Abstract

The Koyna–Warna region in western India, overlain by the Deccan volcanic layer, is globally known for reservoir triggered seismicity. It is located on a high elevated plateau separated by a steep topographic escarpment from the low‐lying Konkan plains on the west. The region is known for its complex structural setting and lateral heterogeneity. To obtain a new velocity model for the region, P‐receiver function analysis has been carried out at 18 seismic stations in the Koyna–Warna region using teleseismic earthquake waveforms in the distance range of 30°–90°. The study delineates the significant discontinuities in the subsurface of this region and the geometry of the Moho. The Moho depth with an average uncertainty of 0.6 km varies between 37.7 and 42 km with an upwarp beneath the seismogenic zone. A higher near‐surface velocity (NSV) west of the escarpment is attributed to a thinner layer of Deccan volcanic trap with some contribution from the granite‐gneiss basement, unlike that of the thicker pile of basalt in the east. An unusually high upper crustal shear‐wave velocity of about 4  km/s at 5 km depth is comparable with that of the lower crust. This high shear‐wave velocity results in a higher rock strength in the Koyna–Warna region, capable of sustaining higher stresses. This coupled with pre‐existing brittle fractures that are triggered by the reservoir load and fluid effects is the likely cause of the continuous seismicity recorded over the last few decades.

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