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Editors: To
view a JPEG file of a section of the
Ojai Quadrangle (Ventura County),
click here. To view a JPEG file of a
section of the quadrangle containing
Rancho Santa Margarita (Orange County),
click here.
SACRAMENTO – Seven
Seismic Hazard Zone maps – six for
Ventura County (and a small portion of
Los Angeles County) plus the 18th and
final one for Orange County -- became
official today. The maps, issued by the
Department of Conservation’s California
Geological Survey, impact local
planners, developers, property sellers
and real estate agents.
If property is
located in a Zone of Required
Investigation, where liquefaction or
earthquake-induced landslides could
occur during a large earthquake, the
local building department must require
geologic studies before projects are
issued permits. Also, property sellers
and real estate agents must inform
buyers if property they're selling is in
a Seismic Hazard Zone, as is the case
when property is in a designated flood
zone.
Orange County is the
first county to be completely mapped for
these types of seismic hazards. Each of
the 18 maps for the county cover
approximately 60 square miles. The maps
affect 33 cities.
The first Orange
County Seismic Hazard Zone Map, the
Newport Beach Quadrangle, was issued on
April 7, 1997. Since then, 76 official
maps affecting six counties (San
Francisco, Alameda and Santa Clara are
the others) have been issued.
“The completion of
this series of maps is a substantial
advance in the geotechnical information
available for Orange County, as well as
a milestone for the Seismic Hazard
Mapping program,” DOC Director Darryl
Young said.
This is a section of the Ojai
Quadrangle, Ventura County.
The latest maps
include the communities of Rancho Santa
Margarita and Mission Viejo in Orange
County as well as the Ventura County
communities of Fillmore, Ojai, Oxnard,
Port Hueneme and Ventura.
Shaking causes most
of the damage during earthquakes, and in
many cases, it is cost effective to
retrofit houses and buildings to
minimize damage caused by severe
shaking. Local public libraries have a
number of publications by the Governor’s
Office of
Emergency Services,
American Red Cross and the Federal
Emergency Management Agency that can be
used as guides to making homes more
earthquake-ready.
Seismic Hazard Zone
maps show areas at risk from the
secondary earthquake hazards of
landslides and liquefaction. It is
generally not as cost effective to
retrofit an existing building for the
impacts of liquefaction or landslides as
it is to build in safety features at the
design stage. Therefore, design changes
to better protect life and property
during future earthquakes are required
before new developments are approved and
built.
“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," Young
said.
Color copies of
official maps can be purchased through
DOC's California Geological Survey at
(213) 239-0878, (916) 445-5716, or (415)
904-7707. The maps also can be viewed
and downloaded from the DOC Web site
here.
Following is a brief
description of the seismic hazards shown
in each map:
FILLMORE
QUADRANGLE -- Two-thirds of this
quadrangle consists of rugged,
mountainous terrain in central Ventura
County. The rest consists of lowlands
along the Santa Clara River and Sespe
Creek. Aside from the City of Fillmore,
the quadrangle is unincorporated land.
A broad liquefaction
zone extends east to west through the
Santa Clara Valley area, covering most
of the City of Fillmore. The area is
defined by Sespe Creek to the west, and
south of the Santa Clara River. A broad
area also extends north of Fillmore into
the Los Padres National Forest valley.
Landslide zones occur north of Fillmore
in the TopaTopa Mountains.
PIRU QUADRANGLE
-- In east-central Ventura County, this
quadrangle consists mostly of rugged,
mountainous terrain except for the
lowlands along the Santa Clara River
valley and in Piru Creek Canyon. The
rural community of Piru is the only
residential area in this quadrangle.
Broad liquefaction
zones occur in the southern portion of
the map in the Santa Clara Valley, from
the foot of the TopaTopa Mountains to
south of the Santa Clara River. Most of
the community of Piru is within the
liquefaction hazard zone. Liquefaction
zones also extend northward from Piru
into the valleys of the TopaTopa
Mountains. Most of the TopaTopa
Mountains north of the liquefaction
zones are zoned for landslide hazards.
The Santa Susana Mountains south of the
Santa Clara River are also are zoned for
landslides.
VAL VERDE
QUADRANGLE -- Homes in this area,
about 37 miles northwest of the Los
Angeles Civic Center, are concentrated
in the small, unincorporated community
of Val Verde and in Castaic, although
residential, commercial, and industrial
development is currently spreading
westward along the Santa Clara River and
Castaic Creek valleys.
Broad liquefaction
zones occur in the southern portion of
the map in the Santa Clara Valley, from
the foot of the TopaTopa Mountains, to
south of the Santa Clara River. Most of
the TopaTopa Mountains to the north and
the Santa Susana Mountains south of the
Santa Clara River valley are zoned for
landslide hazards.
OJAI QUADRANGLE
– This quadrangle, in southern Ventura
County, includes the eastern portion of
the City of Ojai and the unincorporated
community of Summit near the eastern
boundary. Residential development is
concentrated in the valley areas with
scattered development in the canyons, on
the hillsides, and along Sulphur
Mountain Road on the crest of Sulphur
Mountain.
Liquefaction hazard
zones occur along Lion Creek in the Ojai
Valley from Summit School west to
Dennison Park, and from east of Ojai
along Reeves Roard westerly along San
Antonio Creek approximately to Camp
Comfort Park on Creek Road. Liquefaction
zones also cover about a 12-block area
in northwestern Ojai. A mile-wide
liquefaction zone just east of Ojai
extends north from the foothills of the
Black Mountains to the steep foothills
north of Grand Ave. Landslide zones
occur in most of the mountainous areas
around the Ojai Valley.
OXNARD QUADRANGLE
– This is a revised map for this
quadrangle, which lies along the
coastline in southwestern Ventura
County. The on-land portion of the
quadrangle consists of the coastal
lowlands of the Oxnard Plain bordered by
nearly 11 miles of beaches. Except for
residential and commercial development
in Oxnard and Port Hueneme, land use
within the quadrangle consists mainly of
farming.
A liquefaction zone
covers almost the entire Oxnard
Quadrangle except for the slopes north
of the Santa Clara River in the
northwest corner. No Zones of Required
Investigation for earthquake-induced
landslides exist in the quadrangle.
PITAS POINT
QUADRANGLE -- The land portion of
this quadrangle is mostly mountainous
terrain bordering the Pacific Ocean in
western Ventura County. Rincon Point,
the westernmost land in the quadrangle
is about 13 miles northwest of the City
of Ventura along U.S. Highway 101. The
small, rural communities of La Conchita,
Seacliff, and Faria Beach are located
along the coastline in this
unincorporated area.
The liquefaction zone
is restricted to the beach, the
low-lying area between the beach and the
base of the cliffs, and the bottom of
Padre Juan Canyon and Los Sauces Creek.
The zone follows the beach area from
Rincon Point southeast to beyond Pitas
Point. The deeply dissected mountainous
terrain inland results in a landslide
hazard zone that covers about 75 percent
of the land area within the quadrangle.
SANTIAGO PEAK
QUADRANGLE -- Most of the land in
the Santiago Peak Quadrangle lies within
the Cleveland National Forest. Only the
southwestern quarter has been evaluated
because residential development is
underway in the communities of Rancho
Santa Margarita, Trabuco Canyon, Coto de
Caza, and Dove Canyon.
Liquefaction zones
are restricted to portions of the
bottoms of Arroyo Trabuco, Canada
Gobernadora, Tijeras Canyon, Live Oak
Canyon, Modjeska Canyon, Harding Canyon,
Bell Canyon and the Oso Creek drainage
area. The largest liquefaction zone runs
northeasterly along Trabuco Creek
through the northern low-lying parts of
Rancho Santa Margarita. The mountainous
areas of landslide hazards are mostly
unpopulated.
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