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) 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 or 8.1Ms 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). It was the worst natural disaster to strike Nepal since the 1934 Nepal–Bihar earthquake. The earthquake triggered an avalanche on Mount Everest, killing at least 19, making April 25, 2015 the deadliest day on the mountain in history.
The earthquake triggered another huge avalanche in the Langtang valley, where 250 people were reported missing. Hundreds of thousands of people were made homeless with entire villages flattened, 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. 
A major aftershock occurred on 12 May 2015 at 12:51 NST with a moment magnitude (Mw) of 7.3. The epicenter was near the Chinese border between the capital of Kathmandu and Mt. Everest. More than 200 people were killed and more than 2,500 were injured by this aftershock Geology
M6+ Himalayan region earthquakes, 1900–2014
Nepal lies towards the southern limit of the diffuse collisional boundary where the Indian Plate underthrusts the Eurasian Plate, occupying the central sector of the Himalayan arc, nearly one-third of the 2,400 km (1,500 mi) long Himalayas. Geologically, the Nepal Himalayas are sub-divided into five tectonic zones from north to south, east to west and almost parallel to sub-parallel. These five distinct morpho-geotectonic zones are: (1) Terai Plain, (2) Sub Himalaya (Sivalik Range), (3) Lesser Himalaya (Mahabharat Range and mid valleys), (4) Higher Himalaya, and (5) Inner Himalaya (Tibetan Tethys). Each of these zones is clearly identified by their morphological, geological, and tectonic features. The convergence rate between the plates in central Nepal is about 45 mm (1.8 in) per year.
The location, magnitude, and focal mechanism of the earthquake suggest that it was caused by a slip along the Main Frontal Thrust. The earthquake’s effects were amplified in Kathmandu as it sits on the Kathmandu Basin, which contains up to 600 m (2,000 ft) of sedimentary rocks, representing the infilling of a lake. Based on a study published in 2014, of the Main Frontal Thrust, on average a great earthquake occurs every 750 ± 140 and 870 ± 350 years in the east Nepal region. A study from 2015 found a 700-year delay between earthquakes in the region. The study also suggests that because of tectonic stress buildup, the earthquake from 1934 in Nepal and the 2015 quake are connected, following a historic earthquake pattern.
Isoseismal map for the Gorkha earthquake annotated with values on the Mercalli scale According to “Did You Feel It?” (DYFI?) responses on the USGS website, the intensity in Kathmandu was IX (Violent). Tremors were felt in the neighboring Indian states of Bihar, Uttar Pradesh, Assam, West Bengal, Sikkim, Jharkhand, Uttarakhand, Gujarat [better source needed] in the National capital region around New Delhi 11 June 2015, 311 aftershocks had occurred with different epicenters and magnitudes equal to or above 4 Mw and more than 20,000 aftershocks less than 4 Mw.
Disastrous events in very poor and politically paralyzed nations such as Nepal often become a long drawn out chain of events, in that one disaster feeds into another for years or even decades upon end.
The earthquake killed more than 8,600 in Nepal and injured more than twice as many. The rural death toll may have been lower than it would have been as the villagers were outdoors, working when the quake hit. As of 15 May, 6,271 people, including 1,700 from the 12 May aftershock, were still receiving treatment for their injuries. More than 450,000 people were displaced.
A total of 78 deaths were reported in
25 dead and 4 missing, all from the Tibet Autonomous Region.
Avalanches on Mount Everest
This earthquake caused avalanches on Mount Everest. At least 19 died, including Google executive Dan Fredinburg, with at least 120 others injured or missing.
The Dharahara tower
Before the earthquake
After the earthquake
Thousands of houses were destroyed across many districts of the country, with entire villages flattened, especially those near the epicenter Kathmandu Durbar Square
Before the earthquake
After the earthquake
Building damage as a result of the earthquake
Several pagodas on Kathmandu Durbar Square, a UNESCO World Heritage Site, collapsed, as did the Dharahara tower, built in 1832; the collapse of the latter structure killed at least 180 people, The top of the Jaya Bageshwari Temple in Gaushala and some parts of the Pashupatinath Temple, Swyambhunath, Boudhanath Stupa, Ratna Mandir, inside Rani Pokhari, and Durbar High School have been destroyed. In Patan, the Char Narayan Mandir, the statue of Yog Narendra Malla, a pati inside Patan Durbar Square, the Taleju Temple, the Hari Shankar, Uma Maheshwar Temple and the Economic loss
Road damage in Nepal
Concern was expressed that harvests could be reduced or lost this season as people affected by the earthquake would have only a short time to plant crops before the onset of the Monsoon rains. Nepal, with a total Gross Domestic Product of USD$19.921 billion (according to a 2012 estimate), is one of Asia’s poorest countries, and has little ability to fund a major reconstruction effort on its own.
Rajiv Biswas, an economist at a Colorado-based consultancy, said that rebuilding the economy will need international effort over the next few years as it could “easily exceed” USD$5 billion, or about 20 percent of Nepal’s gross domestic product.[not in citation given]
Rescue and relief
Nepal Army and Turkish disaster relief aid workers working together About 90 percent of soldiers from the Nepalese Army were sent to the stricken areas in the aftermath of the earthquake under Operation Sankat Mochan, with volunteers mobilized from other parts of the country. Survivors were found up to a week after the earthquake. As of 1 May 2015[update], international aid agencies like Médecins Sans Frontières (Doctors Without Borders) and the Red Cross were able to start medically evacuating the critically wounded by helicopter from outlying areas, initially cut-off from the capital city, Kathmandu, and treating others in mobile and makeshift facilities. There was concern about epidemics due to the shortage of clean water, the makeshift nature of living conditions and the lack of toilets. Emergency workers were able to identify four men who had been trapped in rubble, and rescue them, using advanced heartbeat detection.
The four men were trapped in up to ten feet of rubble in the village of Chautara, north of Kathmandu. An international team of rescuers from several countries using FINDER devices found two sets of men under two different collapsed buildings. Volunteers used crisis mapping to help plan emergency aid work. Public volunteers from around the world added details into online maps. Information was mapped from data input from social media, satellite pictures and drones of passable roads, collapsed houses, stranded, shelterless and starving people, who needed help, and from messages and contact details of people willing to help.
On-site volunteers verified these mapping details wherever they could to reduce errors. First responders, from Nepali citizens to the Red Cross, the Nepal army and the United Nations used this data. The Nepal earthquake crisis mapping utilized experience gained and lessons learned about planning emergency aid work from earthquakes in Haiti and Indonesia. Reports are also coming in of sub-standard relief materials and inedible food being sent to Nepal by many of the foreign aid agencies. A United States Marine helicopter crashed on 12 May while involved in delivering relief supplies. The crash occurred at Charikot, roughly 45 miles (72 kilometers) east of Kathmandu. Two Nepali soldiers and 6 American soldiers died in the crash.
UNICEF appealed for donations, as close to 1.7 million children had been driven out into the open, and were in desperate need of drinking water, psychological counsel, temporary shelters, sanitation and protection from disease outbreak. It distributed water, tents, hygiene kits, water purification tablets and buckets. Numerous other organizations provided similar support. India was the first to respond within hours, being Nepal’s immediate neighbour, with Operation Maitri which provided rescue and relief by its armed forces. It also evacuated its own and other countries’ stranded nationals. The United Kingdom has been the largest bilateral aid donor to Nepal following the earthquake. The United States, China and other nations have provided helicopters as requested by the Nepali government.
On 26 April 2015, international aid agencies and governments mobilized rescue workers and aid for the earthquake. They faced challenges in both getting assistance to Nepal and ferrying people to remote areas as the country had few helicopters. Relief efforts were also hampered by Nepalese government insistence on routing aid through the Prime Minister’s Disaster Relief Fund and its National Emergency Operation Center. After concerns were raised, it was clarified that “Non-profits” or NGOs already in the country could continue receiving aid directly and bypass the official fund.
Aid mismatch and supply of “leftovers” by donors, aid diversion in Nepal, mistrust over control of the distribution of funds and supplies, congestion and customs delays at Kathmandu’s airport and border check posts were also reported. On 3 May 2015, restrictions were placed on heavy aircraft flying in aid supplies after new cracks were noticed on the runway at the Tribhuvan airport (KTM), Nepal’s only wide-body jet airport.