lecture7-seismicity of india

8/12/2019 Lecture7-Seismicity of India

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Seismicity of India

Lecture-7

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Indian subcontinent is historically proven to be vulnerable to earthquakes.

The movement of Indian plate at a rate of approximately 47 mm/year is the

source of seismicity and slowly rotating anticlockwise.

The Himalayas have risen as a result of a collision between the drifting of the

Indian plate and the Tibetan plate of South Asia about 50 million years ago.

About 54% of the land in India is vulnerable to earthquakes.

The latest version of seismic zoning map of India given in the earthquake

resistant design code of India [IS 1893 (Part 1) 2002] assigns four levels of

seismicity for India in terms of zone factors

The earthquake zoning map of India divides India into 4 seismic zones (Zone 2,

3, 4 and 5) unlike its previous version which consisted of five or six zones for the

country. According to the present zoning map, Zone 5 expects the highest level

of seismicity whereas Zone 2 is associated with the lowest level of seismicity.

Introduction

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India is unique as far as earthquakes are concerned. The northern part of India,

the Himalayan frontal arc, is one of the seismically most active regions in theworld.

Arc-normal convergence across the Himalaya results in the development ofpotential slip available to drive large thrust earthquakes beneath the Himalayas.

Nearly 56% of the subcontinent is prone to different levels of seismic hazard. Thisis amply demonstrated by the fact that more than 650 earthquakes in excess of M

5 have been recorded in India in the last one century.

Four great earthquakes (>8.0M) have occurred in a the period 1897-1950 thelargest subsequent earthquake occurred in Gujarat in 2001.

The 1967 earthquake at Koyna of M 6.3 in Western India confirmed thatpeninsular India, believed until then to be aseismic, is vulnerable to earthquakes.

1993 Killari earthquake of M 6.4 in the Latur was also unexpected and caused lotof damage.

Seismicity of India

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The Indian landmass, covering an area of about 3.2 million sq km, has three broadmorphotectonic provinces, namely

i) Himalaya and Tertiary mobile belt

ii) Indo-Gangetic foredeep

iii) Peninsular shield

All of these areas are characterized by distinctive stratigraphic, tectonic and deep

crustal features.

The Himalaya marks the largest active continent-continent collision zone that has

witnessed four great earthquakes in a short time span of 53 years between 1897

and 1950.

The Peninsular India is a mosaic of Archaean nucleus with peripheral Proterozoic

mobile belts, Cretaceous volcanism and rift-drift Mesozoic passive coastal basins.

Tectonic Provinces of India

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Seismicity of India

Zone V: Highest risk zone

Zone IV: High damage risk zone

Zone III: Moderate damage risk zone

Zone II : Low damage risk zone

IS 1893 (Part 1) 2002 5


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Major & moderate earthquakes in India

DATEEPICENTER

LOCATION MAGNITUDELat(Deg N) Long(Deg E)

1819 June 16 23.6 68.6 KUTCH,GUJARAT 8.0

1869 JAN 10 25 93 NEAR CACHAR, ASSAM 7.5

1885 MAY 30 34.1 74.6 SOPOR, J&K 7.0

1897 JUN 12 26 91 SHILLONG PLATEAU 8.7

1905 APR 04 32.3 76.3 KANGRA, H.P 8.0

1918 JUL 08 24.5 91.0 SRIMANGAL, ASSAM 7.6

1930 JUL 02 25.8 90.2 DHUBRI, ASSAM 7.1

1934 JAN 15 26.6 86.8 BIHAR-NEPAL BORDER 8.3

1941 JUN 26 12.4 92.5 ANDAMAN ISLANDS 8.1

1943 OCT 23 26.8 94.0 ASSAM 7.4

1950 AUG 15 28.5 96.7 ARUNACHAL PRADESH-CHINA BORDER 8.5

1956 JUL 21 23.3 70.0 ANJAR, GUJARAT 7.0

1967 DEC 10 17.37 73.75 KOYNA, MAHARASHTRA 6.5

1975 JAN 19 32.38 78.49 KINNAUR, HP 6.2

1988 AUG 06 25.13 95.15 MANIPUR-MYANMAR BORDER 6.6

1988 AUG 21 26.72 86.63 BIHAR-NEPAL BORDER 6.4

1991 OCT 20 30.75 78.86 UTTARKASHI, UP HILLS 6.6

1993 SEP 30 18.07 76.62 LATUR-OSMANABAD, MAHARASHTRA 6.3

1997 MAY 22 23.08 80.06 JABALPUR, MP 6.0

1999 MAR 29 30.41 79.42 CHAMOLI DIST, UP 6.8

2001 JAN 26 23.0 70.0 BHUJ, GUJARAT 7.6

2005 Oct 08 34.43N 73.54E KASHMIR 7.6

2011 Sept 18 27.723N 88.064E SIKKIM 6.9

Seismicity of India

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Movement of Indian Plate

7Source: wikipedia


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India Colliding with Asia

Fig: Plate tectonic Movements around the globe 8Source: wikipedia


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Indian plate subducting

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Source: wikipedia


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Movement of Indian Plate

Indian Plate is subducting

beneath Eurasian Plate

This is a convergent boundary,

involving mountain building

activity and seismicity.

10Source: wikipedia


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Distribution of earthquakes in India. Source: India Meteorological Department (IMD)

Seismicity of India

(1505 to March,2010) (M>5.0)

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Uttarkashi earthquake, 1991

Earthquake of Mw

6.8 of October 20, 1991 occurred in

the western Himalayan collision zone.

The earthquake is followed by about 125 aftershocks

(M>2.0). The main shock occurred at a depth of 15 km

and the aftershocks occurred at a depth of 015 km.

This is the first strong event in the Himalaya which was

well studied.

The fault plane solution suggested that the main shock

occurred on a low angle thrust faulting, and the

aftershocks show a reverse faulting.

Peak horizontal acceleration observed in this earthquake

was about 0.309 g.

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Source: wikipedia
http://en.wikipedia.org/wiki/File:India_location_map.svg


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Chamoli earthquake, 1999

Earthquake of Mw

6.8 of March 28, 1999 occurred in

the western Himalayas. The epicenter for this

earthquake lies about 100 km southeast of the 1991

Uttarkashi earthquake.


(M>2.5).

The focus of the earthquake was about 21 km deep.

The maximum intensity is bounded by the Main Central Thrust (MCT) to the

north

and by the Alokananda Fault (ANF) to the south. Seismic section of the main

shock and the aftershocks shows that the main shock occurred on the Plane of

detachment, basement thrust zone, where the ANF ends, and the main shock

activated the ANF to generate the aftershocks.

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Source: wikipedia


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Bhuj earthquake, 2001

Gujarat Earthquake of Mw7.7 of January 26, 2001 with Bhuj as

epicenter is one of the largest earthquakes occurred in India

Bhuj earthquake is the second largest event in the western

margin of peninsular India after the 1819 great Kutch

earthquake ( Mw8.0)

This earthquake is an example of a deeper paleo-rift basin

earthquake which occurred at a depth of 25 km in the Kutch

Rift Basin.

The earthquake is followed by about 1000 aftershocks (M>2.0)

involving complicated earthquake process.

The fault interaction models illustrated that the main shock

originated at the base of the paleo-rift basin by reverse faulting

on a deep seated south dipping hidden fault and the

aftershocks occurred by leftlateral strike-slip motion.

Peak horizontal acceleration observed in this earthquake wasabout 0.1 g.14

Source: wikipedia
http://en.wikipedia.org/wiki/File:India_location_map.svg


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Reservoir Induced Seismicity

In many cases, reservoir impoundment has produced largeearthquakes in India.

Koyna earthquake of 1967 is a perfect example for reservoir inducedearthquakes.

There is evidence linking earth tremors and reservoir operation formore than 70 dams.

Reservoirs are believed to have induced five out of the nineearthquakes on the Indian peninsula in the 1980s which were strongenough to cause damage.

Reservoir induced seismicity (RIS) is well documented but relatively

poorly understood.

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t

sn

When the pressure of the water (u) in the rocks increases, it acts to

reduce the normal load (sn) on fault planes thereby reducing thefrictional resistance mobilized and increasing the tendency to shear.

t = c + (sn

u)tan(f)where t is the shearing resistance

c is the cohesion and

f is the friction angle

Note that the principal stresses remain in the same orientation.

Reservoir induced seismicity is

widely explained related to the

extra water pressure created as

the reservoir fills.


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t

sn

In this case the normal load (sn) on fault plane has increased but thedeviatoric stress has changed more to induce failure

t = c + sn tan(f)

where t is the shearing resistance

c is the cohesion and

f is the friction angle

Note that in this case the orientation of the principal stresses arechanged and that this mechanism will only trigger normal faultswhere s1is vertical.

The reservoir inducedearthquakes could also beexplained in terms of increasein the vertical principal stressas a result of the weight ofimpounded water.


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Koyna earthquake, 1967

Earthquake of Mw6.5 of December 11, 1967 occurred in

Maharashtra, with Koynanagar as epicenter.

There have been several earthquakes of smaller magnitude

there since 1967.

This earthquake had caused a 10-15 cm fissure in the

ground which spread over a length of 25 km.

Seismicity at Koyna has close correlation with the filling cycles of the Koyna reservoir.

The 1967 Koyna event, in the watershed of the Krishna River in Maharashtra state, is aclassic example of earthquake activity triggered by reservoir.

The world's worst confirmed reservoir-induced earthquake was triggered by the KoynaDam.

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Source: wikipedia
http://en.wikipedia.org/wiki/File:1993_Latur_earthquake_map.gif


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The height of the Koyna-Dam is 103 m, reservoir volume is 2.78109m3.

Seasonal fluctuations of the lake level are typically 30 to 35 m and aredominated by monsoon rainfalls.

The site is now highly instrumented and the subject of active research

Since its first impoundment in1962, more than 150earthquakes of magnitude 4.0have been recorded.

Events are mostly restricted to

an area 40 25 km2

south ofthe Koyna-Dam.

This marks the area as probablythe best in the world to studythe phenomenon of reservoirinduced/triggered seismicity

(RIS).

Koyna Dam Earthquake

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Killari earthquake, 1993

Earthquake of Mw6.4 of September 30, 1993 occurred in

Deccan province of central India.


(M>2.0). This is a shallow earthquake with the main shock

as well as aftershocks confined to a depth of 015 km.

The earthquake occurred by reverse faulting at a depth of 6km. The deeper aftershocks (615 km) also occurred by

reverse faulting but the shallower aftershocks (


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The Killari earthquake is considered the most devastating SCR (Stable

Continental Region) event in the world. It is the most puzzling event inPeninsular India.

The earthquake struck Killari, Maharashtra in 1993, killing 10,000 people.

The event was totally unexpected as it was located in the Deccan Trap-covered stable Indian Shield. There was no record of any historicalearthquake in the region.

Some seismologists believe that the Killari event was triggered by anearby (Tirna) reservoir.


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The Killari earthquake was about 10 km from the Lower Tirna Reservoir.

The maximum water depth is about 20m, which is at the low end of therange of depths of reservoirs where induced seismicity has beendocumented.

The reservoir level was low at the time of the main shock, which isconsistent with the expected negative effect of the loading by thereservoir on an underlying thrust fault.

Several other recent earthquakes in peninsular India appear to belocated close to reservoirs.

Whether the Killari earthquake was triggered by the Lower Tirnareservoir is not known, but it cannot be ruled out.


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Jabalpur Earthquake, 1997

Earthquake of Mw6.0 of May 22, 1997 occurred in

Jabalpur in Madhya Pradesh, Narmada Valley, CentralIndia.

The epicenter of this earthquake is believed to havebeen about 20-40 kilometers from Bargi Dam, whichcompleted filling in 1990.

Indian seismologists have noted an increase in seismicactivity in the Narmada Valley over the past 20 years,which may be linked to reservoir impoundment.

In the Narmada Valley, a series of tremors were felt soon after the completion of the

Sukta Dam.

This earthquake has focused attention on the seismic risks faced by the large damsplanned for the Narmada Valley, and on the risk of reservoir-induced earthquakes.

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Source: wikipedia
http://en.wikipedia.org/wiki/File:1997Jabalpur.gif


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Source: India Meteorological Department (IMD)

National Seismic Network

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Seismic Microzonation of India

Seismic microzonationis defined as the process of subdividing a region into zones

that have relatively similar exposure to various earthquake-related effects withrespect to some geological and geophysical characteristics of the sites such asground shaking, liquefaction susceptibility, landslide and rock fall hazard,earthquake-related flooding, so that seismic hazards at different locations withinthe area can correctly be identified.

Earthquake waves incident at different sites with variable physical propertiesgenerate variable site response, which if predicted, could be used for preparationof seismic microzonation maps of relative hazards.

Seismic microzonation is based on the principles of site specific ground responseand liquefaction studies. A seismic microzone takes into account local siteconditions like soil, topography, proximity to faults etc. Primarily it is a geographicaldelineation of variations in the potential for earthquake hazards.

In this context 'Seismic Hazard and Risk Microzonation' (SHRM) projects fordifferent cities of India are in progress.

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http://www.imd.gov.in/section/seismo/static/seismicity-map.htm(Accessed on

14 April 2012)

Recent Large Earthquakes in India: Seismotectonic Perspective:

www.isfep.com/Kayal%20Article.pdf(Accessed on 14 April 2012)

Earthquakes in India: http://cires.colorado.edu/~bilham/Erice.htm(Accessedon 14 April 2012)

Indian earthquakes: An overview www.nicee.org/readings/paper4.pdf

(Accessed on 14 April 2012)

Indian Seismicity and past earthquakes: http://www.iitgn.ac.in/web-GEE/GAEE%20Handouts/IndianSeismicity_SKJ.pdf(Accessed on 14 April 2012)

Earthquakes in India and Himalayas: Tectonics, geodesy and history

www.earth-prints.org/bitstream/2122/798/1/36Bilham.pdf(Accessed on 14

April 2012)

Sources
http://www.imd.gov.in/section/seismo/static/seismicity-map.htmhttp://www.isfep.com/Kayal%20Article.pdfhttp://cires.colorado.edu/~bilham/Erice.htmhttp://www.nicee.org/readings/paper4.pdfhttp://www.iitgn.ac.in/web-GEE/GAEE%20Handouts/IndianSeismicity_SKJ.pdfhttp://www.iitgn.ac.in/web-GEE/GAEE%20Handouts/IndianSeismicity_SKJ.pdfhttp://www.earth-prints.org/bitstream/2122/798/1/36Bilham.pdfhttp://www.earth-prints.org/bitstream/2122/798/1/36Bilham.pdfhttp://www.earth-prints.org/bitstream/2122/798/1/36Bilham.pdfhttp://www.earth-prints.org/bitstream/2122/798/1/36Bilham.pdfhttp://www.iitgn.ac.in/web-GEE/GAEE%20Handouts/IndianSeismicity_SKJ.pdfhttp://www.iitgn.ac.in/web-GEE/GAEE%20Handouts/IndianSeismicity_SKJ.pdfhttp://www.iitgn.ac.in/web-GEE/GAEE%20Handouts/IndianSeismicity_SKJ.pdfhttp://www.nicee.org/readings/paper4.pdfhttp://cires.colorado.edu/~bilham/Erice.htmhttp://www.isfep.com/Kayal%20Article.pdfhttp://www.imd.gov.in/section/seismo/static/seismicity-map.htmhttp://www.imd.gov.in/section/seismo/static/seismicity-map.htmhttp://www.imd.gov.in/section/seismo/static/seismicity-map.htm

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