Role of deep crustal fluids in the genesis of intraplate earthquakes in the Kachchh region, northwestern India

Fluids play a prominent role in the genesis of earthquakes, particularly in intraplate settings. In this study, we present evidence for a highly heterogeneous nature of electrical conductivity in the crust and uppermost mantle beneath the Kachchh rift basin of northwestern India, which is host to large, deadly intraplate earthquakes. We interpret our results of high conductive zones inferred from magnetotelluric and 3-D local earthquake tomography investigations in terms of a fluid reservoir in the upper mantle. The South Wagad Fault (SWF) imaged as a near-vertical north dipping low resistivity zone traversing the entire crust and an elongated south dipping conductor demarcating the North Wagad Fault (NWF) serve as conduits for fluid flow from the reservoir to the middle to lower crustal depths. Importantly, the epicentral zone of the 2001 main shock is characterized as a fluid saturated zone at the rooting of NWF onto the SWF.

2-D geoelectric models along the (a) western and (b) eastern profiles. Open circles represent the seismicity (Mw > =2.5) within 15 km on either side of the profiles. Star represents the 2001 Bhuj main shock. The dashed lines are faults inferred from the present study. Major conductive/resistive features are marked with alphabets. Red colored triangles in the eastern profile are the sites omitted due to high RMS misfits.

Vp and Vp/Vs perturbations along the AA’ (a & b) and BB’ profiles. Open circles represent the seismicity (Mw >=2.5) within 15km on either side of the profiles. Star represents the 2001 Bhuj main shock. The dotted lines delimit the well resolved portion of the tomographic models.

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