PASADENA, CA- Southern California, which one year ago suffered a catastrophic series of earthquakes and aftershocks, is likely to experience more of the same and possibly even worse, according to several new studies.

Prior to the Northridge earthquake of 1994 most seismologists concerned themselves primarily with the threat posed by the notorious San Andreas fault which passes some 40 km north of Los Angeles. However, last year's quake shifted researchers attention to smaller, lesser known faults passing directly underneath the highly populated Los Angeles basin. Nearly a hundred active faults have been identified in the L.A. area, of which six are of particular concern. It is new findings about these faults that has geologists sounding the alarm about future quakes.

Researchers at CalTech believe that the L.A. basin has been in a lull between large quakes. An analyses of geologic slip rates and relations between the magnitude of previous quakes, seismic slippage and rupture suggests a series of quakes of similar size to the Northridge quake (i.e. 6.7 on the Richter scale), or one very large quake (Richter 8 or above), or possibly even a combination of the two are overdue. The projections are based on the hypothesis that in a 200 year period a Northridge level quake would be expected every eleven years or so, and larger quakes above 7.2 would be felt every 140 years or so.

"Far too few moderate earthquakes have occurred within the Los Angeles metropolitan region during the 200-year-long historic period to account for observed strain accumulation, indicating that the historic era represents either a lull between clusters of moderate earthquakes or part of a centuries long interseismic period between much larger events," notes Dr. James Dolan, Seismologic Laboratory, California Institute of Technology, Pasadena,CA, in Science.

The data can be interpreted to suggest either that several Richter 6 earthquakes are due, or one really large quake may be coming. Of the two projections, Dr. Dolan believes the latter, the one predicting an earthquake above Richter 7.2 (the level of the recent Kobe quake) is the more plausible. He bases his conclusion on the existing data about strain accumulation on known faults. Such an earthquake would be considerably more destructive than last year's California temblor. This, combined with scenes from Kobe, suggests an urgent need for disaster preparedness on the part of civil authorities in Southern California.

In related study, Dr. S.E. Hough of the U.S. Geologic Survey developed a predictive model indicating a fractal distribution of earthquake rupture areas in the L.A. Basin. His study suggests that one large earthquake (Richter 7.4 to 7.5) would occur every 245 to 325 years and/or that moderate earthquakes (Richter 6.7) would occur every 40 to 52 years. An alternate theory based on research by the National Science Foundation holds that L.A. faults may have been slipping gradually over the centuries, so reducing chance of 'the Big One'.

According to the National Earthquake Information Center, earthquakes ranging from 6.0 to 6.9 on the Richter scale occur 150 times a year somewhere on the planet. One to two dozen earthquakes in the 7.0 to 7.9 range occur each year, along with one earthquake in the 8 to 8.9 range.

The studies by Drs. Dolan and Hough are reported in Science, 1/13/95, v.267.

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