More than a century ago in December of 1811 and January of 1812, residents in the 600,000 square kilometers around New Madrid, Mo., suffered damages from some of the most powerful earthquakes in United States history. Seismologists recently warned that the New Madrid fault didn’t die and still threatens the area where Missouri, Illinois, Kentucky, Tennessee and Arkansas meet.

During those 19th century New Madrid fault quakes, buildings suffered damage as far away as St. Louis and Cincinnati. As the ground fell out from underneath the Mississippi River, waves swept northward, creating the illusion that the river had reversed its course and whole islands disappeared. Closer to the epicenter of the quake, sand erupted from the ground, which dropped up to 6 meters in places.

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The New Madrid seismic fault didn’t fall asleep after that outburst. Since then, dozens of small quakes have continued to shake the area on a regular basis. U.S. Geological Survey seismologists recently used computer simulations to suggest that those frequent tremors mean the fault remains active and could shake the central United States once again.

Some seismologists have argued that the ongoing temblors could be merely aftershocks of the 1811-12 quake. If that were so, then the continuing quakes should have been fewer in number, argued the USGS scientists in their recent paper published in Science. Especially now, two centuries later, aftershocks should be rare, according to computer models built using data from other quakes. Yet, today a large number of small quakes still emanate form the New Madrid fault zone, which signifies a still dangerously active fault.

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The vast increase in population in central United States since the early 19th century amplifies the danger. Although the 1811-12 quakes caused only one death, a modern quake could devastate Memphis, St. Louis, Little Rock, Louisville, Ky. and other cities.

Map: Recent earthquakes are plotted in the New Madrid Seismic Zone. Credit: USGS