Crustal structure in southern and central West Bengal using deep seismic sounding explosion data

Abstract

Deep seismic sounding (DSS) data provides an excellent opportunity to accurately delineate the crustal structure of a given region owing to the fact that the location and origin time of the source (Chemical explosion) are available. India Meteorological Department is carrying out such surveys since early 1970's. In this paper. seismic wave velocities in the upper part of the crust in southern and central West Bengal are estimated from three DSS field surveys conducted during 1987-1990. From the analysis of the data it is noted that the sedimentary layer in the region consists of mainly two layers. The first layer is of thickness 1.25 to 1.49 km with P wave velocity of 2.85 to 2.88 km/s and S-wave velocity of 1.71 to 1.77 km/s. Surface wave data show that near Burdwan, the sedimentary layer includes a thin low velocity layer of thickness 250 m at the top. The thickness of lowest sedimentary layer increases southward from 2.32 km to 3.73 km : in this layer the P-wave velocity is between 3.9 & 4.1 km/s. The sedimentary layers are overlying a granitic layer with P- wave velocity of 5.73 to 5.83 km/s.