Liquefaction a danger in Foster City if quake hits

The Foster City Council and other city officials met with several representatives from the USGS and CGS Monday to discuss the potential danger liquefaction poses to the city in the event of another major Bay Area temblor.

"Because of its location along the San Andreas Fault, San Mateo County is going to be the hardest hit,” said Tom Brocher, Northern California co-coordinator of earthquake hazards investigations for the USGS.

In light of a major earthquake, there would be 100 to 300 deaths and between 50,000 to 100,000 people without shelter in San Mateo County. The damage caused by the earthquake would cost upward of $20 billion, Brocher said.

The majority of Foster City sits atop landfill placed over Bay mud, making it susceptible to liquefaction, Brocher said.

Liquefaction occurs when "the ground is shaking so hard that the water and sand mix together and make a sandy liquid,” Brocher said.

During the magnitude 6.9 Loma Prieta earthquake in 1989, there were two known occurrences of liquefaction in Foster City.

Brocher said that, while 50 percent of all occurrences of liquefaction in the Bay Area have occurred in landfill over bay mud areas, Foster City can do things to diminish the risk of liquefaction.

"We’re not an area that’s going to sink into the sea like the Marina District could,” Foster City councilman Rick Wykoff said. "A lot of risks in Foster City have been mitigated.”

Brocher recommended city officials continue to emphasize personal preparedness to residents, strengthen emergency response units and enforce building codes.

Both Brocher and CGS geologist Keith Knudson said that, though Foster City has a high liquefaction hazard, it doesn’t mean the city is at a high risk for liquefaction.<