Experts Quibble Whether New Madrid Fault Poses Threat

December 16, 2005

The earth under the New Madrid Seismic Zone either isn’t shifting or is barely shifting at all, say independent university analyses of global positioning system stations stuck in the ground and monitored for a decade. The St. Louis Post-Dispatch’s recent story said the cataclysmic shifts of past earthquakes remain unexplained, the mechanism for future earthquakes still a mystery.

The results contradict a study by the University of Memphis. The university study made headlines in June when it said that two GPS stations on opposite sides of the Reelfoot fault had moved closer to each other at a rate that rivaled faults in California. The compression could coil up the faults for future earthquakes.

Eric Calais of Purdue University, said that the University of Memphis results had to be a statistical anomaly, probably an instrumental error and not anywhere close to the motions of the San Andreas fault, which slips more than 10 times as fast as the two Reelfoot fault GPS stations seem to be creeping toward each other.

University of Memphis author Michael Ellis, said his group was trying to show that the motions are consistent with the level of seismic hazard that geologists have already established for New Madrid.

In California, earthquakes are caused by the more predictable process of plate tectonics. The Pacific Ocean plate grinds against the North American plate along the San Andreas fault, which ruptures regularly in earthquakes. New Madrid sits in the middle of the quiet, rigid North American plate.

Ellis’ paper was the first to suggest that the plate is stretching and straining near New Madrid, Mo. The groups agree that the tiny motions they’re arguing about – as much as an eighth of an inch per year – would need to be almost twice as big to build up the strain needed to unleash the huge magnitude 7 or 8 earthquakes that occurred in 1811 on the New Madrid Fault and at regular 500-year intervals for the past few thousand years.

Purdue’s Calais questioned the findings, suggesting that either the past earthquakes weren’t as big as geologists thought, the earthquake process has stopped or it’s in a quiet period that could suddenly start up again.

Officials are trying to decide how important the earthquake hazard is in light of conflicting studies. Last week, Missouri Gov. Matt Blunt met with his Cabinet officials to review earthquake response plans. Less than 41 percent of Missourians have earthquake insurance according to the Governor.

In Missouri, county by county, the percentage of homeowners with earthquake insurance varies wildly, and is not necessarily connected to how close the homeowner is to New Madrid. In some counties near New Madrid, fewer than 50 percent of homeowners have it. Yet in places such as Chesterfield, located far away from the fault, 84 percent of homeowners have insurance.

Some insurance companies have stopped writing business in the Midwest, citing the great uncertainty of setting prices for unpredictable events. Last year, Safeco Insurance stopped offering earthquake policies in Tennessee and stopped offering the coverage in Missouri and Illinois this year.

Scientists differ on whether earthquake insurance makes sense.

“There’s more chance that a tornado will destroy my house than an earthquake,”Ellis said.

But Calais, who is saying that the hazard might not be as great as previously thought, still said he would nonetheless purchase earthquake insurance if he lived in southeastern Missouri.

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