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Earth permanently deformed by earthquakes in Chile

Posted By Kristen Butler, UPI.com   |   April 29, 2013 at 7:31 AM   |   Comments

April 29 (UPI) -- More than a century of research has suggested the Earth rebounds after quakes, with blocks of crust springing back like elastic over the course of months to decades, to the way it was before.

But structural geologist Richard Allmendinger of Cornell University and his colleagues now find that earthquakes of magnitude 7 or greater caused caused the crust in northern Chile to crack permanently.

Allmendinger and his graduate students went to Chile to study something else. Once there, "our Chilean colleague, Professor Gabriel González of the Universidad Católica del Norte, took us to a region where these cracks were particularly well-exposed," Allmendinger told NBC News.

In northern Chile, "the driest place on Earth, we have a virtually unique record of great earthquakes going back a million years," Allmendinger said. "Our record of upper plate cracking spans thousands of earthquake cycles."

Researchers discovered that a small but significant 1 to 10 percent of the deformation of the Earth caused by 2,000 to 9,000 major quakes over the past 800,000 to 1 million years was permanent, involving cracks millimeters to meters large in the crust of the Atacama Desert.

The study, April 28 in the journal Nature Geoscience, "calls into question" the models that geophysicists currently use to study quakes. "Their models generally assume that all of the upper-plate deformation related to the earthquake cycle is elastic -- recoverable, like an elastic band -- and not permanent."

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