assessment of seismic hazard in uttarakhand himalaya

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isaster Prevention and Managementmerald Article: Assessment of seismic hazard in Uttarakhand Himalaya

rabhat Kumar, Ashwini Kumar, Amita Sinvhal

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cite this document: Prabhat Kumar, Ashwini Kumar, Amita Sinvhal, (2011),"Assessment of seismic hazard in Uttarakhand

malaya", Disaster Prevention and Management, Vol. 20 Iss: 5 pp. 531 - 542

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Assessment of seismic hazard inUttarakhand Himalaya

Prabhat Kumar, Ashwini Kumar and Amita SinvhalDepartment of Earthquake Engineering, IIT Roorkee, Roorkee, India

Abstract

Purpose For a state like Uttarakhand, which is located in the seismically active Himalayan regionand in the vicinity of plate boundaries, estimation of seismic hazards and the preparation of a zoningmap are an urgent necessity. This paper aims to focus on this hazard.

Design/methodology/approach In total, 32 potential seismo-tectonic source zones wereidentified in a very wide area in and around the state, on the basis of seismicity and tectonics, andthe longer ones were segmented. The maximum magnitude that each seismo-tectonic source zone cansupport was then estimated. The seismic hazard due to each seismo-tectonic source zone was assessed

at 180 sites, in terms of peak ground acceleration (PGA).Findings The maximum PGA at each site varied between 0.06gand 0.50g. The seismic hazard washighest around the main central thrust and the main boundary thrust, and five other thrusts betweenthese two thrusts. This assessment was adapted to make a seismic zoning map of Uttarakhand, withfive distinct zones.

Research limitations/implications If seismo-tectonic source zones from the contiguous regionsof Nepal and Tibet were included as part of this assessment, then a higher hazard would be expected inUttarakhand.

Practical implications Threat perceptions of a potential earthquake disaster can be assessed inthis zoning map. Disaster mitigation strategies will vary geographically, with priorities defined by thezoning map presented here. The methodology evolved has the potential to be extended to othervulnerable states in the Himalayan arc.

Originality/value The seismic hazard assessed has been adapted to formulate a seismic zoning

map of Uttarakhand.Keywords Himalayas, Seismicity, Tectonics, Uttarakhand, Hazards, Zoning map, Natural disasters,Earthquakes

Paper type Research paper

IntroductionThe Indian subcontinent is a seismically active part of the world. Major seismicactivity in India is concentrated along the geologically young and seismo-tectonicallyactive Himalayan arc due to the ongoing continent-continent collision between theIndian and Eurasian plates. As part of the Alpine Himalayan seismic belt this arc hasexperienced four great earthquakes, i.e. earthquakes with a magnitude greater than 8,

within 53 years. No great earthquake has occurred within the Himalayan arc since1950, i.e. in the last 60 years, and such an earthquake could occur any time soon.

The Himalayan state of Uttarakhand lies in the region between epicenters of twogreat earthquakes, namely the Kangra (1905) and Bihar Nepal earthquakes (1934). Thisseismic gap (Khattri, 1987) has not experienced a major earthquake during a timeinterval when most other segments of the gap have ruptured. Seismic gaps aresupposed to have a high future earthquake potential. Therefore, there is an urgent needto assess seismic hazard and have a detailed zoning map of the state. Seismic hazard

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Assessment ofseismic hazard

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Disaster Prevention and Management

Vol. 20 No. 5, 2011

pp. 531-542

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DOI 10.1108/09653561111178961


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involves a quantitative estimate of ground shaking at a particular site or within anarea.

Seismicity and seismic source zonesTo assess seismic hazard it is essential to first identify seismic source zones. Thisrequires a detailed examination of the seismicity pattern of the area in and aroundUttarakhand. Initially, a very wide area, falling between the great Kangra earthquakeof 1905 and the great Bihar Nepal earthquake of 1934 was selected. This area liesbetween latitude 258N to 378N and longitude 728E to 878E. A catalogue of earthquakedata, as per the India Meteorological Department (IMD), revealed 2,097 epicenters ofmagnitude 4 and above for the period 1552 to 2007, as shown in Figure 1[1]. The spatialdistribution of seismicity is non-uniform. A diffuse pattern was observed over a verylarge area, whereas several clusters of epicenters were aligned in an almostNorthwest-Southeast trending belt, parallel to the Himalayan trend, between theepicenters of the two great earthquakes.

This NW-SE trending seismic belt passes through Uttarakhand. Elevenearthquakes of a magnitude of more than 6.0 have originated within the state sinceAD 1552. The Uttarkashi earthquake of October 20, 1991 (magnitude Ms 7.0, Mw 6.8,mb 6.5, USGS), and the Chamoli earthquake of March 29, 1999 (magnitude Ms 6.6,mb 6.4, USGS) had the highest magnitude of all earthquakes to originate within thestate.

A region where seismicity is concentrated can be considered to indicate apreliminary seismic source zone. The observed pattern of seismicity can be taken torepresent the expected future pattern of seismicity. Since epicentral data available forUttarakhand and the region around it is available for a short span of time as comparedto the average return period between large earthquakes, seismicity alone was notenough to identify seismic source zones. The inclusion of tectonics helped in

circumventing this problem.

Tectonic unitsThe most commonly used tectonic units considered for assessing seismic hazard arefaults and thrusts. Initially, the regional tectonic set-up of the area was examined(Narula et al., 2000), for the same area as for seismicity. Tectonic features such asfaults, thrusts, suture zones and lineaments identified and digitized using a GISsoftware package, are shown in Figure 1. The vast study area for which seismicity wasinitially studied was narrowed down to a distance of about 300 km from every corner ofUttarakhand.

Due to collision zone tectonics a complex network of mega faults, thrusts and suturezones exists in the area. North and South of the Indus Suture Zone (ISZ), which forms

the tectonic boundary between the Indian and Eurasian plates, are the TethysHimalayas and the Main Central Thrust (MCT), respectively. The two mega-thrusts,MCT and the Main Boundary Thrust (MBT), separate three geologically distinctsettings. The Greater Himalayas lie North of the MCT, between the MCT and ISZ; theLesser Himalayas lie between MCT and MBT; and the Outer Himalaya lie South of theMBT. The Main Frontal Thrust (MFT), also known as the Frontal Foothill Thrust,FFT, is South of the MBT, and is a neo-tectonic thrust. These form the foothillsbordering the Indo Gangetic plains. The ISZ, MCT, MBT and FFT manifest

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Figure 1.Seismicity and tectonicsbetween latitudes 258N

and 378N, and longitudes728E and 878E. The outline

of Uttarakhand is shownbetween longitudes 778E

and 818E. The inset showsthe area of study


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throughout the Himalayan arc, between the Eastern and Western syntaxis, and haveprominent surface manifestations at several places. The MCT terminates against theKishtwar fault in Jammu and Kashmir in the Northwest.

The MCT, MBT and FFT traverse prominently through Uttarakhand and are prone

to frequent earthquakes and landslides. The genesis of the Kangra earthquake isassociated with the MBT, and there is a concentration of epicenters on the MBT aroundthe Kangra earthquake. Seismicity is concentrated North of (MBT), mainly betweenMBT and MCT, and in the vicinity and North of MCT. The MBT, also known as KrolBelt in Uttarakhand, shows neo-tectonic activity at several places.

Besides these mega Himalayan thrusts, several other faults and thrusts exist in thestudy area. Karakoram Fault (KF) exhibits a huge offset and extends for more than1,000 km from Central Pamir to North of Uttarakhand Himalayas. The region betweenthe MBT and the MFT is traversed by several thrusts. Some of these, such as

Jwalamukhi Thrust ( JMT), Drang Thrust, (DT), and the Sundernagar Fault (SNF), alsoknown as Manali Fault, can be traced over long distances. Neo-tectonic activity hasbeen documented in Western parts of Jwalamukhi Thrust. In addition to the tectonicfeatures mentioned here, several faults and lineaments are transverse to the Himalayantrend. Prominent among these are the Kaurik fault system, (KFS), the MahendragarhDehradun Fault (MDF), the Great Boundary Fault (GBF), and the Moradabad Fault(MF), which exists in the Delhi-Moradabad region.

Several tectonic features are prominent in Uttarakhand. These include theAlaknanda Fault (AF), which is a conspicuous neo-tectonic feature in the area, NorthAlmora Thrust (NAT), South Almora Thrust (SAT), Martoli Thrust (MT1 and MT2),Vaikrita Thrust (VT), Ramgarh Thrust (RT), and Munsiari Thrust. Besides thesemajor thrusts, the region also has a large number of smaller thrusts, mostly withincurves and loops, most of which are less than 50 km long. To proceed with hazardassessment those potential sources not named in the atlas were given a unique name.

Eight of these were christened Thrust Zones 1 to 8, (TZ1, TZ2, TZ3, TZ4, TZ5, TZ6,TZ7, and TZ8). Faults involving basement and cover were named as Faults G1, G2 andG3, and Fault R1 is a neo-tectonic fault. All the 32 source zones identified are shown inFigures 1 and 2.

Segmentation of seismo-tectonic source zonesIn certain regions there is a clear-cut relationship between faults and earthquakes (e.g.the San Andreas Fault in Southern California). However, in the Himalayas, any spatialassociation of tectonic features with seismicity is poorly understood. For such regions,assessing seismic hazard seismicity has to be considered in association with thetectonics of the region, i.e. seismo-tectonic source zones acquire an enhancedimportance. A seismo-tectonic source is a geological structure that is capable of

generating earthquakes.Discontinuity and intersection of mega-thrusts with neo-tectonic faults were

important diagnostic features that were used as an aid for the segmentation ofmega-thrusts. The very long and highly contorted MCT was divided into foursegments for assessing seismic hazard. Segment MCT1 was in the Western portion ofthe study area. It was considered between two faults that are transverse to theHimalayan trend, i.e. the Kishtwar fault and a small neo-tectonic fault along which theMCT exhibits a pronounced discontinuity. Segment MCT2 was considered between

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this neo-tectonic fault discontinuity, which marked one extremity of MCT1 and the

Sundernagar Fault (SNF), mainly because of the seismicity South of MCT. Segment

MCT3 was marked between Sundernagar Fault (SNF) in the West and its abrupttermination in the East due to the unavailability of tectonic data east of Uttarakhand,

at 818E longitude. This segment is mainly within Uttarakhand. MCT4 is East of the

study area, between approximately 81.68 and 848 longitude, in the Nepalese Himalayas.

MBT was considered as two segments, marked by a pronounced discontinuity across

neo-tectonic fault R1. MBT1 is between 78.48 longitude and 818 longitude. This portion

is mainly within Uttarakhand. MBT2 is the portion between 758 longitude and 818

longitude. Each fault, thrust and segment was used separately for estimating seismic

hazard.

Studies of fault rupture worldwide indicate that during an earthquake the entire

length of a fault does not rupture, but individual segments rupture and this process

appears to repeat through several seismic cycles (Coppersmith, 1991). Therefore, eachsegment aided in estimating the length of rupture likely to occur along that thrust. In

the present study it was assumed that one third of the identified seismo-tectonic

segment was involved in rupture for generating the maximum magnitude earthquake

(Mark, 1977). All identified seismo-tectonic sources that were capable of producing

significant ground motion at a site were idealized as line sources. The rupture length

estimated for various sources ranged from 7 km for fault G3 to 215 km for the segment

of MCT that is within Uttarakhand.

Figure 2.Seismo tectonics of

Uttarakhand


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Seismic hazardThe next important step in assessment of seismic hazard was to assign maximummagnitude to an earthquake that can occur on an identified seismo tectonic source

zone. The size of an earthquake is empirically related to the dimensions of rupture

(Wells and Coppersmith, 1994), and this correlation was used to compute the maximummagnitude that each seismo-tectonic source zone could support. This is also termed themaximum credible earthquake or maximum considered earthquake. Theseemerged in the range 6.1-7.8, a condition that cannot be ruled out within a seismic gap.

A critical part of seismic hazard assessment is the quantitative estimation of strongground shaking expected to occur at a site, and is determined as peak groundacceleration (PGA). This is estimated using a predictive model (Abrahamson andLithehiser, 1989) that correlates acceleration to maximum magnitude and the distancebetween the zone of energy release and the site. This empirical formulation, based onfour independent parameters i.e. magnitude, distance, fault type and tectonicenvironment is one of the very few attenuation formulations that introduces the

concept of the tectonic environment and fault type in estimating peak groundacceleration for earthquakes that have focal depths less than 25 km, a conditionprevalent in Uttarakhand.

The study area was further narrowed down around Uttarakhand, and was

encompassed by longitudes 778300E to 818000 and latitudes 288450 to 318300. As thisarea was divided into a closely spaced grid of 0.258 intervals, the center of each block of180 grid points was considered to be a potential site. To assess the worst-case scenarioit was assumed that the maximum magnitude earthquake in each identifiedseismo-tectonic source would occur at the closest possible distance from the site. Anensemble of PGAs was computed for every site, due to each seismo-tectonic source.The highest of these acceleration values was taken as a measure of the seismic hazardat the center of the grid point under consideration. In this way the highest accelerationvalue was determined for all sites.

The PGA computed in the present study had a large variation, i.e. from 0.06gto 0.5g,and a wide geographical spread all over Uttarakhand and contiguous regions. Twelveseismo-tectonic sources spread over 47 sites generated the highest accelerations, in therange 0.4-0.5g. MBT and MCT emerge as the two most potent thrusts. Several thrustsin the Lesser Himalayas, i.e. between MBT and MCT, also emerge as high contributors.These are the North Almora Thrust, Ramgarh Thrust, and Thrust Zones TZ1, TZ2 andTZ7. The other high contributors FFT, Martoli Thrust MT1 and MT2, South AlmoraThrust, and ISZ are parallel to the Himalayan trend. The other significantcontributors are Fault G3, Karakoram Fault, Great Boundary Fault, MahendragarhDehradun Fault, and Moradabad fault.

Seismic hazards can occur in many forms, such as fault ruptures, ground failure,topographic changes, surface distortions, liquefaction, sand boils, mudflows andground fissures. Waterfalls, the damming and diversion of rivers, changes in drainagesystems, the sloshing of water over stream banks and canals, and floods are some ofthe other water-related disastrous consequences of earthquakes. Other hazards includelandslides in mountainous terrains, a phenomenon highly prevalent in Uttarakhand,even without a seismic trigger. These phenomena often result in adverse consequencessuch as damage to the built environment and loss of life and injuries.

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Hazard zoning mapThe seismic hazard assessed here was used to prepare a hazard zoning map.Iso-acceleration contours, drawn at intervals of 0.1g, show a large variation of PGA inand around the entire state, as shown in Figure 3. The contours follow the trend of the

MBT in the Southern part of the state. An abrupt increase in acceleration occurs allalong the MBT, where the PGA increases from 0.2g to 0.5g. This indicates a sharpincrease of hazard along and North of MBT. This situation is repeated along the MCT.The entire region between MBT and MCT, i.e. the Lesser Himalayas, is beset with highacceleration values, between 0.3g and 0.5g, over a short distance spanning 25 km to40 km. This indicates high seismic hazard along the MBT and the MCT, and in theregion in between, together with several other places in Uttarakhand and beyond.

Of 13 districts in Uttarakhand, large parts of 11 districts have PGA values above0.4g, which indicates a very high level of seismic hazard. This includes Almora,Bageshwar, Chamoli, Champawat, Dehra Dun, Nainital, Pauri, Pithoragarh,Rudraprayag, Tehri and Uttarkashi districts. Only two districts, Haridwar andUdham Singh Nagar, South of the MBT, show accelerations below 0.3g.

The entire state is prone to earthquake hazards, which are expected in the twohighest seismic zones, IV and V, as per the seismic zoning map of India (Bureau ofIndian Standards, 2002). As such, parts of the state are prone to accelerations of 0.24gand 0.36g, respectively. Of the 180 sites considered in the present study, 86 were withinUttarakhand, and 53 of these exhibited PGA values above those for Zone V. Thisindicates that more than 60 percent of the area of the state is prone to PGA values

Figure 3.Map shows variation of

peak ground accelerationin Uttarakhand and

contiguous areas, andMBT and MCT


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above that expected in the earthquake code. Clearly, the code needs an upward revision

in view of these high values in a state like Uttarakhand, which is going through a

phase of rapid techno-economic development. This reveals an increased threat

perception.

With this in mind, the hazard assessed here was adapted to yield a seismic zoning

map of the state. Uttarakhand was divided into five seismic zones, in contrast to the

present two, (Bureau of Indian Standards, 2002). The accelerations expected in each

zone are given in Table I and Figure 4. Zones II, III, IV and V have the same

connotations as in the seismic zoning map of India (Bureau of Indian Standards, 2002),

and an additional zone VI is added that depicts accelerations higher than those given in

the code.

Seismic zone Acceleration (percentage g) Damage implications

II ,0.10 Slight damage

III 0.10-0.16 Moderate damageIV 0.16-0.24 Heavy damageV 0.24-0.36 DestructionVI .0.36 Catastrophic

Table I.Peak acceleration

assigned to differentseismic zones, andperceived damageimplications

Figure 4.Seismic zoning map ofUttarakhand

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Comparison with other studies

The maximum peak ground acceleration observed for the Uttarkashi earthquake of

October 20, 1991 (epicenter 30.758N, 78.868E; Ms 7.0, 6.6 mb, USGS), at a hypo central

distance of 40 km, for the Uttarkashi recording station, was 0.31g (after

Chandrasekaran and Das, 1992). Uttarkashi, Chamoli and Tehri districts suffered

maximum damage in this earthquake. In contrast to this, the zoning map presented in

Figure 3 indicates that an earthquake of a higher magnitude, 7.6Mw, at a closer hypo

central distance of 21 km, due to rupture of 128 km of North Almora Thrust, is expected

to produce a higher PGA of 0.38gat the Uttarkashi recording station. Similarly, for the

Chamoli earthquake of March 29, 1999 (epicenter 30.418N, 79.428E; Ms 6.6, USGS), the

maximum acceleration recorded was 0.41g, at a hypo central distance of 22 km, for the

Gopeshwar recording station (after Shrikhande et al., 2000). Chamoli and Rudraprayag

Districts were the worst affected. However, for the same site, the zoning map reveals a

PGA value of 0.48gat a hypo central distance of 17 km, for an earthquake of magnitude

7.1, produced by a 57 km long rupture of thrust TZ1. This means that a higher

magnitude earthquake, at a closer hypo central distance, is yielding higher PGA (as

given in Figure 3) when compared to recorded data. It is reasonable to expect this, and

it indicates an increased threat perception in the area.

In a seismic hazard map of India and adjoining regions, Bhatia et al. (1999)

computed PGA for 10 percent exceedence in 50 years in grids of 0.58 by 0.58. Since 86

large-sized seismic sources were used, and local tectonic features and sources were

excluded, the values for Uttarakhand ranged between 0.05gand 0.35g, less than those

obtained in the code and in the present study. Another hazard map of India and

adjacent areas used seismograms (Parvez et al., 2003), which were synthesized up to

1 Hz frequency, i.e. for large epicentral distances, on the basis of structural models,

seismogenic zones, focal mechanisms and earthquake catalogues. The PGA valuesobtained for Western Himalaya varied between 0.15g and 0.3g, which is much lower

than those given in earthquake code BIS 1893-2002, and also in the present study. Joshi

and Mohans (2009) method of estimating hazard involved the modeling of rupture

planes along identified lineaments in Uttarakhand. As the Southward dipping North

Almora Thrust was considered in its entirety, and not segmented, it gave PGA values

much higher than anywhere else, of the order of 0.55g, and that too South and West of

MFT, i.e. in the Ganga plains. It is pertinent to note that for the much longer MCT and

MBT this trend is reflected neither in the direction of their down dip nor in the

geographical spread of these high accelerations.

When the severest seismic micro zone that emerged when micro earthquake data

and the tectonics of Tehri Garhwal region were subjected to a pattern recognitiontechnique based on discriminant analysis (Sinvhal et al., 1990, 1991, Sinvhal, 2010) was

subjected to a 7.5 magnitude earthquake on the MBT, at coordinates 3080801000N and

7882003000E, it revealed that 59 percent of the population of the Narendra Nagar

administrative block was at risk, with damage associated with accelerations of 0.41g

(Gupta et al., 2006, 2008; Gupta and Sinvhal, 2010). This PGA is in fair agreement with

the present study, and brings out the efficacy of this study, which gives a

corresponding value of 0.40g at the same site.


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LimitationsSince seismic hazard maps are strongly influenced by the characteristics and size ofseismo-tectonic source zones, non-inclusion of this data from contiguous regions ofNepal and Tibet has a strong bearing on the results of our hazard zoning. If extensions

of MCT and MBT were considered in this area, then reasonably higher hazards wouldresult in Uttarakhand.

Results and discussionTo assess the seismic hazard of Uttarakhand, of 32 potential seismo-tectonic sourcesconsidered, 12 made a maximum contribution towards hazard. These were MCT, MBTand thrusts and faults between these two Himalayan mega-thrusts. It is pertinent tonote that the great Kangra earthquake of 1905 had its genesis in the vicinity of MBT,and the Uttarkashi and Chamoli earthquakes originated in the vicinity of MCT.

The zoning map presented in Figure 4, with five zones, has several applications.Threat perceptions and disaster implications on housing stock, roads andinfrastructure, which can be expected to be profound in an earthquake, can bereasonably assessed in any area within the map. Appropriate long-term, medium-termand short-term action plans can be formulated and implemented which will varygeographically, with priorities defined by the zoning map. Despite the known highseismic hazard in Uttarakhand more than 90 per cent of houses here do not incorporateany earthquake-resistant design, and are made of mud, adobe, burnt brick and stones.That these vulnerable homes become a risk to human life was amply demonstrated bythe earthquakes of Uttarkashi in 1991 and Chamoli in 1999, which together claimedmore than 1,000 human lives in Uttarakhand. A long-term action plan is required,which will include the formulation of earthquake mitigation strategies andpreparedness plans for the entire state. This map also finds useful applications inthe earthquake-resistant design of structures for which it is not possible to carry out

detailed site-specific studies. In the medium-term action plan, seismic upgrading of theexisting and vulnerable built environment can be taken up, phase-wise. Short-term, anaction plan for rescue, relief and emergency management can be developed for theentire state. When applied, all this will have the added advantage that it will reduce theuncertainty of a potential disaster, and simultaneously post-earthquake recovery costswill be reduced tremendously.

ConclusionsWe believe the seismic zoning map presented here gives a reasonably representativeseismic hazard map of Uttarakhand. As the nascent state of Uttarakhand has immensehydro-electric potential and is going through a rapid phase of development, if thebenefits reaped by this are to remain sustainable, then this detailed seismic zoning map

can be used to take urgent mitigation measures before the next earthquake takes itstoll. The methodology evolved here has the potential to be extended to other vulnerablestates in the Himalayan arc.

Note

1. The various tectonic elements in Figure 1 are labeled as: AF, Alaknanda Fault; AtF, AttockFault; ATF, Altyn Tagh Fault; ASL, Ajmer Sandia Lineament; BF, Bhagu Fault; BMAL,Bharatpur Mount Abu Lineament; BNS, Bangong Nujiang Suture; CF, Chahapoli Fault; CF,

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Chau Fault; CJL, Chambal Jamnagar Lineament; DF, Dhandu Fault; DL, Delwar Lineament;DT, Drang Thrust; EL, Everest Lineament; EPF, East Patna Fault; GBF, Great BoundaryFault; GL, Gouri Shankar; HF, Hathusar Fault; ISZ, Indus Suture Zone; JhF, Jhelum Fault; JF,Judi Fault; JMT, Jwala Mukhi Thrust; KaF, Kanti Fault; KaF, Kalu Fault; KCF, Kishanagar

Chipri Fault; KCG, Kung Co graben; KF, Karakoram Fault; KFS, Kaurik Fault System;KISHF, Kishtwar Fault; KKF, Kallar Kabar Fault; KhF, Khatu Fault; LF, Lucknow Fault;LSL, Luni Sukri Lineament; MBT, Main Boundary Thrust; MCT, Main Central Thrust; MDF,Mahendragarh Dehra Dun Fault; MF, Moradabad Fault; MF, Mangla Fault; MFT, MainFrontal Thrust; MKT, Main Karakoram Thrust; MMT, Main Mantle Thrust; MSRF, MungerSaharsa Ridge Fault; MT, Martoli Thrust; NAT, North Almora Thrust; PF, Peshawar Fault;PVL, Pisanyau Vadnagar Lineament; RNL, Raisingh Nagar Fault; RT, Ramgarh Thrust;SaF, Sadassar fault; SoF, Soniasar Fault; SAT, South Almora Thrust; SF, Shinkiari Fault;SNF, Sundar Nagar Fault; SRT, Salt Range Thrust; SS, Shyok Fault; SSF, Sardar ShaharFault; TF, Tarbela Fault; TG, Takhola Graben; TL, Tonk Lineament; TM, Tso Morari Fault;VT, Vaikrita Thrust; WPF West Patna Fault.

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Sinvhal, A., Sinvhal, H., Joshi, G. and Singh, V.N. (1991), A valid pattern of micro zonation,Proceedings of the Fourth International Conference on Seismic Zonation, StanfordUniversity, Stanford, CA, pp. 641-8.

Wells, D.L. and Coppersmith, K.J. (1994), New empirical relationships among magnitude,rupture length, rupture area and surface displacement, Bulletin of Seismological Society of

America, Vol. 84 No. 4, pp. 974-1002.

Corresponding authorAmita Sinvhal can be contacted at: [email protected] [email protected]

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