M7.8 Nepal Earthquake of 25 April 2015

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The April 25, 2015 M 7.8 Nepal earthquake occurred as the result of thrust faulting on or near the main frontal thrust between the subducting India plate and the overriding Eurasia plate to the north. At the location of this earthquake, approximately 80 km to the northwest of the Nepalese capital of Kathmandu, the India plate is converging with Eurasia at a rate of 45 mm/yr towards the north-northeast, driving the uplift of the Himalayan mountain range. The preliminary location, size and focal mechanism of the April 25 earthquake are consistent with its occurrence on the main subduction thrust interface between the India and Eurasia plates.

Although a major plate boundary with a history of large-to-great sized earthquakes, large earthquakes on the Himalayan thrust are rare in the documented historical era. Just four events of M6 or larger have occurred within 250 km of the April 25, 2015 earthquake over the past century. One, a M 6.9 earthquake in August 1988, 240 km to the southeast of the April 25 event, caused close to 1500 fatalities. The largest, an M 8.0 event known as the 1934 Nepal-Bihar earthquake, occurred in a similar location to the 1988 event. It severely damaged Kathmandu, and is thought to have caused around 10,600 fatalities.