An analysis of GPS-derived velocities in the Bengal basin and the neighbouring active deformation zones.

摘要

The Bengal basin, the largest fluvio-deltaic sedimentary system in the world, located in an area covering Bangladesh and three eastern states of India (West Bengal, Assam and Bihar) has been formed by sediments brought by the Ganga, Brahmaputra and Meghna rivers. This complex foreland basin originally emerged on a trailing margin of the Indian continental crust and was later complicated by convergence with Eurasia to the north and oblique convergence with Burma to the east. Apart from these tectonic events, another major source of crustal deformation in the vicinity of the Bengal basin was the formation of the Ninety East Ridge (NER) in the Indian Ocean. The Bengal basin, which is in the near vicinity of these three active boundaries, needs to be studied thoroughly for assessing seismic hazard in this region. A brief discussion of the tectonics of the neighbouring active zones is given here. The GPS-derived velocities of stations located in these zones and that at Kolkata, located in the Bengal basin show that the Kolkata-Coco Island baseline crossing the NER shortens at 18.5+or-1.3 mm/yr, whereas the baseline between Kolkata and Aizawl, Mizoram shortens at 10.5+or-1.5 mm/yr. The Kolkata-Siliguri baseline shortens at 8.1+or-1.5 mm/yr and the Kolkata-Baradighi baseline shortens at 5.2+or-1.4 mm/yr. The difference in shortening rates of these two stations located in the North Bengal foothill Himalayan zone relative to Kolkata is due to the presence of a highly active transverse zone lying between them.