NR 2002-42
September 23, 2002

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


Newly Defined Zones Impact Construction Process

SACRAMENTO – Two Seismic Hazard Zone maps, each covering a 60-square-mile area of Santa Clara County, became official today. The maps, issued by the California Department of Conservation, impact 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.

DOC’s California Geological Survey released the Seismic Hazard Zone maps for the Cupertino and Los Gatos quadrangles in preliminary form in March. They are now official after public review and comment. The maps are on file with local government offices, including the planning department, building department and county recorder's office.

The northeastern half of the Cupertino map includes parts of the communities of Cupertino, Los Altos, Los Altos Hills, Mountain View, San Jose, Santa Clara, Saratoga and Sunnyvale. The remainder of the quadrangle is unincorporated, sparsely populated county land.

Landslide hazard zones occur extensively in the foothills west of Cupertino westerly to the limits of current zoning at the Santa Cruz County line, extending from Foothill College west of the Sierra Freeway, southeasterly to Sanborn Skyline County Park in Saratoga.

Liquefaction hazard zones occur mostly along streams and creeks in the metropolitan areas. Notable are wide areas along Saratoga Creek and Calabazas Creek in Saratoga, Stevens Creek and Permanente Creek in Cupertino and Sunnyvale.

Parts of the communities of Los Gatos, San Jose, Saratoga and Monte Sereno occupy the northern quarter of the Los Gatos quadrangle. The remainder of the quadrangle is mostly steep, forested terrain in the Santa Cruz Mountains that is unincorporated county land.

Landslide hazard zones occur over most of this map, except the northern quarter, which is the Los Gatos metropolitan area.

Liquefaction hazard zones occur mostly along streams flowing down from the slopes, notably Los Gatos Creek from Lexington Reservoir north to Vasona Reservoir in Los Gatos and Ross Creek and Guadalupe Creek in San Jose.

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, 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 to better protect life and property during future earthquakes are required before new developments are approved and constructed.

Eleven maps affecting Northern California are now official. The effort to identify and map seismic hazards is ongoing. Preliminary Seismic Hazard Zone maps for several East Bay areas are scheduled for release in the comings months.

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.