ON SHAKY GROUND

The earthquake hazard here may be greater than you think. And planning for it is less than you'd expect.

There are mysteries in southeast Missouri that have drawn state geologist David Hoffman here time and again. What makes this place different, sets it apart from the rest of the planet, is an upheaval that occurred eons ago, when the earth was younger and more rambunctious. The theory is that hundreds of millions of years in the past, the North American continent tried to rip itself apart here, creating a rift in the earth's crust. The resulting depression allowed the Gulf of Mexico to extend hundreds of miles northward into what is now southern Illinois. As the sea receded, the Mississippi and Ohio rivers formed.

Driving south on Interstate 55 past Cape Girardeau, Hoffman tells how the course of the Mississippi subsequently changed, for unknown reasons. "Back there where we just passed the airport, (the Mississippi) used to go to the west," says Hoffman. "Now it cuts through here just south of Cape Girardeau at a place called Thebes Gap and joins the Ohio down at Cairo, Ill." He has by now entered the Benton Hills, steering his Ford Taurus across a five-mile-wide forested incline reminiscent of the Ozark Plateau. Enigmatic in their own right, the gentle slopes seem to have become somehow separated from the pack, leaving them marooned as a remote series of elevations in the otherwise flat expanse of alluvial plain.

The Benton Hills, Hoffman explains, are an isolated segment of Crowley's Ridge, which runs down to Helena, Ark., a distance of about 200 miles. Why the river abandoned its original path more than 11,000 years ago and carved its way through 100 feet of bedrock so it could flow to the east of Crowley's Ridge is the subject of scientific speculation, as are the origins of the ridge itself.

State geologist David Hoffman in the Benton Hills, where he has investigated seismic activity.
Jennifer Silverberg
State geologist David Hoffman in the Benton Hills, where he has investigated seismic activity.

"It's a very strange formation," Hoffman says. "The traditional explanation is that it's just an erosion element that the river left there. I find that hard to accept. It may have been formed by earthquake-related activity."

For nearly half of his 20-year stint with the Missouri Department of Natural Resources (DNR), Hoffman has been an earthquake specialist in the Division of Geology and Land Survey. On this day, he is carrying the tools of his trade in the trunk of his car: geological charts, work boots and a hoe. With his graying flattop and aviator glasses, Hoffman looks more like a high-school teacher than a haughty scientist, and when he talks about the Benton Hills, he sounds more like an awestruck student.

Hoffman's hypothesis that earthquakes helped form these hills is supported by his own field research. Beginning in 1993, he supervised the excavation of more than a dozen 15-foot-deep trenches in the uplands near Commerce, Mo. The digs uncovered folds in the soil strata showing that seismic activity occurred here in the past. This evidence leads him to believe that the faults in the area remain active.

Hoffman's opinion is bolstered by other seismic authorities, who acknowledge that much remains to be learned about the area's subterranean history. Despite these affirmations, the minimal amount of research funding for the Benton Hills project has been curtailed.

Hoffman's pursuit raises the probability of earthquake activity at an obscure location. But the one recognized cataclysmic source in the state is the New Madrid seismic zone, a 120-mile-long system of faults that traverses the Missouri Bootheel and cuts across five adjacent state lines. And, indications are, that fault system may be more restless than previously thought.

On the basis of its latest mapping efforts, the United States Geological Survey (USGS) issued projections that increase the estimated earthquake hazard for parts of the St. Louis area by 30-40 percent. That dire caveat has been followed by an insurance-industry request to the state to raise earthquake-coverage premiums by as much as 266 percent. The proposed rate hike is based on the industry's own analysis of the latest scientific data -- which point to a significantly increased probability of a damaging earthquake's striking the region.

In the face of this clear evidence, government spending on seismic research and emergency preparedness has nonetheless remained stagnant and, in some instances, has been drastically slashed. The one exception to the rule came last week, when the Missouri Department of Transportation asked for a $32 million increase in the cost of seismically retrofitting the elevated sections of Highway 40 (Interstate 64) downtown, raising the project's cost to more than $65 million. By contrast, the total federal allocation for all types of disaster preparedness in the state of Missouri, the city of St. Louis and St. Louis County amounts to about $300,000 this year. As for the official recommendations of the Missouri Seismic Safety Commission, they are buried under an avalanche of indifference.

Meanwhile, development of the vulnerable floodplains -- Chesterfield being a prime example -- continues unabated.

Geology students call it "the Beach." Located in Pemiscot County, Mo., near the town of Deering, the 136-acre strand is purported to be the largest sand boil in the world, a vestige of the New Madrid earthquakes of 1811-1812. Aerial photographs of the Missouri Bootheel show similar geologic formations throughout the fault zone. Underground pressure associated with the seismic disturbance created tiny volcanoes, which belched up a mixture of sand, mud and water.

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