Basement configuration of the Jhagadia–Rajpipla profile in the western part of Deccan syneclise, India from travel-time inversion of seismic refraction and wide-angle reflection data

Abstract 2-D velocity structure up to the basement is derived by travel-time inversion of the first arrival seismic refraction and wide-angle reflection data along the SW–NE trending Jhagadia–Rajpipla profile, located on the western part of Deccan syneclise in the Narmada–Tapti region. The study region is mostly covered by alluvium. Inversion of refraction and wide-angle reflection data reveals four layered velocity structure above the basement. The first two layers with P -wave velocities of 1.95–2.3 km s −1 and 2.7–3.05 km s −1 represent the Recent and Quaternary sediments respectively. The thickness of these sediments varies from 0.15 km to 3.4 km. The third layer with a P -wave velocity of 4.8–5.1 km s −1 corresponds to the Deccan volcanics, whose thickness varies from 0.5 km to 1.0 km. Presence of a low velocity zone (LVZ) below the high velocity volcanic rocks in the study area is inferred from the travel-time ‘skip’ and amplitude decay of the first arrival refraction data and the wide-angle reflection from top of the LVZ present immediately after the first arrival refraction from Deccan Trap layer. The thickness of the low velocity Mesozoic sediments varies from 0.3 km to 1.7 km. The basement with a P -wave velocity of 5.9–6.15 km s −1 lies at a depth of 4.9 km near Jhagadia and shallows to 1.2 km towards northeast near Rajpipla. The results indicate presence of low velocity Mesozoic sediments hidden below the Deccan Trap layer in the western part of the Deccan syneclise.