Delineation of faults and sedimentary thickness of the Mesozoic Kachchh Rift, India, using seismic refraction data: Implications for seismogenesis and hydrocarbon potential

Summary A seismic refraction study has been carried out across the seismically active pericratonic Kachchh basin, formed as a failed rift during the Mesozoic breakup of Gondwanaland. The basin was significantly affected by the Reunion plume that emplaced massive Deccan flood basalts. Inversion of traveltimes derived from the seismic data reveals a six-layered complex structure, with P-wave velocities ranging between 1.90–5.20 km/s for sediments and 5.85–6.10 km/s for the basement. Synthesis of seismic refraction, reflection, gravity, and well data indicates a variability in the basement depth from 2.2 km in the north to 5.7 km in the south. A basement upwarp of 1.3 and 2.2 km in the north and south is related to the Pachchham and Kachchh mainland uplifts. Traveltime skips of the first arrivals imply low-velocity Mesozoic sediments previously obscured beneath the high-velocity Deccan Traps. We propose thick sediments in the southern part with abundant source, reservoir, and cap rocks, which are potential hydrocarbon prospects. The present study also illuminates several faults, which act as stress concentrators. We postulate that the far-field compressional forces generated due to India-Eurasia collision and local stresses caused by the heterogeneous structure are responsible for the basement upwarp, uplift of the Kachchh mainland, reactivation of faults, and high seismicity of the region. We attribute the western plate boundary located ~400 km away from the Kachchh region as a probable causative for the Median High, a Hinze zone covering the basin and beyond. An evolutionary model of the basin is suggested.