Dr. Sushil Kumar Scientist ‘F’ & Group Head Geophysics€¦ · Dr. Sushil Kumar Scientist...

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Active Tectonics of Himalayan Faults/Thrusts System in Northern India on the basis of recent &

and Paleo Earthquake Studies

Dr. Sushil Kumar Scientist ‘F’ &Group Head Geophysics

Wadia Institute of Himalayan Geology Autonomous institute of Department of Science & Technology (Govt. Of

India)

33 GMS Road, Dehradun, India(e-mail: sushilk@wihg.res.in; sushil_rohella@yahoo.co.in)

Wednesday, March 21, 2018India-Japan Workshop on Disaster Risk Reduction on 19-20 March, 2018

Himalaya rises as a consequence of the collision of Indian Plate with Asian Plate.

Continent-Continent CollisionContinent-Continent Collision

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Wednesday, March 21, 2018India-Japan Workshop on Disaster Risk

Reduction on 19-20 March, 20183

Proposed seismic

Proposed GPS

WIHG Seismic Networks

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GPS convergence ratesWednesday, March 21, 2018 India-Japan Workshop on Disaster Risk Reduction on 19-20 March, 20186

< 1.01.0 – 1.92.0 – 2.93.0 – 3.94.0 – 4.95.0 – 5.96.0 – 6.9

7.0 – 7.9

M8.0, Kangra earthquake 1905

Magnitude

Kangra-Cham

Punjab-R

eentra

Garhwal-KumaonD

19 October 1991, Mb6.4 Uttarkashi earthquake

29 March 1999, Mw6.6 Chamoli earthquake

Space distribution of Seismic events in the NW Himalaya

Histogram of the local Seismic activity

1208040

SEISMICITY OBSERVED DURING 2007-2017

DEPTH(KM)

DEPTH SECTION

10Wednesday, March 21, 2018 India-Japan Workshop on Disaster Risk Reduction on 19-20 March, 2018

Study of attenuation mechanism for Sikkim Himalaya form analysis of coda of 212 aftershocks of September 11, 2011 Sikkim earthquake (M:6.9)

Continuance data recording 2007-Cont. for earthquake

precursory research

Map source: USGSEpicenter distance from MPGO: 636 km

Date Time (hrs)(UTC)

Lat. Long. Dep Epicentre Distance (km)

25.04.15

06:11:26

7.9 28.147

84.708

Some observations

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Magnetic field variations as observed by

the Overhauser Magnetometer at MPGOWednesday, March 21, 2018 17

India-Japan Workshop on Disaster Risk Reduction on 19-20 March, 2018

Period 24/04/2015 to 26/04/2015

Gravity variations as observed by the

Superconducting Gravimeter at MPGO

Himalayan frontal fault zone

Himalayan frontal zone is the active deformation zone that lies between the MBT and the HFT. Deformation and thrusts have migrated to the south. HFT zone show quaternary-Holocene deformation.

Active tectonics of Himalayan frontal zone

In the frontal active zone between the MBT and HFT, there active frontal anticlined like Mohand and Janauri anticline and the HFT.

Distribution of piedmont fans on both N & S slope; and the faults and drainage pattern in the valley are noticeable.

Dun is a synclinal valley. South is Mohand anticline . These active faults, out of sequence Bhauwala fault . HFT demarcate a physiographic tectonic break between the frontal Himalaya and Ganga alluvial plain .

14±2 mm/yr (Weshousky et al. 1999)

Cross-section across Dehradun structures (Thakur et al. 2007)

This is a cross-section along Dehradun and Mohand based on seismic profiling:a) There is HFT dipping NE . In the front is Mohand anticline of Dehradun in both.b) Shortening and slip rates have been estimated on the HFT using uplifted stretch terraced . The shortening ratio is 142 mm/yr .

The Himalayan Frontal Thrust (HFT) zone marking the termination of Himalaya

is identified on the basis of topographic break.

Himalayan Frontal Thrust

~3.6 Ka

~11.9 Ka

Location of HFT. Dating of strata terrace gravel, used for calculating convergence rate.

Piedmont fault?

Piedmont fault, south of HFT

South of Himalayan front (HFT) another fault called “ Piedmont fault” has been recognised in the piedmont zone.

~4.8 Ka

~12 Ka

OSL dating of Piedmont zone

These are OSL dating of the piedmont zone south of the HFT .

Six trenches have been extended on the Himalayan front along the HFT for paleo-seismological study.

The data obtained from six trenches have been analysed to to constrain the timing of earthquake event. Based on this paleo-earthquake dating 1500 AD has been found. This earthquake shows evidence of surface ruptured fault extending some 250 km along strike.

This is the summary of rupture zones located along the Himalayan front .

Some great earthquakes along the Himalaya

This is the rupture areas of historical earthquakes , and slip rates estimated at the Himalayan front.

Seismotectonic model of the NW Himalaya (Garhwal Himalaya) represent that:

1)Segment between HFT and southern extent of Micro-seismicity zone is locked as per GPS measurement.

2)Microseismicity zone represents elastic strain is accumulating there.

3)We get evidence of surface rupture earthquakes in the HFT zone.

4)Inferences that large to great earthquakes take place in locked segment. The rupture produced by the earthquake propagated to south and recorded on the HFT as recorded in the trenches.

5)Future next large to great earthquakes may take place in this locked zone.

Summary

Negishi, H., J. Mori, T. Sato, R. Singh, Sushil Kumar and N. Hirata, 2002. ‘Size and Orientation of the fault plane for the 2001 Gujarat, India Earthquake (Mw 7.7) from Aftershock Observations: A high stress Drop event’, Geophysical Research Letters, vol.29, No.20, 19-49.

India-Japan Joint Team

Univ. Memphis

Station Locations

-1 -0.5 0 0.5 1 1.5

Correlation of station corrections

y = -0.37966 + 1.739x R= 0.97262

P-correction (sec.)S-

ResultRelocated Hypocenters & Station Corrections

P to S ratio; standard Vp/Vs value

1 2 3 4 5 6 7 8 9

P and S wave velocity

Velocity (km/s)1.55 1.6 1.65 1.7 1.75 1.8 1.85 1.9 1.95

Result1-D velocity structure

Afterch

Analysis for 3-D velocity modeling (based on Zhao and Negishi, JGR, 1998)

Grid modeling Raytracing: Pseudo-bending

(modified for low-velocity layers existence)

Determine Vp and Vs simultaneously The result of 1-D inversion is used as an initial model Data for Optimum damping and iteration number are

determined by “Simplified Cross Validation Method” (Inoue et al., PEPI, 1990)

69.8E 70E 70.2E 70.4E 70.6E 70.8E 71E

Depth = 25.5km24N

69.8E 70E 70.2E 70.4E 70.6E 70.8E 71E

Depth = 25.5km24N

69.8E 70E 70.2E 70.4E 70.6E 70.8E 71E

Depth = 25.5km

Vp/Vs perturbation (%)7 % +7 %5 % +5 %5 % +5 %

Vp perturbation (%) Vs perturbation (%)

Depth = 25.5 km

Result3-D velocity model

Vp/Vs perturbation-7.0 % 0.0 +7.0 %

THANK YOU for your kind attention

Dr. Sushil Kumar Scientist ‘F’ & Group Head Geophysics€¦ · Dr. Sushil Kumar Scientist...

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