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Earth sometimes shivers beneath thick blankets of ice

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11:42am, December 22, 2003

From San Francisco, at a meeting of the American Geophysical Union

New analyses of old seismic data have unveiled a previously unrecognized type of earthquake–quakes created by brief surges of massive glaciers.

When fault zones slip, they emit most of their stored energy as high-frequency ground motions, so that's the type of vibrations that scientists typically monitor to detect earthquakes, says Göran Ekström, a geophysicist at Harvard University. However, by using a data-processing technique that considers only low-frequency ground vibrations, he and his colleagues have discerned dozens of quakes of about magnitude 5 that aren't associated with any known fault zone. Instead, Ekström notes, they originated beneath large glaciers.

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