- REUTERS
Foreign tourists staying in Phi Phi island arrive in Phuket , southern Thailand for treatment, yesterday. One of the most powerful earthquakes in history hit Asia yesterday, unleashing a tsunami which devastated coastal areas of Sri Lanka, India, Indonesia and tourist isles in Thailand, killing more than 12,300 people.
LONDON (AP);
THE CHAIN reaction that set off enormous, deadly tidal waves that struck six Asian nations yesterday started miles (kilometres) beneath the ocean floor off the tip of the Indonesian island of Sumatra.
Geologic plates pressing against each other slipped violently, creating a bulge on the sea bottom that could be as high as 10 metres (yards) and as long as 1,200 kilometres (745 miles), one scientist said.
"It's just like moving an enormous paddle at the bottom of the sea," said David Booth, a seismologist at the British Geological Survey, Britain's geoscience agency. "A big column of water has moved, we're talking about billions of tonnes. This is an enormous disturbance."
Moving at about 800 kilometres per hour (500 mph), the waves probably took about two hours to reach Sri Lanka, where the human toll has been horrific, Booth said.
NO WARNING SYSTEM
But because the tidal waves known as tsunamis rarely occur in the Indian Ocean, there is no system in place to warn countries about to be hit as for nations in the Pacific, Booth said.
"With 20-20 vision of hindsight, that'll be reconsidered," he said.
An Australian scientist suggested in September that an Indian Ocean warning system be set up, but it takes a year to create one, Booth said.
He added that those living on the Indian Ocean were less likely than Pacific coastal dwellers to know the warning signs of a tidal wave about to hit water receding unusually fast and far from the shore.
Thousands died in the tidal waves in India, Indonesia, Sri Lanka, Thailand, Malaysia and Bangladesh.
The underwater earthquake, which the U.S. Geological Survey put at magnitude 8.9, is the biggest since 1964, when a 9.2-magnitude temblor struck Alaska.
"All the planet is vibrating" from the quake, Enzo Boschi, the head of Italy's National Geophysics Institute, told Italian state radio.
He likened its power to a million atomic bombs the size of those dropped on Japan in World War II, and said the shaking was so powerful it even disturbed the Earth's rotation.
POWERFUL AFTERSHOCKS
Alessandro Amato, director of Italy's national earthquake centre, said an effect on the rotation was possible but he did not know whether it had yet been established by the most sensitive instruments.
There were at least a half-dozen powerful aftershocks, one of magnitude 7.3.
The quake occurred at a spot where two massive geological plates press against one another with enormous force, Booth said.
The Indian Ocean plate is gradually being forced underneath Sumatra, which is part of the Eurasian plate, at approximately the speed at which a human fingernail grows, he explained.
"This slipping doesn't occur smoothly," he said. Rocks along the edge stick against one another and pent-up energy builds over hundreds of years.
It's "almost like stretching an elastic band, and then when the strength of the rock isn't sufficient to withstand the stress, then all along the fault line the rocks will move," he said.
The quake probably occurred about 10 kilometres (6.2 miles) beneath the ocean floor, Booth said, causing the huge, step-like protrusion on the sea bed and the resulting tsunami.
As the waves move across deep areas of the ocean, they may be almost undetectable on the surface, swells of about a metre (yard) or less.
THE RING OF FIRE
But when they near land, and the sea grows more shallow, the huge volumes of water are forced to the surface and the waves get higher and higher.
"On the beach itself, the wave can be as much as 30 feet (10 metres) high," Booth said.
Indonesia is well known as a major quake centre, sitting along a series of fault lines dubbed the "Ring of Fire."
But scientists are unable to predict where and when quakes will strike with any precision.
The Sumatran temblor hit at 0059 GMT yesterday, Booth said. British detectors puts its magnitude at 8.6, compared to the 8.9 measured by U.S. scientists. He said earthquakes resonate differently around the world and that it often takes time to calculate their true power.
The force of the earthquake shook unusually far afield, causing buildings to sway hundreds of miles (kilometres) from the epicentre, from Singapore to the city of Chiang Mai in northern Thailand, and in Bangladesh.
Booth said instruments at his lab in Edinburgh, Scotland, detected tiny tremors resulting from the quake, although they were far to small for anyone in Britain to feel. He said it was not unusual for seismologists to pick up readings from large quakes that happen very far away.
