2008 Bay Area Earthquake Probabilities

In April 2008, scientists and engineers released a new earthquake forecast for the State of California called the Uniform California Earthquake Rupture Forecast (UCERF). Compiled by USGS, Southern California Earthquake Center (SCEC), and the California Geological Survey (CGS), with support from the California Earthquake Authority, it updates the earthquake forecast made for the greater San Francisco Bay Area by the 2002 Working Group for California Earthquake Probabilities.

The accompanying figure shows the updated probabilities for earthquakes of magnitude 6.7 or greater in the next 30 years. The overall probability of a magnitude 6.7 or greater earthquake in the Greater Bay Area is 63%, about 2 out of 3, which is very close to the probability of 62% obtained by the 2002 Working Group.

The earthquake probability is highest for the Hayward-Rodgers Creek Fault system, 31%, or nearly 1 out of 3. The last damaging earthquake on the Hayward Fault was in 1868. The 140 years since 1868 is same length of time as the average interval between the past 5 large earthquakes on the southern Hayward Fault.

The probability of a large earthquake on the San Andreas Fault in the next 30 years is about 21%, or about 1 out of 5. This fault was responsible for the magnitude 7.8 1906 San Francisco earthquake and the magnitude 6.9 1989 Loma Prieta earthquake.

The Calaveras Fault in the East Bay, and the San Gregorio Fault along the San Francisco Peninsula coast, have probabilities of 7% and 6%, respectively, of producing a magnitude 6.7 or greater earthquake in the next 30 years.

In the East Bay, near the Central Valley, the Greenville Fault, the Mt. Diablo Thrust, and the Concord-Green Valley Fault were assigned probabilities of 3% or less of producing a magnitude 6.7 or greater earthquake in the next 30 years.

Learn more about how these studies were conducted and the uncertainties associated with generation of earthquake probabilities: