Marina, South of Market and Mission Districts at
risk for earthquake liquefaction
By Adam Martin, Bay City News Service
February 24, 2006
digital map released by the U.S. Geological Survey shows the
regions of the Bay Area where the soil is most likely to liquefy
during an earthquake, the USGS announced today.
The places that are most susceptible to this "liquefaction"
of soil are areas where landfill has been placed over the San
Francisco Bay, and areas along larger streams, according to Keith
Knudsen, a senior engineering geologist with the California Geological
Survey, which collaborated with the USGS on the mapping project.
During liquefaction, which is only one of the hazards that can
occur during an earthquake, soil begins to act like a liquid and
loses its ability to support buildings and other structures.
"Regions of man-made landfill fared poorly in the 1906 San
Francisco earthquake and in the 1989 Loma Prieta earthquake. We
can expect history to repeat itself in the next big Bay Area earthquake,"
Some of the Bay Area locales that have the highest risk of liquefaction
include: the Marina, South of Market and Mission districts of
San Francisco; parts of downtown Oakland and areas around the
Oakland International Airport; areas along Alameda Creek in Fremont;
and areas along the Coyote Creek and the Guadalupe River in San
Jose, according to Knudsen.
Liquefaction can lead to what are essentially landslides, causing
buildings to travel down even very gentle slopes and damaging
infrastructure such as pipelines, roads and bridges, Knudsen said.
The USGS and the California Geological Survey also collaborated
to update a second map that shows where soil deposits of different
ages are located around the Bay Area. This soil deposit map provides
the basic data for the liquefaction hazard map, and also provides
information about where
the most severe earthquake shaking may occur.
Knudsen said the maps can be used by cities and counties for
land use and planning purposes, as well as to help plan emergency
The maps are also intended to help educate and inform the public
about the risk of earthquake-related hazards.
"These are not maps meant to scare anyone," Knudsen
Preventive steps work best when it comes to potential earthquake
hazards like liquefaction, Knudsen said. "The ideal case
... is that we catch people before they build their buildings"
in high-risk areas, Knudsen said.
The two maps are more detailed, up-to-date versions of similar
maps that were released about six years ago, according to Knudsen.
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