Mo. quake unrelated to others, say experts

First a massive earthquake in Haiti, then a bigger one in Chile.

Now a quake hits southeast Missouri, and people 150 miles away feel it.

Time to panic?

No, but people are understandably jittery about earthquakes these days.

And, in fact, a big one may be coming to the New Madrid Seismic Zone that affects Missouri. The earthquake that struck March 2 had a magnitude of 3.7, which is greater than usual but not alarmingly so, experts say.

J. David Rogers of the Missouri University of Science and Technology said an earthquake of that magnitude occurs about once every five years, while the region may experience hundreds of much smaller quakes a year.

Also, the quakes in the Caribbean and in South America had nothing to do with the one in Missouri.

"There really isn't an interconnection as far as plate tectonics goes," said Dave Gaunt, a Rolla, Mo.-based geohazards geologist for the Missouri Department of Natural Resources. "It's more of a coincidence."

Another coincidence: That the huge Haiti and Chile quakes occurred so close in time.

The magnitude-7 quake in Haiti and the 8.8 quake in Chile were the result of tensions between plate boundaries in the crust of the Earth, with one plate sliding along or beneath another one. But those two events had nothing to do with each other because they were on different plate systems and were too far apart, Rogers said.

The New Madrid zone, which straddles Missouri, Arkansas, Illinois, Kentucky and Tennessee, is the result of an ancient rift in the North American plate.

A series of quakes in the New Madrid zone in 1811-12 is now estimated to have had magnitudes of 7 or more. They were whoppers, but the population then was nothing compared with today, with Memphis and St. Louis in the danger zone.

The United States Geological Survey forecasts a 7 to 10 percent chance of a magnitude-7 or greater quake in the New Madrid zone in the next 50 years. It is the most seismically active area of the United States east of the Rocky Mountains, according to the USGS.

"The (New Madrid) quake that is overdue is 6 to 6.5, and that will do plenty of damage," Rogers said. "You don't need a repeat of 1811-12 for that."

Generally a shallow quake is not felt as far away as a deeper one. Still, reports that the quake Tuesday was felt 150 miles from the epicenter are not unusual. The geology in the Midwest means tremors may be felt over areas 10 to 20 times larger than those in California, Rogers said.