Seismicity and 3-D seismic velocity structure of the upper crust beneath the Koyna region, western India
Abstract
The Koyna-Warna region located in western India is a well-known site of artificial water reservoir triggered seismicity (RTS) and has so far experienced about 200 earthquakes of magnitude exceeding 4 since the impoundment of Shivaji Sagar Lake, north of Koyna Dam in 1962. In recent time, the largest earthquake happened to be the Mw 4.0 occurred on 3rd June 2017 relatively at a new block near Udgiri, much south of the known epicentral locations of M 4 earthquakes of the study region and in the vicinity of the Western Ghat Escarpment (WGE). A double couple normal focal mechanism has been obtained using the seismic network of 20 stations, which delineated a NW-SEtrending fault plane. Two aftershocks of MW 3.0 and 3.5 are also indicating a similar focal mechanism. Depth distribution of aftershocks is varying from 2 - 8 km with a steep north-east dipping plane. The obtained fault plane correlates with lineaments derived from airborne gravity gradiometry (AGGM) and LiDAR studies. Further, we have also determined the three dimensional P-wave velocity (Vp) and Vp/Vs perturbations of the upper crust beneath the Koyna-Warna seismicity using seismic tomography approach by inverting about 22000 P- wave and 20500 S- wave arrival times obtained from 1700 earthquakes that occurred during 2015-2017 and recorded on a network of 21 Surface and 6 borehole seismic stations. A prominent connection of seismicity is found with the velocity variations estimated at Donachiwada fault, Warna cluster and the recent new block of activity near Udgiri. Importantly, we expect the 3-D velocity structure beneath the Donachiwada fault will provide key inputs for the proposed deep borehole in the vicinity of identified block for target earthquakes. A 3-D density model constructed from AGGM data corroborate with the 3-D velocity model.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.S33D0616S
- Keywords:
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- 7230 Seismicity and tectonics;
- SEISMOLOGYDE: 7260 Theory;
- SEISMOLOGYDE: 7270 Tomography;
- SEISMOLOGYDE: 7290 Computational seismology;
- SEISMOLOGY