Scientists locate Indian tectonic plate under Tibet

Study helps in understanding Himalayan earthquakes better

Almost 55 million years ago, the Indian plate collided with the Eurasian plate leading to the formation of the mighty Himalayas. Since that gigantic collision, tectonic forces were slowly pushing the India to go under Tibet. But nobody knew the Indian plate’s northern limit.

An international team of scientists have now traced the limit at 31 degrees North latitude. It forms the underbelly of Tibet and is way beyond Nepal. The Hi-CLIMB (Himalayan-Tibetan Continental Lithosphere during Mountain Building) team that created in-depth images of the earth’s structure beneath the Himalayas has published their findings in the journal Science last Thursday.

“For the first time, we delineated the Indian plate’s Moho (crust-mantle boundary),” one of the Hi-CLIMB members Soma Nath Sapkota who heads Nepal’s National Seismological Centre in Kathmandu, told Deccan Herald. Crust is the outmost surface of the earth while mantle is the immediate next layer.

Realistic data

The team generated “very realistic” sub-surface seismic data that would help understand one of the fastest growing mountain evolutions of the world better, he said.
The researchers deployed and monitored 230 seismic stations for three years, cutting across 800 km of some of the world’s most remote terrain.

The lowest-elevation station was at 12 metres above sea level in Nepal and the highest was nearly 5,500 metres in Tibet. In fact, 30 of the stations were higher than 5,000 metres (16,400 feet).

“The research took us from the jungles of Nepal to the barren, wind-swept heights of Tibet in areas where nothing grew for hundreds of miles and there were absolutely no humans around,” said John Nabelek from Oregon State University, the project’s principal investigator.

“We have constructed an image of the crust and upper mantle beneath the Himalayas and the southern Tibetan Plateau. The 31°N boundary appears to extend deeper into the uppermost mantle,” Nabelek said.

Remoteness could be one of the reasons for which this region had never previously been completely profiled.

There are previous studies depicting how India under-thrusts the Himalayas at a rate of 1.7-2 cm per year and providing general ideas about the current location of the Indian plate.

But the Hi-CLIMB team created the most complete seismic image of the earth’s crust and upper mantle beneath the Himalayas, discovering unusual geologic features that may explain how the region has evolved in the process.

They discovered that as the Indian and Eurasian tectonic plates collide, Indian lower crust slides under the Tibetan crust, while the upper mantle peels away from the crust and drops down in a diffuse manner.

Besides explaining formation of the world’s largest mountain range, which is still growing, the study will help understand the Himalayan earthquakes better, Sapkota said.

DH News Service