The earthquake in Nepal - part of a chain of tremors in the collision zone between the Indian plate and the Eurasian plate

The history of earthquakes in the Himalayas * The 7.8 magnitude earthquake that occurred in Nepal on April 25, 2015 is the result of a collision of geological replicas at or near the junction of the Indian plate to the south and the Eurasian plate to the north

Based on an article on the US Geological Survey website

Yesterday, April 25, 2015, an earthquake with a magnitude of 7.8 occurred in Nepal, and as of this writing, 4,700 people have died as a result of it and the strong aftershocks that followed it.

At the epicenter of the earthquake, about eighty kilometers northwest of Nepal's capital Kathmandu, the Indian plate is merging with the Eurasian plate at a rate of 45 millimeters per year in a north-northeast direction. One of the resulting phenomena is the elevation of the Himalayan mountain chain. The initial location, magnitude, and focal direction of the April 25 earthquake all fit the plate seam area.

Although it is a boundary between large plates, the history of strong and even very strong earthquakes shows that they are quite rare. Only four earthquakes of magnitude 6 or greater have occurred within 250 kilometers of the current quake in the last century. One earthquake of magnitude 6.9 occurred in August 1988 about 240 southeast of the current earthquake and caused about 1,500 deaths. The largest, a magnitude 8 event known as the 1934 Nepal-Bihar earthquake, occurred at the same point as the 1988 event. It caused severe damage to Kathmandu and is estimated to have killed 10,600 people.

The seismo-tectonics of the Himalayas and their surroundings

From the seismic point of view, the Himalayas are affected by the seam where continents carried on top of the plates collide - India and Eurasia, which merge at a rate of about 40-50 millimeters per year. The northward travel of the Indian plate under the Eurasian plate creates a large number of earthquakes and as a result I have made the area one of the seismologically dangerous areas on Earth. The expression on the surface of the border area is found in the steep slopes of the Sulaiman Mountains in the west, the Indo-Burmese arc in the east and the Himalayan range which is a vast front stretching from east to west in northern India.

The plate boundary between India and Eurasia is a butterfly boundary, where the area near northern India, which lies between the Indus and Tsengpu rivers, is about 200 kilometers north of the Himalayan front and is full of exposed ophiolite chains on the southern margin. The narrow front (less than 200 kilometers) of the Himalayas includes countless parallel structures oriented east-west. The area also has the greatest rate of seismic activity and large earthquakes in the Himalayan region, caused mainly by the movement of the tectonic plates. Examples of significant earthquakes in this densely populated area caused by reverse slope movement are the 1934 magnitude 8 earthquake, the 7.5 magnitude 1905 Kangra earthquake, and the 7.6 magnitude 2005 earthquake in Kashmir. The last two caused a high number of casualties compared to the known earthquakes in the Himalayas so far. Together they killed a hundred thousand people and left millions homeless.
The strongest earthquake recorded in the Himalayas occurred on August 15, 1950 in Assam in eastern India. This earthquake, whose intensity was 8.6, left behind damages in large areas in Central Asia and caused enormous destruction to the villages in the area of ​​the epicenter.
The Tibetan plain, which is north of the Himalayas, stretches for a thousand kilometers in a north-south direction and 2,500 kilometers in an east-west direction. It is geologically and tectonically complex, when it is embedded in several seams between plates hundreds of kilometers long, mostly in an east-west direction. The Tibetan plain is cut by a large number of fragments and copies. These fractures are crossed by secondary fractures that run north-south. Together they form an area where the crust is shortening due to the continuous collision of the Indian and Eurasian plates with replicas where the compression is from south to north and the faults extend from east to west.

Along the western margin of the Tibetan Plateau, in the area of ​​southwestern Afghanistan and western Pakistan, the Indian Plate collides diagonally with the Eurasian Plate, creating the belt of folds and thrusts in the Suleiman Mountain Range. The combination of the copies and fractures of all kinds often causes earthquakes close to the surface and therefore also destructive. The active copy in Chaman is the fastest in the area. In 1505, part of the Chaman monument near Kabul, the capital of Afghanistan, erupted and caused destruction over a large area. In the same area, closer to our time, on May 30, 1935, an earthquake with a magnitude of 7.6 occurred which hit the Sulaiman Mountains in Pakistan and caused the death of 30-60 thousand people.

On the northwestern side of the Tibetan Plateau, beneath the Pamir-Hindu Kush mountains in northern Afghanistan, they occur at depths of up to 200 kilometers. The curved arch of deep earthquakes in the Indo-Kush and Pamir mountains indicate the presence of a lithospheric body in the depths, it is possible that these are the remains of a plate that was previously exposed to the ground. One model estimates that the two plates cause the trampling of each other and the remains of plates under the surface of the ground - each at a different depth, while other models claim that only one of the two plates moves under the other and that the plate being trampled overturns in its place.

Shallow earthquakes also occur near the Pamir fault and other active faults. The main Pamir thrust, north of the Pamir Mountains is an active place where the plates are shortening. The northern part of the replica creates many earthquakes at small depths. On February 18, 1911, an earthquake in the central Pamir Mountains killed an unknown number of people and caused landslides that blocked the Murgahab River.

North of there, the Tien Shan area is a seismically active intercontinental mountain belt that stretches for 2,500 kilometers in a northeast to southwest direction north of the Tarim Basin. The belt is defined by an infinite number of fractures that are east-west. It is estimated that the compression in this area is related to the collision of the Indian plate and the Eurasian plate which causes the series of fractures that characterize the area. Three major earthquakes occurred in this area, the magnitude of which was over 7.6 occurred at the beginning of the 20th century. One of them occurred in 2989 in Atushi and caused the death of approximately 5,000 people. This mountain chain is cut in the east by the Talas Parghana fault. Although this area has not experienced a major earthquake in at least the last 250 years, studies indicate that it has the potential for earthquakes of magnitude 7 and above that could cause significant damage.

In the northern part of the Tibetan Plateau itself, the influence of the movement of three frictional faults, Alain Taf, Kunlun and Ionan, is evident. The Altin Taf fault is the longest of them and is considered a significant part of the plate collision zone. The area has not known significant earthquakes in recorded history, but studies have revealed evidence of prehistoric events of magnitude 7-8 earthquakes.

In the east of the Tibetan Plateau lies the Longman Shan belt. On May 12, 2008, an earthquake with a magnitude of 7.9 occurred there, causing the death of over 87 people and billions of dollars in damages. Landslides were also caused which caused the blocking of several rivers and lakes. In the southeast of the Tibetan Plateau lie two faults - the Red River Fault and the Xiangshuihe-Xiaojiang Fault. On January 4, 1970, an earthquake with a magnitude of 7.5 occurred in Tughai, which killed 10,000 people.

Shallow earthquakes within the Indo-Burmese arc occur due to a combination of strike zones and reverse faults. Between the years 1930 and 1956, six earthquakes with a magnitude of 7 or more occurred in the area, which caused considerable damage in Myanmar, including the creation of landslides, melting of the ground and the loss of 610 lives.

Deep earthquakes (about 200 km) also occurred in this area, although the last of them occurred mainly in the pre-industrial period, one of them on June 12, 1897 caused extensive destruction.

For review on the US Geological Survey (USGS) website