San Francisco And Southern California Preliminary Seismic Hazard Zone Maps Out For Review

November 18, 1996

The latest tool to help protect life and property during an earthquake is in the works, thanks to the California Department of Conservation. The department has just distributed six preliminary seismic hazard zone maps and draft map guidelines to local officials for technical review. The maps show areas in portions of San Francisco, Los Angeles, Orange and Ventura counties that during an earthquake are likely to be susceptible to landslides and/or to water-saturated ground failure known as liquefaction.

The first set of preliminary maps encompass 17 communities including the northern half of San Francisco and in Southern California, Simi Valley, the western portion of Santa Monica and an area from Fullerton and Buena Park south to Newport Beach. Each of the six maps is a 7 1/2-minute quadrangle, covering approximately 60 square miles at a scale of one inch equals 2,000 feet.

Subsequent sets of preliminary maps for portions of Los Angeles, Orange and Ventura counties will be distributed for review approximately every six months until the currently funded total of 38 maps are produced. The mapping was completed in cooperation with the Governor's Office of Emergency Services and the Federal Emergency Management Agency.

Local governments and other interested parties now have until January 7, 1997 to review and comment on the maps and guidelines. Once the maps are made official in March 1997, the Seismic Hazards Act of 1990 requires local governments use them to identify areas where geologic or soils investigation are required before permitting urban development. The guidelines will help guide cities, counties and consulting engineers and geologists in the investigation and mitigation of these types of hazards inside and outside the mapped areas.

"These maps identify areas having an increased likelihood of liquefaction and earthquake-triggered landslides occurring," said Charles Real, supervising geologist, Department of Conservation, at a briefing held for local media. "However, we're not saying the seismic hazards will necessarily occur."

In February 1996, the California Department of Conservation released 16 reconnaissance seismic hazard maps for portions of Southern California. The preliminary seismic hazard zone maps just distributed for technical review cover a different area from the reconnaissance maps and are a refinement of the type of information in the earlier maps, including sub-surface geologic data not present in the reconnaissance maps.

The preliminary Seismic Hazard Zone Maps are available to interested parties for review at cost through two reprographic services. For details, call the Department of Conservation Public Information Offices: Los Angeles (213) 620-3560; San Francisco, (415) 904-7707; or Sacramento (916) 445-5716. Copies of the draft guidelines, a geographic index of the maps released for review and other related information are also available through the Department of Conservation web site:

Comments from interested parties or organizations must be submitted to the State Mining and Geology Board by January 7, 1997.

The six preliminary seismic hazard zone maps released today include these cities or portions of cities: the northern half of San Francisco and in Southern California, Anaheim, Buena Park, Costa Mesa, Fountain Valley, Fullerton, Garden Grove, Huntington Beach, Moor Park, Newport Beach, Orange, Placentia, Santa Ana, Santa Monica, Simi Valley, Stanton and Westminister.

The California Department of Conservation has one of the oldest geological surveys in the United States in its Division of Mines and Geology. An integral part of the survey's purpose is to prevent or minimize injury, death and property damage from geologic hazards. The department also safeguards farmland; oversees oil, gas and geothermal wells; regulates mining; studies earthquakes and landslides; promotes beverage container recycling; and manages California's earth resources.

California Department of Conservation

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