Abstract

We analyzed the configurations of the lineaments derived from imagery and airborne light detection and ranging (lidar) data in the Koyna–Warna region of reservoir‐triggered seismicity (RTS). These lineaments generally correlate with aeromagnetic and gravity anomalies that may be caused by basement discontinuities and fracture systems that are expressed as north–south, northwest–southeast, and northeast–southwest features on the surface. Our results from Synthetic Aperture Radar (SAR) interferometry show displacement fields close to the Warna reservoir after M5.0 earthquakes in 2009. Direct evidence of faulting and slip surfaces is encountered as slickensides in deep boreholes in the region. Acoustic televiewer imaging in these boreholes shows varying patterns of fractures in the basement and in the overlying Deccan basalts. These new data support an inheritance model for basement faulting involving repeated reactivation and upward propagation of basement faults and fractures into the overlying Deccan Trap strata. We suggest that the Koyna and Warna reservoirs overlie a shear zone possibly connecting the eastern and western Dharwar cratons exposed in southern India. The repeated movements along basement faults in this shear zone enhance porosity and permeability of the fractures and provide conduits for water percolation and increase of pore fluid pressure. The presence of such fluid‐filled fractured basement rocks in the Koyna–Warna region may explain the continuously triggered earthquakes during the past five decades.

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