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Western Himalayan region faces big quake risk

jhelum.jpgThe Kashmir region in northwestern India could experience a magnitude 9 earthquake — several times larger than previously assumed. The revised risk estimate is worrying, says Roger Bilham of the University of Colorado, Boulder, who presented the results on 7 December at the American Geophysical Union meeting in San Francisco. “There are many cities and megacities in the region. And there are a couple of nuclear power plants there too,” he says. “You have two nuclear powers facing each other, armed to the teeth, facing a huge amount of damage”. Bilham speculates that perhaps 300,000 people might die in such an earthquake, not counting subsequent problems from political turmoil between India and Kashmir, or flooding.

[image: the Jhelum River in Kashmir could flood from a quake-triggered landslide]


The new estimate comes from 8 years of GPS readings showing how the ground is moving at the northern end of the Himalayas. These show that the compression of India into Asia slows to a crawl much further north than researchers had previously assumed from looking at the region’s topography. This shifts the estimate of where stress in the region is building to further north, which in turn widens the entire area that might slip in an earthquake. Before this data, the 300km-long slip zone was thought to be about 80km wide, with a potential for a magnitude 8.4 quake. That width has now been revised upwards to 200km, with the potential for a magnitude 8.7 or even 9 quake. (The abstract for the presentation can be found by searching for T54B-06 on the AGU 2011 meeting website)

A magnitude 9 quake has hit in the Himalayas before, in the central region of the mountain range. But it would take another thousand years to build up strain in that region for a similarly large quake, says Bilham. The north and south ends of the mountain range, on the other hand, theoretically have that strain built up now. Bilham says more work is needed to better assess the risk.

A large earthquake in the northern Himlayas could theoretically create a large landslide blocking the Jhelum River. That would flood the entire Kashmir valley, and create a potential “weapon of mass destruction”, says Bilham: blowing up the damn, which is often the strategy for getting rid of such blockages, could release a “bomb” of water.

Bilham says that researchers need to start more loudly broadcasting worst-case scenarios, so that earthquakes like those that hit Haiti and Japan don’t continually catch people by surprise. “All these things happen because we’re trained not to cry wolf,” says Bilham. “You have to plan for the worst case.” Earthquake risks are hard to asses in the Himalayas, he adds, because the large earthquakes only happen once every 500 years or more, making it impossible to assess risks from historical statistics. And it is politically difficult to get into the region to study it, he adds.

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