Preliminary maps of proposed Seismic Hazard Zones and Earthquake Fault Zones

Preliminary Review Maps of Proposed New and Revised Earthquake Fault Zones

May 23, 2024

The California Geological Survey released preliminary review maps and reports of proposed new and revised Alquist-Priolo Earthquake Fault Zones to the cities of Palo Alto and Ridgecrest, the towns of Portola Valley and Woodside, and the counties of Inyo, Kern, Los Angeles, San Bernardino, San Mateo, and Santa Clara.

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 with this release.

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.

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 Fault Evaluation Report 268: The San Andreas Fault Zone in the San Mateo, Woodside, Palo Alto, and Mindego Hill 7.5-Minute Quadrangles, San Mateo and Santa Clara Counties, California
  • One (1) Fault Evaluation Report (FER 268);
  • Four (4) Earthquake Zones of Required Investigation Maps (EZRIM).
  
  
  
• Preliminary Fault Evaluation Report 273: The San Andreas Fault Zone in the Burnt Peak, Lake Hughes, and Del Sur 7.5-Minute Quadrangles, Los Angeles County, California
  • One (1) Fault Evaluation Report (FER 273);
  • Three (3) Earthquake Zones of Required Investigation Maps (EZRIM).
  
  
  
• Preliminary Fault Evaluation Report 274: The Paxton Ranch and Salt Wells Valley Fault Zones, with Modifications to the Airport Lake and Little Lake Fault Zones in the White Hills, Burro Canyon, Ridgecrest North, Lone Butte, Westend, Spangler Hills West, Spangler Hills East, and Christmas Canyon 7.5-Minute Quadrangles, Inyo, Kern, and San Bernardino Counties, California
  • One (1) Fault Evaluation Report (FER 274);
  • Eight (8) 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

May 23, 2024

The California Geological Survey released preliminary review maps and reports of proposed new Seismic Hazard Zones to the cities of Danville, Hercules, Lafayette, Martinez, Moraga, Orinda, Pinole, Richmond, San Ramon, and Walnut Creek, and the county of Contra Costa. The index map below shows the locations of the quadrangles included with this release.

Seismic Hazard Zones are regulatory zones that encompass areas that have a potential for future ground deformations caused by liquefaction or landslides.

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.

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 138: Seismic Hazard Zones in the Benicia and Briones Valley 7.5-Minute Quadrangles; Contra Costa County, California
  • One (1) Seismic Hazard Zone Report (SHZR 138);
  • Two (2) Earthquake Zones of Required Investigation Maps (EZRIM).
  
  
  
• Preliminary Seismic Hazard Zone Report 139: Seismic Hazard Zones in the Oakland East and Las Trampas Ridge 7.5-Minute Quadrangles, Contra Costa County, California
  • One (1) Seismic Hazard Zone Report (SHZR 139);
  • Two (2) Earthquake Zones of Required Investigation Maps (EZRIM).
  
  
  
• Preliminary Seismic Hazard Zone Report 140: Seismic Hazard Zones in the Hayward, Dublin, and Livermore 7.5-Minute Quadrangles, Contra Costa County, California
  • One (1) Seismic Hazard Zone Report (SHZR 140);
  • Three (3) Earthquake Zones of Required Investigation Maps (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).