Extension of Godavari Gondwana sediments underneath Trap covered region of Satpura basin as evidenced from seismic studies in Deccan Syneclise, India

Abstract

We present a shallow P-wave velocity structure of the eastern part of Deccan Syneclise, central India, from the refraction and wide-angle reflection data recorded along two ∼100 km long seismic refraction profiles in east–west (E–W) and north–south (N–S) directions using travel time inversion method. In addition to the P-wave velocity model, we have derived S-wave velocity model and estimated Vp/Vs and Poisson’s ratios along the east–west profile. Travel time analysis and inversion of the data revealed three layers above the basement. The first layer with a P-wave velocity of 1.4–1.5 km s −1 represents alluvium and the thickness of this layer is varying between 100–400 m in the E–W and 30–100 m in the N–S profile. The Deccan Trap thickness is observed to be varying between 850 and 1250 m constitutes the second layer. P-wave velocity of the Deccan Traps is 4.8–5.2 km s −1. Amplitude decay and travel time skips in the first arrival refraction data in some of the record sections indicate the presence of a velocity inversion i.e. low velocity zone (LVZ) beneath the Traps. Wide-angle reflection phases from top and bottom of the LVZ (top of basement) together with basement refraction phase are identified and modeled to derive LVZ thickness. The LVZ has been interpreted to be the Gondwana sediments sandwiched between Deccan Traps and basement. These sediments are about 200–450 m thick with a P-wave velocity of 3.6 km s −1. The basement lies at about 1.60 km depth near Khandala in the west and Rajola in the north shows an upward trend towards south–east. The P-wave velocity of the basement is about 6.0–6.2 km s −1. The inferred subtrappean sediments could be the possible extension of Gondwana sediments of the Godavari graben towards the Satpura basin.