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Three-Year Quake Forecast Method Devised by U.S. And Soviet Scientists

October 20, 1988

LOS ANGELES (AP) _ A newly devised mathematical formula will let researchers predict if a region is likely to be rocked by a strong earthquake within three years, Soviet and U.S. scientists reported today.

The formula is based on changes in seismic activity before powerful quakes in California and Nevada. The scientists used the formula in hindsight to successfully ″predict″ 16 of 20 powerful quakes in the Soviet Union, Central Asia, Romania, Belgium and the U.S. Northeast.

The technique hasn’t been used to predict future quakes and won’t allow scientists to predict that a quake will occur in a precise time and place.

But it will allow them to make ″intermediate-term″ predictions that a strong earthquake is likely within three years somewhere in a broad region, said Leon Knopoff, a co-author of the study published in the British journal Nature.

″This is a step toward improving the prediction of large earthquakes in time and space,″ Knopoff, a geophysics professor at the University of California, Los Angeles, said Wednesday.

Scientists now are pretty much limited to making long-range forecasts. For example, the U.S. Geological Survey predicted in July that within 30 years, a major or great quake measuring 7 to 8 or more on the Richter scale is 60 percent likely on the San Andreas Fault in Southern California and 50 percent likely on the the Hayward or San Andreas faults in the San Francisco Bay area.

Knopoff conducted the study with Vladimir Keilis-Borok and I.M. Rotwain, of the Soviet Academy of Sciences’ Institute of the Physics of the Earth, and California Institute of Technology geophysicist-geologist Clarence Allen, the former chairman of the National Earthquake Prediction Evaluation Council.

If the new method is proven valid, it will help government officials and private citizens because ″even a vague description of the area that could be at risk and a refinement in the time scale is valuable,″ said Mike Guerin, spokesman for California’s Office of Emergency Services.

Knowing a big quake is likely within three years in a certain region ″sets a deadline in which they need to accomplish certain preparations and plans,″ he added.

But such a vague prediction would make it ″very difficult to do anything more than is already being done in California in terms of preparedness,″ countered Randall Updike, executive secretary of the quake prediction council and deputy chief of the Geological Survey’s Office of Earthquakes, Volcanoes and Engineering in Reston, Va.

The council reviewed the method during a meeting in June. Members decided that while it was a step forward and should be studied further, it would be premature to use it immediately to predict three-year periods in which large quakes were likely, said James Davis, a council member and chairman of the California Earthquake Prediction Evaluation Council.

The Soviet-American team devised a mathematical formula to identify ″times of increased probability″ - roughly three-year periods in which certain patterns of seismic activity are likely to culminate in a strong earthquake.

They developed the formula by studying seismic patterns that preceded 14 earthquakes of 6.4 magnitude or more in California and Nevada between 1938 and 1984.

The scientists then tested the formula by applying it to 20 quakes in five other regions of the world since 1963. The formula found that 16 of those quakes were preceded by ″times of increased probability″ for large temblors.

The patterns incorporated into the formula included above- or below-normal numbers of smaller jolts, the rate at which such quakes increased or decreased, the size of those smaller quakes, the number of aftershocks following such quakes and whether such quakes in one area were followed immediately by quakes in a distant area.

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