SACRAMENTO -- San Jose State University,
Santa Clara University, San Jose
International Airport, the civic center
and the Compaq Center are on ground
susceptible to liquefaction in the event
of a large earthquake, according to the
San Jose West Seismic Hazard Zone map
released today by the California
Department of Conservation.
use the maps to identify areas that
require site-specific geologic or soil
investigations before new development is
permitted. Design changes on new
development and large remodeling or
restoration jobs can lessen the impact
of seismic hazards and better protect
life and property during future
``Seismic Hazard Zone
maps help communities prepare for
earthquakes and thus help minimize
damage,'' Department of Conservation
Director Darryl Young said. "Now that we
know where liquefaction and landslides
are most likely to occur in this area,
local officials can place special
engineering requirements on new
construction to make buildings and
Young noted that it
is much less expensive to build in
features to minimize the potential
damage of liquefaction and landslides at
the construction phase than to retrofit.
The preliminary map
of the San Jose West quadrangle, which
covers an area of about 60 square miles,
becomes official after a six-month
review period. Once this map is
official, disclosure to the buyer must
be made before property inside a
designated Seismic Hazard Zone is sold,
as is the case for property in
designated flood or wildfire zones.
Shaking causes most
of the damage during an earthquake.
Seismic Hazard Zone maps, produced by
DOC's Division of Mines and Geology,
show areas at risk from landslides and
liquefaction -- hazards that also can be
dangerous -- during an earthquake
magnitude 6.0 or greater.
Liquefaction was a
major cause of damage during the Loma
Prieta earthquake of 1989, especially in
San Francisco's Marina District. It
occurs when water-saturated sandy soil
within 40 feet of the surface is shaken
and temporarily acts like quicksand.
Loma Prieta also caused landslides that
blocked two lanes of Highway 17 and
damaged residences in the Santa Cruz
The San Jose West
quadrangle map covers downtown San Jose.
The southern part of Santa Clara is in
the northwestern corner of the map and
the entire city of Campbell is in the
south-central portion. Parts of the
cities of Los Gatos, Saratoga, and
Sunnyvale also extend into the southern
and western margins of the map.
are widespread in Santa Clara from the
Bayshore Freeway south to San Jose at
Stevens Creek Blvd., and from I-280 at
San Carlos St. south to Blossom Hill
Road, a mile or more wide along the
Guadalupe River. Landslide zones occur
only in the La Rinconada Hills of
northern Los Gatos.
Conservation geologists use computer
models as well as analyses of existing
geological mapping and hundreds of
engineering borings to produce the maps,
which are drawn on a scale where one
inch equals 2,000 feet.
covering more than 115 cities are now
official. The effort to identify
California's seismic hazards is ongoing.
Preliminary mapping is ongoing in the
Los Gatos and Mountain View areas, among
others. The San Jose East map was
released in February followed by maps
for the Milpitas (directly north of San
Jose West) and Calaveras Reservoir
quadrangles in April.
Black and white
copies of the completed maps are
available at cost through BPS
Reprographics Services in San Francisco,
telephone (415) 512-6550.