South Asia a hotbed for quakes
2005-10-10 13:26
Vietnam - The area stretching across Pakistan into India and Afghanistan is a hotbed for seismic activity that erupts each time the Indian subcontinent slams into Asia. But it's the shallow faults that make these temblors so deadly.
Saturday's magnitude-7.6 quake, centred just outside Pakistan's capital, was about 10km deep, causing buildings to sway in three nations and killing thousands as weak structures tumbled, crushing people under mounds of rubble.
"It's how close you are to where the earthquake initiated, because ground motions fall off very rapidly away from the earthquake," said Harley Benz, a seismologist who runs the US Geological Survey's National Earthquake Information Centre in Colorado.
"Shallow earthquakes are very dangerous because they're very close to the built environment, unless they're in remote areas," he said.
'Shallow earthquakes are very dangerous'
In comparison, a 7.5-magnitude earthquake jolted Peru last month. He said it occurred about 13km beneath the surface in a more remote area. Only a handful of people died and several hundred homes were destroyed.
The December magnitude-9.0 earthquake that occurred off Indonesia's Sumatra island and spawned a tsunami that killed more than 176 000 people in 11 countries occurred about 30km below the surface.
The crash between the Indian plate and the Eurasian plate in the latest quake triggered the temblor along a range front that extends about 2 000km, Benz said.
It's the same type of collision that formed the Himalayas, millions of years ago.
About 50 million people are at risk
As the Indian subcontinent continues to creep about 4cm farther north every year, mountains are still being formed in the Himalayan, Karakoram, Pamir and Hindu Kush ranges by the uplift from the collisions, he added.
About 50 million people are at risk of encountering Himalayan quakes in this area, many of them in the densely populated capitals of Bangladesh, Bhutan, India, Nepal and Pakistan, according to research published four years ago by scientists from the University of Colorado who took an in-depth look at the region's seismic activity.
The area along India's northern border in disputed Kashmir is by far the hottest spot in that country, said A K Shukla, director of India's Earthquake Risk Evaluation Centre. He said the latest quake, unfortunately, will not be the last and may not be the largest to come.
"It's not a question of surprise, because that area is a highly seismic one," he said. "It's not surprising at all."
Saturday's quake was centred about 95km northeast of Islamabad in the forested mountains of Pakistani Kashmir. At least 22 aftershocks followed within 24 hours, including a 6.2-magnitude temblor.
In 1935, a magnitude-7.5 earthquake was recorded in Quetta, India, killing 50,000. In 1974, just north of the recent quake's epicentre, a magnitude-6.2 earthquake occurred, generating 5 800 casualties.
- AP