Wake Up, East And Midwest

By J. Madeleine Nash/Chicago

The sleepy cotton fields around New Madrid, Mo. (pop. 3,400), convey no sense of seismic menace. Yet scientists say the area is potentially one of the most dangerous earthquake zones in the world. Early in the past century an unseen fault, obscured by tons of sediment, unleashed a fearsome trio of tremors -- each as powerful, some say, as the earthquake that virtually destroyed San Francisco in 1906. The eyewitness accounts read like the tall tales of Baron Munchhausen. The ground rippled with waves as though it were an ocean. The Mississippi River raged with waterfalls and rapids. Fountains of sand erupted in gritty geysers. Shock waves, pulsing outward for hundreds of miles, wrecked boats in the Charleston, S.C., harbor, cracked masonry in Cincinnati, and caused church bells to peal and buildings to shake as far away as New York City and Boston.

Today the fault at New Madrid remains active, regularly generating small, unnoticeable earthquakes and, from time to time, palpable jolts. Such quakes usually do not stir more than passing interest. But last week residents of southeastern Missouri snapped to attention when a moderate earthquake, rated 4.6 on the Richter scale, rattled windows, spilled coffee and broke ceramic figurines. Reason: the earthquake followed a much publicized prediction that the fault is likely to produce a major shock come Dec. 3, and many people feared last week's tremor could be a precursor. The prediction, which has made its way into several newspapers, was the work of Iben Browning, a New Mexico climate consultant, who based his forecast on an analysis of the gravitational pull of the sun and moon. Many seismologists, worried that public concern could degenerate into panic, have denounced it as unscientific hocus-pocus. At the same time, they agree that the New Madrid fault, which stretches over 225 km (140 miles), poses serious long-term risks, especially to the nearby cities of Memphis and St. Louis.

California has adopted strict building codes to limit earthquake damage, but no other area is so well prepared. If hit by large shocks, the unreinforced highways and bridges of the Midwest and East could collapse. Solid houses of brick and stone might as well be made of playing cards. "The infrastructure in this part of the country has never been tested by a major quake," says Arch Johnston of the Center for Earthquake Research and Information at Memphis State University. Fortunately, when the earthquakes of 1811 and 1812 occurred, the New Madrid region was too sparsely populated to suffer significant damage or injuries. A modern-day replay, however, would make the quake that shook San Francisco last year seem tame. That tremor measured 7.1 on the Richter scale. In contrast, the big quakes that rumbled forth from New Madrid may have exceeded 8.0, or about 10 times that strong.

Earthquakes frequently occur along the boundaries of continental plates, huge sections of the earth's crust that "float" on a mass of superheated rock. California's San Andreas Fault, for instance, marks the dividing line between the North American and Pacific plates, which are slowly slipping past each other. But the New Madrid fault lies in the middle of the North American plate, seemingly far from harm's way. Why do earthquakes occur in such an out- of-the-way spot? By analyzing seismic data, scientists have concluded that the New Madrid fault is a failed rift, or break, in the North American plate. Had it progressed further, the embryonic gap might have created a body of water like the Red Sea, which is slowly widening into an ocean. But hundreds of millions of years ago, the Midwestern rift stopped growing. The New Madrid fault today simply marks a weak spot in the thick midcontinental crust, which periodically ruptures under the pressure exerted by the migrating North American plate. It could take 500 to 1,000 years for enough force to accumulate to trigger a really big quake.

The area around the New Madrid fault is one of several known earthquake zones east of the Rockies. In 1755 Boston experienced a severe jolt, as did Charleston in 1886. Sooner or later a major quake is going to hit these areas again. And unlike the Western U.S., where hot rock close to the surface provides a squishy, shock-absorbing cushion, the middle of the continental plate is cold, hard and thick. Like their precursors in the past century, the next large quakes to strike in the Midwest or East are likely to resonate far and wide, like giant hammers hitting a huge block of steel.