Search the Internet          Tips

Pressure beneath Himalayas may have caused tremors: US expert

P Rajendran in New York

Dr James Neil Brune, a seismologist of international repute at the University of Nevada, has long warned about the possibility of a mammoth earthquake in the Himalayas, one that could raze the Tehri dam and cause devastation that could outmatch the 1975 collapse of the Banqiao and Shimantan dams in China, where the official toll was 85,000 and 230,000 by other estimates.

Oddly enough, it was what was ostensibly his figures that engineers first used to defend the Tehri dam, figures he later said had been misrepresented.

Dr Brune, who has visited India eight times now and spent much time reviewing seismicity in the north, now cautiously theorises that the pressure building up beneath the Himalayas -- a pressure that may yet be released with cataclysmic consequences -- may be what is causing seismic disturbances further south.

Speaking to rediff.com, he said seismologists had known that the area lay on the edge of a zone, indicating a fairly high probability of an earthquake.

"This is quite near the great Rann of Kutch quake (in 1819). The topography, the fact that the ground was elevated to the south of the fault line (the Allah Bund) all made a quake likely," he said, adding that that quake had been to the west.

If the fault line cracked all the way, the pressure would ease up, reducing the chances of more earthquakes. But if a part was stuck the chances increased.

He cited the example of Turkey, which suffered a devastating quake last year.

"Sections of a fault have been affected since 1934, moving westward. The next one, people fear, will be further west, closer to Istanbul." And the likelihood of further quakes depends on whether the stress there has been released. If the segment did not rupture, further quakes could not be ruled out there -- or, for that matter, in Kutch.

He disagreed with the claim of Indian scientists that the magnitude of 6.9 using 'body magnitude' was more accurate.

"Body magnitude used as a measurement is unreliable. The surface magnitude has been measured at 7.9. The US Geological Society's national earthquake information service has centres worldwide. They put the figure at 7.7, not too different from 7.9," he said.

Did the current earthquake tie in with pressures building up in the Himalayas?

"There is an overall seismicity caused by India pushing into Asia. A compressional force exists all over India. Some of this compression force goes all the way down in India, but the stress available decreases with distance from the Himalayas. So when you go south there's less seismicity."

But he does have his own take on the rash of quakes hitting parts of India, all the way down to Kerala.

"I have a theory, not an opinion yet... I believe recent activity in the last two to three hundred years is not consistent with the long-term situation in continental India." He cites the Latur earthquake, which happened in a zone II, 'shield' area, considered relatively safe. He said this indicated that the seismicity in the continent was anomalous over time.

"The reason the stress is high is because stress is not released on the Himalayan front," he says, adding that a very large quake there that would release seismicity in the Indian plate would decrease the chances of earthquakes elsewhere.

"In the last few years there is strong evidence of more intensity of ground motion in the hanging plate (the rising part of a tectonic rift). The ground motion is a lot larger than previously thought, using numerical and physical models."

He based his theory on ground deformation in South California, which is also prone to seismic upheavals.

"Unfortunately, for Dehra Dun, it's very bad news, if true," he said, adding that the hanging wall motion was much more now than even two years ago. And the Tehri dam is built on the hanging wall side of the fault.

He did not buy the American Association for the Advancement of Science view that the Indian subcontinent has been torn, stretched, and strained by aeons of plate tectonic jostling, and that has created weak spots in the crust.

"I think it is misleading; the true scale is millions of years. There is periodic stress and strain but it is stable over time," he said.

Would better structures have reduced the scale of the tragedy?

"It would have made a great difference. People tend to be fatalistic about the place above the epicentre. But if five per cent of the cost of the building has been spent to increase resistance to quakes, the loss of life would have been tremendously reduced."

Dr Brune said Dr A S Arya, pro-vice-chancellor at Roorkee university who is involved in earthquake engineering and has been part of a UNESCO team on the subject, had told him that there was a debate on in India about whether more money ought to be spent on strengthening school buildings. Given the state of school buildings in the quake-affected area, had the quake not occurred on a national holiday, many more children might have died, he said.

The Complete Coverage | List of earthquake sites

Back to top

Tell us what you think of this report