Official Map and Report Release Announcements

New Official Seismic Hazard Zones in Contra Costa and San Mateo Counties (April 4, 2019)

On April 4, 2019, the California Geological Survey (CGS) released five official maps of Seismic Hazard Zones affecting the cities of Antioch, Belmont, Brentwood, Burlingame, Concord, Half Moon Bay, Hillsborough, Millbrae, Oakley, Pacifica, Pittsburg, Redwood City, San Bruno, San Carlos, the towns of Portola Valley and Woodside, and the counties of Contra Costa and San Mateo. These maps were 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 identifying areas that have a potential for future ground deformations caused by liquefaction or earthquake-induced landslides.

List of Official Maps and Reports released April 4, 2019

  • Antioch North quadrangle, showing Seismic Hazard Zones only
    • Related: Seismic Hazard Zone Report 125
  • Antioch South quadrangle, showing Seismic Hazard Zones only
    • Related: Seismic Hazard Zone Report 126
  • Honker Bay quadrangle, showing Seismic Hazard Zones only
    • Related: Seismic Hazard Zone Report 127
  • Montara Mountain quadrangle, showing Earthquake Fault Zones and Seismic Hazard Zones
    • Related: Seismic Hazard Zone Report 128
  • Woodside quadrangle, showing Earthquake Fault Zones and Seismic Hazard Zones
    • Related: Seismic Hazard Zone Report 129

The maps are available as GeoPDF files, which can be viewed using Adobe Acrobat Reader; a GeoPDF file consists of multiple layers and gives the user greater flexibility in viewing and displaying the maps. The maps are also available as digital Geographic Information System (GIS) files. GIS files for both AP Earthquake Fault Zones and Seismic Hazard Zones released by CGS are considered Official Maps. To obtain these maps, reports and GIS data, visit the Regulatory Maps and Reports section of the CGS Information Warehouse. To view individual parcels affected by Seismic Hazard Zones and/or Earthquake Fault Zones, visit our Earthquake Hazards Zone Application ("EQ Zapp").

The index maps below show the general areas in Contra Costa and San Mateo counties affected by this release.

Older Releases: