Northeast India, Myanmar, Bangladesh and Andaman-Sumatra Region

Abstract

Northeastern part of India and its adjoining areas of southeast Asia comprise an interesting seismotectonic region of the world. The region includes eastern and northeastern Himalayas to the north, Indo-Burma ranges/Myanmar to the east, Bangladesh to the south and the Andaman-Sumatra region to the southeast (Fig. 6.1). The Shillong Plateau, Mikir hills, Assam valley, Tripura fold belt and the Bengal basin (Bangladesh) in the study region jawed between the two tectonic arcs, the Himalayan arc to the north and the Burmese-Andaman arc to the east (Fig. 6.2a). The present-day tectonics of the northeast India region is complicated because of interaction between the active north-south convergence along the Himalaya (e.g. Molnar et al. 1977; Ni and Barazangi, 1984) and the east-west convergence and folding within the Indo-Burma ranges, a style of deformation that apparently evolved from subduction (e.g. Mitchell, 1981; Curray et al., 1979 and 1982). Several contrasting views are put forward concerning the seismotectonics of northeast India. Uyeda and Kanamori (1979) postulated that the Alpine-Himalayan orogenic belt and the Andaman-Indonesian mobile belt are linked by a transform fault, and the ophiolites of the Indo-Burma ranges are product of a leaky transform fault. Nandy (1983), on the other hand, postulated that the eastern sector of the Indian plate collided with the Burmese block, and the ophiolites were emplaced along the Benioff Zone (Fig. 6.2b).