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Reasearchers: New Madrid Quake Possible

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By Associated Press

June 23, 2005, 9:12 PM EDT
MEMPHIS, Tenn. -- The New Madrid seismic zone remains under enough strain to unleash devastating earthquakes, University of Memphis researchers say.
The Memphis research team study published in the journal Nature rebuts the conclusions of a Northwestern University researcher's 1998 report that the dangers of the seismic zone had been "vastly overstated."
The U of M team studied the New Madrid, a network of faults branching from near Cairo, Ill., to Marked Tree, Ark., through Global Positioning Systems satellite measurements of the Earth's surface. GPS was used to gauge the buildup of strain on the seismic zone by measuring, in millimeters per year, the movement of 60-foot, antenna-equipped I-beams sunk vertically into the ground.
Their study showed that the crust of the Earth is "deforming," or pressing in on portions of the seismic zone a few millimeters annually.
"We still don't understand why it's deforming, but we can measure the deformation," said Bob Smalley, a research associate professor at the U of M's Center for Earthquake Research and Information and one of four authors of the report.
Arch Johnston, director of the Memphis earthquake center, said this is the first time researchers were able to clearly measure, from the surface, the rate that strain is building up in the New Madrid system.
Earthquakes can happen as a result of the built-up strain that occurs as two pieces of the crust rub together.
In his study presented nearly seven years ago, Northwestern geophysicist Seth Stein had concluded there was very little strain accumulating on the New Madrid zone and therefore only a minute risk of huge quakes occurring.
The new findings follow an unusual spate of widely felt quakes across the New Madrid region during the past four months, including one of magnitude 3.9 on Monday near Clinton, Ky.
In late 1811 and early 1812, the New Madrid zone was the scene of some of the most powerful quakes known to have struck the continental United States. The temblors are said to have formed Reelfoot Lake, spewed towering geysers of sand and water into the air, caused the Mississippi River to flow backward and rung church bells on the East Coast.
Researchers have estimated that during any 50-year period, there's a 7 percent to 10 percent chance of an 1811-12 type quake occurring. The risks of a smaller magnitude-6 temblor have been put at 25-40 percent for a 50-year period.