This study actually consists of two research programs. The first, and probably most important, is an attempt to corroborated the possibility that the maximum sediment thickness in the Bengal basin exceed 22km, rather than the 16km generally cited. The second is the study of two aseismic ridges aligned about N.S in the Bay of Bengal, the Ninetyeast Ridge and the 85 E Ridge. Existing magnetic and seismic reflection data will be combined and extended with gravity network to understand the state of isostasy in the region.