NR 2002-43
September 23, 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 for a 51 square mile area of Orange County, including parts of the communities of San Juan Capistrano and Rancho Santa Margarita, became official today. The map, issued by the California Department of Conservation, 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.

DOC’s California Geological Survey released the Cañada Gobernadora quadrangle map in preliminary form in March. 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.

A portion of Rancho Santa Margarita is in the northwest corner of the map while San Juan Capistrano is in the southwest corner. The Cleveland National Forest extends into the eastern and northeastern parts. Caspers Regional Park spreads across the central part. The remainder of the land in Orange County is unincorporated. The area lies on the western slope of the Santa Ana Mountains, which is characterized by rugged, mountainous terrain, dissected by several large canyons, such as Cañada Gobernadora. Residential development is underway in the unincorporated community of Coto de Caza at the northern end of Cañada Gobernadora and to the west in Cañada Chiquita.

Liquefaction hazard zones are restricted to the bottoms of canyons, especially San Juan Creek, Cañada Chiquita, Cañada Gobernadora and shorter segments of tributary canyons. A zone along Cañada Gobernadora Creek affects the community around Coto De Caza Golf Course, west of Line Ridge Road. The earthquake-induced landslide zone covers about 25 percent 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, 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.

Seventeen maps affecting Orange County are now official. The effort to identify and map seismic hazards is ongoing. A preliminary Seismic Hazard Zone maps for the Santiago Peak quadrangle, just north of Cañada Gobernadora, will become official in December. Several areas of Los Angeles and Ventura counties are also being mapped.

Color copies of official maps can be purchased through DOC's California Geological Survey (213) 239-0878 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.