A kink in the regional fault line below Nepal explains why the highest mountains in the Himalayas are seen to grow between earthquakes, and suggests that another major temblor could take place sooner than previously expected, experts say.
In a new study published in the journal Nature Geoscience, an international team of experts led by John Elliott from the University of Oxford said the kink has created a ramp 20 km below the surface, with material constantly being pushed up and raising the height of mountains.
The experts claim the rupture on the fault stopped 11 km below Kathmandu, which suggests that another major earthquake could take place within a shorter time-frame than earlier expected.
Elliott said: “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.”
He added, “We have shown that the fault beneath Nepal has a kink in it, creating a ramp 20 km underground. Material is continually being pushed up this ramp, which explains why the mountains were seen to be growing in the decades before the earthquake.”
Elliott said the latest earthquake reversed this, dropping the mountains back down again when the pressure was released as the crust suddenly snapped in April 2015, according to a university statement.
“Using the latest satellite technology, we have been able to precisely measure the land height changes across the entire eastern half of Nepal. The highest peaks dropped by up to 60 cm in the first seconds of the earthquake,” he said.
Another key finding of the study shows the rupture in the fault stopped 11 km below Kathmandu, leaving an upper portion that remains unbroken.
Elliott said: “Using the high-resolution satellite images, we have shown that only a small amount of the earthquake reached the surface. This is surprising for such a big earthquake, which we would normally expect to leave a major fault trace in the landscape. This makes it a challenge when trying to find past earthquake ruptures, as they could be hidden.”