Experts split over quake risk

http://www.stltoday.com/stltoday/news/stories.nsf/stlouiscitycounty/story/F0A911
78EC79FBC2862570D8001BAEA3?OpenDocument

By Eric Hand
ST. LOUIS POST-DISPATCH
12/14/2005

The earth under the New Madrid Seismic Zone either isn't shifting or is barely
shifting at all, say three independent university analyses of global positioning
system stations stuck in the ground and monitored for a decade.

So the cataclysmic shifts of past earthquakes remain unexplained, the mechanism
for future earthquakes still a mystery.

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

One of the detractors of that study, geophysicist Eric Calais of Purdue
University, said their results were certainly a statistical anomaly, probably an
instrumental error, and, regardless, 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.

"It's not fair in a scientific paper to scare people with things like that," he
said.

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

A debate among the groups was published today in the journal Nature.

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. But the New
Madrid zone sits in the middle of the quiet, rigid North American plate, about
150 miles from St. Louis.

Ellis' paper was the first to suggest that the plate is stretching and straining
near the New Madrid zone. Yet all four 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 and at regular 500-year
intervals for the past few thousand years.

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, Calais said.

Amid the uncertainty, policymakers are trying to decide how important the
earthquake hazard is. Last week, Missouri Gov. Matt Blunt met with his cabinet
officials to work on earthquake response plans. He said he was concerned that
fewer than 41 percent of Missourians have earthquake insurance.

County by county, the percentage of homeowners with earthquake insurance varies
wildly, and not necessarily according to how close one is to the New Madrid
seismic zone. In some counties near New Madrid, fewer than 50 percent of
homeowners have it. Yet in places such as Chesterfield, which is far away from
New Madrid and would have much lower shaking, 84 percent have insurance.

Meanwhile, insurance companies are pulling out of the Midwest, citing the great
uncertainty of setting prices for unpredictable events. Last year, Safeco
Insurance stopped offering earthquake policies in Tennessee. This year, they
stopped in Missouri and Illinois.

Even the scientists differ on whether earthquake insurance makes sense.

Ellis, who is saying that the hazard could be as high as geologists think, did
not have earthquake insurance when he lived in Memphis. He was frustrated by its
high cost and high deductibles, which can now be as much as 10 or 15 percent.

"There's more chance that a tornado will destroy my house than an earthquake,"
he said.

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

"I guess I like to live on the safe side," he said.



Alan

http://www.veloceraptor.free-online.co.uk/enigma.html

http://veloceraptor.blogspot.com/
.

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