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The crustal depth section obtained from deep seismic soundings along the Koyna II (Kelsi-Loni) profile, which lies near latitude 18°N roughly in the east-west direction in that part of the Deccan Trap Maharashtra State, India, shows a number of reflection segments below the Deccan Traps down to the Moho discontinuity. A deep fault below the Deccan Traps 13 km east of Mahad divides the entire cross-section including the Moho boundary into two crustal blocks. The reflection segments show updip towards the west coast in the western block. The Moho discontinuity which is at a depth of 39 km near the deep fault starts rising towards the coast, reaching a depth of 31.5 km at the west coast. The eastern block is thrown up by 1.5 km with respect to the western block along the deep fault. A structural contour map of the Moho discontinuity for the Koyna reservoir area has been prepared from the present results and the crustal information obtained along the Koyna I profile (Kaila et al., 1979a), shows that the deep fault in the Koyna area is aligned in the NNW-SSE direction.

The evolution of the Vindhyan basin has been studied from deep seismic soundings. Block tectonics appear to be active throughout the geological history in this region. The crust is divided into four major blocks by deep faults at Narsinghgarh, Katangi and Jabalpur. The crustal block between Narsinghgarh and Katangi forms a graben in the crystalline basement, giving rise to the great Vindhyan basin in which Precambrian Vindhyan sediments of about 5.5 km thickness are deposited. The crustal block between Katangi and Jabalpur is a horst block which represents the Narmada-Son lineament.