Lineaments in Deccan Basalts: The Basement Connection in the Koyna–Warna RTS Region

by Kusumita Arora, Y. Srinu, D. Gopinadh, R. K. Chadha, Haris Raza, Valentin Mikhailov, Alexander Ponomarev, Elena Kiseleva, and Vladimir Smirnov

Trends of surface lineaments derived from airborne Lidar data in the Koyna–Warna region of reservoir-triggered seismicity (RTS), when correlated with trends from aeromagnetic and gravity anomalies reflecting basement discontinuities and fracture systems reveal striking similarities of trends in the north–south, northwest–southeast, and northeast–southwest directions. Direct evidence of faulting and slip surfaces in the form of slickensides in borehole cores and Acoustic televiewer imaging in these boreholes illustrate coincidence of trends with geophysical data in the dominant features, which is also overprinted with fracture patterns having a wide scatter in azimuth and dips. These observations support an inheritance model of faulting involving repeated reactivation and upward propagation of basement faults and fractures of a pre-existing shear zone into the overlying Deccan Trap strata. The repeated movements have enhanced permeability of the fractures and provided conduits for water percolation and increase of pore fluid pressure, which may explain the continuously triggered earthquakes during the past five decades.

Citation: Kusumita Arora, Y. Srinu, D. Gopinadh, R. K. Chadha, Haris Raza, Valentin Mikhailov, Alexander Ponomarev, Elena Kiseleva, and Vladimir Smirnov,  Lineaments in Deccan Basalts: The Basement Connection in the Koyna–Warna RTS Region, BSSA, DOI:10.1785/0120180011

Figure Map of compiled trends of structural features from lidar (pink), gravity-aeromagnetics (black), borehole data averaged over the depth of each borehole (yellow and brown), distinguished as shallow and deep in panels (a) and (b), respectively. Interpreted seismogenic faults are traced in blue, and the location of displacement fields from InSAR are indicated by circles. In the insets in each panel, arrows delineate examples of structural features classified as shallow and deep, based on the width and amplitude of their respective curvatures.