NR 2003-18
July 8, 2003

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

Liquefaction, Landslide Potential Affects New Construction

SACRAMENTO – A new Seismic Hazard Zone map covering the City of Ventura and the unincorporated community of Casitas Springs became official today. The map, issued by the Department of Conservation’s California Geological Survey, impacts 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.

“This map will help improve public safety by ensuring these earthquake hazards are taken into account during new construction,” DOC Director Darryl Young said.

The liquefaction zone in the Ventura quadrangle covers the urbanized lowlands occupied by the City of Ventura, the Ventura River floodplain, the beaches, and the bottoms of some creek canyons. Landslide zones cover more than half of the land portion of the quadrangle.

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. “It’s easier and less expensive – not to mention better for public safety -- to institute design changes as a precaution in the construction phase than to rebuild after liquefaction or landslide damage,” Young said.

With this new map, the California Geological Survey has issued 89 official Seismic Hazard Zone Maps, 72 for Southern California and 17 for the Bay Area. Another 17 maps are in various stages of public review. Each map covers about 60 square miles.

DOC/California Geological Survey geologists use computer models as well as analyses of existing geological mapping and hundreds of engineering borings to produce the maps, which are drawn on a scale where one inch equals 2,000 feet.

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 at