On 25April 2015,an Mw 7.8 earthquake struck the village of Barpak,Gorkha district,central Nepal.This disaster claimed the lives of more than 8,000 people and devastated the city of Kathmandu and thesurrounding areas.This earthquake occurred along the collision zone between the Indian and the Eurasiantectonic plates that converge at a rate of～20 mm/yr.The stressaccumulated by this convergence is periodically released in large earthquakes that occurred in the fault systemof the Himalayan front.Actually,before the numerical values quantifying Himalayan convergence wasavailable,geophysicists and geologists in the early 1990s had anticipated great earthquake hazard wouldhappen in Nepal.During the past century,the Himalayan arc has experienced several great thrust earthquakes,such as the Kashmir earthquake,the Kangra earthquake ,the Assam earthquake and the Bihar Nepal earthquake.However,none of their coseismic surface deformations orfault slip models were extensively studied with geodetic data,except for the Mw 7.6 Kashmir event mapped bythe Aster images with the Sub-pixel correlation method.As for this Nepal earthquake,modern geodetic technologies permit a much more detailed study than was possible for anypervious large earthquakes.So this event provides an excellent opportunity to study the source parameters of large earthquake and assess the potential seismic hazard in the Northern India and Nepal.
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