San Francisco Bay Region Geology and Geologic Hazards

A cooperative project with the California Geological Survey

Factors of Liquefaction

Three factors are required for liquefaction to occur:

loose, granular sediment — typically "made" land and beach and stream deposits that are young enough (late Holocene) to be loose.

saturation of the sediment by ground water (water fills the spaces between sand and silt grains).
In much of the San Francisco Bay region the ground water is closest to the surface (saturating the younger sediment) in the Winter/Spring, during and following the "wet season". In 1906, the Bay region was fortunate that the previous wet season had been relatively dry. In 1989, the Loma Prieta earthquake occurred at the end of the dry season in October, when ground water levels are relatively deep beneath the ground surface — still, there was considerable liquefaction-related damage!

strong shaking — all parts of the San Francisco Bay region have the potential to be shaken hard enough for susceptible sediment to liquefy.

click to view extended caption
The expected severity of ground shaking and damage in the San Francisco Bay region from anticipated future earthquakes.
(click to enlarge)

 

Accessibility FOIA Privacy Policies and Notices

Take Pride in America home page. FirstGov button U.S. Department of the Interior | U.S. Geological Survey
URL: /sfgeo/
Page Contact Information: ask@usgs.gov
Page Last Modified: 8/18/2006