DEEP SEISMIC-SOUNDING IN THE GODAVARI GRABEN AND GODAVARI (COASTAL) BASIN, INDIA

Deep Seismic sounding investigations along two profiles, one along and the other across the Godavari Graben delineate the northeastern extension of the Bapatla Ridge which separates the Godavari Graben from the Godavari (coastal) Basin. The Godavari Graben is filled with a maximum of 2.8 km thick Lower Gondwana (Upper Permian to Lower Triassic) sediments. It is inferred on the basis of P-wave velocities that the Upper Precambrian Pakhal Formation does not continue south of Paloncha. The Upper Gondwana (Upper Jurassic to Lower Cretaceous rocks with marine incursions appear to continue towards the southeast for about 15 km from the exposures, below the Rajahmundry sandstone (Mio-Pliocene). Two-dimensional velocity modelling of the upper crust indicates a major interface at 3.5 km depth in the upper crust where the velocity increases from 5.4-5.5 km s-1 to 6.2-6.4 km s-1. This interface shows a dpmal upwarp across the Godavari Graben which may be an indication of NE-SW crustal extension in this region. The deeper part of the crust consists of a large number of almost horizontal small reflector segments. Two-dimensional crustal velocity modelling for some correlatable wide-angle reflections yielded a three-layered structure below 10 km depth, with the Moho at about 41 to 43 km. © 1990.