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SACRAMENTO --
Planning officials, developers and
homeowners in three parts of Orange
County have a new tool with which to
work in preparing for future
earthquakes.
The California
Department of Conservation today
released Seismic Hazard Zone maps
covering three 60-square-mile sections
of Orange County. The maps detail areas
that are susceptible to the secondary
earthquake hazards of landslides and
liquefaction. They are used to plan for
safer buildings to help protect life and
property. These maps cover portions of
the communities of Anaheim, Orange,
Yorba Linda, Irvine, Laguna Hills,
Mission Viejo and El Toro. In addition,
a revised map was issued for the Tustin
area.
Liquefaction occurs
when water-saturated sandy soil within
40 feet of the surface is shaken and
temporarily acts like quicksand. That
was a major cause of damage in the King
Harbor area of Redondo Beach during the
Northridge earthquake of 1994. The
Northridge earthquake also caused more
than 11,000 landslides, some of which
blocked roads.
``These maps are a
tool that can help communities minimize
earthquake damage by being prepared,"
Department of Conservation Director
Darryl Young said. ``Local officials can
place special engineering requirements
on new construction to make buildings
and people safer now that we know where
these hazards are most likely to occur."
On the map of the
Black Star Canyon quadrangle,
liquefaction zones are shown along the
Santa Ana River at Feathery Regional
Park and the Green River Golf Course in
East Anaheim and along Wier Canyon Road
south of the Riverside Freeway.
Liquefaction zones are also found along
Santiago Creek, around Santiago
Reservoir (Irvine Lake), and in Irvine
Park and Fremont Canyon. Landslide zones
are shown over much of the hilly area
between Feathery Park and Santiago
Reservoir.
On the El Toro
quadrangle map, which shows part of
Irvine and the El Toro area,
liquefaction zones are shown along Aliso,
Serrano, Oso, Santiago and San Diego
creeks; in Borrego Canyon; and in some
areas north and east of the Marine Corps
Air Station. There are landslide zones
north and east of El Toro.
The Prado Dam
quadrangle covers part of Orange and San
Bernardino counties, but the San
Bernardino portion is unmapped. It shows
a landslide zone east of Yorba Linda and
a liquefaction zone along the Santa Ana
River.
The Tustin quadrangle
includes portions of Irvine, Tustin and
Santa Ana. It was revised to modify the
liquefaction zone in two areas. A
channel of San Diego Creek east of
Jeffry Road was added; in the northeast
corner of the map, the upper part of
Rattlesnake Canyon north of the Portola
Parkway was taken out of the zone. In
Irvine, there are liquefaction zones in
the Bonita Canyon Drive area south of
Aldrich Park, along Macarthur Boulevard.
from Ford Road to San Diego Creek, and
along San Diego Creek. Also affected are
areas east of UC Irvine along Culver
Drive, and most of Irvine north of the
San Diego Freeway (Highway 405),
including Woodbridge. Areas in Irvine
susceptible to landslides include the
hillsides south of Ford Road and east of
Bonita Reservoir as well as some
hillside areas east of the Turtle Rock
area. Also affected are the slopes of
French Hill, within the UC Irvine
campus.
Areas in Tustin
susceptible to liquefaction include all
areas north of the Irvine boundary to
approximately Chestnut Avenue, and from
Irvine Boulevard at Browning Avenue west
to the Santa Ana boundary. Santa Ana is
affected from Flower Street east to the
Tustin city boundary, from First Street
south to the San Diego Freeway.
Geologists from the
Department of Conservation's Division of
Mines and Geology use computer models as
well as analyses of existing geological
mapping and hundreds of engineering
borings to produce seismic hazard zone
maps. Before becoming official, the maps
are reviewed by local planning, public
works and building permits departments.
Each map covers
approximately 60 square miles and is
drawn on a scale where one inch equals
2,000 feet. Building officials use the
maps to identify areas that need
site-specific geologic or soil
investigations before permitting new
development. Construction sites where
the DOC Division of Mines and Geology's
investigations indicate landslide or
liquefaction hazards are present, can
introduce design changes to minimize the
impact on new development and large
remodeling or restoration projects. With
the release of these official maps,
property sellers must disclose to buyers
if the property is in a state-mapped
seismic hazard zone.
Fifty-two maps have
now been released, covering more than
120 cities. The effort to identify
California's seismic hazards is ongoing.
Mapping is ongoing in Southern
California in several areas, including
in and around San Juan Capistrano, Dana
Point, Rancho Margarita, San Clemente,
Trabuco Highlands and Coto De Caza.
Black and white
copies of the completed maps are
available at cost through BPS
Reprographics Services of San Francisco,
telephone (415) 512-6550. Color copies
are available for $12 each from the
DOC's Division of Mines and Geology in
Los Angeles at (213) 239-0878. The
charge for rolled maps shipped in a tube
will be slightly higher.
In addition to its
program to identify and map seismic
hazards, the Department of Conservation
manages California's earth resources
through its programs that safeguard
farmland and open space; oversee oil,
gas and geothermal wells; ensure mined
land reclamation; study earthquakes; and
promote beverage container recycling.
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