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NR 2003-09
April 21, 2003

Contact: Ed Wilson
Mark Oldfield
Don Drysdale
(916) 323-1886

DOC’S SEISMIC HAZARD MAPPING WORK
NEARS COMPLETION IN LOS ANGELES, VENTURA COUNTIES

SACRAMENTO – An eight-year project to protect public safety by zoning seismic hazards in Los Angeles, Ventura and Orange Counties took a major step toward completion today as the California Department of Conservation released five official and nine preliminary maps.

Compiled by DOC’s California Geological Survey, the maps 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 became the first county to be completely mapped for those seismic hazards in December.

Four maps in northeastern Los Angeles County – the Condor Peak, Agua Dulce, Hi Vista and Lovejoy Buttes quadrangles -- and the Matilija quadrangle in Ventura County became official today. The quadrangles are about 60 square miles in size.

Fifteen other maps for northeastern Los Angeles County are in various stages of public review. The newest – the final eight for the county -- will become official in October. In Ventura County, the last two preliminary maps – covering the Ventura and Santa Paula Peak quadrangles – will become official in June and October, respectively.

While the mapping work in Los Angeles, Orange and Ventura counties will soon be complete, zoning continues in Northern California. The California Geological Survey plans to map parts of the Inland Empire, San Diego and other Southern California areas in the future.

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.

“The structures that have been built in zoned areas since the program began will be safer in the next major earthquake than they would otherwise have been,” Department of Conservation Director Darryl Young said. “With the knowledge of where liquefaction and landslides are most likely to occur, local officials can require special engineering steps on new construction that enhance public safety."

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 on the Web here

Following is a brief description of the seismic hazards shown in each map:

LOVEJOY BUTTES: This quadrangle consists of unincorporated Los Angeles County land. The center of the quadrangle is about 18 miles east of Palmdale and 45 miles northeast of the Los Angeles Civic Center. The liquefaction zone covers a broad region in the western half of the quadrangle in the vicinity of Big Rock Wash and extends into the central part of the quadrangle. There is a very small landslide zone.

HI VISTA: Part or all of the rural communities of Lake Los Angeles, Wilsona Gardens and Hi Vista are within the quadrangle, which is 18 miles east of Lancaster and 50 miles northeast of the Los Angeles Civic Center. There is a small landslide zone and no liquefaction zones in the quadrangle.

CONDOR PEAK: Small portions of the cities of Los Angeles, Glendale and Pasadena are in the southwestern quarter of this map. The quadrangle is 15-20 miles north of the Los Angeles Civic Center. Most of it is in the Angeles National Forest, which cannot be developed and thus was not evaluated. The liquefaction zone covers the bottoms of Big Tujunga Canyon and Mill Creek Canyon near Hidden Springs. Landslides and large rockslides are widespread and abundant. The earthquake-induced landslide zone covers about 74 percent of the area evaluated in the quadrangle.

AGUA DULCE: The quadrangle is centered 13 miles east of Santa Clarita and 25 miles north of Los Angeles. The unincorporated rural communities of Agua Dulce and Soledad are in the northern half; the Angeles National Forest is in the southern half. Zoning was limited to developable areas. At present, development is limited to rural homes and small ranches, aggregate mining in Soledad Canyon, and recreational facilities in Soledad Canyon. Liquefaction zones exist in the bottom of canyons, especially along the Santa Clara River and Agua Dulce Canyon. Although actual landslides are scarce, steep slopes are common, and the earthquake-induced landslide zone covers about a third of the evaluated portion of the quadrangle.

MATILIJA: This quadrangle includes mostly mountainous terrain in southern Ventura County. Most of the City of Ojai, the only incorporated land within the quadrangle, lies along the eastern boundary. Several unincorporated communities – Meiners Oaks, Mira Monte, Live Oak Acres and Oak View – are shown. Much of the land in the quadrangle is being converted from orchards to residential development. About one-third of the quadrangle was not evaluated for zoning because it lies within the Los Padres National Forest. Liquefaction zones cover the areas around the Ventura River, San Antonio Creek, Santa Ana and Poplin creeks north of Lake Casitas, and a small portion of the Ojai Valley. The earthquake-induced landslide zone covers more than a third of the evaluated portion of the quadrangle.

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