The United States Geological Survey (USGS) recently issued two new maps that outline the probability of liquefaction by region in the Bay Area. Although they are intended to be used by the public to assess risk from earthquakes, the information contained in these maps may be misleading for Foster City residents.

On these maps, regions that are built on landfill are automatically considered to be at great risk of liquefaction. However, when the maps were created, no distinction was made between areas with engineered landfill and areas with fill that did not undergo the same rigorous engineering. Foster City’s landfill was carefully designed and constructed to mitigate the risk of liquefaction.

Besides its construction on well-engineered landfill, Foster City has recognized the potential impact of earthquakes and, thus, has implemented a number of mitigation measures that reduce the impact of earthquake activity on the buildings and infrastructure in Foster City. These mitigation measures are listed in a Local Hazard Mitigation Plan and have been reviewed by the Governor’s Office of Emergency Services and approved by the Federal Emergency Management Administration (FEMA). These mitigation measures include:

• When constructing buildings within the city, a soils analysis report is required to determine the appropriate foundation for the structure.
• Any building (4) stories or above, or as dictated by the soil analysis report, are required to be built on a pile-supported foundation.
• All critical structures within the city have had a soil analysis report completed and the appropriate foundation was constructed.
• The most current building codes for earthquake safety are used and rigorously enforced.
• Underground utilities where they are connected to above ground utilities or structures are fitted with flexible connections to withstand shaking and settling.
• The levee is inspected regularly and was strengthened within the last 10 years.

In the 1989 Loma Prieta earthquake, Foster City suffered very little damage. Foster City’s property losses were among the lowest in the region. The careful construction of the City’s buildings and infrastructure is a key component in mitigation of earthquake impacts.

As residents of the Bay Area, Foster City residents know that an earthquake may occur at any time and that it is important to be prepared for earthquakes. Regardless of the type of soil or the quality of construction, there is always the possibility of damage in an earthquake. Foster City provides free training and resources to residents to assist them to prepare themselves for the potential effects of an earthquake. For more information about training or to download resources, visit www.fostercity.org/Services/safety/fire/Emergency-Preparedness.cfm. The USGS also has useful information at http://pubs.usgs.gov/gip/2005/15/.

City officials will continue to meet with the USGS to clarify and update the information contained in the maps to better account for the measures that have been implemented in Foster City to reduce the chance of liquefaction and to reduce the effects of earthquakes that do occur in the area.