"One of the biggest earthquakes in U.S. history didn't occur in California. Or Alaska. It happened in the country's midsection some 200 years ago in an area where today seven states straddle the Mississippi River Valley."

"And seismologists from the United States Geological Survey believe they've uncovered evidence that the New Madrid Seismic Zone, as the area that spawned the 1811-12 quakes is known, is still alive and kicking.

In the early 19th century, not many people lived in the region, but for those who did, the earthquakes must have been a gut-wrenching experience, says Susan Hough, a seismologist with the USGS in Pasadena, Calif., in an interview with NPR's All Things Considered."