---

Sub-Basalt Velocity Image of the Main Seismogenic Fault at Koyna, an Intraplate Active Region in Western India, Using Borehole Seismic Network.

Shashidhar D, Mahesh P, Gupta S, Mallika K.

SEISMOLOGICAL RESEARCH LETTERS

https://doi.org/10.1785/0220250319 

Data from 5325 local earthquakes recorded on eight deep borehole seismic sensors to generate a sub-basalt velocity model for the Koyna Reservoir region, India. For the first time, the VP and Vp/Vs images reveal strong lateral and vertical heterogeneity within the granitic basement, with distinct velocity anomalies across the Donachiwada fault (DF) at 6-10km depth, coinciding with a dense cluster of seismicity. DF is the plausible source of the 10 December 1967 (M 6.3) earthquake - the largest reservoir-triggered event documented globally.

Cross sections across the DF of (a) P-wave velocity and (b) VP=VS. The dashed line (white) indicates the presence of DF at depths.

Permanent borehole seismic stations and seismicity at the Koyna Warna region, western India.

---