LOS ANGELES — The New Madrid fault zone in the nation's midsection is active and could spawn future large earthquakes, scientists reported Thursday.
It's "not dead yet," said U.S. Geological Survey seismologist Susan Hough, who was part of the study published online by the journal Science.
Researchers have long debated just how much of a hazard New Madrid poses. The zone stretches 150 miles, crossing parts of Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri and Tennessee.
In 1811 and 1812, it unleashed a trio of powerful jolts — measuring magnitudes 7.5 to 7.7 — that rattled the central Mississippi River valley. Chimneys fell and boats capsized. Farmland sank and turned into swamps. The death toll is unknown, but experts don't think there were mass casualties because the region was sparsely populated.
Unlike California's San Andreas and other faults that occur along boundaries of shifting tectonic plates, New Madrid is less understood because it's in the middle of the continent, far from plate boundaries.
Hough and USGS geophysicist Morgan Page in Pasadena, Calif., analyzed past quakes in the New Madrid region and used computer modeling to determine that continuing tremors are not related to the big quakes two centuries ago.
"Our new results tell us that something is going on there, and therefore a repeat of the 1811-1812 sequence is possible," Hough said.
The USGS estimates there's a 7 to 10 percent chance of that happening in the next 50 years.