An earthquake is caused by a sudden slip on a fault. The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth's crust and cause the shaking that we feel.( readanddigest.com/what-is-an-earthquake)
The April 2015 Nepal earthquake (also known as the Gorkha earthquake)[6][9] killed more than 8,800 people and injured more than 23,000. It occurred at 11:56 NST on 25 April, with a magnitude of 7.8Mw[1] or 8.1Ms[2] and a maximum Mercalli Intensity of IX (Violent). Its epicenter was east of the district of Lamjung, and its hypocenter was at a depth of approximately 15 km (9.3 mi).[1] It was the worst natural disaster to strike Nepal since the 1934 Nepal–Bihar earthquake.[10][11][12]
The earthquake triggered an avalanche on Mount Everest, killing at least 19,[13] making April 25, 2015 the deadliest day on the mountain in history.[14] The earthquake triggered another huge avalanche in the Langtang valley, where 250 people were reported missing.[15][16]
Hundreds of thousands of people were made homeless with entire villages flattened,[15][17][18] across many districts of the country. Centuries-old buildings were destroyed at UNESCO World Heritage sites in the Kathmandu Valley, including some at the Kathmandu Durbar Square, the Patan Durbar Squar, the Bhaktapur Durbar Square, the Changu Narayan Temple and the Swayambhunath Stupa. Geophysicists and other experts had warned for decades that Nepal was vulnerable to a deadly earthquake, particularly because of its geology, urbanization, and architecture.[19][20]
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A major aftershock occurred on 12 May 2015 at 12:51 NST with a moment magnitude (Mw) of 7.3.[22] The epicenter was near the Chinese border between the capital of Kathmandu and Mt. Everest.[23] More than 200 people were killed and more than 2,500 were injured by this aftershock