Amazing: Plate Shift, Quake Caused Asia Tsunami

Monday, May 23, 2005
Plate Shift, Quake Caused Asia Tsunami
By John Fleck
Albuquerque Journal Staff Writer

Imagine a land area the size of California sliding 50 feet.
That is what happened Dec. 26 when the Indo-Australian plate slid beneath Sumatra, setting off a tsunami that killed nearly 300,000 people.
While the human toll is well-known, scientists are only beginning to grasp the staggering forces involved in the event, according to Socorro geophysicist Rick Aster.
Aster and colleague Susan Bilek, both at the New Mexico Institute of Mining and Technology, are part of a team of scientists trying make sense what happened.
In Friday's edition of the journal Science, they offer the first detailed look at the largest earthquake in four decades and the first such massive quake since a worldwide network of seismic instruments was set up.
"We've never observed anything like this with anything like the instruments we have now," Aster said in an interview.
The quake happened when a piece of Earth's crust beneath the Indian Ocean slid eastward beneath a neighboring piece of crust.
Called "subduction," the process is a big part of the seismic process that shapes the Earth, Aster explained.
Bilek studied the difference between earthquake activity before and after the quake. The area around the quake site was relatively quiet before the quake, she found, as the two moving plates "locked" before the earthquake suddenly released the pent-up strain.
After a quick seven-minute burst of movement, the lower plate continued sliding slowly under the upper plate for an hour, the scientists found.
The resulting force released as the plates moved was staggering?- the equivalent of 1,400 one-megaton nuclear bombs buried at half-mile intervals along the entire length of the earthquake zone, according to Aster.