ON SHAKY GROUND

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

The zone -- which zigzags northeasterly from Marked Tree, Ark., to Cairo, Ill. -- is considered the second most active earthquake region in the United States. It is named after the small town of New Madrid, Mo., which bore the brunt of the earthquakes that beset the region early in the last century. Scientists reckon the New Madrid quakes to be among the largest seismic bursts in the history of the United States.

The first of a series of earthquakes struck the region in the early-morning hours of Dec. 16, 1811. Major shocks also occurred on Jan. 23 and Feb 7, 1812. In each instance, the earth's movement was felt as far away as the East Coast. On the basis of eyewitness accounts from the time, scientists now estimate that the quakes reached 7.5 or more on the Richter scale. Historical accounts tell how the quake created at least two waterfalls in the Mississippi River and caused the current to temporarily reverse its flow. The uplifting and subsidence of ground in nearby western Tennessee resulted in the creation of Reelfoot Lake, which today is 16 miles long and four miles wide.

Though the seismic event irrevocably changed the face of nature, destruction of human life and habitat was minimal simply because few people then lived in the region. St. Louis was a small pioneer village in 1811-12, and Memphis didn't even exist. If a temblor of the same magnitude occurred today, the effects would be far more devastating.

The United States Geological Survey 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 United States Geological Survey 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.
Souvenir T-shirts from the New Madrid Museum
Jennifer Silverberg
Souvenir T-shirts from the New Madrid Museum

It has been more than a century since St. Louisans experienced quivering originating from the New Madrid area. That quake, which was centered near Charleston, Mo., occurred at about 5:10 a.m. on Oct. 31, 1895. The shaking lasted almost a minute. About 150 miles from the epicenter, ground movement did structural damage to Holy Ghost German Lutheran Church at Eighth and Walnut streets in downtown St. Louis.

The long lapse since the last major earthquake in the New Madrid area has led many scientists to speculate that a moderate-to-severe earthquake is overdue. Other experts downplay the possibility of a large-scale natural disaster.

The late Iben Browning, a business consultant and climatologist, had predicted a 50-50 chance of an earthquake along the New Madrid Fault between Dec. 1 and 5, 1990. Browning based his prognostication on the gravitational pull of the moon. Most scientists didn't take the prediction seriously, but intense media coverage of the forecast fueled an overreaction. Concerned citizens flooded government agencies with calls. Fear led many people to stockpile food and water. Meetings were held and emergency drills initiated. Retailers capitalized on the expected disaster by advertising specials on everything from guns to water-purification systems. As doomsday approached, schools and businesses closed.

Despite the absurdity of Browning's prediction, it temporarily galvanized popular awareness of the hazard and spurred public officials to address a long-ignored issue.

Since then, the scientific debate has continued, reaching a new crescendo earlier this year, when a group of scientists from Northwestern and other universities published research based on a seven-year study. The project involved monitoring ground movement through satellite observations. Using a network of portable Global Positioning System (GPS) receivers, the scientists sought to ascertain the amount of strain on the fault zone. Their findings led them to conclude that the earthquake hazard in the New Madrid seismic zone has been overestimated.

The study, published in the journal Science in April, prompted a flood of letters from experts in the field who disagreed with the conclusions, but the periodical refused to publish them. One of the harshest critics is Arch Johnston, who directs the Center for Earthquake Research and Information at the University of Memphis. "The conclusions that they drew were very premature because of the uncertainties," Johnston says. "The uncertainties are big enough that they allow zero strain or they allow strain comparable to current estimates of the hazard -- either one." In other words, the margin of error, as defined by the researchers, was larger than the detected ground motion. Within the next few years, Johnston expects to have result from his own research, which will include data from a dozen permanent GPS monitoring stations.

Another article in the Nov. 5 issue of Science contradicted the Northwestern study. In this study, scientists dug trenches near Reelfoot Lake to determine the amount of ground movement. Folds in the soil strata indicated a shift of 5 or 6 mm a year, which equates to about a 3-foot change in position since the great earthquakes of 1811-12.

Johnston says the gradual movement of the fault is analogous to the stretching of a rubber band: Eventually something must give. "The whole rubber band is stressed," says Johnston, "but it snaps only in one place." Once the earth's elasticity stretches beyond its breaking point, its reverberations will cause catastrophic consequences. Another major New Madrid quake might come tomorrow, or it could happen decades from now.

Nobody knows.

But MoDOT isn't taking any chances. The agency, which asked for $32 million to retrofit Highway 40 downtown to withstand an earthquake, says it based its call on the work of Johnston and his cohorts at the University of Memphis. On Tuesday, the agency's request was approved by the East West Gateway Coordinating Council, which oversees all federal highway spending for the St. Louis area.

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