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USU Geophysicist says Fault Movement Continues Since 2004 Tsunami

Thursday, Oct. 18, 2007

tsunami image

A coastal community in Sri Lanka is pounded by a tsunami generated by the 2004 Great Sumatra-Andaman Earthquake. Satellite image courtesy of DigitalGlobe.

USU geophysicist Tony Lowry

USU geophysicist Tony Lowry, pictured at a GPS receiver site, is part of an NSF-funded research team investigating fault movement following the massive 2004 Asian tsumani-generating earthquake. Photo by Donna Barry.

The day after Christmas 2004 is indelibly etched into the memory of people around the world. Surreal images of sunny Asian beaches suddenly shattered by huge walls of water burst onto television screens as viewers watched one of the globe’s deadliest natural disasters unfold.

The Great Sumatra-Andaman Earthquake, which triggered massive tsunamis known in catastrophe-struck areas as the Asian Tsunami and the Boxing Day Tsunami, claimed the lives of more than 230,000 people. Ocean waves inundated coastal communities from East Africa to Southeast Asia.
The huge quake occurred when a portion of the Indo-Australian Plate slipped under the Eurasian Plate southeast of Indonesia. A 750 mile-long underwater rupture in the Earth’s crust ensued, which soon spread northward at more than 6,000 miles per hour.
Since the quake, Utah State University geophysicist Tony Lowry and colleagues from the University of Memphis’ Center for Earthquake Research and Information, the University of Colorado and India’s Society for Andaman and Nicobar Ecology have studied the restless seismic movements of the Indian Ocean’s Andaman Islands, a focal point of the disaster. Their findings are reported in the article, “Postseismic Deformation of the Andaman Islands following the 26 December, 2004 Great Sumatra-Andaman Earthquake” in the October 13, 2007, issue of Geophysical Research Letters.
“Parts of the Andaman Islands subsided or rose by up to a yard during the earthquake,” says Lowry, assistant professor in USU’s Geology Department. “Since then, we’ve used GPS technology to measure how the ground has continued to move.”  
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. Lowry and colleagues collected GPS measurements of postseismic deformation at 11 sites in the Andaman Islands starting three weeks after the quake. These sites recorded from six inches to more than a foot of continued uplift and even larger horizontal motion to the southwest.
A topic of hot debate is what causes the movement.
“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,” says Lowry. “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.”
Study findings have further implications for the earthquake cycle on faults, including how stress accumulates in the time between quakes, he says.
“The data we’re collecting may eventually help us to better understand how and how often these sorts of really big earthquakes happen,” Lowry says.
Related links:
Contact:  Anthony R. “Tony” Lowry [], 435-797-7096
Writer:  Mary-Ann Muffoletto [], 435-797-1429

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