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Another major earthquake in Nepal can happen much sooner than anticipated

another-major-earthquake-in-nepal-can-happen-much-sooner-than-anticipated

A new study conducted by an international team of scientists suggests a kink in the regional fault line below Nepal is responsible for the growth of the Himalaya mountains between earthquakes. The scientists have studied the devastating April 2015 Nepal (Gorkha) earthquake and discovered that only a small amount of energy was released, indicating another major earthquake can happen much sooner than anticipated.

The kink in the fault has created a ramp located 20 km (12.4 miles) below the surface. The material is constantly being pushed up, which is why the mountains have been growing decades before the earthquake. After the earthquake occurs, the released pressure causes the mountains to drop down again.

The research has been conducted in cooperation with the UK's Center for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET), the University of Oxford, the University of Cambridge and experts from the USA California Institute of Technology, PSL Research University France, and engineering consultancy Arup.

The study discovered that the rupture on the fault stopped 11 km (6.8 miles) below Kathmandu. This could mean another major earthquake might occur in the area in less than centuries of the expected timeframe.

"Nepal has some of the highest mountain ranges in the world that have been built up over millions of years because of the collision of India with Asia. But the way in which mountains grow and when this occurs is still debated," lead author Dr John Elliott of Oxford University, a member of the COMET team, said.

"We have shown that the fault beneath Nepal has a kink in it, creating a ramp 20 km (12.4 miles) underground. The material is continually being pushed up this ramp, which explains why the mountains were seen to be growing in the decades before the earthquake. The earthquake itself then reversed this, dropping the mountains back down again when the pressure was released as the crust suddenly snapped in April 2015."

The scientists have used the satellite technology to measure the changes in land height across the eastern half of Nepal and found out that the highest mountain peaks dropped down by up to 60 cm (almost 2 feet) during the first seconds of the earthquake.

Mount Everest is located over 50 km (31 miles) east of the earthquake zone and, therefore, too far away to suffer the consequences of the subsidence.

"We successfully mapped the earthquake motion using satellite technology on a very difficult mountainous terrain. We developed newly processing algorithms to obtain clearer displacement maps, which revealed the most likely fault geometry at depth. Such geometry makes sense of the puzzling geological observations," Dr Pablo Gonzalez of the University of Leeds, a member of the COMET team, said.

Because the rupture in the fault stopped 11 km (6.8 miles) below Kathmandu, only a small amount of the earthquake reached the surface. According to Dr Elliott, this is surprising for an earthquake of such size which would normally leave a major fault trace in the landscape. This also represents a challenge when trying to find past ruptures because it means they could be hidden.

"We found that the rupture from April's earthquake stopped 11 km beneath Kathmandu, and that this sudden break is because of damage to the fault from interactions with older faults in the region. This is important because the upper half of the fault has not yet ruptured, but is continuously building up more pressure over time as India continues to collide into Nepal."

"As this part of the fault is nearer the surface, the future rupture of this upper portion has the potential for a much greater impact on Kathmandu if it were to break in one go in a similar sized event to that of April 2015. Work on other earthquakes has suggested that when a rupture stops like this, it can be years or decades before it resumes, rather than the centuries that might usually be expected."

However, currently, there is no way to predict precisely when another earthquake might occur. The countries and cities should do everything in their power to ensure they are well prepared for such an event.

Reference:

  • "Himalayan megathrust geometry and relation to topography revealed by the Gorkha earthquake" – J. R. Elliott, R. Jolivet, P. J. González, J.-P. Avouac, J. Hollingsworth, M. P. Searle & V. L. Stevens – Nature Geoscience (2016) – doi:10.1038/ngeo2623

Featured image: Le Langtang Lirung, Himalaya, Népal, January 21, 2013. Image credit: Jean-Pierre Dalbéra (Flickr-CC)

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