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Caltech scientist analyzes Sichuan quake

May 12, 2008 12:00:00 AM PDT
The massive earthquake in China left more nearly 10,000 people dead. That number will almost certainly go higher, as thousands more people are still missing. The quake measured magnitude 7.9 on the Richter scale. For perspective, that is much stronger than the 1994 Northridge earthquake, measured at 6.9.The pictures coming out of the hardest hit areas of China show widespread destruction: Buildings toppled, roads impassable, and thousands buried in all the debris. The epicenter was located on a spot in central China, Chengdu, in Sichuan Province, home to a population approaching 100 million people.

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It was the middle of the day when the earthquake struck, a destructive pulse of energy rocketing up a huge fault line.

"During the passage of that pulse, the fault slipped by about 30 feet, with eastern Tibet moving up over Sichuan Basin," said Professor Jean-Philippe Avouac.

Prof. Avouac is a seismologist at the California Institute of Technology who specializes in Asian earthquakes. He said a vertical wall of earth approximately three stories high thrust upward in spots, along the 200-mile-long rupture. The death toll, he surmises, will almost definitely soar from its current estimate, perhaps, he says, reaching the millions.

The Sichuan Basin, he says, has not seen many major quakes so its population was not prepared, its construction standards not strict enough to withstand something of this magnitude.

"In terms of the energy released by the earthquake, is a factor of 30 larger than the Northridge earthquake," said Prof. Avouac. That Northridge earthquake back in 1994 is the standard by which many Southern Californians judge earthquakes. It had a magnitude of 6.9, lasted just 10 to 20 seconds, and killed 57 people.

The Chinese quake not only had a magnitude of 7.9, but it shook for about three times longer than in Northridge. In an ironic twist, Prof. Avouac said the frequency of quakes in Southern California actually protects us.

"It's better to release the strain by many small earthquakes than by infraction by a very large earthquake," said Prof. Avouac.

That was the curse in Sichuan Province, which Avouac said was primed for a massive quake by centuries' worth of pressure building underground, pressure that finally surfaced, creating a swath of intense damage some 10 times the size of the Northridge quake.

 

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