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

Abstract

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 240km long Hirapur–Mandla profile in central India have been inverted. A blocky, laterally heterogeneous, three-layer velocity model down to a depth of 10km has been derived. The first layer shows a maximum thickness of the upper Vindhyans (4.5kms−1 ) of about 1.35km and rests on top of normal crystalline basement, represented by the 5.9kms−1 velocity layer. The anomalous feature of the study is the absence of normal granitic basement in the great Vindhyan Graben, where lower Vindhyan sediments (5.3kms−1 ) were deposited during the Precambrian on high-velocity (6.3kms−1 ) metamorphic rock. The block beneath the Narmada–Son lineament represents a horst feature in which high-velocity (6.5kms−1 ) lower crustal material has risen to a depth of less than 2km. South of the lineament, the Deccan Traps were deposited on normal basement during the upper Cretaceous period and attained a maximum thickness of about 800m.