Abstract The subsurface electrical resistivity and density information are vital factors in assessing the seismic potential of a region, as they provide crucial insights into fault zone characterisation, such as the presence of fluid, stress accumulation and release, mechanical and thermal properties of the rocks, etc. Therefore, to elucidate the electrical characteristics of the seismically active Donachiwada fault in the Koyna Seismic Zone (KSZ), an intra-plate seismogenic region in Western India, a magnetotelluric (MT) investigation is carried out across the fault. The study brings out the electrical signature of the fault as a moderate conductor (~100–500 Ωm) within the very high resistive (≈20,000 Ωm) granite–gneiss basement. Using this electrical information as input, a joint gravity, gravity gradient (gDD), and magnetic 2.5 D modelling along the same transect is carried out, which maps the Donachiwada fault as a higher density basement block (2.82 g/cc) than the surrounding basement (2.75 g/cc). The vp/vs ratio and Poisson’s ratio associated with the basement blocks are calculated from the resistivity values, and found that the Donachiwada fault is characterised by a higher vp/vs ratio (1.8) and Poisson’s ratio (0.28) than the either sided basement’s vp/vs ratio (1.6) and Poisson’s ratio (0.18). The fault zone, having moderate conductivity with a high vp/vs ratio and a high Poisson’s ratio, indicates the presence of fluid in the fault zone, and high-density material with high P-wave velocity signifies the probable igneous intrusion. The percolation of fluid and igneous intrusion into a fault zone often uses the fault as a channel and therefore, alters the mechanical and thermal properties of the fault zone and the surroundings, modifies the local stress regime, and may trigger larger seismic activity in future. Research highlights <UnorderedList Mark="Bullet"> <ItemContent> MT study delineates the fault as moderate conductor within high resistive basement. </ItemContent> <ItemContent> Gravity study estimates higher density for the fault than the surrounding basement. </ItemContent> <ItemContent> vp/vs ratio estimated from resistivity shows higher value for the fault. </ItemContent> <ItemContent> These fault characteristics indicate fluid presence and probable igneous intrusion. </ItemContent> </UnorderedList>

Subsurface resistivity and density characterization across the M 6.3 Koyna earthquake—Donachiwada fault, Western India

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发表日期：

2026年3月19日

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Ujjal K Borah,
Prasanta K Patro,
Satrughna Mishra,
Virendra M Tiwari

摘要

Abstract

The subsurface electrical resistivity and density information are vital factors in assessing the seismic potential of a region, as they provide crucial insights into fault zone characterisation, such as the presence of fluid, stress accumulation and release, mechanical and thermal properties of the rocks, etc. Therefore, to elucidate the electrical characteristics of the seismically active Donachiwada fault in the Koyna Seismic Zone (KSZ), an intra-plate seismogenic region in Western India, a magnetotelluric (MT) investigation is carried out across the fault. The study brings out the electrical signature of the fault as a moderate conductor (~100–500 Ωm) within the very high resistive (≈20,000 Ωm) granite–gneiss basement. Using this electrical information as input, a joint gravity, gravity gradient (g_DD), and magnetic 2.5 D modelling along the same transect is carried out, which maps the Donachiwada fault as a higher density basement block (2.82 g/cc) than the surrounding basement (2.75 g/cc). The v_p/v_s ratio and Poisson’s ratio associated with the basement blocks are calculated from the resistivity values, and found that the Donachiwada fault is characterised by a higher v_p/v_s ratio (1.8) and Poisson’s ratio (0.28) than the either sided basement’s v_p/v_s ratio (1.6) and Poisson’s ratio (0.18). The fault zone, having moderate conductivity with a high v_p/v_s ratio and a high Poisson’s ratio, indicates the presence of fluid in the fault zone, and high-density material with high P-wave velocity signifies the probable igneous intrusion. The percolation of fluid and igneous intrusion into a fault zone often uses the fault as a channel and therefore, alters the mechanical and thermal properties of the fault zone and the surroundings, modifies the local stress regime, and may trigger larger seismic activity in future.

Research highlights

MT study delineates the fault as moderate conductor within high resistive basement.

Gravity study estimates higher density for the fault than the surrounding basement.

v_p/v_s ratio estimated from resistivity shows higher value for the fault.

These fault characteristics indicate fluid presence and probable igneous intrusion.