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Investigating the influence of Deccan Volcanism and hydrothermal alteration on seismic hazards in the Koyna-Warna Seismogenic Region, Western India

Piyal Halder1,2 , Anupam Sharma^1,2^, Matsyendra Kumar Shukla3, Kamlesh Kumar1,2

  • Affiliations: 1Birbal Sahni Institute of Palaeosciences (DST, Govt. of India), Lucknow-226007, Uttar Pradesh, India; 2Academy of Scientific and Innovative Research (AcSIR), Ghaziabad- 201002, India; 3Govt. of India, Ministry of Earth Sciences (MoES), Borehole Geophysics Research Laboratory (BGRL), Karad-415105, India 

  • Presentation type: Talk

  • Presentation time: Thursday 14:45 - 15:00, Room R290

  • Programme No: 3.8.7

  • Theme 3 > Session 8

Abstract

The Koyna-Warna Seismogenic Region over the Deccan Volcanic Province (DVP) in Western India has experienced >1,00,000 low-magnitude earthquakes during the last six decades soon after the Koyna Dam's impoundment. The Seismogenic faults in this region are N-S oriented indicating their generation due to the Deccan volcanism and Western Ghats upliftment rather than Indo-Eurasian Collision. Hence, apart from the plate boundary stress transferred through fault interaction and hydrostatic stress due to reservoir water, the stress concentration resulting from the high-density magma intrusion can't be ruled out. The scientific drilling unravelling the thicker basaltic sequences over the basement rocks in the central part of this area relative to other segments confirms the role of Deccan volcanism in stress accumulation in the shallow crustal faults. The mineralogical studies on the core samples from these faults upto 3 km depth find the transformation of biotite into chlorite and epidote, plagioclase into illite and albite as well as precipitation of calcite. The geochemical analyses additionally answer how the porous and vesicular Deccan lava sequences acted as the fluid percolation pathways and resulted in propylitic hydrothermal alteration. Further, this study demonstrates that the strength of the hydrogen bond connecting the talc-like layers with brucite-like sheet in the hydrothermally produced chlorite may help to accommodate strain in its crystal through ripplocations and result in fault creep responsible for the recurrence of low-magnitude quakes. This hypothesis also explains how hydrothermal alteration in this part of DVP gave rise to rheological heterogeneity suitable for Type-2 earthquakes of Mogi's Model.