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Sumatra Quake was longest ever recorded
05/19/2005 11:36 PM
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[link to www.cnn.com]
Scientists: Sumatra quake longest ever recorded
Temblor big enough to ´vibrate the whole planet ´
By Marsha Walton
Thursday, May 19, 2005 Posted: 3:53 PM EDT (1953 GMT)
The Sumatra-Andaman quake released an amount of energy equal to a 100 gigaton bomb.
(CNN) -- Dramatic new data from the December 26, 2004, Sumatran-Andaman earthquake that generated deadly tsunamis show the event created the longest fault rupture and the longest duration of faulting ever observed, according to three reports by an international group of seismologists published Thursday in the journal "Science."
"Normally, a small earthquake might last less than a second; a moderate sized earthquake might last a few seconds. This earthquake lasted between 500 and 600 seconds (at least 10 minutes)," said Charles Ammon, associate professor of geosciences at Penn State University.
The quake released an amount of energy equal to a 100 gigaton bomb, according to Roger Bilham, professor of geological sciences at the University of Colorado.
And that power lasted longer than any quake ever recorded.
The quake, centered in the Indian Ocean, also created the biggest gash in the Earth´s seabed ever observed, nearly 800 miles. That´s as long as a drive from northern California into southern Canada.
Scientists estimated the average slippage (ground movement up and down) along the entire length of the fault was at least 5 meters (16.5 feet) -- with some places being moved nearly 20 meters (50 feet).
Scientists have also upgraded the magnitude of the quake from 9.0 to between 9.1 and 9.3, a dramatically more powerful event. As a comparison: the ground shook 100 times harder during December´s earthquake than what was felt in the 1989 Loma Prieta quake in California. That 6.9 magnitude quake caused extensive damage from Santa Cruz to San Francisco.
The stunning power of Asia´s earthquake and tsunamis last December has left even veteran scientists in awe.
"I think it was humbling for everyone that analyzed the earthquake," said Thorne Lay, professor of earth sciences and director of the Institute of Geophysics and Planetary Physics at the University of California, Santa Cruz.
"We´re sitting in our laboratories working on the signals from this earthquake, trying to understand what happened scientifically, and then watching TV at night and seeing the death toll rising for weeks," he said.
The enormous human toll from the natural disasters spurred Lay to organize dozens of scientists from all over the world to share their data and analysis of the quake. The long-term goal is to try to get more, and more accurate tsunami warning systems in place.
Whole planet vibrated
A wide array of instruments were used for the first time to study the earthquake, and its many aftershocks.
Global broadband seismometers recorded the ground in Sri Lanka, a thousand miles from the epicenter, moved up and down by more than 9 centimeters (3.6 inches), according to the report.
But no place on Earth escaped movement.
"Globally, this earthquake was large enough to basically vibrate the whole planet as much as half an inch, or a centimeter. Everywhere we had instruments, we could see motions," Ammon said.
Much of that information came from digital broadband seismometers, a new era of instruments that the National Science Foundation and the U.S. Geological Survey began deploying around the world several years ago.
Lay says the equipment is sensitive enough to pick up the motion of wind blowing through trees, or cows walking in a field, or the massive motions produced by this earthquake.
"We´d never seen signals from an earthquake of this size, and the availability of this instrumentation was a real breakthrough in being able to see the complete rupture process of one of these truly monstrous events," Lay said.
Other tools added to the scientists´ understanding. Underwater cameras documented the huge crack in the ocean floor. Tsunami buoys, and sonar from the British Navy helped with the analysis.
And a fortunate bit of timing enabled researchers to get a view of the tsunami they have never seen before.
"Two hours after the earthquake has occurred, the wave is spreading out from the Bay of Bengal," Lay said. "Two satellites went over, with the capability of measuring the elevation of the ocean surface. The satellites saw the south-going wave and the north-going part of the wave. "It was just good luck that the passage of the satellites caught the tsunami in motion," he said.
Crunching numbers, and creating maps and models is taking on a new urgency for some of the scientists involved in this research.
"There will be more earthquakes of this type, and with more humans exposed to the hazard there will be more devastating losses of life. What we hope to do is develop technologies that can minimize that loss," Lay said.
The risk far outweighs any benefit as the risk will vary from child to child.
12/08/2005 10:16 AM
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