EFL
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.
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. |