Mississippi's Triple Temblors

Second only to California, the New Madrid seismic zone, which extends for 100 miles along the Mississippi river from Missouri to Arkansas, is the most earthquake-prone region in the U.S. (see seismic map right). In 1811 three powerful quakes in a row--measuring approximately 7.5 to 8.3 on the Richter scale--ripped along the fault there, ringing church bells as far away as Boston. Ever since, the question has lingered: will it soon happen again? A report in the April 1999 issue of Science said probably not, but a paper in today's issue takes a different view.

"If you live in the New Madrid area, you may still have an earthquake problem, says Paul Segall at Stanford University. He and co-author Shelley Kenner base much of their concern on a new model, and doubts about the earlier study, which tracked ground movement in the New Madrid area using Global Positioning System (GPS) satellites. The author of that study, geologist Seth Stein of Northwestern University, suggested that the amount of movement they measured was insufficient to create much stress along the fault for thousands of years. But Kenner and Segall don't think it's that clear.

They point out that, although Stein's GPS data is accurate, his conclusion is based on earthquake-prediction models for the San Andreas fault, a so-called transform fault. The New Madrid crack is an entirely different kind, called an intraplate fault. "As scientists, we don't understand what's happening in the intraplate setting all that well," Kenner says. "What we tried to do in our current Science study is to come up with a model that's a better approximation of the New Madrid seismic zone." That model predicts that another triple temblor could hit the area by the middle of century, if not sooner.