SEISMICITY IN

NORTH-EAST INDIADr. Sandip Das

Assistant ProfessorDept. of Civil Engineering

IIT Guwahati

Content

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• Seismic environment of Northeast India• Major faults and seismotectonic zones

• Magnitude-recurrence relationship• G-R relationship• Return period

• Seismic hazard analysis• PSHA

• Local site effects• Seismic demand for design

• Design spectrum• Spectrum compatible ground motion

SEISMIC ENVIRONMENT OF NORTH-EAST INDIATectonic Map with Major Faults

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SEISMIC ENVIRONMENT OF NORTH-EAST INDIA

Zone-2

Zone-3

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SEISMIC ENVIRONMENT OF NORTH-EAST INDIA

SeismotectonicZones Year Magnitude

(Mw)

Zone-011934 8.31787 7.81885 7.0

Zone-02

1908 7.51954 7.31938 7.21957 7.21906 71932 71950 71988 7

Zone-03 1947 7.71697 7.2

Zone-04 1950 7

Zone-05 1806 7.7

Zone-06

1951 8

1411 7.7

1952 7.5

1915 7.1

Major Earthquakes in Different Seismotectonic Zones

SeismotectonicZones Year Magnitude

(Mw)

Zone-071950 8.51905 7.11950 71950 7

Zone-081918 7.61762 7.51869 7.5

Zone-09

1897 8.1825 8

1990 81943 7.21923 7.11930 7.1

Zone-10

1912 81839 7.81946 7.81931 7.61946 7.5

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SEISMIC ENVIRONMENT OF NORTH-EAST INDIA

Seismogenic Zones with Maximum Credible Earthquakes

Zone Mmax (ISC) Mupper (CRISIS)

1 7.7 7.7

2 7.1 7.6

3 7.2 7.7

4 6.9 7.4

5 4.7 6.3

6 7.5 8

7 7.9 8.5

8 6.1 7.6

9 7.2 8.9

10 7.5 8

ISC – International Seismological CentreCRISIS – Software package for computation of seismic hazard 6

MAGNITUDE-RECURRENCE RELATIONSHIPGutenberg-Richter Recurrence Law

• G-R relationship: linear relation between earthquake magnitude 𝑚𝑚 and the Mean Annual Rate of Exceedance 𝜆𝜆𝑚𝑚 of earthquakes of magnitude 𝑚𝑚

𝐥𝐥𝐥𝐥𝐥𝐥𝟏𝟏𝟏𝟏 𝝀𝝀𝒎𝒎 = 𝒂𝒂 − 𝒃𝒃𝒎𝒎

𝑎𝑎 and 𝑏𝑏: constants obtained by linear regression analysis

• 𝑏𝑏: relative likelihood between small and large earthquakes

• G-R relation in exponential form 𝝀𝝀𝒎𝒎 = 𝒆𝒆𝜶𝜶−𝜷𝜷𝒎𝒎

𝛼𝛼 = 2.303𝑎𝑎 and 𝛽𝛽 = 2.303𝑏𝑏

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MAGNITUDE-RECURRENCE RELATIONSHIP

𝒂𝒂 and 𝒃𝒃 for Northeast India (using ZMAP software)

Zones 𝒂𝒂 𝒃𝒃

1 1.770 0.443

2 1.607 0.406

3 3.796 1.020

4 3.805 0.965

5 3.053 0.827

6 2.053 0.493

7 5.711 1.740

8 1.956 0.477

9 2.594 0.646

10 3.494 0.955

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MAGNITUDE-RECURRENCE RELATIONSHIP

Occurrence Model• Poisson process (memory-less): suitable for smaller earthquakes

Probability that the number of occurrences of an event (𝑿𝑿𝒕𝒕) in a time interval 𝑡𝑡 be equal to 𝑥𝑥 is given by

𝑷𝑷 𝑿𝑿𝒕𝒕 = 𝒙𝒙 =𝝀𝝀𝒎𝒎𝒕𝒕 𝒙𝒙

𝒙𝒙!𝒆𝒆−𝝀𝝀𝒎𝒎𝒕𝒕

𝒙𝒙 = 𝟏𝟏,𝟏𝟏,𝟐𝟐, … … .

𝜆𝜆m: average number of occurrences of the event per unit time or mean occurrence rate1𝜆𝜆𝑚𝑚

= 𝑇𝑇𝑅𝑅: Mean return period (from G-R relationship)

Return PeriodThe probability that an event, greater than a specified magnitude, occurs at least once in a time interval tFor Poisson occurrence model

𝑃𝑃 𝑋𝑋𝑡𝑡 ≥ 1 = 1 − 𝑃𝑃 𝑋𝑋𝑡𝑡 = 0 = 1 − 𝑒𝑒𝜆𝜆𝑚𝑚𝑡𝑡

Characteristic Earthquake: periodic maximum earthquake magnitude (fault-wise)• mean return period not following G-R relationship• uniform distribution of return period 9

SEISMIC HAZARD ANALYSISProbabilistic SHA

Seismic hazard: Probability of exceedance of a given level of ground intensity measure (hazard parameter) in a specific time interval

Components• Probability distribution of source-to-site distance

• From fault geometry and site location• 𝑓𝑓𝑅𝑅 𝑟𝑟 = 𝑟𝑟

𝐿𝐿𝑓𝑓 𝑟𝑟2−𝑟𝑟𝑚𝑚𝑚𝑚𝑚𝑚2

• Probability distribution of Earthquake Magnitude• From G-R relationship• 𝑓𝑓𝑀𝑀 𝑚𝑚 = 𝛽𝛽𝑒𝑒−𝛽𝛽(𝑚𝑚−𝑚𝑚0) 𝑚𝑚0 is the lower threshold magnitude

• Probability of exceeding specified value of ground motion parameter• From attenuation model

• 𝑃𝑃 |𝑌𝑌 > 𝑦𝑦 𝑚𝑚, 𝑟𝑟 = 1 − 𝐹𝐹𝑌𝑌 𝑦𝑦 = 1 − 12𝜋𝜋 ∫−∞

𝑧𝑧 𝑒𝑒−𝑠𝑠2

2 𝑑𝑑𝑑𝑑 = 12𝜋𝜋 ∫−∞

−𝑧𝑧 𝑒𝑒−𝑠𝑠2

2 𝑑𝑑𝑑𝑑• Annual probability of exceedance due to the seismic sources

• 𝜆𝜆𝑖𝑖𝑖𝑖 = 𝜆𝜆𝑚𝑚0 𝑃𝑃[𝑌𝑌 > 𝑦𝑦] 𝜆𝜆𝑖𝑖 = ∑𝑖𝑖=1𝑁𝑁𝑠𝑠 𝜆𝜆𝑖𝑖𝑖𝑖

• Mean value of return period• 𝑃𝑃𝑡𝑡 𝑌𝑌 > 𝑦𝑦 = 𝑃𝑃 𝑋𝑋𝑡𝑡 ≥ 1 = 1 − 𝑃𝑃 𝑋𝑋𝑡𝑡 = 0 = 1 − 𝑒𝑒𝜆𝜆𝑦𝑦𝑡𝑡 10

SEISMIC HAZARD ANALYSIS

Probabilistic SHAExample :The site shown in Figure is located in western United States and two active faults are near the site.

Fault 1 Fault 2

Closest distance to site (km) 10 20

Maximum distance to site (km) 18 31

Length of fault (km) 30 65

Max. Magnitude of earthquake 7.5 8.5

a & b values a=2.25, b=0.75 a=3.3, b=0.88

Find the probabiltiy of exceeding a PGA of 0.3g at the site in 100 years considering a lower threshold magnitude of 5.0 for both faults.Assume an avg. shear wave velocity of 1396 m/s for the soil deposits at site.Assume also that the closest distances to the faults correspond to their geometric centers.11

SEISMIC HAZARD ANALYSIS

Probabilistic SHASolution :

Mean annual frequency of earthquakes of magnitude >= 𝑚𝑚0, 𝜆𝜆𝑚𝑚0 = exp(𝛼𝛼 − 𝛽𝛽𝑚𝑚0)

𝜆𝜆𝑚𝑚0 = exp 2.303 2.25 − 2.303 0.75 5.0 = 0.032 events/year for Fault-1

𝜆𝜆𝑚𝑚0 = exp 2.303 3.30 − 2.303 0.88 5.0 = 0.079 events/year for Fault-2

𝐸𝐸[ln𝐴𝐴𝐻𝐻] = −0.242 + 0.527(𝑀𝑀𝑤𝑤 − 6) − 0.778 ln 𝑅𝑅2 + 5.572𝜎𝜎ln 𝐴𝐴𝐻𝐻 = 0.520

𝑧𝑧 =ln𝐴𝐴𝐻𝐻 − [−0.242 + 0.527(𝑀𝑀𝑤𝑤 − 6) − 0.778 ln 𝑅𝑅2 + 5.572]

0.520

Attenuation equation proposed by Boore, Joyner and Fumal for PGA,

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SEISMIC HAZARD ANALYSIS

Probabilistic SHASolution :

𝑧𝑧 = −1.1850 − 1.013 𝑚𝑚 − 6 + 1.496 ln 𝑟𝑟2 + 31.025

Fault-1 : 𝑃𝑃 𝑌𝑌 > 0.30𝑔𝑔 = 2(1.727)2𝜋𝜋(30)∫𝑟𝑟=10

18 ∫𝑚𝑚=57.5 ∫𝑠𝑠=−∞

−𝑧𝑧 𝑟𝑟𝑒𝑒−𝑠𝑠22 +1.727(𝑚𝑚−5)

𝑟𝑟2−102d𝑑𝑑d𝑚𝑚d𝑟𝑟 = 0.01539

Fault-2 : 𝑃𝑃 𝑌𝑌 > 0.30𝑔𝑔 = 2(2.027)2𝜋𝜋(65)∫𝑟𝑟=20

31 ∫𝑚𝑚=58.5 ∫𝑠𝑠=−∞

−𝑧𝑧 𝑟𝑟𝑒𝑒−𝑠𝑠22 +2.027(𝑚𝑚−5)

𝑟𝑟2−202d𝑑𝑑d𝑚𝑚d𝑟𝑟 = 0.00182

Fault-1 : 𝜆𝜆1𝑖𝑖 = 0.032 0.01539 = 4.925x10−4 events/yearFault-2 : 𝜆𝜆2𝑖𝑖 = 0.079 0.00182 = 1.438x10−4 events/year

𝜆𝜆𝑖𝑖 = 4.925x10−4 + 1.438x10−4 = 6.363x10−4 events/year

𝑃𝑃100 𝐴𝐴𝐻𝐻 > 0.30𝑔𝑔 = 𝑃𝑃 𝑋𝑋100 ≥ 1 = 1 − 𝑒𝑒− 6.363 x10−4 100 = 0.06213

SEISMIC HAZARD ANALYSIS

Uniform Hazard Spectrum (P = 0.5 in 100 Yrs)

Uniform hazard PSA spectra horizontal for four different sites

in Northeast India.Hazard map for horizontal PSA in g at T=0.17 s

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LOCAL SITE EFFECTSEffect of Site Conditions on Ground Motions

Frequency response functions for hypothetical soft (Site A) and stiff

(Site B) soil deposits

Schematic representation of a building on different topographic,

geological and soil conditions

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LOCAL SITE EFFECTSEffect of Site Conditions on Ground Motions

Ground motion recorded at hill site in Mexico City during

the 1985 Michoacanearthquake

Ground motion recorded at soft-soil in Mexico City during

the 1985 Michoacanearthquake

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Evaluation of Site Effects using Analytical TechniquesOne-Dimensional Continuous Model

Profile of horizontal deposit of homogeneous soil Shear-beam model

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LOCAL SITE EFFECTS

SEISMIC DEMAND FOR DESIGN

Elastic Design Spectrum1. Specified by some regulatory body to characterize hazard2. Hazard level and soil specific

Design spectrum for different soil types specified in IS-1893 (Part 1) : 200218

SEISMIC DEMAND FOR DESIGN

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Spectrum Compatible Ground Motion

LITERATURE1

Geotechnical Earthquake Engineering, Steven L. Kramer, 1996, Prentice Hall International Series in Civil Engineering and Engineering Mechanics.

2Fundamental Concepts of Earthquake Engineering, Roberto Villaverde, 2009, CRC Press,Taylor & Francis Group.

3Earthquake Catalogue in and around North Eastern Region of India (including Historical Earthquakes) First Interim Report (Medieval Period to 1999), Geoscience Division NEIST Jorhat, 2013.

4Earthquake Catalogue in and around North Eastern Region of India (2000-2013), Geoscience Division NEIST Jorhat, 2013.

5Temporal and Spatial Variations in the Magnitude of Completeness for Homogenized Moment Magnitude Catalogue for North East India, Ranjit Das, H.R Wason, M L Sharma,2012

6Seismotectonics in Northeast India: a stress analysis of focal mechanism solutions of earthquakes and its kinematic implications, Jacques Angelier, Saurabh Baruah,2009

7Ground motion parameters in Shillong and Mikir Plateau supplemented by mapping of amplification factors in Guwahati City, Northeastern India, Saurabh Baruah, Santanu Baruah, Aditya Kalita, J. R. Kayal,2011

8A Probabilistic Seismic Hazard Analysis of Northeast India, Das S, Ishwer D. Gupta I.D and Gupta V.K, 2006, Earthquake Spectra, 22, 1-27.

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LITERATURE

9Probabilistic Seismic Hazard Assessment of India, Nath S.K and Thingbaijam K.K.S, 2012, Seismological Research Letters, 83.

10Estimation of Maximum Earthquakes in Northeast India, Thingbaijam K.K.S and Nath S.K, 2008, Pure and Applied Geophysics, 165, 889-901.

11Himalayan tectonic model and the great earthquakes: an appraisal, Kayal J.R, 2010, Geomatics, Natural Hazards and Risk, 1, 51-67.

12Probabilities for the occurrences of medium to large earthquakes in northeast India and adjoining region, Yadav R.B.S, Tripathi J.N, Shanker D, Rastogi B.K, Das M.C and Kumar V, 2011, Nat Hazards, 56, 145-167.

13Return Period Analysis of Earthquakes of Northeast India and its Adjoining Region, Devi A and Kalita S, 2013, International Journal of Engineering Science Invention, 2, 15-28.

14The Dauki Fault at the Shillong Plateau-Bengal Basin Boundary in Northeastern India: 2D Finite Element Modeling, Md Shofiqul Islam and Shinjo R, 2012,Journal of Earth Science, 23, 854-864.

15A Software Package to Analyze Seismicity: ZMAP, Wiemer S, 2001,Seismological Research Letters, 72, 374-383.

16Aftershock Statistics, Shcherbakov R, Turcotte D.L and Rundle J.B, 2005,Spure and Applied Geophysics, 162, 1051-1076.

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LITERATURE

17Assessing the Quality of Earthquake Catalogues: Estimating the Magnitude of Completeness and its Uncertainty, Woessner J and Wiemer S, 2005, Bulletin of the Seismological Society of America, 95, 684-698.

18Earthquake Hazard After a Mainshock in California, Reasenberg P.A and Jones L.M,1988, REPORTS, 1173-1176.

19Long-term earthquake clustering, Kagan Y.Y and Jackson D.D, 1991, Geophysical Journal International, 104, 117-133.

20A GIS based tectonic map of northeastern India, Baruah S and Hazarika D, 2008, Current Science, 95, 176-177.

21Seismotectonics in Northeast India: a stress analysis of focal mechanism solutions of earthquakes and its kinematic implications, Angelier J and Baruah S, 2009, Geophysical Journal International.

22Minimum Magnitude of Completeness in Earthquake Catalogs: Examples from Alaska, the Western United States and Japan, Wiemer S and Wyss M, 2000, Bulletin of the Seismological Society of America, 90, 859-869.

23Temporal and spatial variations in the magnitude of completeness for homogenized moment magnitude catalogue for northeast India, Das R, Wason H.R and Sharma M.L, 2012, Journal of Earth System, 121, 19-28.

24The 2009 Bhutan and Assam felt earthquakes (Mw 6.3 and 5.1) at the Kopili fault in the northeast Himalayan region, Kayal J.R, Arefiev S.S, Baruah S, Tatevossian R, Gogoi N, Sanoujam M, GautamJ.L, Hazarika, D and Borah D, 2010, Geomatics, Natural Hazards and Risk, 1, 273-281.

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