incised to an extent of 10 to 80 m. The central zone of the study area can be termed as a zone of the incision. The presence of faults and associated incision along trunk streams of Sabarmati basin further confirm their association with tectonic activity during the formation of ravines.

Paleochannel

Paleochannel is a vanished course of past river system (Pettijohn, 1975). The occurrence of paleochannel provides

evidence of channel movements that have taken place in Gujarat alluvial plains through time (Raj et al., 2014). In the present study, approximately 20 km long N-S oriented paleochannel of Hathmati River is documented. The channel morphology, sediment characteristics and linkage with present day river indicate that in the geologic past the channel was occupied by Hathmati River. The river gradually shifted towards west due to vertical movement of the Bok fault. Two uplifted blocks were identified towards the footwall of N-S oriented Bok fault and NW-SE trending Mahudi Fault. The Relative Motion along these two faults

Figure 9. (a-b) Development of Ravine surfaces near Mahudi village. (c-d) Development of Ravine surfaces near Oran village.

Figure 10. (a) Close view of Paleochannel. (b) Birds eye view of paleochannel near Prantij. (Note: The Bok fault passes from the paleochannel)


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resulted in uplift of the ground .This in turn caused lateral migration and incision of river channel giving rise to present day paleochannel (Figure 10).

DISCUSSION AND CONCLUSION

Seismotectonically the Sabarmati-Cambay basin is one of the major seismically active parts of western peninsular India (Pancholi, 2017 (in press)). The basin has witnessed occurrence of several micro to moderate earthquakes in the recent past. About 625 earthquakes in Cambay Rift region have been recorded by Gujarat state seismic network from mid-2006 through 2012. Their magnitude ranged from~1 to 4.4. A Larger number of located earthquakes since 2008 may be due to improved delectability, with the establishment more number of surveillance network. Annually, on an average 10-20 shocks of M 2-2.9 and 2-3 shocks of M ≥ 3 are being recorded (Pancholi, 2017). The entire length of the basin from north to south and entire width from west to east seem to be active.

The tectonic signatures along Sabarmati River, Gujarat, India have been examined in the central portion of the basin using satellite data and detailed field check. The morpho stratigraphy of the basin suggests that the upper fluvial sequences are overlying Aeolian sand (Srivastava

et al., 2001). The optical chronology of fluvial sequences suggests that these were deposited between 55 and 12 ka during the Oxygen Isotope Stage-3 (Srivastava et al., 2001).

The incised valleys and ravine surfaces suggest that the river reached present stage after 12 ka. Previous studies show that the river adjustment in the central portion of Sabarmati river basin is caused by several phases of tectonic pulses between 12 ka and 3 ka. The presence of scroll plains and abundant paleochannels in the area are witness to Holocene tectonic movement along faults (Srivastava et al., 2001).

Based on Geomorphic development, it is inferred that the zone of Incision is one of the most active segments of the study area compared to the zone of Higher Elevation and the zone of Compressed Meanders (Figure 11) .The landform development in the central segment of the area is controlled by NNW-SSE, NW-SE, and NE-SW trending faults. Geomorphic developments such as uplifted strath terraces, incised ravine surfaces, wind gap, paleochannels, offset of drainage pattern, compressed meandering are linked with the tectonic movement along NNW-SSE, NW-SE, and NE-SW trending faults. Based on stream offset, several new faults have been identified. The presence of these geomorphic features together suggests tectonically active nature of the terrain. The luminous Chronology of the sediments found in Mahudi area (Srivastava et al.,

Figure 11. Geomorphological Map of study area (showing 3 zones and Major Geomorphic features with Major Lineaments present in the area)


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2001), suggests that Sabarmati River aligned to its present course as the result of tectonic activity in the region. The timing of incision and uplift is bracketed between 12 and 3ka. Evidence of tectonic activity during the Mid-Holocene is indicated by the preservation of three scroll plains (Srivastava et al., 2001). The Geomorphic mapping of landforms in the central segment of Sabarmati river basin will be useful for future earthquake hazard assessment and town mitigation planning.

ACKNOWLEDGEMENTS

The authors are grateful to Geology Department, M. G. Science Institute for their support for the present Research study. We are thankful to Dr. Girish Ch. Kothyari and Dr. Mahendrasinh Gadhvi for critical review and useful suggestions to enhance the quality of the manuscript. Authors are also thankful to Vasu Pancholi for his encouragement. We are thankful to Maulik Patel for field support. We thank the Chief Editor for his continued support, guidance, encouragement and detailed re-structuring of the manuscript and precise editing.



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Received on: 24.3.17; Revised on: 17.5.17, Re-Revised on: 12.6.17; Accepted on: 4.8.17


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Paleoproterozoic magmatism in the Cuddapah basin, IndiaV. V. Sesha Sai1*, Vikash Tripathy2, Santanu Bhattacharjee2 and Tarun C. Khanna3

1Petrology Division, Geological Survey of India, Southern Region, Hyderabad-India-682Geological Survey of India Training Institute, Hyderabad-India-68

3CSIR-National Geophysical Research Institute, Hyderabad-India-07*Corresponding Author: [email protected]

ABSTRACTThe Proterozoic Cuddapah basin of Southern India, with an aerial extent of 44,500 km2, is one of the largest sedimentary basins in the world that witnessed significant events of magmatism during its evolution. Initiated around 2.1 – 2.0 Ga, the basin preserves a protracted history of sedimentation, magmatism and tectonism from Paleo to Neoproterozoic. Through this paper we explicate the Paleoproterozoic ultramafic-mafic-felsic magmatic events that are contemporaneous with the sedimentation of Cuddapah Supergroup. The ~ 1.9 Ga ultramafic-mafic sills, along with basic and felsic volcanics and the interbedded tuffaceous rocks are stratigraphically confined to the Cuddapah Supergroup; that hosts substantial sedimentary sequence in the Cuddapah basin of Eastern Dharwar Craton. We provide a chronological illustration of Paleoproterozoic ultramafic-mafic-felsic magmatic events with details of available geochronological ages; their location and position in the stratigraphic succession constituting the Cuddapah Supergroup (see Table 1). Confinement of the Paleoproterozoic ultramafic-mafic sills within the clastic to shallow marine non-clastic sequences of Papaghni and Chitravathi sub basins, their configuration parallel to the basins arcuate western margin, associated Paleoproterozoic felsic volcanic, disposition of this geological domain along the eastern margin of the stabilised Dharwar craton, indicate a continental arc extensional setting for the evolution Paleoproterozoic segment of Cuddapah basin, India.

Key words: Proterozoic magmatism, extensional tectonics, Cuddapah basin, eastern Dharwar craton, India

INTRODUCTION

The Proterozoic Era in peninsular India is characterised by the deposition of thick sequences of clastic / non-clastic sedimentary rocks in platform-type continental margin shallow marine basins (Eriksson et al., 1998; Sharma et al., 2014; Kale, 2016). The Proterozoic Cuddapah basin of peninsular India (Figure 1) is one of the largest sedimentary basins in the world that preserves a thick sequence of clastic and non-clastic rocks, and associated magmatic rocks (King, 1872; Nagaraja Rao et al., 1987; Bhasker Rao et al., 1995; Mazumder and Eriksson, 2015). Petrological and geochronological studies of the magmatic rocks in the Cuddapah Supergroup have provided significant insights into the nature of tectono-magmatic processes that emerged during the basin evolution (e.g., Chatterjee and Bhattacharji, 2001; Anand et al., 2003; French et al., 2008; Chalapathi Rao et al., 2004; Sheppard et al., 2017).

Keeping in view of the broad interest of the readers in this globally significant sedimentary basin, we provide a chronological illustration of the Paleoproterozoic magmatic events, with details of geographical locations, nature of occurrence in various stratigraphic horizons in the Cuddapah Supergroup (see Table 1 & Figure 4). This Geology review signifies the role of a short lived Paleoproterozoic magmatic regime in the initiation and early evolution of Cuddapah basin in a continental

arc extensional setting along the eastern margin of the stabilised Dharwar craton, India.

Regional Geology

The crescent shaped Proterozoic Cuddapah basin has an aerial extent of 44,500 km2and it is considered to be one of the most important Purana basins in Southern India (Nagaraja Rao et al., 1987; Basu and Bickford, 2015). The basin is bounded by Archaean greenstone belts and Peninsular Gneissic Complex (Figure 1). The basin extends over a length of 440 km, with a maximum width of 145 km in the central part. The Nallamalai sub basin (Figure 1), occupies the eastern half of the Cuddapah Basin. The basin has gained prominence in the context of regional tectono-stratigraphy related to the evolution of Precambrian basins of India (Holland, 1909; Radhakrishna, 1987), and its role in the global configuration of supercontinent assembly (Sharma et al., 2014; Saha and Deb, 2014; Mazumder and Eriksson, 2015; Kale, 2016). King (1872) established the stratigraphy of the Cuddapah basin. GSI (1981); Nagaraja Rao et al., (1987); Lakshminarayana et al., (2001); Chakrabarthi et al., (2013), contributed on aspects related to sedimentation and stratigraphy.

Specular haematite mineralisation along the Veldurti - Gani Fault was reported by Krishnan and Balasundaram (1944). The structural and tectonic aspects of the Cuddapah


Paleoproterozoic magmatism in the Cuddapah basin, India

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basin were studied by Narayanswami (1966); Nagaraja Rao et al., (1987); Chetty (2011); Tripathy and Saha (2015). The Proterozoic Cuddapah basin consists of: (i) The Cuddapah Supergroup and (ii) The Kurnool Group. The Papaghni sub-basin (western part of the Cuddapah basin) hosts undeformed rocks of Papaghni and Chitravathi groups, whereas, the Nallamalai sub-basin (eastern part) hosts deformed rocks of the Nallamalai group. The ~ 1.9 Ga ultramafic-mafic sills, along with basic and felsic volcanics and the interbedded tuffaceous sequence in the Cuddapah Supergroup are contemporaneous with the sedimentation and hence form part of the magmato-stratigraphy in the undeformed western part of the Cuddapah basin. The objective of this paper is to outline the key events of Paleoproterozoic ultramafic-mafic-felsic magmatic events that are contemporaneous with the evolution of Papaghni sub-basin (Ramakrishnan and Vaidyanathan, 2008).

Paleoproterozoic magmatism in the Cuddapah Supergroup

The Cuddapah domain represents one of the major Paleoproterozoic terranes in Peninsular India (Santosh, 2012). The Cuddapah basin during its early evolution witnessed significant events of Paleoproterozoic magmatism. The detailed discussion related to the ultramafic, mafic, and felsic magmatic events and interbedded tuffaceous sequence (Table 1) contemporary to the sedimentation in the Papaghni, Chitravathi and Nallamalai groups of the Cuddapah Supergroup is as follows.

Papaghni GroupKing (1872) has observed that the basic flows, along with some igneous rocks remarkably follow bedding plane (sills) in the lower Cuddapah (Figure 2). Vesicular tholeiitic basalt

Figure 1. Geological map of the Cuddapah basin (after GSI 1981; Nagaraja Rao et al., 1987) showing the Paleoproterozoic magmatic domains in the Cuddapah Supergroup.


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flows (Figure 3a, b) and basic sills represent prominent mafic magmatism associated with the Vempalle formation within the Papaghni sub-basin (Figure 1 and 2; Murthy, 1964; Jhanwar, 1964; Sen and Narasimha Rao, 1967; Srikantia, 1984; Nagaraja Rao et al., 1987; Chatterjee and Bhattacharji, 2001; Chakraborty et al., 2016). Crawford and Compston, (1973) provided an Rb-Sr age of 1583 ± 147 Ma for the basic lavas from Vemula area in south-west part of the Cuddapah basin. A Pb-Pb radiometric age of 1756 ± 29 Ma has been interpreted as the timing of uranium mineralisation in the Vempalle formation with predominantly carbonate sequence (Zachariah et al., 1999). Pyroclastic volcanism in the Papaghni sub-basin (Figure 4) has been reported from the south-west part of the Cuddapah basin (Sesha Sai, 2014). Geochemical studies (Chakraborty et al., 2016) suggested that basic flows in the Vempalle formation resulted due to low degree of partial melting of a mantle peridotite source.

Chitravati Group Widespread Proterozoic magmatic events were recorded in the Tadpatri formation of the Chitravathi Group (Nagaraja Rao et al., 1987; Bhasker Rao et al., 1995; Anand et al., 2003; French et al., 2008; Chakraborty et al., 2016; Sheppard et al., 2017). Disposed parallel to the basin configuration in its southwestern part, the NNW-SSE to NW-SE trending ultramafic-mafic sills (Sesha Sai, 2011) and interbedded felsic magmatic rocks are contemporaneous with the sedimentation, and form part of the magmato-stratigraphy in the Tadpatri Formation (Figure 2).

The ultramafic sill (Figure 3d) is confined to lower part of Tadpatri Formation. The middle and upper part of the Tadpatri Formation are characterized by dolerite (porphyritic at places), mafic sill with elongated clinopyroxene phenocryst (Chakraborty et al., 2016) and olivine gabbro sill (Sesha Sai, 2011) along with rhyolite and fine-grained albite rich rock (vesicular on surface) that are interbedded

Figure 2. Geological map of SW part of the Proterozoic Cuddapah basin. Note the mafic-ultramafic sills disposed parallel to the basin configuration along its western margin. Section A-B from western margin of the basin- Pulivendela-Tonduru-Muddanuru-Gandikota transcets through Papaghni and Chitravathi Groups. Abbreviations: DV- Dondlavagu; M-Mallela; PK- Peddakudala; VM- Vemula; VP- Velpula


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with dolomite-shale sequence (Figure 3e, f). During the course of cut-off trench excavation near Simhadripuram, large sized spindle shaped bodies resembling pyroclastic (5mm to 500mm diameter) were observed in Tadpatri formation (Babu and Satyanarayana, 2007 a). The basalt flows of Vempalle Formation (e.g., Srikantia, 1984; Murthy et al, 1987; Chatterjee and Bhattacharji, 2001; Chakraborty, et al., 2016) represent the early stage of volcanism in the Cuddapah basin. Incidentally, the basic volcanic flows are

not seen in the stratigraphic horizons above the Papaghni group. However, felsic volcanics and fine-grained albite rich rocks are reported in Tadpatri and Nallamalai groups (Sesha Sai et al., 2016b; Das and Chakraborty, 2017; Figure 4). In a recent geochronologic study, Sheppard et al., (2017), indicated an age of 1862 ± 9 Ma for the felsic tuff in upper part of Tadpatri sequence in Chitravathi Group. A concealed body of olivine gabbro has been intersected in borehole during drilling at exit portal of Gandikota Tunnel,

Figure 3. (a) Vesicular basic flow in Vempalle Formation, east of Motnutalapalle, SW part of the Cuddapah basin. (b) Basic flow over Vempalle dolomite, Vanambayi section, SW part of the Cuddapah basin. (c) Pillowed basalt fragments in mafic agglomerate Vanambayi section, SW part of Cuddapah basin. (d) Ultramafic sill in Tadpatri Formation, Loyala College section, Pulivendula, SW part of Cuddapah basin. (e) Rhyolite band within the dolomite-shale sequence of Tadpatri Formation, Mallela section, Cuddapah basin. (f) Mafic sill within the dolomite, Mallela section, SW part of the Cuddapah basin (g) Photomicrograph in PPL showing olivine in ultramafic sill. (h) Photomicrograph in PPL showing enstatite in ultramafic sill.


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Table 1. Paleoproterozoic magmatic events along with their geographical locations, ages and nature of occurrence at various stratigraphic horizons in the Cuddapah Supergroup (by Sesha Sai et al., present work; modified after Nagaraja Rao et al., 1987).

SUPERGROUP / GROUP

AGE STRATIGRAPHIC SUCCESSION

MAGMATIC ROCKS IN CUDDAPAH SUPERGROUP

LOCATION IN CUDDAPAH BASIN AVAILABLE AGE DATA

Kurnool Group (Kurnool and Palnad sub basins)

~~~~~~~~~~~~~~~~~~~~Unconformity~~~~~~~~~~~~~~~~~~~~

CU

DD

APA

H S

UP

ER

GR

OU

P

PAL

EO

PR

OT

ER

OZ

OIC

Srisailam QuartziteConglomerate, arenite,

siltstone sequenceNo Igneous rocks are reported within Srisailam Quartzite

NA

LL

AM

AL

AIG

RO

UP

Cumbum / Pullampet Formation

Shale, dolomite and arenite sequence

Tuffaceous sequences / associated (lapilli rosette) baryte

(Karunakaran, 1976; Neelakantam, 1987; Deb and

Bheemalingeswara, 2008) ultrapotassic rocks (Reddy, 1999)

Mafic sills and felsic volcanics (Das and Chakraborty, (2017)

Mangampeta area in Pullampet sub basin.

(Southern part of the NFB)

Rajampet areas in Pullampet sub basin.

(Southern part of the NFB)

No age data available

Bairenkonda / Nagari QuartziteConglomerate and arenite sequence

Southern part of NFBRajampet area

No age data available

~~~~~~~~~~~~~~~~~~~~Unconformity~~~~~~~~~~~~~~~~~~~~

CH

ITR

AVAT

IGR

OU

P

Gandikota QuartziteShale and arenite

Olivine gabbro (Babu and Satyanarayana, 2007 b) No age data available

Tadpatri FormationShale, dolomite, chert,

jasper, shale and arenite sequence

Olivine Gabbro

Rhyolite / Felsic tuff / Albite rich volcanic

Ultramafic-mafic sills(contemporaneous with basin

evolution)

Velupucherla section

Mallela section

Peddakudala-Pulivendla-Velpula section in SW part

of Cuddapah basin

No age data availableFelsic tuff - 1862 ± 9 Ma

(Sheppard et al., 2017)

Ultramafic sill1817±24 Ma Rb-Sr

Bhasker Rao et al. (1995)1.9 Ga 40Ar-39Ar,

(Anand et al., 2003)1885.4±3.1 Ma U-Pb (French et al., 2008)

Pulivendla QuartziteConglomerate and arenite sequence

No Igneous rocks reported in Pulivendla Quartzite

~~~~~~~~~~~~~~~~~~~~Disconformity~~~~~~~~~~~~~~~~~~~~

PAPA

GH

AN

I G

RO

UP

Vempalle FormationDolomite, chert and siltstone sequence

Basic flows, felsic tuff, Mafic pyroclastics and mafic sills

Rai, et al., (2015) Pb-Pb age of 1900-2000 Mafor dolomitisation

and uranium mineralisationZachariah et al., (1999) 1756 ± 29 Ma, uranium mineralisation

in Vempalle Formation

Kuppalapalle-Vemula-Lingala-Lopatnutala

section in SW part of basin

1841±71 Ma K-Ar(Murty et al., 1987)

1583±143 Ma Rb-Sr(Crawford and Compston,

1973)

Gulcheru QuartziteConglomerate and arenite sequence

Initiation of sedimentation ~ 2.1 Ga Gulcheru Red beds

(Sesha Sai et al., 2016 a)

Western margin of Cuddapah basin -

~~~~~~~~~~~~~~~~~~~~Nonconformity~~~~~~~~~~~~~~~~~~~~

Archaean granite-greenstone basement of eastern Dharwar craton


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upstream of Gandikota Dam, (Babu and Satyanarayana, 2007 b; Figure 4).

Pulivendla sill, IUGS nomenclature and its position in Cuddapah stratigraphy Pulivendla Formation, with rudaceous and arenaceous succession is overlain conformably by the Tadpatri Formation of Chitravathi Group (see GSI, 1981; Nagaraja Rao et al., 1987). Most importantly, Pulivendla Formation is devoid of any igneous activity. Geographically, the ‘Pulivendla’ ultramafic sill occurs over a stretch of 12 km (Sesha Sai, 2011) from Peddakudala in NW to Velpula in SE and passes through Pulivendla town where it attains maximum width of 600 m. Stratigraphically, this ultramafic sill falls in the lower part of the Tadpatri Formation. In this context, the Table-1, will be useful to view various magmatic rocks (with geographical locations and ages) occurring at different stratigraphic horizons in the Cuddapah Supergroup.

Earlier the Pulivendla sill was identified names as “picrite” (Murthy, 1964; Somayajulu & Singhal, 1968; Nagaraja Rao et al., 1987; Sesha Sai, 2011); “mafic-ultramafic sill” (Anand et al., 2003; French et al., 2008) and “mafic-ultramafic sills of gabbroic and dolerite composition” (Chakraborty et al., 2016). Recent petrographic studies and modal analyses of 20 representative samples (thin sections) collected from the length of the sill indicated that this rock is predominantly made of olivine (36% to 44%). Among the pyroxene, enstatite is dominant and ranges from 25 to 28%, while the modal content of augite ranges from 15 to 22%. Both the orthopyroxene (enstatite) and the clinopyroxene (augite) together make upto 40%. Plagioclase varies from 5% to > 10%. Olivine (Figure 3g) is noticed as equant

chadacrysts that are enclosed in larger oikocrysts of orthopyroxene, clinopyroxene and plagioclase resulting in poikilitic texture; a magmatic co-precipitation texture formed due to variation of rate of nucleation and rate of growth of the olivine chadacrysts enclosed in larger oikocrysts. Enstatite occurs as large euhedral grains showing well developed cleavage and high relief in plane polarised light (Figure 3h). Phlogopite varies from 5 to 8%. In IUGS Olivine-Pyroxene-Plagioclase diagram (Streckeisen, 1976), mineralogically the rock falls in the field of plagioclase bearing ultramafic to olivine gabbro norite. Samples with plagioclase < 10% fall in the field of plagioclase bearing ultramafic, while samples with > 10% plagioclase fall in the field of olivine gabbro norite (For mineral analyses, see Anand et al., 2003; Sesha Sai, 2011).

Concealed high velocity igneous body beneath the SW part of Cuddapah basinOn the basis of a significant geophysical study, the ‘presence of a high velocity igneous body was indicated beneath the southwestern part of the Cuddapah basin’ (Tewari and Rao, 1987). A positive gravity anomaly in the central part of the concentric sills points out the presence of a lopolith that probably originated through mantle upwelling during the early part of the basin’s history (e.g., Mishra and Tiwari, 1995; Tewari and Rao, 1987; Chatterjee and Bhattacharji, 2001; Reddy et al., 2004). Bouguer anomalies indicate presence of a basic lopolith beneath the western part of the Cuddapah basin (Singh and Mishra, 2002). In the southwestern part of the basin, possible exhumation of mid crustal layer is indicated (Chandrakala et al., 2013), while Lakshmi and Rambabu (2002), through basement structure studies indicated a NW-SE elongated depression within a 10-km depth near Muddanuru. Based on geophysical

Figure 4. Chronostratigraphic illustration of the Paleoproterozoic magmatic rocks in various stratigraphic horizons in the Cuddapah Supergroup. Litholog not to scale, (modified after Nagaraja Rao at al., 1987).


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studies (Chandrakala et al., 2010), a possible plume origin for the magmatism in the southwestern part of the Cuddapah basin was suggested. Sesha Sai (2011) observed that the mafic - ultramafic sills in SW part of the basin are the surface expression of a concealed high velocity igneous body as indicated by Tewari and Rao (1987). We observe that, through geophysical studies it is important to ascertain the exact depth of this high velocity igneous body, since a large ultramafic body is a potential host for Cr-Ni ± PGE orthomagmatic mineralisation.

Nallamalai GroupThe southern part of the Nallamalai sub basin (Figure 1), is characterized by the presence of extensive sequences of dolomite and argillites with intercalated carbonaceous - variegated tuffaceous rocks (see GSI, 1981; Nagaraja Rao et al., 1987). The Mangampeta baryte deposit (Neelakantam, 1987), in Pullampet sub basin is perhaps the world’s largest single bedded baryte deposit.

Karunakaran (1976) ascribed a volcanogenic origin for the bedded baryte near Mangampeta. Deb and Bheemalingeswara (2008) suggested the role of barium rich hydrothermal solution in submarine conditions with prolific biologic activity for the origin of the bedded baryte. Presence of fine dusty opaque material and two generations of pyrites and detrital clastic components are noticed in the carbonaceous shale of Pullampet Formation (Sesha Sai and Rajesham, 2010). Manikyamba et al., (2008) studied the geochemical aspects of black shale in Cuddapah basin. Ultra-potassic rocks, mafic sills and rhyolite have been recorded in the Pullampet sub basin (Reddy, 1999; Das and Chakraborty, 2017).

DISCUSSIONS

The clastic sediments of Gulcheru Formation and non-clastic sediments of Vempalle Formations of Papaghni Group in the western part of the basin are the earliest sedimentary sequences in Cuddapah Supergroup (see GSI, 1981). Initiation of sedimentation took place along the western margin of the Cuddapah basin with the deposition of Gulcheru red beds (Sesha Sai, et al., 2016a). The dolomite-chert non-clastic sequence of Vempalle Formation overlies the Gulcheru Formation. Establishing the ‘Pb-Pb age of 1900-2000 Ma for the deposition, dolomitisation and the uranium mineralization associated with the Vempalle dolomites’ by Rai et al., (2015) is a significant contribution. Aspects like the tectonic foundation, lithospheric substrate and proximity to a plate margin need to be considered for classification of basins (e.g. Allen et al., 2015). Lithospheric stretching can result in subsidence during the early stages in the extensional continental arc basins (eg. Busby, 2012). The Proterozoic Cuddapah basin of EDC, at its earliest stage of evolution, was a destiny to the craton derived

clastic sediments constituting the Gulcheru Formation along its arcuate western margin. Confinement of the ~ 1.9 Ga ultramafic-mafic sills within the basin, but close to its western margin of the basin signifies a localised thermally active Paleoproterozoic magmatic domain. Further, the spatial association of the felsic volcanics with the Paleoproterozoic basic volcanics, ultramafic-mafic sills within the craton derived clastic and shallow marine non-clastic sequences in the Cuddapah Supergroup indicate a continental arc extensional setting. The ~1.9 Ga ultramafic / mafic magmatism associated with concomitant intracontinental rifting and basin development preserved along much of the south-eastern margin of the south Indian shield is a widespread geologic phenomenon on Earth (French et al., 2008). The fragments of Kenorland reassembled and attained maximum packing around 1.8 Ga to form the supercontinent Columbia (Ernst et al., 2013); an event that was marked by formation of a Large Igneous Province (LIP) in the Southern Indian Block (French et al., 2008; Ernst and Srivastava, 2008).

Role of subsidence and initiation of sedimentationSubsequent to an Eparchaean interval of ~ 400 Ma, sedimentation in the Cuddapah basin was initiated during ~2.1 - 2.0 Ga over a thermally active magmatic domain along the eastern margin of Dharwar craton. The ~ 1.9 Ga mantle derived ultramafic-mafic sills indicate the role of deep seated mantle originated tectonomagmatic processes and its implications of the possible subsidence in SW part of Cuddapah intracratonic basin. Geophysical studies indicate that the Cuddapah basin was initiated in its western part due to the down faulting of the crustal block during the Paleoproterozoic (Kaila and Tewari, 1985). DSS studies (Kaila et al., 1987) indicate a gentle easterly dipping shallow basement in the western part of the Cuddapah basin near Parnapalle. Incidentally the linear pyroclastic mafic agglomerate zone (Sesha Sai, 2014) falls in the southern continuity of Parnapalle. In the recent significant works dealt with the origin of Proterozoic basins; the role of magmatism in extensional setting and its implications on the initiation of the intra cratonic basins of Africa have been discussed (e.g., Hartley and Allen, 1994; Armitage and Allen, 2010). Heine et al., (2008) noted that deep seated processes may result in subsidence in intra cratonic domains that have attained tectonic stability.

Disposition of the mafic-ultramafic rocks in SW part of the Cuddapah basinPresence of the ~1.9 Ga mafic-ultramafic sills disposed in an arcuate manner in the SW part of the Cuddapah basin, indicates the existence of deep seated linear fracture system for emplacement of mantle derived rocks. Presence of deep-seated faults has been identified by geophysical studies near Parnapalle-Tonduru areas in the Cuddapah


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basin (Reddy et al., 2004). Absence of such linear ~ 1.9 Ga mafic-ultramafic sills outside the western margin of the basin indicates the confinement of the thermally active regime beneath the SW part of Cuddapah basin. The mafic-ultramafic sills in the Papaghni and Chitravati sub basins are perhaps, the surface expression of the concealed ultramafic body beneath the SW part of Cuddapah basin (Tewari and Rao, 1987).

CONCLUSION

The Proterozoic Cuddapah basin of Peninsular India, one of the largest sedimentary basins in the world during its early evolution witnessed Paleoproterozoic ultramafic-mafic-felsic magmatism. Subsequent to an Eparchaean interval of ~ 400 Ma, sedimentation in the basin was initiated over a thermally active magmatic domain along the eastern margin of the stabilised Dharwar craton during ~2.1 - 2.0 Ga. The high density igneous body beneath the SW part of Cuddapah basin possibly represents a concealed ultramafic feeder for the mafic-ultramafic sills in the Papaghni and Chitravati Groups. The linear zone of Paleoproterozoic ultramafic-mafic sills is confined to the Papaghni and Chitravathi sub basins. Further, configuration of the ultramafic-mafic sills parallel to the basin`s arcuate western margin, associated Paleoproterozoic felsic volcanics, association of these magmatic rocks with the craton derived clastic sediment and shallow marine non-clastic sequences indicate a continental arc extensional setting for the evolution Paleoproterozoic segment of Cuddapah basin, India.

ACKNOWLEDGEMENTS

Director General, Geological Survey of India, is acknowledged for valuable support. Dr. Michael Doublier, Geoscience Australia, and Prof. Rajesh K Srivastava, BHU, India, are thanked for helpful suggestions. Prof. R. Pavanaguru (formerly Emeritus), Osmania University, Hyderabad and Dr. K.J. Babu are gratefully acknowledged for constructive review and altruistic nature in disseminating new information on field aspects in Cuddapah basin. VVSS pays tributes to Late Prof. A. Suryaprakasa Rao, Osmania University, India, who discerned the importance of study of magmatic rocks in Cuddapah basin in 1980s. We dedicate this work to Late Ch. Narasimha Rao, (former Director), GSI, for his invaluable contribution towards understanding the Cuddapah basin. Dr. P.R. Reddy, Chief Editor is thanked for editorial handling.



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Dust storms and their influence on optical and chemical properties of aerosols along north-western Indo-Gangetic Plains

Disha Sharma and Umesh Kulshrestha*School of Environmental Sciences, Jawaharlal Nehru University, New Delhi, India


ABSTRACTDust storms are an important climatic phenomenon in the Indian subcontinent affecting air quality in the pre monsoon season. In this study, the variation in the optical and the chemical properties of mineral dust aerosols along the north-western Indo Gangetic Plains (IGP) is recorded during major dust storm events during April to June, 2015. Dustfall fluxes were measured at five sites lying on the downwind trajectory of the long-transported dust plume. The sites were - Bikaner (BK), Jaipur (JP), Hisar (HS), Delhi (DL) and Agra (AG). Five major dust storm events were identified based on the aerosol optical depth (AOD) values derived from the MODIS and OMI instruments and corroborated by the ground monitored dust fall flux measurements. An analysis of the optical properties reveals the dominance of coarse mode particles during all the events with MODIS Angstrom Exponent (AE) values lying in the range of 0.40 – 0.03 for dust events observed at the sites located in the close proximity of Thar desert. Chemical characterization of the samples showed that Ca2+ was the most dominating cation with flux in the range of 106.7 mg/m2/day (at BK) to 7.4 mg/m2/day (at DL), indicating the dominance of crustal sources in the dust aerosols. Among anions, highest flux was recorded for SO4

2- and NO3-. NO3

- flux was observed to increase downwind towards the sites (DL and HS) with high anthropogenic emissions. The flux Na+ and Cl-was also high during major dust events. However, it was seen to decrease downwind indicating the influence of sea salt fraction in the dust plume transported from the Arabian sea.

Key words: Dust Storms, Air quality, Optical and chemical qualities of aerosols, Aerosol optical depth, MODIS and OMI instruments, North western Indo-Gangetic Plains.

INTRODUCTION

Mineral dust aerosols play an important role in modulation of the atmospheric radiative budget (Ramanathan et al., 2001; Tegen et al., 2004; Bollasina et al., 2008), the hydrological cycle and the monsoon circulation and rainfall distribution (Gautam et al., 2009, 2011; Srivastava et al., 2010; Giles et al., 2011; Das et al., 2013; Dumka et al., 2014; Vinoj et al., 2014). The arid and the semi arid desert areas are recognized as the main source of atmospheric dust (Prospero et al., 2002; Ginoux et al., 2012; Crosbie et al., 2014) with global flux estimations of 1500–2600.

Tg yr 1 (Zender and Milelr, 2004). Meteorological conditions, mainly wind speed and wind direction, induce long range transport of dust thousands of kilometers from the source (Liu et al., 2012; Nastos, 2012). Dust outbreaks are known to affect air quality land use, society and biodiversity (Gou- die, 1983; Goudie and Middleton, 1992, 2006; Middleton and Gou- die, 2001; Washington et al., 2003; Engelstaedter et al., 2006; Kaskaoutis et al., 2010; Kulshrestha and Sharma, 2015). Physical characteristics like the particle size, shape and minerology (Mahowald et al., 2005) decide the optical and chemical properties of dust aerosols and are in turn determined by the sources from which the soil sediments are entrained

and their chemical composition (Claquin et al., 1998; Singh et al., 2004).

The Indo-Gangetic Plains (IGP) receive dust from the sources located in Middle East, Arabia, North Africa and the Thar desert (Dey et al., 2004; Prasad and Singh, 2007; Sharma et al., 2012; Gharai et al., 2013; Aher et al., 2014). The highest frequency of dust storms in the north- western parts of India is observed in the pre-monsoon season, from April to June, under the influence of south – westerly winds (Prasad and Singh, 2007). The north-western part of IGP reports very high AOD and suspended particulate matter (SPM) levels (Sharma and Kulshrestha, 2014). As a result, dust strongly affects the aerosols characteristics over the IGP under the influence of the local pollutants.

The present study is conducted to analyze the variation in the optical as well as the chemical properties of mineral dust aerosols during major dust storm events in the north western IGP. The satellite observations are corroborated with the ground monitored data to see the change in the aerosol properties in the study region. The trajectories of the dust plume are also plotted in order to see the influence of the dust sources in the Arabian Peninsula in modulating climate and air quality over the Indian subcontinent.



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Data and Methods

Dustfall samplingIn order to sketch a complete picture of the influence of the local emissions on the trans boundary dust pollution/plume, five sites were chosen along the downwind trajectory of dust storms, starting from Thar desert till the ‘aerosol hotspots’ (Lau WMO 2008), the Indo – Gangetic Plains (IGP) (Figure 1) . The first two sites, Bikaner (BK(28.01O N, 73.31 OE)) and Jaipur (JP(26.91 ON, 75.7 OE)), lie in the northwestern state of Rajasthan that marks the entry point of trans boundary dust storms in India and are in the close proximity of Thar desert. Next site along the

downwind dust storm trajectory was chosen to be Hisar (HS(29.15 ON, 75.72 OE). It lies in the relatively less ‘dusty’ state of Haryana (table 1), however, it is characterized as a fast-developing city center. Sampling was also done in the capital city of Delhi (DL(28.70 ON, 77.10 OE) as it was vital to observe the chemical characteristics of dust aerosols in the city, which records a very high level of AOD (Sharma and Kulshrestha, 2014), other atmospheric pollutants and also influenced by dust storms. The last site chosen along IGP was Agra (AG(27.18 O N, 78.01 OE).

The dust samples were collected from April 2015 to June 2015, which is the period when maximum number of pre monsoon dust storms are observed in the Indian

Figure 1. Study region along the north-western part of Indo-Gangetic Plains, with five sampling sites at Bikaner, Jaipur, Hisar, Delhi and Agra.

Figure 2. Monthly mean soil moisture (mm) variation over India for the month of April, May and June, 2015, respectively (NCEP reanalysis volumetric soil moisture 0 – 10 cm BGL (units: mm).


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subcontinent. Dry deposition flux of dust aerosols was measured by collecting dustfall on non-reactive propylene petriplates with 140mm diameter. In order to ensure sufficient dust collection, the plates were exposed for a period of two weeks for composite sampling for the entire dust storm season. For dust storm event sampling, amount of dust loading was measured by collecting samples on the day of the dust storm. The plates were placed on selected rooftops ensuring least resistance and undisturbed free flow to the free fall of dust particles for taking representative samples. This method of passive sampling of atmospheric dust has been validated in previous studies (Tiwari and Kulshrestha, 2016). The collected samples were stored and transported to lab where they were subjected to ion chromatography (IC) to measure the concentration of major anions (F-, Cl-, SO4

2- and NO3- ) and cations (Mg2+, Ca2+,

K+, NH4+, Na+).

Moderate Resolution Imaging Spectroradiometer (MODIS) MODIS is a sensor onboard Terra and Aqua satellites. It has high radiometric sensitivity (12 bit) over 36 spectral bands with wavelengths ranging from 0.41 µm to 14.4 µm. MODIS sensors measure the AOD with an estimated error of ± (0.05 + 0.15) over land (Chu et al., 2002) and 0.03 ± 0.05 over the ocean (Remer et al., 2005). The Aqua and Terra level 3 (MYD08_D3_v6 and MOD08_D3_V6) AOD daily data products from Terra and Aqua Deep Blue AOD, at .55 µm, with a spatial resolution of 10 × 10 km from 1st April to 30th June, 2015 are utilized in this study. Deep blue Angstrom Exponent (AE) for land in 0.412 – 0.47 µm range was also used. AOD and AE for the entire sampling period were obtained from MODIS, by averaging Terra and Aqua, AOD and AE values, respectively. More information can be found at https://giovanni.gsfc.nasa.gov/giovanni/.

Ozone Monitoring Instrument (OMI)OMI instrument is based on the NASA’s Total Ozone Mapping Spectrometer(TOMS) instrument and the European Space Agency (ESA) Global Ozone Monitoring Experiment (GOME) instrument (on the ERS-2 satellite). It can distinguish between aerosol types, such as smoke, dust, and sulfates, and measures cloud pressure and coverage, which provides data to derive tropospheric ozone. The hyperspectral imaging offered by the instrument provides it the ability to measure more atmospheric constituents than TOMS and enables much better ground resolution than GOME (13 km x 25 km for OMI vs. 40 km x 320 km for GOME). AOD 500 µm values from OMI (daily, 1 degree product) were also recorded for this study, alongside MODIS AOD values.

Back trajectory and reanalysis productBack trajectories were computed using the HYSPLIT model. The air mass back trajectories were calculated during major

dust storm events, at the first site (BK), which marks the entry point of dust storms in India. In order to identify the route of local and long range transport of dust, trajectories were computed for a period of 5 days (120 hours) at three levels; 500m, 100m and 1500m. Back trajectory analysis provides important information about types of aerosols and their source region (Kaskaoutis et al., 2010). NCEP reanalysis monthly soil moisture product was also used to see the spatial and temporal variation of moisture content in the soil during the sampling period.

RESULTS AND DISCUSSION

Soil moisture analysis for the pre-monsoon dust seasonDust outflow is known to increase tremendously in the pre-monsoon months of April – June (Askary et al., 2006). It is known that the heightened dust activity is observed in arid and semi-arid regions, globally (Prospero et al., 2002). Thus, soil moisture content is an important pre-condition for triggering dust storm episodes in the region. Figure 2 shows the variation in the soil moisture content in millimeters (0 – 10 cm BGL; acquired from NCEP Reanalysis Daily Mean) over entire India. It is observed that there is a subsequent decrease in the moisture content over the northwestern part of IGP, covering the Thar desert. This explains the increase in dust emissions from the desert areas in the pre-monsoon season, from all the dust sources influencing aerosol load over India.

Aerosol optical properties and identification of dust stormsThe western part of IGP experiences more dust events as compared to the eastern part in the months of May and June (Middleton, 1986). The variation of AOD at the study region was taken from the OMI and MODIS instruments (Figure 3, Table 1). Days that recorded OMI AOD500 and MODIS AOD550 (greater than 0.5) were considered as the days of the dust storm (Sharma et al., 2012). The peak AOD value recorded during the interval with high dust loadings is reported and used for correlation analysis at all the sampling sites. Five major dust events (Es) were identified from April to June. Based on satellite observations and dust fall monitoring measurements the five major dust storm events are identified on the following days; 04 April (E1), 20 April (E2), 30 April (E3), 15 May (E4) and 30 June (E5). Figures 4 a and b show the dust storms on the 3rd of April and 27th of June, 2015 using corrected reflectance images of MODIS. Most of the dust storm events occurred in the month of April and the highest AOD value recorded was greater than 2.0 and the dust fall flux measured was ~8465 mg/m2/day in BK. For most of the events, AOD values exceeding 1 were recorded at BK and JP sites, which are under the influence of Thar desert. Dust fall flux lies in the range for these dust storm events. The observations show that dust outflow during dust storms


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leads to elevated AOD levels downwind. However, the maximum dust loading is observed in the regions lying in the proximity of the dust source.

Table 1 shows aerosol optical characteristics during the five major dust storm events (Es) observed during the study period at all the study sites. The Angstrom Exponent (AE) is another important optical property indicative of the contribution from the fine mode particles. High values of AOD corresponding with low values of AE have been reported at some parts of the IGP (Dey et al., 2004; Singh et al., 2004; Pandithurai et al., 2008) and the Sahara region (Tanre et al., 2003). In the present study, for all the dust storm events at BK, AE value was low (<0.4) indicating the abundance of coarse mode particles, which in this case come from desert dust aerosols, both local and transported. For most of the dust storm events at all the sites, low AE values were seen.

Further, the air mass back trajectories calculated over the first site, BK, from where the long-transported dust plume enters India, shows the source of dust that

enters into India (Figure 5). The dust plume is seen to pass over dust sources located in the Arabian Peninsula covering Iran, southwest Asia, Pakistan and the Thar desert. For event E5, the air mass at higher altitude transports the dust plume from north western Africa crossing the Arabian Sea to India. Thus, influence of local and distant sources is seen for all the major dust storm events in India.

Chemical characteristics of aerosols during dust storm eventsIn order to understand the chemical composition of the atmospheric aerosols during major dust events observed in this study, flux of major ions and cations was calculated (Figures 6 & 7). It was found that at all the sites the dominating cation was Ca2+ with the maximum composite value for all events recorded as 106.7, 83.5, 35.5, 7.4 and 17.5 mg/m2/day at BK, JP, HS, DL and AG respectively. The flux was seen to decrease eastwards, indicating the abundance of crustal sources in the sites

Table 1. Event wise AOD from MODIS and OMI, MODIS AE and dustfall flux (mg/m2/day) at the five sampling sites.

Site Event (E) AOD_MODIS AOD_OMI AE Dustfall Flux

BK 1 2.42 - - 8465

2 1.34 0.80 0.40 6778

3 1.21 0.98 0.07 5675

4 - - 0.03 3360

5 1.41 - 0.32 4396

JP 1 0.75 - 1.35 2840

2 0.45 0.73 1.24 3544

3 0.48 0.54 0.69 2619

4 0.50 - 1.8 3983

5 0.39 - 1.8 -

HS 1 1.59 - 1.5 1795

2 0.90 0.59 0.14 2006

3 0.84 1.05 0.22 1369

4 1.2 0.79 0.20 1184

5 0.90 0.38 1.8 1113

DL 1 1.17 - 1.5 279

2 0.68 0.74 0.43 734

3 0.66 0.72 0.56 818

4 - 0.79 0.55 378

5 0.65 - - 470

AG 1 0.65 - 1.79 1018

2 0.78 1.07 1.21 3040

3 0.75 0.61 0.69 965

4 0.52 - 0.71 2303

5 0.56 - - 697


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lying in close proximity of the Thar desert. The second highest flux was seen for Na+ ions at BK and JP (15.4 and 6.0 mg/m2/day, respectively). The flux Na+ was also seen to decrease downwind indicating the influence of sea salt fraction in the dust plume transported from the Arabian sea.

The dominance of crustal sources explains the low AE values reported for the major dust events. The dominating anions with the maximum flux values were seen to be SO4

2- and NO3- at all the sites, during all the five dust

storm events. The flux for SO42- did not show much

variation downwind. Much of this SO42- has been reported

as calcium sulphate in Indian region due to the adsorption of atmospheric SO2 onto the CaCO3 rich dust particles (Kulshrestha et al., 2003a, 2003b). Thus being acidic gas, the ambient SO2 is effectively scavenged by the alkaline dust in the region (Kulshrestha, 2004; Kulshrestha et al., 2009).

This is the main reason for very low concentrations of SO2 in ambient air in most parts of north India. However, NO3

-flux was the highest in DL (4.7 mg/m2/day) followed by HS (2.0 mg/m2/day), which shows the dominance of anthropogenic emissions in bigger cities. Daily flux for Cl- followed similar site wise trend as was seen in the case of Na+ flux, further strengthening the impact of distant sources on local air quality in India. Further, as the highest flux was reported for SO4

2-, NO3-

and Ca2+, the ability of Ca2+ in neutralizing SO42- and

NO3- for all dust events at all sites was calculated (Figure

8). For events E1, E3 and E5 the correlation coefficient was positive. The value of Pearson Coefficient (r), at 95% significance level, is 0.70, -0.31, 0.57, -0.22 and -0.92 for the five dust events, respectively. This indicates the availability of Ca2+ in the dust aerosols in providing surface for neutralization of SO4

2- and NO3-.

Figure 3. Day to day MODIS AOD variation from April to June, 2015 at all five sampling sites.

Figure 4. MODIS images a and b showing the dust storms on the 3rd April and 27th June, 2015, respectively.


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Figures 6 & 7. Total flux of major cations and anions at all the sampling sites during all five dust storm events.

Figure 5. Back trajectory analysis for the five dust storm events at Bikaner.


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CONCLUSIONS

In this study, we identified five major dust storm events based on the AOD values (>0.5) derived from the MODIS and OMI instruments and corroborated by the ground monitored dust fall flux measurements at the sampling locations. An analysis of the optical properties shows the dominance of coarse mode particles during all the events with low MODIS AE values recorded for dust events observed at the sites located in the close proximity of Thar desert. Back trajectory analysis showed the influence of dust sources in the north-west Africa and the Middle East on the air quality observed over the IGP. Chemical characterization of the dust fall samples showed that Ca2+

was the most dominating cation indicating the dominance of crustal sources at all the sites. The highest flux was recorded for SO4

2- and NO3-. The NO3

- flux was observed to increase downwind towards the sites (DL, HS) with high anthropogenic emissions. The fluxes of Na+ and Cl- were also high during major dust events. However, they were seen to decrease downwind indicating the influence of sea salt fraction in the dust plume transported from the Arabian sea.

ACKNOWLEDGEMENTS

We thank the Department of Science and Technology (DST) PURSE Fund for providing resources for successful

Figure 8. Correlation between Ca2+ and SO42- and NO3

- at the sampling sites for all the dust storm events.


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completion of this project. D.S. sincerely thanks the CSIR for SRF funds to carry out this research. We are also thankful to GIOVANNI NASA and MODIS websites for enabling access to satellite data used in this project. We thank Dr. Prasenjiit Acharya for objective evaluation of the manuscript. Thanks are also due to Chief Editor for his constant support and proper editing.



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“These dust storms.... Poor farmer spent a lifetime fixin’ his farm and everything, goes out and looks down at it, and it’s up above him”. -HYPERLINK “http://www.azquotes.com/author/12553

-Will_Rogers”Will Rogers (1879 – 1935) was a motion picture actor and social commentator.***

“The storm took place at sundown; it lasted through the night, When we looked out next morning, we saw a terrible sight We saw outside our window where wheat fields they had grownWas now a ripping ocean of dust the wind had blown”.

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Types of Irrigation and Historical development - a comprehensive compilation

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Types of Irrigation and Historical development -

a comprehensive compilationP.R.Reddy

Director Grade Scientist (Retd), CSIR-NGRI, Hyderabad- 500007, Telangana [email protected]

INTRODUCTION

We often read in Newspapers, see in TV programs and hear in political circles about lack of sufficient irrigation facilities, leading to deceleration of food production. The word irrigation, many a time, is wrongly used as we are not exposed to various facets of irrigation and apt use of proper irrigation technique that is area specific. As our economy is agriculture based and as monsoon aberrations have introduced number of problems in properly applying irrigation in time and space, it is essential for all those interested in our country`s economy and there by wish to contribute to sustainable development of our economy and in turn their own wellbeing, to learn about irrigation. An attempt is made here to introduce the reader to irrigation and its importance in enhancing agriculture/ horticulture output. Since the topic requires coverage of various facets of irrigation and as readers may feel fatigued in reading a lengthy write up I have sub divided the contents in to 3 parts, viz, 1) Introduction, types of irrigation and Historical development; 2) Present Irrigation practices and their applicability & limitations 3) Irrigation in India and needed strategies to strengthen irrigation facilities. The first part is covered below. The rest will be presented later.

WHAT IS IRRIGATION?

Irrigation is the artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and re-vegetation of disturbed soils in dry areas and during periods of inadequate rainfall. Additionally, irrigation also has a few other uses in crop production, which include protecting plants against frost, suppressing weed growth in grain fields and preventing soil consolidation. In contrast, agriculture that relies only on direct rainfall is referred to as rain-fed or farming. Irrigation systems are also used for dust suppression, disposal of sewage, and in mining. Irrigation is often studied together with drainage, which is the natural or artificial removal of surface and sub-surface water from a given area. Irrigation has been a central feature of agriculture for over 5000 years. Probably one of the oldest methods of irrigating fields is surface irrigation (also known as flood or furrow irrigation), where farmers flow water down small trenches running through their crops. Humans’ first invention after learning how to grow plants

from seeds was probably a bucket. For most of human history, people did not have mechanized spray irrigation systems to apply water to crop fields.

Sources of irrigation water can be groundwater extracted from springs or by using wells, surface water withdrawn from rivers, lakes or reservoirs or non-conventional sources like treated wastewater, desalinated water or drainage water. A special form of irrigation using surface water is spate irrigation, also called floodwater harvesting. Spate irrigation areas are in particular located in semi-arid or arid, mountainous regions. (Source: http://en.wikipedia.org/wiki/Irrigation)

TYPES OF IRRIGATION:

Various types of irrigation techniques differ in how the water obtained from the source is distributed within the field. In general, the goal is to supply the entire field uniformly with water, so that each plant has the amount of water it needs, neither too much nor too little.Surface Irrigation: In surface (furrow, flood, or level basin) irrigation systems, water moves across the surface of agricultural lands, in order to wet it and infiltrate into the soil. Surface irrigation can be subdivided into furrow, border-strip or basin irrigation. It is often called flood irrigation when the irrigation results in flooding or near flooding of the cultivated land. Historically, this has been the most common method of irrigating agricultural land and still is in most parts of the world.a) Furrow Irrigation: Furrows are small channels, which carry water down the land slope between the crop rows. Water infiltrates into the soil as it moves along the slope. The crop is usually grown on the ridges between the furrows. This method is suitable for all row crops and for crops that are affected in water for long periods such as 12-24 hours.b) Basin Irrigation: Basins are flat areas of land, surrounded by low bunds. The bunds prevent the water from flowing to the adjacent fields.

Basin irrigation is commonly used for rice grown on flat lands or in terraces on hillsides. Trees can also be grown in basins, where one tree is usually located in the middle of a small basin.

In general, the basin method is suitable for crops that are unaffected by standing in water for long periods such as 12-24 hours.


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c) Border Irrigation: Borders are long, sloping strips of land separated by bunds. They are sometimes called border strips. Irrigation water can be fed to the border in several ways: opening up the channel bank, using small outlets or gates or by means of siphons or spiles. A sheet of water flows down the slope of the border, guided by the bunds on either side. Localized Irrigation: Localized irrigation is a system where water is distributed under low pressure through a piped network, in a pre-determined pattern, and applied as a small discharge to each plant or adjacent to it. Drip irrigation, spray or micro-sprinkler irrigation and bubbler irrigation belong to this category of irrigation methods.Subsurface textile irrigation: Subsurface Textile Irrigation (SSTI) is a technology designed specifically for subsurface irrigation in all soil textures from desert sands to heavy clays. A typical subsurface textile irrigation system has an impermeable base layer (usually polyethylene or polypropylene), a drip line running along that base, a layer of geotextile on top of the drip line and, finally, a narrow impermeable layer on top of the geotextile. Unlike standard drip irrigation, the spacing of emitters in the drip pipe is not critical as the geotextile moves the water along the fabric up to 2m from the dripper.Drip irrigation: Drip (or micro) irrigation, also known as trickle irrigation, functions as its name suggests. In this system water falls drop by drop just at the position of roots. Water is delivered at or near the root zone of plants, drop by drop. This method can be the most water-efficient method of irrigation if managed properly, since evaporation and runoff are minimized. The field water efficiency of drip irrigation is typically in the range of 80 to 90 percent when managed correctly.Sprinkler Irrigation: In sprinkler or overhead irrigation, water is piped to one or more central locations within the field and distributed by overhead high-pressure sprinklers or guns. A system utilizing sprinklers, sprays, or guns mounted overhead on permanently installed risers is often referred to as a solid-set irrigation system. Sprinklers can also be mounted on moving platforms connected to the water source by a hose. Automatically moving wheeled systems known as traveling sprinklers may irrigate areas such as small farms.Center pivot Irrigation: Center pivot irrigation is a form of sprinkler irrigation consisting of several segments of pipe (usually galvanized steel or aluminum) joined together and supported by trusses, mounted on wheeled towers with sprinklers positioned along its length. The system moves in a circular pattern and is fed with water from the pivot point at the center of the arc. These systems are found and used in all parts of the world and allow irrigation of all types of terrain. Newer systems have drop sprinkler heads Lateral move (side roll, wheel line) Irrigation: A series of pipes, each with a wheel of about 1.5 m diameter

permanently affixed to its midpoint and sprinklers along its length, are coupled together at one edge of a field. Water is supplied at one end using a large hose. After sufficient water has been applied, the hose is removed and the remaining assembly rotated either by hand or with a purpose-built mechanism, so that the sprinklers move 10 m across the field. The hose is reconnected. The process is repeated until the opposite edge of the field is reached.Sub-irrigation: Sub-irrigation has been used for many years in field crops in areas with high water tables. It is a method of artificially raising the water table to allow the soil to be moistened from below the plants’ root zone. Sub-irrigation is also used in commercial greenhouse production, usually for potted plants. Automatic, non-electric using buckets and ropes: Besides the common manual watering by bucket, an automated, natural version of this also exists. Using plain polyester ropes combined with a prepared ground mixture can be used to water plants from a vessel filled with water. Using water condensed from humid air: In countries where at night, humid air sweeps the countryside, water can be obtained from the humid air by condensation onto cold surfaces. This is for example practiced in the vineyards at Lanzarote using stones to condense water or with various fog collectors based on canvas or foil sheets.In-ground irrigation: Most commercial and residential irrigation systems are “in ground” systems, which means that everything is buried in the ground. With the pipes, sprinklers, emitters (drippers), and irrigation valves being hidden, it makes for a cleaner, more presentable landscape without garden hoses or other items having to be moved around manually. (Source: http://en.wikipedia.org/wiki/Irrigation)

SELECTION OF IRRIGATION METHOD:

To choose an irrigation method, the farmer must know the advantages and disadvantages of the various methods. He or she must know which method suits the local conditions best. Unfortunately, in many cases there is no single best solution: all methods have their advantages and disadvantages. Testing of the various methods - under the prevailing local conditions - provides the best basis for a sound choice of irrigation method.

The suitability of the various irrigation methods, i.e. surface, sprinkler or drip irrigation, depends mainly on the following factors:

1)natural conditions 2)type of crop 3)type of technology 4)previous experience with irrigation 5)required labour inputs 6) costs and benefits.

Even though all the factors cited above are useful to select a type of irrigation Natural Conditions play crucial role in selecting the best possible method. Some specifics are detailed below:


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Natural Conditions:The natural conditions such as soil type, slope, climate, water quality and availability, have the following impact on the choice of an irrigation method:Soil type: Sandy soils have a low water storage capacity and a high infiltration rate. They therefore need frequent but small irrigation applications, in particular when the sandy soil is also shallow. Under these circumstances, sprinkler or drip irrigation are more suitable than surface irrigation. On loam or clay soils all three irrigation methods can be used, but surface irrigation is more commonly found. Clay soils with low infiltration rates are ideally suited to surface irrigation. When a variety of different soil types is found within one irrigation scheme, sprinkler or drip irrigation are recommended as they will ensure a more even water distribution. Slope: Sprinkler or drip irrigation are preferred above surface irrigation on steeper or unevenly sloping lands as they require little or no land levelling. An exception is rice grown on terraces on sloping lands. Climate: Strong wind can disturb the spraying of water from sprinklers. Under very windy conditions, drip or surface irrigation methods are preferred. In areas of supplementary irrigation, sprinkler or drip irrigation may be more suitable than surface irrigation because of their flexibility and adaptability to varying irrigation demands on the farm. Water availability: Water application efficiency is generally higher with sprinkler and drip irrigation than surface irrigation and so these methods are preferred when water is in short supply. However, it must be remembered that efficiency is just as much a function of the irrigator as the method used. Water quality: Surface irrigation is preferred if the irrigation water contains much sediment. The sediments may clog the drip or sprinkler irrigation systems. If the irrigation water contains dissolved salts, drip irrigation is particularly suitable, as less water is applied to the soil than with surface methods. Sprinkler systems are more efficient than surface irrigation methods in leaching out salts. (Source: http://www.fao.org/docrep/s8684e/s8684e08.htm)

HISTORY-GLOBAL SCENARIO:

Historically, civilizations have been dependent on development of irrigated agriculture to provide agrarian basis of a society and to enhance the security of people. A prerequisite in the rise of the first state societies seems to have been the development of complex farming systems involving labour intensive irrigation, in which cereals and grain legumes were usually the main crops. Ancient irrigation is, however, often difficult to identify directly because of the destruction of associated ground structures. As an alternative, other methods have been

proposed to assess irrigation. One indirect method takes into consideration the development of seeds; for example, from the size of charred flax seeds which may occur in an archaeological assemblage of plant remains. A more direct method for identifying ancient irrigation is based on the increased deposition of silica in cereal plants when they grow under irrigation. Comparison of the resulting distinctive characteristics of the phytoliths produced by crops under irrigation with rain-fed ones has been proposed in mid 1990s as a method to assess the presence of ancient irrigation in cereal cultures. In one such study this method was applied to investigate whether ancient irrigation was practiced in the southeast Iberian Peninsula. Whereas in the Near East, irrigation has been inferred archaeologically from the early stages of civilization .Indirect evidence for irrigation in the western Mediterranean basin is scarce and inconclusive until the Roman period. There is a strong debate about when irrigation started in the south-eastern part of the Iberian Peninsula (Spain), one of the regions of the western Mediterranean basin in which advanced social structures first appeared. Although there is agreement among archaeologists that irrigation in the south-east of Spain spread after the end of the 3rd millennium BP, no clear picture emerges from earlier times. In this context some of the current theories adduced to explain the strong cultural development of the southeast of the Iberian Peninsula during the Copper and Bronze Ages (5th and 4th millennia BP) have placed great importance on the control of the environment, because attempts to control it (for example, by hydraulic works) could lead to an organized (i.e. hierarchical) society. From different theoretical approaches and on the assumption that the environment has not changed substantially, scientists have proposed that intensive agriculture based on irrigation was necessary to maintain a growing population in an arid zone such as the south-east of the Iberian Peninsula. They point out that water control and hydraulic works such as irrigation channels, canals, dams and cisterns were among the most valued elements in these societies. Indeed, if the information on early agricultural sites in the Near East may be considered as a guide, it could be assumed that cultivation whenever possible was based on sowing on alluvial fans and terraces as well as on the edges of freshwater swamps where the water table was always high and the soil fertilized by silt deposited by periodic floods. However, the occurrence of irrigation at these times remains controversial. (Source: Jose´ Luis Araus et al., 1997, Journal of Archaeological Science (1997) 24, 729–740). Such an environment was indeed present in Harappa and Mohenjo-Daro region (Indus Aryan Civilization).

Archaeological investigation has identified evidence of irrigation where the natural rainfall was insufficient to support crops. Perennial irrigation was practiced in the Mesopotamian plain whereby crops were regularly watered

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throughout the growing season by coaxing water through a matrix of small channels formed in the field. Ancient Egyptians practiced Basin irrigation using the flooding of the Nile to inundate land plots which had been surrounded by dykes. The flood water was held until the fertile sediment had settled before the surplus was returned to the watercourse. There is evidence of the ancient Egyptian pharaoh Amenemhet III in the twelfth dynasty (about 1800 BCE) using the natural lake of the Faiyum Oasis as a reservoir to store surpluses of water for use during the dry seasons, the lake swelled annually from flooding of the Nile. The Ancient Nubians developed a form of irrigation by using a waterwheel-like device called a sakia. Irrigation began in Nubia sometime between the third and second millennium BCE. It largely depended upon the flood waters that would flow through the Nile River and other rivers in what is now the Sudan. In sub-Saharan Africa irrigation reached the Niger River region cultures and civilizations by the first or second millennium BCE and was based on wet season flooding and water harvesting.

Terrace irrigation is evidenced in pre-Columbian America, early Syria, India, and China. In the Zana Valley of the Andes Mountains in Peru, archaeologists found remains of three irrigation canals radiocarbon dated from the 4th millennium BCE, the 3rd millennium BCE and the 9th century CE. These canals are the earliest record of irrigation in the New World. Traces of a canal possibly dating from the 5th millennium BCE were found under the 4th millennium canal .Sophisticated irrigation and storage systems were developed by the Indus Valley Civilization in present-day Pakistan and North India, including the reservoirs at Girnar in 3000 BCE and an early canal irrigation system from circa 2600 BCE. Large scale agriculture was practiced and an extensive network of canals was used for the purpose of irrigation in Ancient Persia (modern day Iran) as far back as the 6th millennium BCE, where barley was grown in areas where the natural rainfall was insufficient to support such a crop. The Qanats, developed in ancient Persia in about 800 BCE, are among the oldest known irrigation methods still in use today. They are now found in Asia, the Middle East and North Africa. The system comprises a network of vertical wells and gently sloping tunnels driven into the sides of cliffs and steep hills to tap groundwater. The noria, a water wheel with clay pots around the rim powered by the flow of the stream (or by animals where the water source was still), was first brought into use at about this time, by Roman settlers in North Africa. By 150 BCE the pots were fitted with valves to allow smoother filling as they were forced into the water. The irrigation works of ancient Sri Lanka, the earliest dating from about 300 BCE, in the reign of King Pandukabhaya and under continuous development for the next thousand years, were one of the most complex irrigation systems of the ancient world. In

addition to underground canals, the Sinhalese were the first to build completely artificial reservoirs to store water. Due to their engineering superiority in this sector, they were often called ‘masters of irrigation’. Most of these irrigation systems still exist undamaged up to now, in Anuradhapura and Polonnaruwa, because of the advanced and precise engineering. The system was extensively restored and further extended during the reign of King Parakrama Bahu (1153–1186 CE).The oldest known hydraulic engineers of China were Sunshu Ao (6th century BCE) of the Spring and Autumn Period and Ximen Bao (5th century BCE) of the Warring States period, both of whom worked on large irrigation projects. In the Szechwan region belonging to the State of Qin of ancient China, the Dujiangyan Irrigation System was built in 256 BCE to irrigate an enormous area of farmland that today still supplies water. By the 2nd century AD, during the Han Dynasty, the Chinese also used chain pumps that lifted water from lower elevation to higher elevation. These were powered by manual foot pedal, hydraulic waterwheels, or rotating mechanical wheels pulled by oxen. The water was used for public works of providing water for urban residential quarters and palace gardens, but mostly for irrigation of farmland canals and channels in the fields. In 15th century Korea, the world’s first rain gauge, uryanggye was invented in 1441. It was installed in irrigation tanks as part of a nationwide system to measure and collect rainfall for agricultural applications. With this instrument, planners and farmers could make better use of the information gathered in the survey. In North America, the Hohokam were the only culture to rely on irrigation canals to water their crops, and their irrigation systems supported the largest population in the Southwest by AD 1300. The Hohokam constructed an assortment of simple canals combined with weirs in their various agricultural pursuits. Between the 7th and 14th centuries, they also built and maintained extensive irrigation networks along the lower Salt and middle Gila rivers that rivaled the complexity of those used in the ancient Near East, Egypt, and China. These were constructed using relatively simple excavation tools, without the benefit of advanced engineering technologies, and achieved drops of a few feet per mile, balancing erosion and siltation. The Hohokam cultivated varieties of cotton, tobacco, maize, beans and squash, as well as harvested an assortment of wild plants. Late in the Hohokam Chronological Sequence, they also used extensive dry-farming systems, primarily to grow agave for food and fiber. Their reliance on agricultural strategies based on canal irrigation, vital in their less than hospitable desert environment and arid climate, provided the basis for the aggregation of rural populations into stable urban centers. (Source: http://en.wikipedia.org/wiki/Irrigation)

A set of carefully-constructed ditches, thought to be the earliest evidence of Roman irrigation in Britain, have


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been discovered by archaeologists working as part of a £1 billion development by the University of Cambridge in an area occupied by settlements since Prehistoric times. A lost medieval village is now being pursued by experts at the northern end of the North West Cambridge site, where they hope to investigate how civilisation has adapted to living in an area isolated from river valley water supplies. The area has a ridge-way where the gravels meet the clay. Cambridge University findings from excavating around the ridge-way have unearthed zebra-like stripes of Roman planting beds that are encircled on their higher northern side by more deep pit-wells. The gully-defined planting beds were closely set and were probably grapevines or possibly asparagus. Extraordinarily, after carefully peeling off the clays, archaeologists saw a series of ditches lining the wells and the horticultural beds. Clearly, in dry spells, water could have been poured from the pit-wells into the ditches to reach the beds. This is a tremendously significant find that reflects the area’s intense agricultural regime from the Roman period. The findings suggest communities lived in the area from as early as the later Neolithic period, between 2800 and 2200BC, and through the later Bronze, Iron and Roman ages. (Source:http://www.culture24.org.uk/history-and-heritage/archaeology/art473068-Earliest-evidence-Roman-irrigation-found-by-archaeologists-near-medieval-village).

The development of water control systems in the Asian region began from a small- scale/community system to become an integrated larger system of a kingdom. Technological development had been in line with the accumulation of knowledge and wisdom in the local areas. Over the years, resource endowments have led to different paths of development for rice- producing countries. All rice-exporting countries in Asia (Thailand, Myanmar, Cambodia and Vietnam) have major river deltas, and water control in these areas requires huge investment and management capacity. Such development did not begin until the arrival of the colonial powers in the nineteenth century. Rice cultivation in Thailand, Myanmar and Cambodia remains extensive, with large areas under rain-fed lowland or deep water cultivation. Vietnam is moving into the second stage of developing its delta areas with an increased share of irrigation and better control of water, resulting in a higher yield level. There are differences between the Asian and Western approach to development. The Western approach tends to be dominating and controlling, placing more emphasis on engineering theory and making light of traditional wisdom or human/institutional factors. The Asian approach, on the other hand, is more flexible and is in harmony with nature and the socio-cultural environment

(Source: The evolution of irrigation development in monsoon Asia and historical lessons by Nobumasa Hatcho et al; DOI: 10.1002/ird.542. Irrigation and Drainage, Special Issue: Selected Papers of the 20th ICID Congress,

Lahore, Pakistan, Volume 59, Issue 1, pages 4–16, Feb 2010).

Ancient China remains an important case to investigate the relationship between statecraft development and ‘total power.’ While important economic and social developments were achieved in the late Neolithic, it was not until the late Bronze Age (first millennium BC) that state-run irrigation systems began to be built. Construction of large-scale irrigation projects, along with walls and defensive facilities, became vital to regional states who were frequently involved in chaotic warfare and desperate to increase food production to feed the growing population. Some of the irrigation infrastructures were brought into light by recent archeological surveys. We scrutinize fast accumulating archeological evidence and review rich historical accounts on late Bronze Age irrigation systems. While the credibility of historical documents is often questioned, with a robust integration with archeological data, they provide important information to understand functions and maintenance of the irrigation projects. We investigate structure and organization of large-scale irrigation systems built and run by states and their importance to understanding dynamic trajectories to social power in late Bronze Age China. Cleverly designed based on local environmental and hydrological conditions, these projects fundamentally changed water management and farming patterns, with dramatic ecological consequences in different states. Special bureaucratic divisions were created and laws were made to further enhance the functioning of these large-scale irrigation systems. We argue that they significantly increased productivity by converting previously unoccupied land into fertile ground and pushed population threshold to a new level. A hypothesis should be tested in further archeological research. (Source: WIREs Water 2017, 4:e1217. doi: 10.1002/wat2.1217)

HISTORY OF IRRIGATION DEVELOPMENT IN INDIA:

Ministry of Water Resources, Govt. Of India, on its web site briefly explains the history of irrigation development in India which can be traced back to prehistoric times. The history of irrigation development in India can be traced back to prehistoric times. Vedas and ancient Indian scriptures made reference to wells, canals, tanks and dams which were beneficial to the community and their efficient operation and maintenance was the responsibility of the State. Civilization flourished on the banks of the rivers and harnessed the water for sustenance of life. According to the ancient Indian writers, the digging of a tank or well was amongst the greatest of the meritorious acts of a man. Brihaspathi, an ancient writer on law and politics, states that the construction and the repair of dams is a pious work and its burden should fall on the shoulders of rich

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men of the land. Vishnu Purana enjoins merit to a person who patronages repairs to well, gardens and dams.

In a monsoon climate and an agrarian economy like India, irrigation has played a major role in the production process. There is evidence of the practice of irrigation since the establishment of settled agriculture during the Indus Valley Civilization (2500 BC). These irrigation technologies were in the form of small and minor works, which could be operated by small households to irrigate small patches of land and did not require co-operative effort. Nearly all these irrigation technologies still exist in India with little technological change, and continue to be used by independent households for small holdings. The lack of evidence of large irrigation works at this time signifies the absence of large surplus that could be invested in bigger schemes or, in other words, the absence of rigid and unequal property rights. While village communities and co-operation in agriculture did exist as seen in well-developed townships and economy, such co-operation in the large irrigation works was not needed, as these settlements were on the fertile and well irrigated Indus basin. The spread of agricultural settlements to less fertile and irrigated area led to co-operation in irrigation development and the emergence of larger irrigation works in the form of reservoirs and small canals. While the construction of small schemes was well within the capability of village communities, large irrigation works were to emerge only with the growth of states, empires and the intervention of the rulers. There used to emerge a close link between irrigation and the state. The king had at his disposal the power to mobilize labour which could be used for irrigation works.

Man`s knowledge in developing water storage structures, especially in areas that are environmentally hosti le is exhibited in Dholavira. Dholavira is an archaeological site at Khadir bet in Bhachau Taluka of Kutch District. Khadir bet island is in the Kutch Desert Wildlife Sanctuary in the Great Rann of Kutch. The site contains ruins of an ancient Indus Valley Civilization/Harappan city. It is one of the five largest Harappan sites and most prominent archaeological sites in India belonging to the Indus Valley Civilization. The site was occupied from c.2650 BCE, declining slowly after about 2100 BCE. The most striking feature of the city is that all of its buildings, at least in their present state of preservation, are built of stone, whereas most other Harappan sites, including Harappa itself and Mohenjo-daro, are almost exclusively built of brick. Dholavira is flanked by two storm water channels; the Mansar in the north, and the Manhar in the south. The kind of efficient system of Harappans of Dholavira, developed for conservation, harvesting and storage of water speaks eloquently about their advanced hydraulic engineering, given the state of technology in the third millennium BCE. One of the unique features of Dholavira is the sophisticated water conservation system of

channels and reservoirs, the earliest found anywhere in the world, built completely of stone. The city had massive reservoirs, three of which are exposed. They were used for storing fresh water brought by rains or to store water diverted from two nearby rivulets. This clearly came in response to the desert climate and conditions of Kutch, where several years may pass without rainfall. A seasonal stream which runs in a north-south direction near the site was dammed at several points to collect water. The inhabitants of Dholavira created sixteen or more reservoirs of varying size. Some of these took advantage of the slope of the ground within the large settlement, a drop of 13 metres (43 ft) from northeast to northwest. Other reservoirs were excavated, some into living rock. Recent archaeological excavation work has revealed two large reservoirs, one to the east of the castle and one to its south, near the Annexe. The reservoirs are cut through stone vertically, and are about 7 m (23 ft) deep and 79 m (259 ft) long. They skirt the city, while the citadel and bath are centrally located on raised ground. There is also a large well with a stone-cut trough connecting it to a drain meant for conducting water to a storage tank. The bathing tank had steps descending inwards. In October 2014 excavation began on a rectangular step-well which measured 73.4 m (241 ft) long, 29.3 m (96 ft) wide, and 10 m (33 ft) deep, making it three times bigger than the Great Bath of Mohenjo-Daro. This finding clearly exhibits the significant knowledge of Harappans and may motivate present day inquisitive irrigation engineers to use the architectural finer points in serving individual small urban hamlets in environmentally difficult and hostile terrains.

In the south, perennial irrigation may have begun with construction of the Grand Anicut by the Cholas as early as second century to provide irrigation from the Cauvery River. Wherever the topography and terrain permitted, it was an old practice in the region to impound the surface drainage water in tanks or reservoirs by throwing across an earthen dam with a surplus weir, where necessary, to take off excess water, and a sluice at a suitable level to irrigate the land below. Some of the tanks got supplemental supply from stream and river channels. The entire land-scape in the central and southern India is studded with numerous irrigation tanks which have been traced back to many centuries before the beginning of the Christian era. In northern India also there are a number of small canals in the upper valleys of rivers which are very old.

Irrigation during Medieval IndiaGhiyasuddin Tughluq (1220-1250) is credited to be the first ruler who encouraged digging canals. Fruz Tughluq (1351-86) is considered to be the greatest canal builder. Irrigation is said to be one of the major reasons for the growth and expansion of the Vijayanagar Empire in southern India


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in the fifteenth century. Babur, in his memoirs called ‘Baburnamah’ gave a vivid description of prevalent modes of irrigation practices in India at that time. The Gabar Bunds captured and stored annual runoff from surrounding mountains to be made available to tracts under cultivation.

Irrigation Development under British RuleClose to nineteenth century according to sources of irrigation; canals irrigated 45 %, wells 35 %, tanks 15 % and other sources 5 %. Famines of 1897-98 and 1899-1900 necessitated British to appoint first irrigation commission in 1901, especially to report on irrigation as a means of protection against famine in India. As a result of recommendations of first irrigation commission total irrigated area by public and private works increased to 16 Mha in 1921. From the beginning of 19th century to 1921 there was no significant increase in tube well irrigated area. During 1910 to 1950 growth rate of irrigation was estimated at 2.0 % per annum for government canal irrigation, 0.54 % per annum for well irrigation and 0.98 % per annum in respect of irrigation from all sources.

Irrigation Development at Time of IndependenceAt time of independence net irrigated area of India under British rule which include Bangladesh and Pakistan was 28.2 Mha. After partition net irrigated area in India and Pakistan being 19.4 Mha and 8.8 Mha respectively. (Source: Irrigation Development in India: History & Impact, PareshB.Shirsath,2009;http://indiairrigation.blogspot.com/2009/01/history-of-irrigation-development-in_01.html)& https://www.revolvy.com/main/index.php?s=Dholavira)

CONCLUSIONS:

From the archaeological information civilizations survived and thrived by optimally utilising water resources, adapting area specific irrigation practices. The scriptures clearly show that during ancient times realizing the value of water Man has taken needed decisions to optimally utilize water resources, for drinking and agriculture/ horticulture activities. Community Development was given importance by one and all starting from the King down to a peasant. Till the mechanized implements, for faster extraction and transmission, have come in to use Man has availed the natural resources, including water, in a limited way allowing the environment more or less undisturbed and safe from

degradation. Man needs food. But, he needs to be satisfied and content with the food that is sufficient to keep him survive and grow. During historic and pre-historic times Man was satisfied with the products produced by him using apt irrigation practices. The needs were limited and people, in general, were content. The invention of less laborious mechanized systems has created more problems in meeting ever increasing demand for food products by ballooning population. Mechanized farming should basically aim at conservation of water and limited usage of unskilled labour, but not for over exploitation of natural resources, including water. The degradation and pollution of environment started surfacing with the focus diverted towards higher production of varied types of food products, without taking in to consideration the ill effects of disorganized irrigation practices. The age old irrigation practices, if continued, would have made the Man less avaricious. If not a reversal to the earlier irrigation practices, the basic objective behind optimum utilization of water resources through controlled irrigation practices need to be re-introduced to avoid total annihilation of our water resources. While optimally utilizing limited water resources (~ 3% of fresh water in entire globe) it is essential for the human race to use apt irrigation methods taking in to consideration various natural and artificial factors in locating a water source, extracting optimal quantities, storage of extracted and naturally available resources, distributing the available resources and optimally utilizing available waters to grow area specific agriculture/horticulture products. In this exercise it is essential not only use mechanized irrigation practices but also age old successfully adapted irrigation practices.

ACKNOWLEDGEMENTS:

Even though it may not be categorized as a research article it is prepared to motivate earth scientists to use it for taking up an important societal research activity that can help the farming community in introducing a combination of historical and present day irrigation methods. I am thankful to Google and Yahoo search bases. The write up has been prepared mainly using internet inputs (Source links are duly referred in the text). My contribution is confined to properly link the available information and build a useful write up. This write up has been compiled mainly as my parting contribution to JIGU.

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Quotations on Rivers and Irrigation

“For life and death are one, even as the river and the sea are one”. Khalil Gibran (1883 – 1931) an Lebanese-American artist, poet, and writer

***“The man who has grit enough to bring about the afforestation or the irrigation of a country is not less worthy of honor than its conqueror”.

- J. Arthur Thomson (1861–1933) an Scottish naturalist and an expert on soft corals.***

Keep your rivers flowing as they will, and you will continue to know the most important of all freedoms—the boundless scope of the human mind to contemplate wonders, and to begin to understand their meaning.

— David Brower (1912 – 2000) a prominent environmentalist ***

“If agriculture goes wrong, nothing else will have a chance to go right in the country”. -M.S.Swaminathan (1925--) known as “Indian Father of Green Revolution”

***“A few little flowers will spring up briefly in the dry gulley through which torrents of water pass occasionally. But it is steady streams that bring thick and needed crops. In the agriculture of the soul that has to do with nurturing attributes, flash floods are no substitute for regular irrigation”.

- Neal A. Maxwell(1926 – 2004) an apostle ***

“A brook can be a friend in a special way. It talks to you with splashy gurgles. It cools your toes and lets you sit quietly beside it when you don’t feel like speaking”.

- Joan Walsh Anglund (1926--) an American poet and children’s book author***

“More than one-half of the world’s major rivers are being seriously depleted and polluted, degrading and poisoning the surrounding ecosystems, thus threatening the health and livelihood of people who depend upon them for irrigation, drinking and industrial water”.

- Ismail Serageldin (1944--) Director of the Bibliotheca Alexandrina***

“Of all the works of civilization that interfere with the natural water distribution system, irrigation has been by far the most pervasive and powerful”.

- Al Gore (1948--) 45th Vice President of the United States ***

“Additionally, Smart Irrigation Month serves to recognize advances in irrigation technology and practices that produce not only more but also higher quality plants with less water”.

- Jim Costa (1952-- )an U.S. Representative for California’s 16th congressional district ***

“Your success lies in your own hands. You must therefore not wait for the grass to become greener by magic. You have the hands to irrigate your own territory by doing what is expected of you!”

- Israelmore Ayivor (1989--) an Inspirational Writer***

“Sit by a river. Find peace and meaning in the rhythm of the lifeblood of the Earth”. - (Anonymous)

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* Dr.K.S.Krishna Chief Scientist of NIO-Goa after serving for 33 years joined University of Hyderabad as Professor.

* Professor Supriyo Mitra was awarded the “National Geoscience Award (2016)” by Ministry of Mines in recognition of significant contribution to Applied Geology.

* Professor Supriyo Mitra has been selected as Member of the Research Advisory Committee, National Center for Seismology (NCS), Ministry of Earth Sciences (2016-2017).

NeWs AT A GlANCe

SCIENCE NEWS

### Volcanic Eruptions-series of unknown mysteries

Preamble:

India is affected by different types of natural hazards. It is, however, not directly affected in the recent past by any major volcanic eruptions. It witnessed 65 million years back Deccan Volcanism that wiped out dinosaurs, due to significant sudden climate change caused by huge volumes of gasses and molten lava spewed by the series of eruptions from number of vents present both on land and in the adjoining seas, covering a vast stretch of western India. Presently it has one known volcano in the Barren Island, northern part of Bay of Bengal. Barren island volcano which had started showing activity in 1992 after lying dormant for over 150 years has again started spewing ash, smoke and lava since January, 2017, the researchers of NIO, Goa have reported. They have told that during the daytime only ash clouds were observed. However, after sundown, the team observed red lava fountains spewing from the crater into the atmosphere and hot lava flows streaming down the slopes of the volcano. This activity assumes importance as this part of Bay of Bengal, located about 140 km north east of Port-Blair was aseismic when Andaman-Sumatra region was significantly active since 2004. Present volcanic activity may possibly lead to seismic activity, extending towards land part of Burma and India/Bangladesh.

Since major eruptions from many volcanoes present in different parts of the earth can harm us immensely as winds carry the pollutants from hundreds of km, this recent activity assumes significance. To brush up our knowledge about volcanic activity, which was not taken seriously by Indian volcanologists/ seismologists, results from some significant studies are given below to help young researchers carry out studies with focus on volcanic activity and volcano related seismic activity.

***How hazardous are massive volcanic eruptions?

The Earth currently has 1,500 ‘active volcanoes’ - meaning they have had at least one eruption during the past 10,000 years. This is aside from the continuous belt of volcanoes on the ocean floor, about 500 of which have erupted in historical time. However, not all eruptions are the same. As per experts one can broadly categorise eruptions into two different types. The first, effusive, produces lava flows and lots of gas. The second, explosive, produces ash and gas. The difference in activity is controlled mostly by the viscosity of the magma. The more viscous the magma, the more difficult it is to get gas out of the system and the more likely one has to have an explosion. Despite the type of eruptions differing massively, if all the world’s volcanoes erupted at the same time, the results would be catastrophic in a number of ways.

Firstly, the people in the firing line of the eruption would be affected, not only by the flow of magma from the volcano, but also from the huge ash clouds expelled. Pyroclastic flows are fast-moving clouds of rock, ash and gas that are very hot, with temperatures rising up to 1000°C. These would be impossible to outrun or even drive, as they can travel up to 450 miles per hour. As well as affecting people near the volcano itself, pyroclastic flows can cause destruction for up to 100 miles from the site. For number of people living near volcanoes, the destruction is massive. For example, around three million people live near Mount Vesuvius, while 130 million people live on the island of Java which alone has 45 active volcanoes. But

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the destruction close to the volcanoes would just be the beginning. The eruptions would send plumes of volcanic ash into the sky that could travel for thousands of miles. Ash is pretty unpleasant stuff. It comprises tiny fragments of glass, crystals and rock. When the mixture of this stuff reaches villages/towns/ cities it can devastate vast stretches of habitable locations, making millions lose everything. Fatalities also reach significant level. You may remember the worldwide flight cancellations caused by the 2010 eruption of Eyjafjallajökull in Iceland, in the fears of damage to airplane engines. Breathing in ash can cause massive problems to our lungs, including silicosis, and damage that sends our immune systems into overdrive, leading to a range of secondary problems. Essentially, there would be no buildings, no vehicles run by an engine, and you would not be able to go anywhere without a gas mask. To add to this, communication channels would be out of the question - ash can disrupt satellite dishes and block radio waves.

The volcanic eruptions would cause long-lasting changes to the Earth’s climate. While we usually associate volcanoes with being hot, the huge amount of ash and gas released into the atmosphere would actually lower the temperature globally. The initial injection of sulphur dioxide, converted to small particles called aerosols in the presence of water, would reflect sunlight back out into space. This would cool the planet significantly, potentially even to get to ice-age like conditions.

However in the longer term, we could see a reverse effect with temperatures rising. ‘Over hundreds of years, carbon dioxide released by volcanoes might heat the planet up. In 1815, Mount Tambora in Indonesia erupted. This one eruption can be seen in global climate records, lowering temperatures worldwide and causing heavy rain which ruined crops. If one eruption can have that effect, we can only begin to imagine what destruction would be caused if all 1500 active volcanoes went off simultaneously. Hypothetically, if every volcano on Earth erupted simultaneously, you could argue that all life might well be wiped out. In that sense it is a doomsday scenario. However, such an eventuality is very unlikely. (Source:http://www.dailymail.co.uk/sciencetech/article-3642494/What-happen-Earth-s-1-500-volcanoes-erupted-Experts-outline-terrifying-doomsday-scenario.html).

***Crustal limestone platforms feed carbon to many of Earth’s arc volcanoes

A new analysis suggests that much of the carbon released from volcanic arcs, chains of volcanoes that arise along the tectonic plates of a subduction zone, comes from remobilizing limestone reservoirs in the Earth’s crust. Previous research suggested carbon was sourced from the mantle as a result of the subduction process. The discovery ultimately impacts the amount of organic carbon scientists believe was buried in the past. Carbon cycling between surface reservoirs and the mantle over geologic history is important because the imbalance greatly influences the amount of total carbon at Earth’s surface. However, the source for carbon from volcanic arc out-gassing remained uncertain. Emily Mason and colleagues compiled a global data set of carbon and helium isotopes to determine the origin of the carbon. The data reveal that many volcanic arcs mobilize carbon from large, crustal carbonate platforms -- particularly in Italy, the Central American Volcanic Arc, Indonesia, and Papua New Guinea. In contrast, arcs located in the northern Pacific, such as Japan and Kuril-Kamchatka, release carbon dioxide with an isotope signature indicative of a mantle source. The recognition of a large amount of crustal carbon in the overall carbon isotope signature requires, from a mass balance consideration, downward revision of how much organic carbon was buried in the past. (Source: Emily Mason, Marie Edmonds, Alexandra V. Turchyn. Remobilization of crustal carbon may dominate volcanic arc emissions. Science, 2017; 357 (6348): 290 DOI: 10.1126/science.aan5049).

***Cold plates and hot melts: New data on history of Pacific Ring of Fire

About 2000 km east of the Philippine Islands lies one of the most famous topographical peculiarities of the oceans: the Mariana trench. Reaching depths of up to 11,000 meters below sea level, it holds the record as the deepest point of the world’s ocean. This 4000-kilometer-long trench extends from the Mariana Islands in the south through the Izu-Bonin Islands to Japan in the north. Here, the Pacific Plate is subducted beneath the Philippine Sea Plate, resulting in intense volcanic activity and a high number of earthquakes. The entire area is part of the “Pacific Ring of Fire.”But when and how exactly did the subduction of the Pacific Plate begin? This is a controversial topic among scientists. An international team led by the GEOMAR Helmholtz Centre for Ocean Research, Kiel, the Japan Agency for Marine Earth Science and Technology (JAMSTEC) and the Australian National University investigated this early phase of subduction along the Izu-Bonin-Mariana trench.

The study is based on a drill core that was obtained by the International Ocean Discovery Program (IODP) in 2014 with the US research drilling vessel 600 km west of the current Izu-Bonin Trench. “For the first time, we were able to obtain samples of rocks that originate from the first stages of subduction,” says Dr. Philipp Brandl from GEOMAR. “It is known that the active subduction zone has been moving eastwards throughout its history and has left important geological traces on the seabed during its migration. We have now drilled where the process has begun.”The team of the JOIDES RESOLUTION was able to drill more than 1600 meters deep on the seabed. Based on analysis of this drill core, the researchers were able to trace the history of the subduction zone layer by layer up to the approximately 50 million year-old rocks at the bottom of the core, which are typical for the birth of a subduction zone. Brandl and his colleagues were now able to acquire and analyze microscopic inclusions of cooled magma from the rocks. The data obtained provide the scientists with insights into the history of volcanic activity at the Pacific Ring of Fire 30-40 million years ago. The researchers found evidence that volcanism was only beginning to gain momentum. The volcanic activity intensified with the rollback of the subduction zone towards the east and the huge explosive strato volcanoes formed, similar to those present nowadays, for example along the western rim of the Pacific Ring of Fire. However, further drilling is necessary to test the validity of these observations. The question of how subduction zones develop is not only interesting to understand the history of the earth. Subduction zones are the drivers for the chemical exchange between the earth’s surface and the earth’s interior. (Source: Philipp A. Brandl, et al. The arc arises: The links between volcanic output, arc evolution and melt composition, Science Letters, 2017; 461: 73 DOI: 10.1016/j.epsl.2016.12.027).

***Can Water Vapour Help Forecast When a Volcano Will Blow?

The magma that bursts out of volcanoes is propelled upward largely by dissolved gases, which are released into the atmosphere once the molten rock approaches the surface. The most abundant of these gases is water vapour, and scientists have long searched for a way to accurately measure volcanic water vapour emission rates. Recently Kern et al. present a possible new method to do just that based on research conducted at the 6000-meter-high Sabancaya Volcano in Peru. Six months prior to the onset of the volcano’s current eruptive crisis, which began in November 2016, the team measured the volcanic water vapour output using a method called passive visible-light differential optical absorption spectroscopy (DOAS). DOAS instruments measure the absorption of sunlight by gases in the atmosphere and the volcanic plume above them. The technique is widely used to measure sulfur dioxide emissions, but these were the first successful DOAS measurements of volcanic water vapour.

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The team found that prior to the current eruptive phase, the Sabancaya plume contained an exceptionally high, 1000:1 ratio of water vapour to sulfur dioxide, about an order of magnitude higher than typically found in volcanic gases. They hypothesize that as Sabancaya’s buoyant magma rose to shallower depths, it likely began to boil off water stored in the volcano’s underground network of fluid-filled cracks and fissures, called its hydrothermal system.

This commonly happens prior to volcanic eruptions. The team suggests that visible-light DOAS stations be set up around the world to detect when other active volcanoes are getting steamier. (Source: Journal of Geophysical Research: Solid Earth, https://doi.org/10.1002/2017JB014020, 2017).

***How do volcanoes affect world climate?

In 1784, Benjamin Franklin made what may have been the first connection between volcanoes and global climate while stationed in Paris as the first diplomatic representative of the United States of America. He observed that during the summer of 1783, the climate was abnormally cold, both in Europe and back in the U.S. The ground froze early, the first snow stayed on the ground without melting, the winter was more severe than usual, and there seemed to be “a constant fog over all Europe, and a great part of North America.

What Benjamin Franklin observed was indeed the result of volcanic activity. An enormous eruption of the Laki fissure system (a chain of volcanoes in which the lava erupts through a crack in the ground instead of from a single point) in Iceland caused the disruptions. The Laki eruptions produced about 14 cubic km of basalt (thin, black, fluid lava) during more than eight months of activity. More importantly in terms of global climate, however, the Laki event also produced an ash cloud that may have reached up into the stratosphere. This cloud caused a dense haze across Europe that dimmed the sun, perhaps as far west as Siberia. In addition to ash, the eruptive cloud consisted primarily of vast quantities of sulfur dioxide (SO2), hydrogen chloride (HCl), and hydrogen fluoride gases (HF). The gases combined with water in the atmosphere to produce acid rain, destroying crops and killing livestock. The effects, of course, were most severe in Iceland; ultimately, more than 75% of Iceland`s livestock and 25% of its human population died from famine or the toxic impact of the Laki eruption clouds. Consequences were also felt far beyond Iceland. Temperature data from the U.S. indicate that record lows occurred during the winter of 1783-1784. In fact, the temperature decreased about one degree Celsius in the Northern Hemisphere overall. That may not sound like much, but it had enormous effects in terms of food supplies and the survival of people across the Northern Hemisphere. For comparison, the global temperature of the most recent Ice Age was only about five degrees C below the current average.

There are many reasons that large volcanic eruptions have such far-reaching effects on global climate. First, volcanic eruptions produce major quantities of carbon dioxide (CO2), a gas known to contribute to the greenhouse effect. Such greenhouse gases trap heat radiated off of the surface of the earth forming a type of insulation around the planet. The greenhouse effect is essential for our survival because it maintains the temperature of our planet within a habitable range. Nevertheless, there is growing concern that our production of gases such as CO2 from the burning of fossil fuels may be pushing the system a little too far, resulting in excessive warming on a global scale. There is no doubt that volcanic eruptions add CO2 to the atmosphere, but compared to the quantity produced by human activities, their impact is virtually trivial: volcanic eruptions produce about 110 million tons of CO2 each year, whereas human activities contribute almost 10,000 times that quantity.

By far the more substantive climatic effect from volcanoes results from the production of atmospheric haze. Large eruption columns inject ash particles and sulfur-rich gases into the troposphere and stratosphere and these clouds can circle the globe within weeks of the volcanic activity. The small ash particles decrease the amount of sunlight reaching

the surface of the earth and lower average global temperatures. The sulfurous gases combine with water in the atmosphere to form acidic aerosols that also absorb incoming solar radiation and scatter it back out into space. The ash and aerosol clouds from large volcanic eruptions spread quickly through the atmosphere. On August 26 and 27, 1883, the volcano Krakatau erupted in a catastrophic event that ejected about 20 cubic km of material in an eruption column almost 40 km high. Darkness immediately enveloped the neighbouring Indonesian islands of Java and Sumatra. Fine particles, however, rode atmospheric currents westward. By the afternoon of August 28th, haze from the Krakatau eruption had reached South Africa and by September 9th it had circled the globe, only to do so several more times before settling out of the atmosphere. Initially, scientists believed that it was volcanoes’ stratospheric ash clouds that had the dominant effect on global temperatures. The 1982 eruption of El Chichin in Mexico, however, altered that view. Only two years earlier, the major Mt. St. Helens eruption had lowered global temperatures by about 0.1 C. The much smaller eruption of El Chichin, in contrast, had three to five times the global cooling effect worldwide. Despite its smaller ash cloud, El Chichin emitted more than 40 times the volume of sulfur-rich gases produced by Mt. St. Helens, which revealed that the formation of atmospheric sulfur aerosols has a more substantial effect on global temperatures than simply the volume of ash produced during an eruption. Sulfate aerosols appear to take several years to settle out of the atmosphere, which is one of the reasons their effects are so widespread and long lasting.

The atmospheric effects of volcanic eruptions were confirmed by the 1991 eruption of Mount Pinatubo, in the Philippines. Pinatubo`s eruption cloud reached over 40 km into the atmosphere and ejected about 17 million tons of SO2, just over two times that of El Chichin in 1982. The sulfur-rich aerosols circled the globe within three weeks and produced a global cooling effect approximately twice that of El Chichin. The Northern Hemisphere cooled by up to 0.6 °C during 1992 and 1993. Moreover, the aerosol particles may have contributed to an accelerated rate of ozone depletion during that same period. Interestingly, some scientists argue that without the cooling effect of major volcanic eruptions such as El Chichin and Mount Pinatubo, global warming effects caused by human activities would have been far more substantial. Major volcanic eruptions have additional climatic effects beyond global temperature decreases and acid rain. Ash and aerosol particles suspended in the atmosphere scatter light of red wavelengths, often resulting in brilliantly coloured sunsets and sunrises around the world. The spectacular optical effects of the 1883 Krakatau eruption cloud were observed across the globe, and may have inspired numerous artists and writers in their work. The luminous, vibrant renderings of the fiery late day skyline above the Thames River in London by the British painter William Ascroft, for instance, may be the result of the distant Krakatau eruption. In 1815, the Indonesian volcano Tambora propelled more ash and volcanic gases into the atmosphere than any other eruption in history and resulted in significant atmospheric cooling on a global scale, much like Krakatau a few decades later. New England and Europe were particularly hard hit, with snowfalls as late as August and massive crop failures.

The cold, wet, and unpleasant climatic effects of the eruption led 1816 to be known as “the year without a summer,” and inspired Lord Byron to write:

“The bright Sun was extinguished, And the stars Did wander darkling in the Eternal space Ray less and pathless,

And the icy earth Swung blind and blackening in the moon less air; Morn came and went and came, And brought no day” --Lord Byron,

(Source:https://www.scientificamerican.com/article/how-do-volcanoes-affect-w/)

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***Volcano’s Toxic Plume Returns as Stealth Hazard

Toxic airborne emissions from volcanoes in Iceland may be dangerous even when pollution-monitoring instruments indicate that the air is safe, according to a new study. Volcanologists observing a 2014–2015 eruption in Iceland have found that even when air quality detectors had determined that sulfur dioxide (SO2) gas had fallen to acceptable levels in the air downwind from an eruption, another form of contamination known as sulfate aerosols had sneaked back, sullying the air.

The aerosols’ ingredients, tiny particles of sulfuric acid and trace metals, likely also harm people, but less is known about their toxicity than about the health consequences of SO2. These pollutants contain heavy metals found in human-made air pollution that are linked to negative health effects. More than a cubic km of lava gushed from the rift, along with record-breaking amounts of sulfur dioxide gas. For 6 months spanning the end of 2014 and the beginning of 2015, an eruption from the Holuhraun fissure in the Bárðarbunga volcanic system of south-eastern Iceland captivated the world. More than a cubic km of lava gushed from the rift, along with record-breaking amounts of SO2, a common volcanic emission that can be extremely harmful to humans. Readings came from the volcano site and monitoring stations in cities downwind from the eruption. Also during the eruption, Ilyinskaya and her collaborators collected their own gas samples from a helicopter hovering just tens of meters above the fiery rift. Long after the eruption had ended, when the researchers started analyzing their data along with data from monitoring stations in areas surrounding the volcano, something odd stuck out. In two cities, a small town called Reykjahlíð, 100 km downwind from the eruption, and Iceland’s capital, Reykjavík, 250 km downwind, the researchers noticed that on some days when monitoring stations detected low levels of SO2, their data indicated simultaneous high levels of sulfate aerosols, which arise from sulfur dioxide cooling in the air while reacting with other airborne molecules with the help of sunlight. Ilyinskaya and her team found that a plume of sulfur dioxide would evolve into aerosols and travel back toward Iceland in a matter of days—they dubbed these secondary plumes “plumerangs.”. The researchers were stunned to see that the SO2 plumes could last long enough to “mature,” or fully convert into plumes of aerosols. On at least 18 days during the 6-month-long eruption, the plumerang was in the capital city of Reykjavík, while the official forecast showed ‘no plume.

The researchers are currently conducting a follow-up study to determine what kinds of health effects resulted from the plumerangs, Ilyinskaya said. In the meantime, the researchers suggest that SO2-to-aerosol conversions should be considered in future air pollution forecasts, especially considering the profuse SO2 emissions known to come from Iceland’s volcanoes.

Source: Wendel, J. (2017), Volcano’s toxic plume returns as stealth hazard, Eos, 98,https://doi.org/10.1029/2017EO078265.

From a recent study it is evident that in future Iceland will be devastating parts of earth as it is sitting over a molten lava chamber of significant dimensions. Please read the following to know more details.

***Getting to the root of Iceland’s molten rock origins

New data reveal an unprecedented depiction of a region of partially molten rock deep within the Earth, which appears to be feeding material in the form of a plume to the surface, where Iceland is located.

The finding, in combination with evidence from previous studies, suggests that these molten regions deep below, near the core-mantle boundary of the Earth, may cause basaltic ocean island chains to form along the surface. Around the Earth’s core-mantle boundary are regions called ultralow-velocity zones (ULVZs), which are characterized by liquid rock with velocities up to 30% lower than surrounding material.

However, depicting ULVZs has been particularly difficult given their extreme depths. ULVZs have been detected below the Polynesian country of Samoa

and the Hawaiian islands, yet a clear depiction of their shape has eluded scientists. The proximity of these ULVZs below volcanic island chains has prompted theories suggesting that the giant reservoirs of molten rock feed the mantle plumes that create the islands on Earth’s surface.

Here, Kaiqing Yuan and Barbara Romanowicz used seismic tomography, which constructs an x-ray-like picture of the Earth’s interior using seismic waves, to probe a ULVZ below Iceland.

Based on their results, there appears to be a massive circular blob of partially molten rock, approximately 800 km in diameter and 15 km in height, along the core-mantle boundary, feeding the plume directly below the basaltic island.

The authors note that this ULVZ’s location, shape and large diameter, which is proportionate with the width of the plume higher up in the lower mantle, suggests a close link between the ULVZ and the rising plume above it.

These new data, in combination with the known presence of ULVZs below Samoa and Hawaii, led the authors to propose that a specific class of large ULVZs form at the roots of broad plumes that feed active hotspots. (Source: Kaiqing Yuan, Barbara Romanowicz. Seismic evidence for partial melting at the root of major hot spot plumes. Science, 2017; 357 (6349): 393 DOI: 10.1126/science.aan0760)

***A Volcanic Trigger for Earth’s First Mass Extinction?

Abnormally high levels of mercury in Ordovician rocks may imply that a huge surge of volcanism took place at a time when much of the planet’s ocean life vanished. Five major mass extinctions punctuate the history of life on Earth. The first is the Late Ordovician mass extinction, which began about 445 million years ago, triggered by a severe ice age and subsequent global warming that exterminated more than 85% of all marine species. Why the ice age that sparked the event was so drastic, however, is not clear. Recent research has suggested that large-scale volcanism before and during the extinction may be to blame. In a new study, researchers report the discovery of rock layers formed about the time of the extinction that are rich in the chemical element mercury, which they say is a telltale sign of volcanic activity.

Geochemist David Jones , collected Late Ordovician rocks from the Monitor Range mountains in Nevada, as well as from Wangjiawan in south China. When he analyzed the rocks in his laboratory, he found mercury concentrations that shot through the roof around the time of the great die out. Because volcanoes are the largest natural source of mercury to Earth’s surface, discovering such a surge suggested that a connection may exist between the volcanism and the extinction.

The same kind of surge occurs in the south China rocks, in which mercury levels reach far above an average concentration of about 50 to 100 parts per billion to almost 400 parts per billion, he added.

Studying spikes in mercury concentrations is one of the best ways to try and correlate volcanic activity with extinction, particularly when there is a dearth of actual volcanic rock evidence in the rock record. Scientists now have strong evidence for volcanism occurring just prior to and during the extinction. Before, the Late Ordovician mass extinction (LOME) was the only one of the “Big Five” extinctions not associated with volcanic activity.

It’s well known to geoscientists that LOME began during the Hirnantian age as large ice sheets grew over the single supercontinent that existed at that time, Gondwana, and reached their maximum extent between 445.2 and 443.8 million years ago. What’s more, those ice sheets dwarfed those of Earth’s most recent ice age, which reached its maximum extent about 20,000 years ago. Geochemical evidence suggests that total ice volume during the Hirnantian glacial maximum was significantly more.

Geochemists have found evidence likely helped drive the glaciation. Although volcanoes emit carbon dioxide, which, at sufficient

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concentrations, can warm the planet, geochemists explained that previous modeling work suggests that weathering of volcanic rock can lead to a drawdown of carbon dioxide in the atmosphere through the chemical weathering of that province. In addition to so-called Snowball Earth event wherein ice sheets covered much of the planet volcanoes also emit sulfur dioxide gas into the atmosphere, which can form sulfate ions that scatter incoming solar radiation, cooling the planet in the process. Although other researchers warmly welcomed the mercury evidence of volcanism, the cooling part of the scenario has raised eyebrows. Volcanism is often thought of as an agent of warming, so teasing out how it may also cause cooling is tricky. However, volcanism does not necessarily mean warming will ensue because how much carbon dioxide ancient volcanoes emitted into the atmosphere depended on how carbon-rich the sedimentary rocks surrounding the extruding lavas were. The amount of carbon dioxide released would depend critically on the geology of the region in which the eruption occurred, because the lava would help release the gas into the air. Further study of the geology will help reveal whether or not this was the case.

However the volcanic cooling hypothesis pans out, the biggest revelation in the new work is that there is now evidence that each of the five major mass extinctions coincided with widespread volcanism. The new findings may imply that a large igneous province is almost a precondition to have a mass extinction. Source: Joel, L. (2017), A volcanic trigger for Earth’s first mass extinction?, Eos, 98,https://doi.org/10.1029/2017EO074813.

Outstanding Contribution in Oceanography

Tadepalli Satyanarayana Murty

Dr. Murty was born in 1938 in India and carried out initial schooling and college education in India. He is presently having Indo-Canadian nationality. He has significant research experience in Oceanography.

Tad S. Murty is an expert on tsunamis. He is the former president of the Tsunami Society. He is

an adjunct professor in the departments of Civil Engineering and Earth Sciences at the University of Ottawa. Murty has a PhD degree in oceanography and meteorology from the University of Chicago. He is co-editor of the journal Natural Hazards with Tom Beer of CSIRO and Vladimir Schenk of the Czech Republic.

Affiliations

* Natural Resources Stewardship Project (NRSP) — Past “Allied Expert.” The NRSP is now defunct.

* International Climate Science Coalition (ICSC) — “Consultant Science Adviser.”

* International Climate and Environmental Change Assessment Project (ICECAP) — “Expert.”

Climate change

He has taken part in a review of the 2007 Intergovernmental Panel on Climate Change. Murty characterizes himself as a global warming skeptic. In an August 17, 2006 interview, he stated that “I started with a firm belief about global warming, until I started working on it myself...I switched to the other side in the early 1990s when Fisheries and Oceans Canada asked me to prepare a position paper and I started to look into the problem seriously.” There is no global warming due to human anthropogenic activities”. Murty was among the sixty scientists from climate research and related disciplines who authored a 2006 open letter to Canadian Prime Minister Stephen Harper criticizing the Kyoto Protocol and the scientific basis of anthropogenic global warming.

His main research interests include mathematical modeling of natural hazards, which include hurricanes, winter storms, storm surges, ocean

waves, tides, coastal inundation, tsunamis, river floods, coastal erosion and sedimentation and how climate change affects these phenomena. He is one of the editors of the renown international scientific journal, Natural hazards, published by Springer in the Netherlands, Senior Associate editor of Marine Geodesy published by Taylor & Francis in New York and is on the editorial board of Science of Tsunami Hazards, published by the International tsunami Society in Honolulu.

He is the Vice-president of the International Tsunami Society and a member of the Expert Advisory Group of the Kalpasar Project (the largest civil engineering project ever in Indian history and among the largest in the world) in the state of Gujarat in India. He is a Visiting Scientist at the Beijing Institute of Technology and the Indian Institute of technology in New Delhi, India.

He received numerous national and international awards, including the Lifetime Achievement Award from the International Tsunami Society, the Gold Medal in Oceanography from the Indian Geophysical Union, Applied Oceanography Prize from the Canadian Meteorological & Oceanographic Society, and the Professional Man of the Year Award from the Indo-Canada Chamber of Commerce.

Since receiving the Ph.D. from the University of Chicago, Dr. Murty served as Senior Research Scientist in the Canadian Federal Department of Fisheries & Oceans, as the Director of Australian National Tidal facility and Professor of Earth Sciences in Flinders University in Adelaide. Later he worked as a Senior Scientist with Baird & Associates Coastal Engineers in Ottawa, prior to joining the University of Ottawa as an Adjunct Professor.

Dr. Murty has some 20 books to his credit, as an author, co-author and editor and has published extensively in peer reviewed scientific journals. He has been a co-supervisor for M.S. and Ph.D. students in various universities worldwide. He served as a consultant to various United Nations Organizations and also as a resource person for various workshops worldwide. He also participated in scientific projects in several countries on all the continents.

Fields of Interest

* Mathematical modelling of natural hazards; * Climate change; * Cyclones; * Tsunamis; * Storm surges; * Coastal Zone Management

Resources

1) “Murty, Tad,” Faculty of Engineering at the University of Ottawa. Accessed January, 2012.

2) “Submission from the Lavoisier Group to the Garnaut Climate Change Review: Appendix B” (PDF), The Lavoisier Group. Accessed January, 2012.

3) Cindy Robinson. “Global warning?,” Carleton University, Spring 2005 Cover Story. Archived December 18, 2005.

4) Professor Tad Murty. “We now know what we don’t know about climate change,” The Ottawa Citizen, December 12, 2005. Retrieved January, 2012, from iberica2000.org.

5) “Independent Summary for Policymakers of the IPCC Fourth Assessment Report (Working Group I),” Retrieved January, 2012, from Ross Mckitrick’s homepage at the University of Guelph (www.uquelph.ca/~rmckitri).

6) “NRSP People,” The Natural Resources Stewardship Project. Archived January 21, 2007.

7) “WHO WE ARE,” International Climate Science Coalition. Accessed January, 2012.

8) “Experts,” ICECAP. Accessed January, 2012. 9) “Tad Murty,” Wikipedia Entry. 10) Exxon Secrets Factsheet: Tad Murty. P.R.Reddy

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Quotes on Volcanic eruptions “Each volcano is an independent machine—nay, each vent and monticule is for the time being engaged in its own peculiar business, cooking as it were its special dish, which in due time is to be separately served. We have instances of vents within hailing distance of each other pouring out totally different kinds of lava, neither sympathizing with the other in any discernible manner nor influencing other in any appreciable degree.”

- Clarence Edward Dutton (1841- 1912) was an American geologist .***

“All civilization has from time to time become a thin crust over a volcano of revolution.” - Havelock Ellis (1859 - 1939), an English writer, intellectual and social reformer

***“If your heart is a volcano, how shall you expect flowers to bloom?”

- Khalil Gibran (1883 - 1931) was a Lebanese-American artist and poet.***

“Obviously people want social calm, but if you do not let clever and ingenious people to participate, obviously there must be some dormant volcano that will erupt, sooner or later”.

- Lech Walesa (1943--) is a retired Polish politician ***

“The fact that a cloud from a minor volcanic eruption in Iceland—a small disturbance in the complex mechanism of life on the Earth—can bring to a standstill the aerial traffic over an entire continent is a reminder of how, with all its power to transform nature, humankind remains just another species on the planet Earth.”

- Slavoj Žižek (1949--) is a continental philosopher ***

“Remind me that the most fertile lands were built by the fires of volcanoes.” ― Andrea Gibson,( 1975--) an American poet

***“I noticed that volcanoes, earthquakes and floods, though are not good events, they are better than the silence of good people when bad people take the podium. The latter are to an extent uncontrollable, but the former can be stopped.”

- Israelmore Ayivor (1989--) an Inspirational Writer ***

“Mount Kilauea spilled glowing lava like cords of orange neon-lighting from seemingly nowhere. In the blackness that engulfed the night, electric heat lit flowing streams that fell into the sea, disappearing in a cloud of steam with a sizzling splash.”

- Victoria Kahler, US author

Shipboard Automated Meteorological and Oceanographic system (SAMOS) – a critical component of Global Ocean Observation Framework

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TECHNICAL NEWS

Shipboard Automated Meteorological and Oceanographic system (SAMOS) – a critical component of Global Ocean Observation Framework

Raja AcharyaIndian Meteorological Department, Regional Meteorological Centre, Kolkata (Ministry of Earth Science)

INTRODUCTION

A Shipboard Automated Meteorological and Oceanographic System (SAMOS) is a typical form of a computerized data logging system connected to sensors. It continuously records navigational (ship’s position, course, speed, and heading), meteorological (winds, air temperature, pressure, moisture, rainfall, and radiation), and near-surface oceanographic (sea temperature and salinity) parameters while the vessel is at sea (Shawn R. Smith, 2005). The SAMOS initiative provides routine access to accurate, high-quality marine meteorological and near-surface oceanographic observations from research vessels and select voluntary observing ships.

OBJECTIVES

SAMOS aims to improve the quality of meteorological and near-surface oceanographic observations collected in-situ on research vessels and select volunteer observing ships (VOS).Scientific objectives of SAMOS include:• Creating quality estimates of the heat, moisture,

momentum, and radiation fluxes at the air-sea interface

• Benchmarking new satellite and model products• Providing high quality observations to support

modeling activities and global climate programs

SAMOS Working System:-The flowchart of SAMOS observations starts with the computer logging system on the SAMOS Research vessel. At the end of each observation day, a set of meteorological, oceanographic, and navigational parameters at one minute interval are bundled into a single ASCII file. The daily file is attached to an email (with compression if desired) and sent via satellite communication from the vessel directly to the SAMOS DAC (Data Assembly Centre). Normally, daily files are transmitted shortly after 0000 UTC for each day a recruited vessel is at sea. All SAMOS data can be accessed through the SAMOS web page: http://samos.coaps.fsu.edu

Advantages of SAMOS:-The world Ocean Circulation Experiment (WOCE) recognized a need for an improved understanding of air-sea fluxes (Thompson et al., 2001). High quality, high accuracy fields of air-sea fluxes are

necessary to support the activities of the Global Ocean Data Assimilation Experiment (GODAE). Over the ocean surface these fields can be derived using in-situ and remote sensed observations in combination with flux models. Regardless of the method used to derive the flux fields there is a requirement of standard bench marking of the flux fields. (Bourassa, M.A., 2010). The SAMOS measurements are recorded at high-temporal sampling rates (typically 1 minute or less). The high sampling rate allows more accurate estimates of the turbulent air-sea fluxes to be determined (Smith et al., 2011) and makes SAMOS data ideal for validating flux fields from numerical weather prediction models (Smith et al., 2011; Renfrew et al., 2002). The SAMOS observations have also proven to be ideal sources of validation data for new satellite systems (Bourassa et al., 2003). SAMOS observations are anticipated to provide some of the highest quality validation data for comparison with present and future remote sensing instruments and numerical models. Limitations: The accuracy in recording of oceanographic and meteorological data depends on the proper calibration of sensors mounted on the SAMOS ships. Absence of manual observations poses challenges to the data accuracy of automated equipments. Interruptions in marine and meteorological observations occur due to sudden machine faults. Moreover lack of SAMOS ships in remote locations also affect optimum data coverage required by the scientific community.

Future Strategies for SAMOS to support Ocean Observation:• The SAMOS vessel should provide for manual

observations which will fill the gap in case due to sudden interruptions in continuous recording of oceanographic and meteorological data on account of machine faults or other factors.

• Provisions to be made for periodic sensor calibration on board the Research Vessel to ensure SAMOS data accuracy.

• The Port Meteorological Offices around the globe can play a leading role in servicing the SAMOS vessels for upkeep of SAMOS instruments and sensor calibration for data accuracy.


Raja Acharya

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• The Data accuracy of SAMOS equipments can be addressed through the results of Computational Fluid Dynamics (CFD) modelling of the airflow around vessels, which will help to determine optimum sensor locations and adjust measurement biases caused by airflow around various ship structures.

ACKNOWLEDGEMENTS:

This technical news has been compiled using internet and other sources, basically to propagate the importance of SAMOS systems. I unequivocally state that the technical details given above have not been developed by me either directly or indirectly. I thank the Chief Editor of JIGU for editing and publishing this technical news item.

REFERENCES AND BIBLIOGRAPHY:

Bourassa, M.A., Legler, D.M., O’Brien, J.J., and Smith, S.R.,

2003. SeaWinds validation with research vessels. Journal

of Geophysics. Res., DOI 10.1029/2001JC001081., v.108

Bourassa, M.A., 2010. Observations to quantify air-sea fluxes and

their role in climate variability and predictability.

Picture Courtesy: SAMOS initiative Marine Data Center, Center

for Ocean-Atmospheric Prediction Studies, (COAPS) The

Florida State University.

Renfrew, I.A., Moore, G.W.K., Guest, P.S., and Bumke, K., 2002.

A comparison of surface layer and surface turbulent-flux

observations over the Labrador Sea with ECMWF analyses

and NCEP reanalyses. Journal of Physical Oceanography.,

v.32, pp: 383-400.

samos.coaps.fsu.edu/

Shawn R. Smith, 2005. Ship Board Automated Meteorological

and Oceanographic Systems- a key component of an Ocean

Observing System.

Smith, S.R., et al., 2011. Automated underway oceanic and

atmospheric measurements from ships.

Thompson, B. J., Crease, J., and Gould, W. J., 2001. The

Origins, Development and Conduct of WOCE, of Ocean

Circulation and Climate: Observing and Modelling the

Global Ocean (editors G. Siedler, J. Church, and J. Gould).

International Geophysics Series, Academic Press, 2001.,

v.77, pp: 31-43.

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References should be given in the following form:Kaila, K.L., Reddy P.R., Mall D.M., Venkateswarlu, N., Krishna V.G. and Prasad, A.S.S.S.R.S., 1992. Crustal structure of the west Bengal Basin from deep seismic sounding investigations, Geophys. J. Int., v.111,no., pp:45-66.

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