Earth Permanently Deformed: How Did Chile's Earthquakes Change The Planet?

Anyone who has witnessed or seen the after math of an earthquake can attest that they change the surface of our planet. But a new study journal "Nature Geoscience" suggests that earthquakes can also change interior of our planet as well.

Generally speaking, our planet bounces back to its original state after an earthquake over a span of months or decades. This rebound, which is measured via satellite-based GPS systems now, was seen after the 1907 San Francisco earthquake that destroyed 80 percent of the city.

But scientists from Cornell University, who investigated the earthquakes in Chile over the past million years, have concluded that the Earth is permanently deformed due to earthquakes. Specifically, structural geologist Richard Allmendinger and his colleagues have found that earthquakes with a magnitude of 7 or higher have resulted in a permanent crack in the crust in northern Chile.

"My graduate students and I originally went to northern Chile to study other features," Allmendinger told OurAmazingPlanet. "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," added Allmendinger. "What were these features and how did they form? Scientists hate leaving things like this unexplained, so it kept bouncing around in my mind."

Allmendinger discloses that northern Chile is unique since there are records of earthquakes going back a million years and the record of upper plate cracking goes back thousands of earthquake cycles. This comprehensive record allows researchers to better observe patterns.

Allmendinger and his team noticed a small pattern that revealed that the crush of the Earth may not be as elastic as it was once believed to be. They found that 1 to 10 percent of the deformation of the Earth causes by earthquakes (some 2,000 to 9,000 quakes) over the past million years is permanent.

What are the deformations? Cracks ranging from millimeters to meters in the crust of the Atacama Desert.

"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."

The significance of this study--apart from realizing the planet is permanently deformed--is that it allows geophysicists to change their model for studying earthquake cycles.

"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," notes Allmendinger. "If some of the deformation is permanent, then the models will have to be rethought and more complicated material behaviors used."

Allmendinger also warns that the region they studied, the Iquique Gap, has not had a great earthquake in the last 100 years and thus, will most likely see one in the next few decades.