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NR 2005-03
February 17, 2005

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

NEW EARTHQUAKE MAPS FOR LANCASTER-PALMDALE AREA

SACRAMENTO -- The California Department of Conservation today released six maps for the Lancaster-Palmdale area that help protect public safety in the event of a large earthquake.

“Once we know where the potential problems are most likely to occur, we can improve public safety by requiring builders to take preventative steps to minimize the hazard,” Acting State Geologist Michael Reichle said.

These Seismic Hazard Zone Maps identify areas that are subject to liquefaction and landslides. Those hazards are potential side effects of earthquakes in the magnitude 5.5 or greater range. Landslides and liquefaction can cause destruction over and above the damage done by shaking. Liquefaction occurs when water-saturated, sandy soil is violently shaken and temporarily loses its ability to support structures. Liquefaction was a major cause of damage in Kings Harbor area of Redondo Beach during the Northridge earthquake of 1994. The Northridge earthquake also caused more than 11,000 landslides, some of which damaged structures or blocked roads.

The new maps, created by DOC’s California Geological Survey, establish Zones of Required Investigation. If property is located in a zone, the local building department must require -- before permits are issued -- that a registered geologist investigate the site to determine whether mitigation steps are necessary. 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.

“The structures that have been built in zoned areas since the program began will be safer in the next big earthquake than they otherwise would have been,” said Chuck Real, the Supervising Geologist in charge of the Seismic Hazard Zone Mapping Program.

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.

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. Thus, the Seismic Hazard Zone maps are aimed primarily at new construction. They require that design changes - such as deep foundations in liquefaction zones and slope stabilization in landslide zones - be made in the planning stage.

Each map covers about a 60-square mile area known as a “quadrangle.” Here's a closer look at what each map shows:

♦ Rosamond Quadrangle: This map shows land in both Los Angeles and Kern counties in the central Antelope Valley, centered about 10 miles north of Lancaster. The Kern County portion was not evaluated. Portions of Lancaster and Edwards Air Force Base are covered in this map. No earthquake-induced landslide zones were identified. The liquefaction zone covers an area along the eastern margin of the quadrangle, where recent groundwater depths have been less than 40 feet; an area occupied by the wash of Amargosa Creek; and the sewage treatment facility at State Route 14 and Avenue D.

♦ Del Sur Quadrangle: About 1.5 square miles of the southeastern corner of this map are within the Palmdale city limits. Portions of Lancaster -- North of Avenue M and/or the California Aqueduct and east of 110th Street West – also are included. Liquefaction zones are noted in the Leona Valley and the narrow trough-like valley to the north, the bottoms of canyons, and within wash areas. Earthquake-induced landslide zones cover about 3 percent of the quadrangle.

♦ Lancaster West Quadrangle: Most of the land in the map area is within the City of Lancaster, including the community of Quartz Hill. The land east of the Antelope Valley Freeway south of Avenue M is within Palmdale’s city limits, as is a small area south of Avenue N in the southwestern corner. The liquefaction zone includes a swath of low ground to the west of Lancaster; the Amargosa Creek channel; and water-reclamation ponds at the county park at the east end of Fox Air Field. There are no zones for potential landslides.

♦ Lancaster East Quadrangle: Portions of Lancaster and Palmdale are covered. The liquefaction zone is limited to the narrow Little Rock Wash. The terrain is nearly level, and no landslide hazards are noted.

♦ Alpine Butte Quadrangle: Part of the eastern boundary of Palmdale and a few square miles of Lancaster located between Avenue J and Avenue K are on this map, although there are only scattered rural homes and ranches in the coverage area. There are no liquefaction zones on this map. Very small patches on Alpine Butte and Rocky Buttes lie within the earthquake-induced landslide zones that make up less than one percent of the quadrangle.

♦ Little Buttes Quadrangle: No seismic hazard zones were identified. The Little Buttes Quad is in central Antelope Valley along the boundary of Los Angeles and Kern counties. The Kern County portion was not evaluated. The center of the quadrangle is approximately 15 miles northwest of Lancaster. Small parcels of the City of Lancaster extend into the southeastern corner, east of 70th Street West and between 100th and 110th Street West. The rural community of Antelope Acres is also in the southeastern quarter of the quadrangle.

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