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SACRAMENTO --
Portions of several Orange County
communities are on ground susceptible to
landslides or have a potential for
liquefaction during a strong earthquake,
according to official Seismic Hazard
Zone maps released today by the
California Department of Conservation.
The communities
affected are Alison Viejo, Irvine,
Rancho Santa Margarita, San Juan
Capistrano, San Clemente, Dana Point,
Laguna Hills, Laguna Beach, Laguna
Niguel and Mission Viejo.
During an earthquake
magnitude 6.0 or greater, strong shaking
causes most of the damage. However,
Seismic Hazard Zone maps, produced by
DOC's Division of Mines and Geology,
show areas at risk from ground failure
due to landsliding or liquefaction
triggered by shaking. The dangerous
effects of these secondary hazards exist
when there are poor soil or rock
conditions present in the subsurface.
Liquefaction was a
major cause of damage in the Kings
Harbor area of Redondo Beach during the
Northridge earthquake of 1994. The
Northridge earthquake also caused more
than 11,000 landslides, some of which
damage structures or blocked roads.
"Knowing where
liquefaction and landslides are most
likely to occur means that local
officials can require special
engineering steps on new construction to
make people and buildings safer,"
Department of Conservation Director
Darryl Young said.
City planning and
building officials 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 in future earthquakes.
Generally, it is more cost effective to
build improvements into new structures
than to retrofit existing ones.
With the official
release of the maps, new building
permits issued inside the zones will
require a geologic study to determine
whether the hazard exists on a
particular site. If a hazard is found,
measures to lessen the impact must be
proposed. All property sold in
California requires that a natural
hazards disclosure be provided to the
buyer prior to sale. Property inside a
designated Seismic Hazard Zone will be
part of that disclosure, as is the case
for property in designated flood or
wildfire zones.
The Dana Point and
San Juan Capistrano quadrangle maps each
encompass 60-square mile areas. The Dana
Point map extends from Three Arch Bay in
Laguna Beach southeast to the City Beach
in San Clemente. The San Juan Capistrano
map covers an area from north Laguna
Hills south to the Ortega Highway at
Highway 5 in San Juan Capistrano and
from Laguna Beach east to San Juan Creek
in eastern San Juan Capistrano and
O'Neill Regional Park in Mission Viejo.
A description of each map follows:
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Dana Point: The
zones of required investigations for
landslides occur over broad areas of
the hills east of the San Diego
Freeway in San Juan Capistrano and San
Clemente, and scattered areas west of
the freeway to the beach area in Dana
Point and Laguna Beach. Liquefaction
Hazard Zones occur along all beach
areas in San Clemente, Dana Point, and
Laguna Beach. A broad zone occurs
along San Juan Creek east of the San
Diego Freeway from the beach to
Highway 74, and in the valley along
Prima Deshecha Cañada Creek from the
beach area to the San Juan Capistrano
city boundary in San Clemente. A small
zone occurs in Laguna Niguel at the El
Niguel Golf Course.
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San Juan
Capistrano: The zones of required
investigation for landslides occur in
widely scattered areas in the hills of
northern San Juan Capistrano, Laguna
and Mission Viejo, in and around
O'Neill Regional Park. Landslide zones
are more widespread along the eastern
and western border areas of the map
where there are natural, undeveloped
hill slopes. Liquefaction zones occur
in the major drainages along the
Interstate 5 corridor from Ortega
Highway in San Juan Capistrano north
to La Paz Road in Mission Viejo, and
from I-5 at Rancho Viejo within
Trabuco Canyon through O'Neill
Regional Park in Las Flores. Zones
also occur from the Coast Highway in
Laguna Beach along Aliso Creek
northwesterly all the way through
Laguna Hills along Alicia Parkway.
Department of
Conservation geologists use computer
models as well as analyses of existing
geological mapping and numerous
engineering borings to produce the maps,
which are drawn on a scale where one
inch equals 2,000 feet.
The Department of
Conservation has mapped more than 3,000
square miles in California, including
most of Los Angeles, Ventura and Orange
counties, and has provided this hazard
information to more than 135 cities for
their use in planning and issuing
construction permitting.
A preliminary map of
the San Clemente quadrangle, which
covers the remaining portions of San
Clemente and San Juan Capistrano, and
the Santa Paula quadrangle in Ventura
County were also released today for 90
days of technical review. Mapping in
Southern California is ongoing in
Ventura County and is planned for the
Lancaster and Palmdale areas of Los
Angeles County.
Color maps can be
purchased through DOC's Division of
Mines and Geology at (415) 904-7707 or
(916) 445-5716.
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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