The annual Great Shake Out international earthquake drill, set to take place on Thursday, will take on heightened importance in the San Francisco Bay area, which this week learned that four major area fault lines are primed, ready and overdue to produce destructive seismic events, according to a new earthquake risk study.
While the San Andreas Fault, California’s best-known seismic feature, is still a major concern, especially in Southern California, the next big quake in the Bay Area is likely to originate on faults to the north and east of San Francisco, including the Hayward Fault, which cuts through densely populated East Bay cities like Oakland and Berkeley.
Perhaps more worrisome is the little-known Green Valley Fault in Solano County, which seismologists think could produce a 7.1 magnitude quake. A large quake there could damage water infrastructure and disrupt the delivery of drinking water to cities across the region and water for irrigation in the agriculturally important Central Valley, KABC-TV reported on Monday.
Napa County, which was hit by a 6.0 magnitude earthquake on Aug. 24, is also at risk from a major seismic event on the Green Valley Fault, but as the Napa Valley Register reports, county emergency management officials have more concerns with the Rodgers Creek Fault, which the U.S. Geological Survey estimates “has a 15.2 percent probability over the next 30 years of having an earthquake magnitude 7 or greater.”
As the 6.9 magnitude Loma Prieta earthquake in 1989 demonstrated, a far-off epicenter doesn’t necessarily assure safety. The extent of localized damage can depend on a variety factors, especially if buildings and infrastructure are built on soft soils susceptible to liquefaction during shaking. That deadly quake, centered near Santa Cruz, caused buildings to collapse in San Francisco and a double-decker freeway viaduct in Oakland to pancake.
Watch CalOES’s promotional video for Thursday’s event.