Nepal at Risk of Another Major Earthquake

Nepal is at risk of a major earthquake that could affect millions of people and cause more destruction than the quake that occurred in April this year, a new study has warned.

The study, published in the journals Nature Geoscience and Science, found that the 25 April earthquake which struck Gorkha, near the Nepalese capital of Kathmandu, earlier this year did not release all of the pent-up stress that had built up over hundreds of years, but instead transferred some of it west towards Nepal's border with India. The Gorkha earthquake killed more than 8,400 people and injured more than 17,500, according to the Nepal Red Cross Society. Another smaller earthquake struck east of Kathmandu a few weeks later, killing at least 37 people.

Jean-Philippe Avouac, a professor in the Earth Sciences department at the University of Cambridge and the study's lead author, says that a future event on the Nepalese-Indian border could result in far more destruction, particularly since a major earthquake has not occurred in the region for around five centuries. "The more you wait, the more energy there is to be released and that's one reason why in western Nepal we are sure there could be a really large earthquake," says Avouac. "It would affect the Gangetic Plain of northern India, where there are a lot of people living. So I think that if you look at the area where the intensity [of the earthquake] could exceed 8 [on the Richter scale], you probably encompass an area with five to 10 million people."

Researchers used data from a network of GPS stations in Nepal and other seismological data to map the path of the Gorkha earthquake. The earthquake occurred along the Main Himalayan Thrust—a geological faultline where the Indian tectonic plate pushes under the Eurasian Plate, driving the Himalayas upwards at a rate of about 2cm per year. Large portions of this faultline are locked, and stress between the two plates is typically released via large earthquakes, where the upper tectonic plate breaks free from the drag created by the lower plate, producing shockwaves. However, the study found that the Gorkha earthquake only ruptured a fraction of the locked zone, indicating that further severe earthquakes could be coming in the future, although they are unable to predict when.

The researchers also found that the April earthquake propagated eastward from its epicentre in the Gorkha district, 75 km (46.6 miles) north-west of Kathmandu, at a rate of around 2.8 km per second (1.7 miles per second). Avouac says it was fortunate that the quake proceeded eastward rather than westward, or else it could have released a far larger proportion of the locked faultline and caused even greater damage. According to the study, western Nepal last experienced a large earthquake in 1505, which was believed to have measured over 8.5 magnitude. The BBC reported that the stress released by the Gorkha quake has now been shifted onto an area stretching from the west of Pokhara in Nepal to the north of the Indian capital, Delhi.

Bill McGuire, Professor of Geophysical and Climate Hazards at University College London, says he is not surprised by the new findings. McGuire says the tension released due to one earthquake is often loaded onto a neighbouring fault through a mechanism known as stress transfer, which heightens the possibility of a rupture in the recipient fault. "If the second fault is primed and ready to go, this extra stress—which could be little more than the pressure of a handshake—could be enough to trigger it," he says.

In light of the research, Avouac says more monitoring equipment, such GPS stations, must be installed to allow researchers to gather information on the region. He adds that Nepalese families must be equipped with the resources to properly protect themselves from future events. "A lot of families are building their own houses and they try to do it at minimum costs, which means they don't use much cement or iron, and that makes such a difference because with these materials you can make small buildings hold relatively well," says Avouac. The Nepalese government has been criticised for obstructing the flow of aid supplies to remote regions affected by the April earthquake by allegedly levying import taxes on the supplies or blocking the delivery of consignments. The Nepalese finance secretary strongly denied these claims.

The British Red Cross (BRC), which has been working with its Nepalese counterparts for a number of years to prepare people for earthquakes, welcomed the study for raising awareness of the risk of another disaster. "Disasters can strike anywhere and at any time, and the Red Cross is highly aware that another earthquake is possible in Nepal at any time," says Luke Tredget, the BRC's Asia programme officer. He adds that the BRC will be assisting people with rebuilding homes designed to be more resilient to future events.