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Sunday, Oct 09, 2005

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More powerful earthquakes in the offing?

N. Gopal Raj

`Central Himalayan Gap' has the potential to generate more than one great earthquake, warn seismologists

THIRUVANANTHAPURAM: Seismologists have long feared that a great earthquake might be "overdue" in the Himalayas, although no one knew when or where it might happen. The key question now is whether Saturday's earthquake could increase stress at other points along the Himalayan arc and thereby trigger more, perhaps even more powerful, quakes.

The Himalayas were pushed to their majestic heights when the Earth's plate carrying India slammed into the plate bearing Asia some 40 million years ago. Since the Indian plate continues to push into the Asian plate, stresses build up at the faults marking the boundaries between the two plates. Earthquakes occur when the stress in a region becomes too great and the fault there ruptures. Some of the Himalayan earthquakes have been `great earthquakes' with a magnitude greater than eight.

There are a dozen examples of regions extending across the Himalayas, from the eastern Indian plate boundary at Myanmar to the western plate boundary through Pakistan, Afghanistan and Baluchistan, that could

experience a future great earthquake, warned Roger Bilham of the University of Colorado in the United States during a talk earlier this year.

Prof. Bilham gave his talk at a conference to mark the centenary of the magnitude 7.8 earthquake that occurred near Kangra in Himachal Pradesh, which is thought to have killed tens of thousands of people.

The Himalayan region has seen several powerful earthquakes with magnitude 7.5 to 8.5 and the first half of the last century saw three such quakes, points out the website of the Seismology Research Group at the Centre for Earth Science Studies (CESS) here. "However, the past fifty years has been exceptionally quiet in terms of large earthquakes and this has raised concerns about the future hazard scenario."

Of special concern was the 500-800-km-long central segment, popularly known as the "Garhwal-Kumaun Himalaya", where earthquakes greater than magnitude eight had not occurred since historic times.

This region, termed the `Central Himalayan Gap', has "the potential to generate more than one great earthquake in the immediate future", warns the group.

According to Prof. Bilham too, the Central Himalayan Gap is "potentially the most dangerous" of the regions in the Himalayas that could produce a great earthquake.

Asked whether Saturday's earthquake might jolt other stressed faults in the Himalayas, such as the Central Himalayan Gap, into rupturing and producing powerful earthquakes, Kusala Rajendran, seismologist at CESS, replied, "it could". Earthquakes in the Himalayas had a tendency to occur in clusters, she added. If an earthquake of the size of the 1905 Kangra earthquake were to recur, it could claim up to 300,000 lives, noted Harsh K. Gupta, former secretary to the Union Government's Department of Ocean Development, in an article published in December 2000.

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