India slid under Nepal by a few feet during monster quake

  • Agencies, Washington/Sydney
  • Updated: Apr 29, 2015 01:36 IST

The earthquake that devastated Nepal and left thousands of people dead shifted the earth beneath Bihar by up to several feet underneath Nepal in a matter of seconds, a geologist said on Tuesday.

Saturday’s 7.9-magnitude earthquake also moved Kathmandu by up to several metres south, but the height of Mount Everest likely stayed the same, other experts added.

"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 at the US-based Columbia University.

He added that the length of the shift could be between 1 to 10 feet."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.

All of northern India is sliding north under Nepal constantly in a process that began millions of years ago and created the Himalayan mountain range.

“The point is that the sliding takes place abruptly at different patches at different times," 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.

According to University of Cambridge tectonics expert James Jackson, early seismological data obtained from sound waves that travel through Earth after an earthquake suggest the ground beneath the Kathmandu may have moved about three metres (10 feet) southward.

His analysis was similar to that of Sandy Steacy, head of the physical sciences department at the University of Adelaide.

"It's likely that the earthquake occurred on the Himalayan Thrust fault, a plate boundary that separates the northern moving Indian sub-continent from Eurasia," said Steacy.

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.

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