Structure of the Lower Crust Revealed by One- and Two-dimensional Modeling of 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-Palashi-Kandi, 227-km long profile in the north-south direction and (ii) Taki-Arambagh, 120-km long profile in the east-west direction. The data were acquired using multichannel digital seismic instruments with close station spacing. The crustal model, initially derived by 1-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 seismograms computation. The structural contour map of the Moho prepared from the present data set, indicates the crustal thickness of about 37 km in the western margin of the basin, thinning to about 28 km in the east with an upwarp in the Moho boundary. The upwarp in the Moho and the inferred structural features may be indicative of crustal rifting. The well-known gravity anomaly in the West Bengal basin, ʹCalcutta gravity high,ʹ appears to have resulted from the Moho upwarp in combination with the huge thickness of sediments deposited east of the steep flexure of the crystalline basement representing the ʹHinze zone.ʹ