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Small New Madrid quakes likely aftershocks of 19th centuries monsters

By Rachel Lippmann

St. Louis – New research shows that many of the recent small earthquakes along the New Madrid fault may not be signs that the "next big one" is coming.

Researchers at Northwestern University and the University of Missouri believe those quakes are more likely aftershocks from the major quakes, all measuring more than 8 on the Richter Scale, that occurred when the fault ruptured violently in 1811 and 1812. The New Madrid fault stretches 150 miles southwest from the Missouri Bootheel.

Aftershocks are the quake "clean-up" crew, said Northwestern University geological sciences professor Seth Stein; signs that a fault line is resettling.

"It's really like after a car accident," Stein said. If you have a kind of efficient clean-up crew, they'll clean up in an hour. If you have very very slow clean-up crew, it could take them all day.

"Ten years after an earthquake on the San Andreas, you pretty much don't know that there was an earthquake there. Most of the leftover stresses on the fault are gone. Whereas at New Madrid, because nothing is happening there now, the biggest thing we see now is what happened 200 years ago," he said.

GPS measures show the New Madrid fault is basically stationary, Stein said, meaning less energy is building up that would need to be released. Any speculation that the fault is "due" for another big quake goes against all recent science, he said.