Entire Himalayan arc can produce major earthquakes: study

 The Himalayas can likely generate destructive, major earthquakes along its entire length of 2,400 kilometres - even in Bhutan, a country sandwiched between India and China, which was thought to have little history of major seismological events, a new study has found.

Combining historical documents with new geologic data, the study shows the previously unstudied portion of the fault in the country Bhutan is capable of producing a large earthquake and did so in 1714.

"We are able for the first time to say, yes, Bhutan is really seismogenic, and not a quiet place in the Himalayas," said lead author Gyorgy Hetenyi, from the University of Lausanne in Switzerland.

The Himalayas have produced some of the world's largest earthquakes, like the April 2015 Gorkha earthquake that devastated Nepal.

However, scientists had not been able to prove whether every region along the 2,400-kilometre arc was seismogenic, or capable of producing quakes.

Bhutan was one of the last open gaps along the mountain chain: the country had no records of recent major earthquakes and no major seismological work had been done there.

Confining a major earthquake to Bhutan in 1714, like the new study does, means the entire Himalayan arc has experienced a major earthquake in the past 500 years, according to the study's authors.

By filling this gap, the study helps the millions of residents in the region understand its potential for natural hazards, according to Hetenyi.

The highest mountain range on Earth, the Himalayas are the product of the Indian tectonic plate subducting under the Eurasian Plate.

Throughout the 20th century, Bhutan, a small nation east of Nepal sandwiched between India and China, had been relatively isolated from the outside world and scientists were rarely allowed inside its borders.

Until recently, researchers thought Bhutan could be the only major segment of the Himalayas not to have experienced a major earthquake in the last 500 years, according to Hetenyi.

However, after a magnitude six earthquake struck the country in 2009, the government opened the door for scientists to perform geophysical research, Hetenyi said.

Researchers dug trenches around the fault line to see if one side of it had moved vertically with respect to the other - which would be considered evidence of a major earthquake.

They found evidence of rock uplift on one side of the fault had taken place between 1642 and 1836.
Hetenyi combined the results from that study with historical records of the 1714 earthquake to pinpoint where the 1714 quake happened and how large it was.

The analysis showed the 1714 quake likely caused the rock uplift observed around the fault.
The earthquake likely occurred in west central Bhutan, where most of the population lives, and had a magnitude of at least 7.5 to 8.5, Hetenyi said.The study was published in the journal Geophysical Research Letters.