Existence of a sedimentary graben in the western part of Narmada Zone: seismic evidence

The seismic refraction and wide angle reflection data were acquired in the analog form along the 260 km Thuadara-Sendhwa-Sindad DSS profile across the Narmada Lineament Zone. The first arrival refraction data over mostly expo sed Deccan Traps region were analysed based on 2D ray tracing technique, fr om all the 25 shot points of this profile. This analysis reveals a graben b etween rivers Narmada and Tapti. Within the graben the depth to the basemen t (velocity 6.0-6.2 km s(-1)) is about 3000 m between Narmada and Sendhwa, and 5000-5500 m between Sendhwa and Tapti. This graben contains 1000-2800 m thick low velocity (velocity 3.2 - 3.6 km s(-1)) sediments under a thick ( 2000-2700 m) cover of the Deccan Traps. The graben is bound by two faults, one south of Narmada (Barwani-Sukta) and the other north of Tapti river. Th e Barwani-Sukta fault here appears to divide the Narmada Zone, the south-we stern part representing a graben and the north-eastern part a basement upli ft. The graben appears to extend towards the south-east. (C) 2000 Elsevier Science Ltd. All rights reserved.