Since When Does Illinois Have Earthquakes?

When the New Madrid fault produced a minor earthquake centered under a tiny town in Illinois last week, it wasn't exactly top news. But in 1811 and 1812, that fault line produced two of the biggest quakes in U.S. history.

Though the Midwest fault is not as active as California's hot zone, geologist Michael Gibson says it is capable of producing a "big one."

"We're in one of the most active seismic zones that the country has," says Gibson, who teaches at the University of Tennessee. He says he chose to stud seismic activity after he saw the 1974 film Earthquake. "I was about to walk off to college," he says, and the film made the idea of studying quakes "very relevant."

An 'Ancient Scar'

The California activity — along what is known as the San Andreas fault — is a result of the North American plate riding over the Pacific plates and continually building stress, Gibson says. The New Madrid fault, on the other hand, is an "ancient scar" where two very old plates are slowly pulling apart.

But it, too, is capable of dramatics, Gibson says. The New Madrid seismic zone extends across parts of the Midwest and the South. "We're poised to be able to have large quakes," Gibson says.

During the past 1,500 years, the New Madrid fault has had three episodes that produced five large quakes, with the biggest occurring during a month and a half in the early 1800s, Gibson says.

Back then, few people were around to see the devastation — Native Americans, a few trappers and European settlers. But today, the Midwest is home to tens of millions of people.

Average residents of the Midwest may not be on a first-name basis with their neighborhood earthquake-maker, Gibson says, but state and city officials certainly are. In fact, the day of the West Salem quake last week, officials in Memphis were set to run a mock earthquake disaster drill, he says.

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