Shallow subsurface imaging of the Wagad active fault system (Kachchh, northwestern India) by time domain electromagnetic studies

Abstract

The Kachchh rift basin (KRB) in the northwestern Indian shield is one of the most seismically active intraplate regions of the world. It has witnessed four large earthquakes in the past two centuries that leads the region most vulnerable for seismic hazard. For effective seismic hazard assessment, detailed information on faults and its subsurface geometry is essential. Recently, shallow subsurface geophysical studies, particularly electrical resistivity studies have become a successful practice in imaging of fault zones and their attribute. In the present study, we carried out the time domain electromagnetic (TDEM) investigations across the Wagad highland of eastern KRB to map shallow subsurface structure and imaging fault zones in terms of resistivity. Resistivity section obtained after combining one dimensional models of 21 sites display significant details of the fault structures and geometry of shallow basin infill down to 200 m. The shallow layer of the basin infill across the South Wagad fault (SWF) and the North Wagad fault has a wedge shape made of unconsolidated deposits with thickness of \(\sim \)15–20 m. We infer that it might be due to syntectonic sedimentation due to the footwall subsidence across a branch fault of the SWF. The section indicates a \(\sim \)60–65 and 50–55 m estimates of cumulative throws for the SWF and NWF, respectively. Across the Gedi fault, the section indicates least block displacements, which might either be due to dominate strike-slip nature of faulting or more activeness of NWF compared to GF during the recent geological past. The results from the study affirm the ongoing Holocene deformation in the region signifying active nature of these faults.