Hydraulically conductive fault zone responsible for monsoon triggered earthquakes in Talala, India

Abstract

The Deccan volcanic province (DVP) in the northwestern part of the Indian subcontinent is the largest continental volcanic province in the world. Talala, located in the middle of the DVP, experience seismicity with swarm-like behavior towards the end of, or shortly after, the annual monsoon period. Between the years 2007 and 2012, seismic activity was recorded with moment magnitudes up to Mw 5.1. Although there is a statistical correlation between seismic activity and monsoon rainfall, there is little information about the geometry or attributes of the potentially causative fault system to date. We conducted geophysical surveys in the Talala seismogenic region to investigate the structure of the causative fault, with two Time-Domain Electromagnetic (TDEM) profile measurements, and Magnetotelluric (MT) measurements across the fracture zone to characterize deeper structures. TDEM measurements in the E-W direction revealed an electrically conductive zone within highly resistive surroundings, and the MT measurements revealed high electrical resistance along a curved structure that correlates with the seismogenic area and is likely associated with fractured crystalline rock. These fracture systems or networks can act as conduits for channeling and focusing intense rainfall events and develop significant fluid over-pressures to drive the swarm sequences. Numerical modelling results of fluid pressure evolution indicate increased groundwater and reservoir levels are likely responsible for earthquake generation.