A cooperative project with the California Geological Survey
Liquefaction Maps of the San Francisco Bay Area
Maps of liquefaction hazard are used to show how the hazard differs from
place to place, the likelihood of liquefaction in different earthquake
scenarios, and to define hazard zones for regulatory purposes. Basic information
used in making these regional maps includes the distribution of different
kinds of geologic materials, estimates of depth to ground water, geotechnical
borings, and predicted levels of shaking during future earthquakes. Scientists
continue to develop methods to characterize the hazard, particularly at
the site-investigation level, while maps based on current methods provide
regional estimates and regulatory tools.
Map of liquefaction susceptibility that shows the varying susceptibility in different
parts of the region. Susceptibility is delineated in five units from Very
High to Very Low hazard. Roughly one quarter of the San Francisco Bay region
may be exposed to liquefaction — the area mapped in the Very High, High
and Moderate categories makes up about 25% of the 9-county region.
Maps of "Zones
of Required Investigation"
maps prepared by the California Geological Survey are State-mandated
regulatory maps that show "Zones of Required Investigation" for
liquefaction (and landslide) hazard. They do not depict different
degrees of hazard, rather they identify zones within which site specific
studies will be required for new construction. These zone maps
also are used in real estate transactions - sellers of properties
within a "Zone of Required Investigation" must disclose
that fact to prospective buyers.