California’s regulatory earthquake-zone map is a different product from a national probabilistic seismic model. Before relying on a map or report, confirm that it is the current official zone for the exact site. A preliminary map can show a proposed designation under review, not an adopted zone.
Check the authoritative status and map
The California Geological Survey (CGS) identifies the Regulatory Maps Geo Application (EQ Zapp) as the authoritative source for official Earthquake Zones of Required Investigation. CGS adds a zone there when it becomes official. Beginning in May 2026, CGS stopped publishing these maps as standalone PDF sheets; new maps appear as plates in Fault Evaluation Reports and Seismic Hazard Zone Reports. Use the current EQ Zapp layer and related report rather than an old standalone sheet.
CGS may publish preliminary fault-zone or seismic-hazard reports for public review. A preliminary release is not an official zone designation. The Seismic Hazards Mapping Act framework describes a 90-day public-comment period before a preliminary map is revised and an official map issued. Record whether the parcel is in an official zone, near a preliminary area, or outside the mapped coverage, and verify any uncertainty with the city or county that will review the permit.
Ask what a mapped zone requires for the project
California Seismic Hazard Zone maps identify areas for investigation of liquefaction or earthquake-induced landslides. Cities and counties use the maps in planning and building-permit processes. For most development designed for human occupancy in a mapped Zone of Required Investigation, the Act calls for a site-specific geotechnical investigation before permitting. A qualified, state-licensed engineering geologist or civil engineer evaluates whether a significant hazard exists and, where needed, recommends mitigation; the local agency reviews the report.
The map does not establish that a hazard exists at the ADU footprint, that the project has no statutory exception, or what mitigation is needed. Ask the local permitting agency which map and project rule apply, who may prepare the report, and what work area and submittal it requires. For national model coverage and its separate limits, see U.S. seismic-hazard screening.