Two centuries ago, a series of giant earthquakes rocked the tiny town of New Madrid, Missouri, collapsing chimneys and shaking houses more than 1000 kilometers away. It was even said that parts of the Mississippi River momentarily flowed backward as the riverbed heaved upward. Modern seismologists estimate that all three quakes in 1811–1812 registered above a 7.0 on the Richter scale—the largest known quakes east of the Rocky Mountains. Even today, the New Madrid Seismic Zone (NMSZ) generates more than 200 small tremors each year—and now a team of geophysicists thinks it knows what causes all the shaking.

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