10:45 AM - 11:00 AM
[S02-4-02] Seismotectonics of the Koyna region, India: based on focal mechanism solutions using borehole and surface seismological networks
invited
Artificial water reservoir triggered earthquakes have continued to occur at the Koyna region of western India since the impoundment of the Shivaji Sagar Lake in 1962. The seismicity is confined to a small region of about 30 km x 20 km. Recently, six borehole seismometers are deployed at depths varying from 981 m to 1522 m, surrounding the seismicity and well below the Deccan basalt cover to improve the accuracy of locations of these triggered earthquakes. Focal depths are estimated using waveform inversion approach and are mostly between 4 and 8 km in the Koyna-Warna region. Well constrained fault plane solutions are derived which provide vital information regarding the orientation of the fault planes. Analysis of the recent large earthquake of Mw 4.8 that occurred on 14 April 2012 has indicated a N30E oriented left-lateral strike-slip fault along the Donachiwada fault zone, where the largest M 6.3 Koyna earthquake of 10 December 1967 also occurred. For the first time, reliable fault plane solutions for about 50 smaller earthquakes of ML > 1.9 are estimated, that occurred since January 2015 using the sharp onsets on the high quality borehole seismic records which are complimented by a dense surface seismic network data. Our analysis presents a significant improvement in the estimation of absolute locations and fault plane solutions of earthquakes at Koyna.