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Preliminary Review Maps of Proposed Revised Earthquake Fault Zones
August 24, 2023
The California Geological Survey (CGS) released preliminary review maps and reports of proposed revised Alquist-Priolo Earthquake Fault Zones to the city of Santa Rosa and the county of Sonoma. 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 map below shows the locations of the quadrangles included with this release.
Index map showing outlines of the Earthquake Fault Zone maps in this release. Click the image to open a larger version in a new window.
The maps and reports are available as PDF files, which can be viewed using Adobe Acrobat Reader. To download these maps and reports, follow the link provided below.
- Preliminary Fault Evaluation Report 270: The Southern Rodgers Creek Fault Zone in the Sears Point, Petaluma River, Glen Ellen, Cotati, and Santa Rosa 7.5-minute quadrangles; Sonoma County, California
Included with this release:
- One (1) Fault Evaluation Report (FER 270);
- Nine (9) separate Plates (1a through 3c);
- Five (5) Earthquake Zones of Required Investigation Maps (EZRIM).
Related Reference Material
- Reference Guide for Assessing Fault Rupture Hazards (Special Publication 42: Earthquake Fault Zones - A Guide for Government Agencies, Property Owners/Developers, and Geoscience Practitioners for Assessing Fault Rupture Hazards in California). This document contains technical guidelines for evaluating surface fault rupture hazards and for reviewing geologic reports.
Preliminary Review Maps of Proposed New Seismic Hazard Zones
August 24, 2023
The California Geological Survey (CGS) released preliminary review maps and reports of proposed new Seismic Hazard Zones to the cities of Concord, Danville, El Cerrito, Hercules, Lafayette, Martinez, Pinole, Pleasant Hill, Richmond, San Pablo, San Ramon, and Walnut Creek, and the county of Contra Costa. 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 map below shows the locations of the quadrangles included with this release.
Index map showing outlines of the Seismic Hazard Zone maps in this release. Click the image to open a larger version in a new window.
The maps and reports are available as PDF files, which can be viewed using Adobe Acrobat Reader. To download these maps and reports, follow the links provided below.
- Preliminary Seismic Hazard Zone Report 134: Seismic Hazard Zones in the Richmond, Mare Island, and San Quentin 7.5-minute quadrangles; Contra Costa County, California
Included with this release:
- One (1) Seismic Hazard Zone Report (SHZR 134);
- Three (3) Earthquake Zones of Required Investigation Maps (EZRIM).
- Preliminary Seismic Hazard Zone Report 135: Seismic Hazard Zones in the Vine Hill 7.5-minute quadrangle, Contra Costa County, California
Included with this release:
- One (1) Seismic Hazard Zone Report (SHZR 135);
- One (1) Earthquake Zones of Required Investigation Map (EZRIM).
- Preliminary Seismic Hazard Zone Report 136: Seismic Hazard Zones in the Walnut Creek 7.5-minute quadrangle, Contra Costa County, California
Included with this release:
- One (1) Seismic Hazard Zone Report (SHZR 136);
- One (1) Earthquake Zones of Required Investigation Map (EZRIM).
- Preliminary Seismic Hazard Zone Report 137: Seismic Hazard Zones in the Diablo 7.5-minute quadrangle, Contra Costa County, California
Included with this release:
- One (1) Seismic Hazard Zone Report (SHZR 137);
- One (1) Earthquake Zones of Required Investigation Map (EZRIM).
Related Reference Material
- Reference Guide for Evaluating Seismic Hazards (Special Publication 117A: Guidelines for Evaluating and Mitigating Seismic Hazards in California). This document constitutes the guidelines for evaluating seismic hazards other than surface fault rupture, and for recommending mitigation measures as required by Public Resources Code Section 2695(a).
