NR 2001-39
April 17, 2001

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


Most Likely Areas for Liquefaction, Landslides are Shown
In Dana Point, San Juan Capistrano, Oxnard and Malibu Areas

SACRAMENTO -- Significant areas around Dana Point, San Juan Capistrano, Oxnard and Malibu could be susceptible to landslides or liquefaction in the event of an earthquake magnitude 6.0 or greater, according to four Seismic Hazard Zone maps released today by the California Department of Conservation.

These preliminary maps, each of which covers an area of about 60 square miles, become official after a six-month review and comment period. Once they are official, disclosure to the buyer must be made before property in a Seismic Hazard Zone is sold.

Shaking causes most of the damage during an earthquake. Seismic Hazard Zone Map maps, produced by DOC's Division of Mines and Geology, show only areas at risk from landslides and liquefaction, secondary hazards that also can be dangerous.

Liquefaction occurs when water-saturated sandy soil within 40 feet of the surface is shaken and temporarily acts like quicksand. It was a major cause of damage in the King Harbor area of Redondo Beach during the Northridge earthquake of 1994. The Northridge earthquake also caused more than 11,000 landslides, some of which blocked roads.

Planning officials use the maps to identify areas that require site-specific geologic or soil investigations before new development is permitted. Design changes on new development and large remodeling or restoration jobs can lessen the impact of seismic hazards and better protect life and property during future earthquakes.

``These maps tell local governments where they should take extra steps to make people and buildings safer," Department of Conservation Director Darryl Young said. "It is much less expensive to build in features to minimize the potential damage of liquefaction and landslides than to retrofit."

A closer look at what each map shows:

  • The Dana Point quadrangle map covers an area from Three Arch Bay in Laguna Beach southeast to the City Beach in San Clemente.

Liquefaction zones occur along all beach areas in San Clemente, Dana Point, and Laguna Beach. A broad zone occurs along San Juan Creek east of the San Diego Freeway from the beach to Highway 74, and in the valley along Prima Deshecha Cañada Creek from the beach area to the San Juan Capistrano city boundary in San Clemente. A small zone occurs in Laguna Niguel at the El Niguel Golf Course.

Landslide zones occur over broad areas of the hills east of the San Diego Freeway in San Juan Capistrano and San Clemente, and scattered areas west of the freeway to the beach area in Dana Point and Laguna Beach.

  • The San Juan Capistrano quadrangle map covers an area generally from north Laguna Hills south to the Ortega Highway at Highway 5 in San Juan Capistrano and from Laguna Beach at the coast east to San Juan Creek in eastern San Juan Capistrano and Oneill Regional Park in Mission Viejo.

Liquefaction zones occur along the Highway 5 corridor from Ortega Highway in San Juan Capistrano north to La Paz Road in Mission Viejo, and from I-5 at Rancho Viejo within Trabuco Canyon through Oneill Regional Park in Las Flores. Liquefaction zones also occur from the Coast Highway in Laguna Beach north along Aliso Creek northwesterly all the way through Laguna Hills along Alicia Parkway.

Landslide zones occur in widely scattered areas in the hills of northern San Juan Capistrano, densely covering eastern Laguna Niguel, and scattered areas in the hills of eastern Mission Viejo in and around Oneill Regional Park.

  • The Malibu Beach quadrangle map covers an area from Dan Blocker County Beach east to Las Flores Beach, and from approximately the southern boundary of Calabasas south to the Pacific Ocean at Malibu.

Liquefaction zones occur in narrow areas along Highway 1 on the coast, in a mile-wide area beginning from the coast at Malibu Point north to the northern border of Malibu. Narrow zones also occur in the Canyons of Agoura Hills north of Mulholland Highway. Landslide zones occur heavily throughout this map, but become less dense immediately north of Monte Nido and along the Mulholland Highway.

The Oxnard quadrangle map covers an area from approximately Ventura Marina, east to Nyland, and from Montalvo to the southern boundary of Port Hueneme.

Liquefaction zones occur throughout the map, except in the area north of the Santa Clara River basin from Montalvo to the Ventura Marina. There are no landslide zones on the map.

Department of Conservation 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.

Fifty-one maps covering 115 cities are now official. The effort to identify California's seismic hazards is ongoing. Mapping is ongoing in several Southern California areas from San Clemente to Camarillo.

Black and white copies of the completed maps are available at cost through BPS Reprographics Services in San Francisco, telephone (415) 512-6550.

In addition to its program to identify and map seismic hazards, the Department of Conservation manages California's earth resources through its programs that safeguard farmland and open space; oversee oil, gas and geothermal wells; ensure mined land reclamation; study earthquakes; and promote beverage container recycling.