Shallow velocity structure along the Hirapur-Mandla profile using traveltime inversion of wide-angle seismic data, and its tectonic implications

Abstract

SUMMARY In order to investigate the velocity structure, and hence shed light on the related tectonics, across the Narmada‐Son lineament, traveltimes of wide-angle seismic data along the 240 km long Hirapur‐Mandla profile in central India have been inverted. A blocky, laterally heterogeneous, three-layer velocity model down to a depth of 10 km has been derived. The first layer shows a maximum thickness of the upper Vindhyans (4.5 km s1) of about 1.35 km and rests on top of normal crystalline basement, represented by the 5.9 km s1 velocity layer. The anomalous feature of the study is the absence of normal granitic basement in the great Vindhyan Graben, where lower Vindhyan sediments (5.3 km s1) were deposited during the Precambrian on high-velocity (6.3 km s1) metamorphic rock. The block beneath the Narmada‐Son lineament represents a horst feature in which high-velocity (6.5 km s1) lower crustal material has risen to a depth of less than 2 km. South of the lineament, the Deccan Traps were deposited on normal basement during the upper Cretaceous period and attained a maximum thickness of about 800 m.