Stanford geophysicists said that The Himalayan range was formed, and remains currently active, due to the collision of the Indian and Asian continental plates.
Scientists have known for some time that India is subducting under Asia, and have recently begun studying the complexity of this volatile collision zone in greater detail, particularly the fault that separates the two plates, the Main Himalayan Thrust (MHT), a Stanford statement said.
Previous observations had indicated a relatively uniform fault plane that dipped a few degrees to the north.
To produce a clearer picture of the fault, Warren Caldwell, a geophysics doctoral researcher at Stanford, has analysed seismic data from 20 seismometers deployed for two years across the Himalayas by the National Geophysical Research Institute of India.
The data imaged a thrust dipping a gentle two to four degrees northward, as has been previously inferred, but also revealed a segment of the thrust that dips more steeply (15 degrees downward) for 20 kilometres.
Such a ramp has been postulated to be a nucleation point for massive earthquakes in the Himalayas.
Although Caldwell emphasised that his research focuses on imaging the fault, not on predicting earthquakes, he noted that the MHT has historically been responsible for a magnitude 8 to 9 earthquake every several hundred years.
"What we're observing doesn't bear on where we are in the earthquake cycle, but it has implications in predicting earthquake magnitude," Caldwell said.
"From our imaging, the ramp location is a bit farther north than has been previously observed, which would create a larger rupture width and a larger magnitude earthquake," he said in a statement.
Caldwell's adviser, geophysics Professor Simon Klemperer, added that recent detections of magma and water around the MHT indicate which segments of the thrust will rupture during an earthquake.
"We think that the big thrust vault will probably rupture southward to the Earth's surface, but we don't expect significant rupture north of there," Klemperer said.
Researchers said the findings are important for creating risk assessments and disaster plans for the heavily populated cities in the region.
