The Unusual Bay of Bengal Earthquake of 21 May 2014 (Mw 6.1)

Online Material: Tables of peak ground accelerations and peak ground velocities. The Bay of Bengal earthquake of 21 May 2014 ( M w 6.1) was unusual because of its depth and the large distances over which it was felt. It was an intraplate, strike‐slip event, located far from plate boundaries. The depth reported by different agencies ranges between 51 and 61 km (Table 1). This puts the event in the oceanic mantle at a depth where brittle rupture is not expected. The earthquake was felt over a large area in India, in cities as far as Delhi and Jaipur (Δ∼1600  km; Martin and Hough, 2015). This seems surprising in view of the oceanic location of the earthquake and its moderate magnitude. View this table: Table 1 Reported Source Parameters of the Bay of Bengal Earthquake of 21 May 2014 Two linear tectonic features, the 90° E and 85° E ridges, dominate the Cretaceous oceanic lithosphere of the Bay of Bengal (Rao and Bhaskar Rao, 1986). These ridges, formed due to Kergulean and Crozet hotspot activity, are at present aseismic. The earthquake was located in the region between these two ridges, called the Central basin. Diffuse internal deformation of the Indian plate resulting from collision of India with the Eurasian plate to the north and subduction of the Indian plate below Sumatra to the east has been recognized by several authors (e.g., Stein and Okal, 1978; Gordon et al. , 1990, 1998; Royer and Gordon, 1997; Delescluse and Chamot‐Rooke, 2007). Gordon et al. (1990) delineate the area of deformation to the south of 10° N. Much of the seismicity in the Indian Ocean occurs in this area (e.g., fig. 3 of Abercrombie et al. , 2003). These intraplate earthquakes have a predominantly strike‐slip mechanism, including the Warton basin earthquake of 18 June 2000 ( M w 7.9) (Abercrombie et al. , 2003) and the …