Nepalese residents walk past road damage following an earthquake in Kathmandu on April 26, 2015. (AFP Photo)
A part of India slid about one foot to 10 feet northwards and underneath Nepal in a matter of seconds during the devastating 7.9-magnitude earthquake that hit the neighbouring country on Saturday, a US scientist has said.
"Saturday's slip took place over an area about 1,000 to 2,000 square miles over a zone spanning the cities of Kathmandu and Pokhara in one direction, and almost the entire Himalaya mountain width in the other," said Colin Stark, Lamont Associate Research Professor at the Lamont-Doherty Earth Observatory, Columbia University.
"A part of India slid about one to 10 feet northwards and underneath Nepal in a matter of seconds," Stark said.
"The rock (we call it the "crust", or more precisely 'lithosphere') below Bihar slid under Nepal along a zone from Bharatpur, through Hetauda, to Janakpur," Stark told PTI.
"It's important to realise that all of northern India is sliding north under Nepal etc, all the time. The point is that the sliding takes place abruptly at different patches at different times," Stark said.
Geophysicists have long monitored how fast the Earth's plates are moving, and it is known that the entire subcontinent of India is being driven slowly but surely underneath Nepal and Tibet at a speed of around 1.8 inches per year, Stark earlier wrote in an article published on CNN website.
Over millions of years, the squeezing has crushed the Himalayas like a concertina, raising mountains to heights of several miles and triggering earthquakes on a regular basis from Pakistan to Burma.
"Saturday's quake was neither unusual nor unexpected, although it was larger than most," Stark said.
In the 81 years since the 1934 Bihar earthquake, which killed around 10,000 people, the land mass of India has been pushed about 12 feet into Nepal.
"Think of all that movement getting stored in a giant spring lying under Nepal. The spring is stuck on a broad, rough surface which we call a fault plane," Stark said.
Sometimes, energy stored in the spring gets big enough to slip catastrophically, releasing all that pent-up strain and generating shaking strong enough to destroy buildings and kill people over a huge area, he explained.
The bigger the area that slips, and the larger the pent-up energy, the greater the damage.
The death toll in Nepal's devastating earthquake today crossed 5,000, with more than 8,000 people injured.