April 13, 2016 Earthquake: Assam, Bangladesh, India, Myanmar

Tectonic Summary

The April 13, 2016 M 6.9 earthquake southeast of Mawlaik, Burma, occurred as the result of oblique reverse faulting at an intermediate depth, approximately 140 km beneath western Burma. The epicenter of the earthquake is located some 500 km to the northeast of the Sunda Trench, where lithosphere of the India plate begins subducting to the northeast beneath Sunda and Eurasia. Focal mechanisms indicate rupture occurred on either a west-striking fault dipping steeply to the north, or on a southeast striking structure dipping moderately to the southwest. The location, depth and faulting parameters all indicate this earthquake occurred within the lithosphere of the subducting India plate. At the location of this earthquake, the India plate moves north-northeast with respect to the Sunda and Eurasia plates, at a velocity of 44-49 mm/yr. Regionally, the subducted India plate is seismically active to a depth of about 150 km.

Earthquakes like this event, with focal depths between 70 and 300 km, are commonly termed "intermediate-depth" earthquakes. Intermediate-depth earthquakes represent deformation within subducted slabs rather than at the shallow plate interface between subducting and overriding tectonic plates. They typically cause less severe shaking on the ground surface directly above their foci than is the case with similar magnitude shallow-focus earthquakes, but large intermediate-depth earthquakes beneath populated regions may nonetheless cause damage and casualties, and they may be felt at great distance from their epicenters.

The Burma region experiences earthquakes somewhat regularly, and 38 other events of M 6 or larger have occurred within 400 km of the April 13, 2016 event over the preceding century. Eleven of these occurred at intermediate depths. The largest nearby earthquake was a M 8.0 event in September 1946, 130 km to the northeast of the April 2016 earthquake, whose epicenter has been calculated to be within the earth's crust. Little is known about the effects of that earthquake. At intermediate depths, the largest nearby event over the preceding century was a M 7.3 earthquake in August 1988 in northern Burma, 200 km to the north of the April 2016 event. The 1988 earthquake caused several fatalities and dozens more injuries.

At least 2 people killed, 70 injured and power outages occurred in Assam, India. Felt (V) at Agartala, Bara Bazar and Chakdaha; (IV) at Bankra, Guwahati, Kolkata, Salt Lake City and Shiliguri. Felt in Assam, Bihar, Jharkhand, Manipur, Meghalaya, Mizoram, Nagaland, Odisha, Sikkim, Tripura, Uttar Pradesh, West Bengal and as far as Delhi. At least 50 people injured and 4 buildings damaged in the Chittagong area, and about 50 people were injured fleeing buildings at Dhaka and Sylhet, Bangladesh. Felt (VI) at Sylhet, (V) at Chittagong and (IV) at Barisal, Dhaka and Tungi. Felt (III) at Rangoon, Burma, at Thimphu, Bhutan and at Kathmandu, Nepal. Felt in other parts of Bangladesh, Bhutan, Burma and Nepal. Also felt at Dali, China. Brahman Bariya, Brāhman Bariya, Bangladesh - CDI: 6; Silhaţ, Silhaţ, Bangladesh - CDI: 6; Bhaluka, Maimansingh, Bangladesh - CDI: 5; Maimansingh, Maimansingh, Bangladesh - CDI: 5; Raghudebbati, Bangla, India - CDI: 5

(above from reference #13456)

2 dead, 182 injured (reference #13215)