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Science & Environment

No Faults Or Rifts, So Why The Earthquakes Here?

Berk Biryol
UNC Chapel Hill
A conceptual model of the plate and upper mantle structure beneath the southeastern US.

Scientists have long wondered why the southeastern United States gets so many earthquakes. A UNC Chapel Hill study offers one answer. 

If you know even the basics of geology, you know this: earthquakes happen when two tectonic plates interact with each other. That's why it's not surprising that California which straddles two plates has so many earthquakes.  But what about the southeastern US?

We're about 1,000 miles from any plate boundary and still we get occasional earthquakes, usually small ones. In 2011, a moderate quake in eastern Virginia shook the nation's capital and was felt throughout the Carolinas.

BerkBiryol at UNC Chapel Hill believes, at one time, parts of the North American plate beneath this region broke off.

"The plate effectively becomes thinner and when that happens you'll have a weaker plate," says Biryol.

You'll also have more earthquakes.  Biryol says this happened fairly recently, at least in geologic time, 15 million years ago. 

Biryol and his team came to this conclusion by measuring seismic waves to create 3D images of the North American plate and the mantle directly below it.