Structure of the lower crust revealed by one- and two-dimensional modelingof wide-angle reflections - West Bengal basin, India

The crustal structure in the West Bengal basin, India has been investigated by means of wide-angle reflection data recorded along (i) Bishnupur-Palash i-Kandi, 227-km long profile in the north-south direction and (ii) Taki-Ara mbagh, 120-km long profile in the east-west direction. The data were acquir ed using multichannel digital seismic instruments with close station spacin g. The crustal model, initially derived by I-D forward modeling of the wide -angle reflection data, has been iteratively refined by 2-D ray tracing and modeling of travel-time observations and the corresponding synthetic seism ograms computation. The structural contour map of the Moho prepared from th e present data set, indicates the crustal thickness of about 37 km in the w estern margin of the basin, thinning to about 28 km in the east with an upw arp in the Moho boundary. The upwarp in the Moho and the inferred structura l features may be indicative of crustal rifting. The well-known gravity ano maly in the West Bengal basin,'Calcutta gravity high,' appears to have resu lted from the Moho upwarp in combination with the huge thickness of sedimen ts deposited east of the steep flexure of the crystalline basement represen ting the 'Hinze zone.'