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
strong shaking — all parts of the San
Francisco Bay region have the potential to be shaken hard enough for
susceptible sediment to liquefy.
The expected severity of ground shaking
and damage in the San Francisco Bay region from anticipated future
(click to enlarge)