- © 2015 by the Seismological Society of America
On 21 May 2014, an earthquake of magnitude 6.0 occurred within the Bay of Bengal at 16:21:54 UTC. This event, with latitude 18.2046° N, longitude 88.0298° E, and a depth of 47 km (U.S. Geological Survey [USGS], 2014), is an unusually strong earthquake in a region of relatively low seismicity. The region is bordered by the tectonically active Burma and Andaman arcs to the east (Curray, 2005) and a nascent, diffuse plate boundary zone separating the Indian plate from the Australian plate in the south (Rao and Kumar, 1996). On the western and northern sides lies the Indian continental margin. The diffuse deformation zone is identified as the plate boundary where the Australian plate has an anticlockwise rotation with respect to the Indian plate (DeMets et al., 1990), due to smooth subduction of the former beneath the Sunda arc as compared with a resistant India–Eurasia collision in the north (Stein and Okal, 1978). This complex rotational kinematics enables both convergence and divergence on the same plate boundary, as evidenced by thrust‐type focal mechanisms in the east and normal‐fault earthquakes in the west on the Chagos‐Laccadive ridge. The scenario is further complicated by accommodation of the deformation through a peculiar strike‐slip motion along the 5000 km long Ninetyeast ridge which runs into the Burma–Andaman arc. Subrahmanyam et al. (2008) based on gravity data and Gahalaut et al. (2010) using Global Positioning System (GPS) data have suggested the Ninetyeast ridge subducts obliquely beneath the Andaman arc.
The Burmese arc to the east marks the eastern boundary of the Indian plate and is characterized by a recent cessation of subduction and transformation into a strike‐slip zone (Le Dain et al., 1984; Kumar and Rao, 1995; Kumar et al., 1996; Rao and Kumar, 1999; Vigny et al., 2003; Rao and Kalpna, 2005; Gahalaut and …