The Bay Area is in the heart of Earthquake Country. The Bay Area is crossed by many active faults. This map figure shows that major active faults run through or adjacent to all nine Bay Area counties. While research by the U.S. Geological Survey (USGS) has provided more reliable probability information for future Bay Area earthquakes than for any other area of the country (63% probability of a magnitude 6.7 or larger earthquake), it has a wide error range – plus or minus 22%!
Smaller earthquakes are more likely to occur and can still produce significant damage over localized areas.
Probability of the rupture of individual faults has also been prepared by USGS, as shown in map.