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A new probability report was released in 2003 by Working Group '02. This report concludes that the Bay Area faces a 62% probability of an M6.7 or larger earthquake over the next 30 years (2003-2032). This study updates and refines previous studies published in 1988, 1990, and 1999.

In 1988, the Working Group on California Earthquake Probabilities published a report which concluded that there was a 50% probability for an earthquake of magnitude 7 or larger within the San Francisco Bay Area in 30 years or less. Following the Loma Prieta earthquake in 1989, this panel convened to reassess earthquake probabilities in the Bay Area. The 1990 report evaluated four fault segments (San Andreas, Hayward, Rodgers Creek) and concluded that the total 30-year probability of one or more large earthquakes in the San Francisco Bay Area was 67%.

On the 10th anniversary of Loma Prieta, Working Group '99 revisited the probabilities. The 1999 report incorporated new results about Bay Area faults from paleoseismology and geodetic studies, new insights about the interaction of faults, and new interpretations of historical seismicity. The Working Group expanded the 1990 study to include the San Gregorio, the Calaveras, the Concord-Green Valley, the Greenville and the Mt. Diablo thrust faults. The study was also based on a different methodology from the 1988 and 1990 reports. The Working Group considered a much more complex set of possible rupture models and computed the probabilities using three different procedures. As a result, the Working Group '99 assessed the odds of a magnitude 6.7 or higher over 30 years (2000-2030) - as 70% in the San Francisco Bay Area, with an uncertainty of 10%.

Since 1999, Working Group scientists have been working to improve the probability models. As in 1999, the latest study includes recent new results from paleoseismology, historical seismicity, geodesy, and fault interactions. In particular, the Working Group has developed new models for handling fault creep - aseismic slip - which occurs along portions of several Bay Area faults as well as for analyzing the effects of the 1906 "stress shadow". In the current study, scientists have made a greater effort to quantify and model the uncertainties in these studies. They have also developed a detailed computer model which can easily to updated to reflect new results.

References

• Working Group on California Earthquake Probabilities, Summary of Earthquake Probabilities in the San Francisco Bay Region: 2003 to 2032, 2003.

• Working Group on California Earthquake Probabilities, Earthquake Probabilities in the San Francisco Bay Region: 2000 to 2030 - A Summary of Findings, USGS Open-File Report 99-517, 1999. Online version

• Working Group on California Earthquake Probabilities, Probabilities of Large Earthquakes in the San Francisco Bay Region, California, USGS Circular 1053, 1990. Online information

• Working Group on California Earthquake Probabilities, Probabilities of Large Earthquakes Occurring in California on the San Andreas Fault, USGS Open-File Report 88-398, 1988.

• Working Group on Northern California Earthquake Potential, Database of Potential Sources for Earthquakes Larger than Magnitude 6 in Northern California, USGS Open File Report 96-705, 1996. Online version

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Last modified: Wed Sep 17 09:20:44 PDT 2008