FREQUENCIES OF QUAKES POINT TO PREPAREDNESS

Despite their well-intended efforts, scientists as yet have been unable to accurately predict when and where major earthquakes will occur. This was evidenced by a recent Geophysical Union meeting in Baltimore, at which researchers reported on frequencies and probabilities of quakes occurring along the New Madrid Fault of Southeast Missouri and faults on both U.S. coasts.

Unlike the late Iben Browing, whose prediction that a major earthquake would occur along the New Madrid Fault in early December 1991, did not come true, scientists at the meeting made no such projections. Instead, they dealt with the history of movement along major U.S. faults, and came up with likelihoods of how often major shakers can be expected along them.

Eugene Schweig of the U.S. Geologic Survey in Memphis found that a major earthquake has occurred along the New Madrid Fault about every 1,000 years and that the fault, which runs generally from near Cairo, Ill., to just west of Memphis, has produced a series of large earthquakes over the past 4,000 years. Until now, those facts were unclear, said Schweig.

Another study detected movement of land along the fault of about one-third inch a year. Arch Johnston of Memphis State University said such movement is slower than that recorded along some California faults, but it is rapid enough to produce a great quake of 8 or more on the Richter scale every 1,000 years. Based upon that, he said, quakes measuring 6 and 7 on the scale can be produced more often, every 70 to 90 years.

A quake estimated at a powerful 8 on the Richter scale occurred along the New Madrid Fault in 18ll, and it is considered one of the largest quakes verified in North America. That was only 182 years ago, but, without a major quake having occurred along the fault since, long enough ago to be concerned that another major one could occur at any time.

Although Browning's prediction proved wrong, it served to make people more aware of the lively seismic zone on which we live, and motivated many people to prepare for a major quake, which scientists say is inevitable. Browning's prediction put preparedness at the forefront, and probabilities of quakes that came out of the Baltimore meeting point even more strongly to the need to be prepared.