No Quake Deficit In
Southern California
AP Science Writer
LOS ANGELES ( -- Scientists who warned three years ago that Southern California was having too few earthquakes for all the stress on its faults -- and that one good magnitude-8 quake or many more good-size shakers could fill the gap -- now say they were wrong and there's no "quake deficit."
What's changed their thinking?
Researchers went back to the historical record of quakes since 1850. It was used for the 1995 study from the Working Group on California Earthquake Probabilities, produced from models that suggested there should be nearly twice as many moderate to large quakes as had been recorded.
This time, the researchers analyzed only those quakes observed since 1903. They assumed records would likely be more complete after the turn of the century because Southern California had relatively few inhabitants before then.
With the smaller, more focused study, they calculated that the rate of quakes larger than magnitude-6 was much closer to what the models predicted, Thomas C. Hanks, a geophysicist with the U.S. Geological Survey in Menlo Park, said in an interview Tuesday.
Hanks was scheduled to present the findings Wednesday to the Seismological Society of America annual meeting in Boulder, Colo. The paper has been accepted for publication in the summer issue of the Bulletin of the Seismological Society of America.
Ross Stein, a USGS geophysicist and study co-author, said the new findings, which pinpoint flaws in a document used for state earthquake policy, hold important implications for earthquake insurance, which is based in part on the size and frequency of quakes.
Stein said the revised quake catalogue compiled by Hanks should be on the Internet within days for others to review.
Edward Field of the University of Southern California and David Jackson of the University of California, Los Angeles -- a principal author of the 1995 report -- were scheduled Wednesday to present a new mathematical model that also finds no quake deficit.
The case for one, whopping magnitude-8 or larger event to clear out the deficit was proposed by Jackson, who said Tuesday that he generally agrees with Hanks' and Stein's findings and acknowledges "the fact we overpredicted" in the 1995 report.

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