ST. LOUIS (AP) -- For the second time this week, residents in southeast Missouri felt the rumble of a small earthquake. But an expert said it's nothing to worry about -- small quakes strike in the New Madrid seismic zone roughly 200 times a year.
The U.S. Geological Survey's website said the latest earthquake was centered near Caruthersville in the Missouri Bootheel, a magnitude 2.7 quake that struck at 7:27 p.m. Thursday. There were no reports of damage or injuries. Caruthersville is about 100 miles north of Memphis, Tenn., and 200 miles south of St. Louis.
Two days earlier, another 2.7-magnitude quake was centered near Portageville, Mo. That quake also was harmless.
Steve Horton, a research scientist at the Center for Earthquake Research and Information at the University of Memphis, said the New Madrid seismic zone remains very active. It is the most active earthquake zone in North America east of the Rocky Mountains.
The region was the epicenter for massive quakes in 1811 and 1812, temblors so strong they reportedly caused the Mississippi River to flow backward and rang church bells in Boston. The region remains on alert for the possibility of that happening again.
Horton said experts believe there is a 7-10 percent probability in any 50-year period that similarly strong earthquakes will happen again in the region.
For that reason, major structures in southeast Missouri but also in St. Louis, Memphis and other places are built to withstand a major quake. In many cases, older structures have been retrofitted.