Earth Permanently Deformed? Quake Study Suggests Planet's Crust Damaged

Earthquakes can permanently crack the Earth, say researchers after investigating quakes that have rocked Chile over the past million years, according to OurAmazingPlanet.

Longstanding research suggested that the Earth rebounds after quakes, as blocks of the world's crust elastically spring back to the way they initially were, over the course of months or decades depending on how severe the rumble was.

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The devastating 1906 San Francisco temblor was one of the first times experts noticed the crust rebounded, despite that the quake destroyed more than 80 percent of the city.

Scientists have been able to monitor the crust's condition after a quake using satellite-based GPS systems that monitor Earth's movements.

But experts are finding that major earthquakes, of magnitudes 7 or greater like those in northern Chile, have caused the crust to crack permanently.

"My graduate students and I originally went to northern Chile to study other features," structural geologist Richard Allmendinger of Cornell University said. "While we were 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."

"I still remember feeling blown away — never seen anything like them in my 40 years as a geologist — and also perplexed," Allmendinger told OurAmazingPlanet.

Northern Chile is "the driest place on Earth," where there is a "unique record of great earthquakes going back a million years," Allmendinger said.

Allmendinger's study, published April 28 in the journal Nature Geoscience, is among the most comprehensive in the realm of earthquake research. He said the data he and his colleagues compiled spans thousands of earthquake cycles while others only analyze a few quake cycles.

The meticulous study allowed researchers to determine long-term patterns and ultimately see a fuller picture of the impact of earthquakes on the Earth's crust.

OurAmazingPlanet reported that the team 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. This means that the Earth's crust may behave less elastically than previously thought.

"We have every reason to believe that our results would be applicable to other areas, but is simply not preserved for study the way that it is in the Atacama Desert," Allmendinger said.

Perhaps the study will change the way researchers conduct future studies on earthquakes.
"[The study] calls into question the details of models that geophysicists who study the earthquake cycle use," Allmendinger said. "If some of the deformation is permanent, then the models will have to be rethought and more complicated material behaviors used."

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