Variation of Crustal Velocity Structure in India as Determined from DSS Studies and their Implications on Regional Tectonics

The Indian subcontinent has been divided into six crustal velocity zones based on P-wave velocity structure obtained along 20 Deep Seismic Sounding (DSS) profiles, covered in India from 1972 to 1992. Zone - 1 consists of two parts: zone  - 1.a comprises the Dharwar craton, Cuddapah basin, Godavari graben and the Koyna region, and zone- 1 .b consists of the western margin of the Bengal basin and the Singhbhum craton. Zone - 2 covers the West Bengal sedimentary basin and the Mahanadi coastal basin. Zone - 3 includes Bundelkhand craton and the Vindhyan basin. Zone - 4 covers Cambay basin north of the Narmada lineament and the Aravalli - Delhi fold belt. Zone - 5 lies south of the Nannada lineament covering the Tapti graben extending up to the west coast of India. Zone - 6 comprises the northwest Himalaya up to the Nangaparbat including Jammu and Srinagar sedimentary basins. Detailed crustal velocity structures in these six zones have been described with their bearing on regional tectonics. Velocity structure of the lower crust in some of these zones, suggests that crustal underplating has played a very important role in the evolution of the Indian continental crust and lithosphere. Some petrological inferences have also been drawn for the Indian crust from crustal velocity zonation.