Earth permanently deformed? The Earth's crust is relatively elastic, but earthquakes of more than magnitude 7 will leave the planet permanently deformed, says new research.

A new study by geologists at Cornell University has shown that earthquakes can leave the Earth deformed.

Cornell geologist Richard Allmendinger told LiveScience that strong earthquakes in Chile have left permanent cracks in the surface of the Earth. The findings "perplexed" Allmendinger and his colleagues, as the Earth is known to "rebound" after earthquakes - an effect that is chronicled using satellite technology. Deformation, such as cracks, in the Earth's surface is generally thought to be temporary, with geological processes erasing them in "days or weeks."

From the LiveScience report:

"It is only in a place like the Atacama Desert that these cracks can be observed - in all other places, surface processes erase them within days or weeks of their formation, but in the Atacama, they are preserved for millions of years," Allmendinger said." 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."

Atacama exposed

In northern Chile, "the driest place on Earth, we have a virtually unique record of great earthquakes going back a million years," Allmendinger said. Whereas most analyses of ancient earthquakes only probe cycles of two to four quakes, "our record of upper plate cracking spans thousands of earthquake cycles," he noted.

Model rethink

This work "calls into question the details of models that geophysicists who study the earthquake cycle use," Allmendinger said. "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. If some of the deformation is permanent, then the models will have to be rethought and more complicated material behaviors used.

The area the researchers studied, theIquique Gap, "is one of the few places along western South America that has not had a great earthquake in the last 100 years and thus has a high probability of a major earthquake in the next couple of decades," Allmendinger added. "We may get to test out predictions about earthquakes if the next great earthquake there happens in the next couple of decades."