Preliminary Release Announcements

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Preliminary Review Maps of Proposed New and Revised Earthquake Fault Zones

February 18, 2021

The California Geological Survey (CGS) released preliminary review maps and reports of proposed new and revised Alquist-Priolo Earthquake Fault Zones to the cities of Fillmore and San Diego, and the counties of San Diego and Ventura. These maps are released under the authority of the Alquist-Priolo Earthquake Fault Zoning Act (Alquist-Priolo Act) that was passed following the 1971 San Fernando earthquake. The Alquist-Priolo Act is a state law designed to reduce the hazard from surface fault rupture during an earthquake.

Earthquake Fault Zones are regulatory zones that encompass surface traces of active faults that have a potential for future surface fault rupture. The index maps below show the locations of the quadrangles included in this release.

The maps and reports are available by request as PDF files, which can be viewed using Adobe Acrobat Reader. To request these maps and reports, follow the links provided below.

Downloadable Files Related to this Release

Point Loma and La Jolla (San Diego County)

Fillmore (Ventura County)

Reference Guide for Assessing Fault Rupture Hazards

Preliminary Review Maps of Proposed New Seismic Hazard Zones

February 18, 2021

The California Geological Survey (CGS) released preliminary review maps and reports of proposed new Seismic Hazard Zones to the cities of Brisbane, Clayton, Colma, Concord, Daly City, Half Moon Bay, Pacifica, Pittsburg, San Bruno, South San Francisco, and Walnut Creek, and the counties of Contra Costa and San Mateo. These maps are released under the authority of the Seismic Hazards Mapping Act that was passed following the 1989 Loma Prieta earthquake. The Seismic Hazards Mapping Act is a state law designed to reduce the hazards from soil liquefaction and landslides during an earthquake.

Seismic Hazard Zones are regulatory zones that encompass areas that have a potential for future ground deformations caused by liquefaction or landslides. The index maps below show the locations of the quadrangles included in this release.

The maps and reports are available by request as PDF files, which can be viewed using Adobe Acrobat Reader. To request these maps and reports, follow the links provided below.

Downloadable Files Related to this Release

Clayton and Clifton Court Forebay (Contra Costa County)

Half Moon Bay and San Francisco South (San Mateo County)

Reference Guide for Evaluating Seismic Hazards

Review Comment Period

The February 18, 2021 release date begins a 90-day public comment period designed to provide the opportunity for the State Mining and Geology Board to receive technical review comments that may have a bearing on the proposed maps. Comments must be sent to the State Mining and Geology Board before May 19, 2021. Please direct comments to:

Jeffrey Schmidt, Executive Officer
State Mining and Geology Board
801 K Street, MS 20-15
Sacramento, CA 95814
(916) 322-1082
smgb@conservation.ca.gov

The State Mining and Geology Board will hold a public hearing near the end of the 90-day review period. For more information on the date and location of the public hearing, contact the State Mining and Geology Board.

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