Fault Movement Continues Since 2004 Asian Tsunami

Description
Researchers say ongoing uplift following the 2004 Great Sumatra-Andaman Earthquake, which triggered massive tsunamis the day after Christmas, is caused by continuing slip on the quake fault.


“Parts of the Andaman Islands subsided, or rose, by up to a yard during the earthquake,” said Utah State University geophysicist Tony Lowry who, along with colleagues in Tennessee, Colorado and India, has monitored restless tectonic movements using GPS technology in the remote Indian Ocean islands, a focal point of the disaster. The findings were published October 13, 2007, in Geophysical Research Letters.

Scientists have observed dramatic post-earthquake movement following several large temblors, including the 2004 quake, though the latter boasts the largest movement recorded since GPS technology became available. GPS sites in the Andamans have recorded uplift ranging from six inches to more than a foot since the earthquake and even larger horizontal movements toward the southwest.

A hot topic of debate is what causes the movement.

In a study funded by the National Science Foundation, Lowry and associates from the University of Memphis’ Center for Earthquake Research and Information, the University of Colorado and India’s Society for Andaman and Nicobar Ecology collected GPS measurements at 11 sites in the Andaman Islands starting three weeks after the quake.

“Post-quake movement has generally been modeled as either deep rock flow in response to the stress change during an earthquake or as continued slip on the fault,” said Lowry, assistant professor in USU’s geology department. “Our research indicates that the Andaman post-earthquake movements resulted mostly from continuing silent slip on the fault, below the depth that slipped during the 2004 earthquake.”

The findings have further implications for the earthquake cycle on faults, including how stress accumulates in the time between quakes, he said.

“The data we’re collecting may eventually help us to better understand how and how often these sorts of really big earthquakes happen,” Lowry said.(Newswise)