NR 2002-29
June 20, 2002

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

Newly Defined Zones Impact Construction Process

SACRAMENTO -- A Seismic Hazard Zone map covering a 60-square-mile area that extends from the Los Altos Hill and Cupertino in the south to the San Francisco Bay shorelines becomes official Friday. The map impacts local planners, developers, property sellers and real estate agents.

If property is located in a “zone of required investigation,” where liquefaction or 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 potential buyers if property they're selling is in a Seismic Hazard Zone, as is the case when property is in a designated flood or wildfire zone.

The Seismic Hazard Zone map for the 60-square-mile Mountain View quadrangle was released in preliminary form in December by the California Department of Conservation. It is now official after public review and comment. The map is on file with local government offices, including the planning department, building department and county recorder's office.

The "zone of required investigation" for liquefaction covers most of the flat ground that lies east of the Foothill Expressway and north from Highway 280 to the bay, including the Naval Air Station at Moffett Field.

There are narrow bands of liquefaction zones along Adobe, Hale, Permanente and Stevens creeks. Landslide Hazard Zones occur along the steep stream banks in the Los Altos Hills area. For more information, contact your local building department.

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 produced by DOC's California Geological Survey show areas at risk from the secondary earthquake hazards of landslides and liquefaction, which also can be dangerous. 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 are required before new developments are approved and constructed in order to be effective. Changes made during the planning phase can lessen the impact and better protect life and property during future earthquakes. The new maps are an important tool that land developers will use to ensure project feasibility.

Nine maps affecting Northern California are now official. The effort to identify and map seismic hazards is ongoing. Preliminary Seismic Hazard Zone maps for the east Bay Area are scheduled for release in August. The Cupertino and Los Gatos quadrangles are currently being reviewed and will become official in September.

Color copies of official maps can be purchased through DOC's California Geological Survey (415) 904-7707 or (916) 445-5716. The maps also can be found on the Web here.

In addition to studying and mapping earthquakes and other geologic phenomena, the Department of Conservation maps and classifies areas containing mineral deposits; ensures reclamation of land used for mining; regulates oil, gas and geothermal wells; administers agricultural and open-space land conservation programs; and promotes beverage container recycling.