Glacier's movement offers earthquake clues

Aug. 24, 2012 at 4:14 PM
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UNIVERSITY PARK, Pa., Aug. 24 (UPI) -- Repeating earthquakes in an Antarctic ice sheet may shed light on both glacial movement and on earthquakes like those on the San Andreas fault, researchers say.

They analyzed seismic activity recorded on the David Glacier in Antarctica from 2002 to 2003 and found the local earthquakes, about 20,000 of them, were predominantly the same and occurred every 25 minutes, give or take 5 minutes.

"No one has ever seen anything with such regularity," said Lucas K. Zoet, who participated in the research while at Penn State and is now a postdoctoral fellow at Iowa State University. "An earthquake every 25 minutes for a year."

The earthquakes result from the glacier repeatedly rupturing as it passes over a half-mile diameter hill poking up from the bedrock underneath, the researchers suggest.

That creates a so-called "stick/slip" situation much like that on the San Andreas fault, as the ice sticks on the hill and stress gradually builds until the energy behind the obstruction is high enough to move the ice forward, a Penn State release said Thursday.

That occurs in a step-by-step manner rather than smoothly, resulting in the regularly repeating earthquakes, they said.

The findings can provide a simple model for the stick/slip earthquakes that occur between landmasses, Penn State geosciences Professor Richard B. Alley said.

"We have not completely explained how ice sheets flow unless we can reproduce this effect," he said. "We can use this as a probe and look into the physics so we better understand how glaciers move."

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