Earthquakes · Property safety guide · Reviewed July 14, 2026
California earthquake fault zones
A practical first stop for Alquist-Priolo fault zones, seismic hazard zones, disclosure, and local planning-office checks before you buy or build.
The short version
A zone is a closer-look signal, not a prediction
Use EQ Zapp to see whether the parcel is in an official fault-rupture, liquefaction, or earthquake-landslide zone. A hit is a signal, not a verdict: it does not mean damage is certain or building is banned. Instead, it tells buyers, owners, and local permit staff which reports and rules to check next.
What changes the answer: A blank or unevaluated result does not mean no earthquake hazard. Preliminary maps and old screenshots are not the current official layer.
A fault-zone map is not a prediction that a home will fall down. An existing home is not automatically unsafe or illegal just because it sits inside a zone. The map is a regulatory starting point that says surface fault rupture needs a closer look.
Alquist-Priolo zones cover active fault traces. Seismic hazard zones are a separate map family. Those cover liquefaction and quake-triggered landslides.
EQ Zapp is now CGS's sole authoritative map source for official Earthquake Zones of Required Investigation. A preliminary report, old PDF, real-estate map, or screenshot is not the same as the current official layer.
The simple rule: use the state map for a first check. Then confirm with the city or county what it means for the exact parcel.
How it works
California uses two map families
An Alquist-Priolo Earthquake Fault Zone follows the surface traces of active faults. It deals with ground breaking at the surface. It does not map all shaking, liquefaction, landslides, tsunami, or fire danger.
A Seismic Hazard Zone covers a different problem. It marks areas where loose wet soil may lose strength, or where a slope may fail during an earthquake. A zone does not say that every spot inside it will fail in the next quake.
The map starts the permit check
For many new projects in an Alquist-Priolo zone, the local agency needs a geologic study before it can issue a permit. The study helps show where the active fault is and keeps covered buildings for people off that fault.
A building for people generally may not sit across an active fault trace. Unless a detailed study shows otherwise, the usual planning presumption covers the ground within 50 feet of that trace. The geologist's site work can locate the fault more closely; a map line by itself cannot.
For many projects in a Seismic Hazard Zone, a site study looks for the mapped soil or slope problem and sets out ways to reduce it. One state exemption covers a wood-frame single-family home of two stories or less when it is not part of a development of four or more homes. A local agency can still use stricter rules.
For example, a parcel can sit in both an Alquist-Priolo zone and a liquefaction zone. That does not create an automatic building ban. It means the permit file may need one study for surface fault rupture and another look at the soil response, followed by the measures the local agency requires.
Buying and building use the map differently
During a sale, an official zone can appear in the natural hazard disclosure. Read the current disclosure and get any geologic or soil reports already tied to the parcel. The form tells you about a mapped zone. It does not tell you the condition of the foundation or the likely repair cost.
For construction, bring the parcel number and a simple project description to the city or county planning or building office. Confirm the official zone, earlier permit files, recorded studies, and the report the new work needs. A licensed geologist or engineer handles the site work when the law or local office requires it.
Official, preliminary, and unevaluated are different
EQ Zapp is the state's sole authoritative source for current official Earthquake Zones of Required Investigation. The May 21, 2026 map release is still preliminary during its 90-day review period, which runs through August 19, 2026. Those lines are not official unless the state later adds them to EQ Zapp.
EQ Zapp can also say that an area has not been evaluated. Its parcel layer is updated twice a year and can lag local records. Use the local parcel map, official reports, and permit files when a line is close or the result is unclear.
First moves
- 1
Look up the parcel in EQ Zapp, the state's official zone map.
- 2
Check which zone applies: an Alquist-Priolo fault zone, a seismic hazard zone, or both.
- 3
If you are buying, review the natural hazard disclosure and any reports already on file.
- 4
If you are building or remodeling, call the local planning or building office before design work gets expensive.
- 5
If the map line is close, use a licensed professional or the local office. Do not guess from a screenshot.
Watch for
- 1
Alquist-Priolo covers surface fault rupture only. It does not measure shaking, tsunami, or fire risk.
- 2
Seismic hazard zones can trigger liquefaction or landslide review even far from a fault line.
- 3
A preliminary earthquake-zone release is open for review and is not yet the official regulatory layer. Use EQ Zapp to check what is official today.
- 4
EQ Zapp can say an area has not been evaluated, and its parcel layer can lag local parcel records. A blank result is not proof of no earthquake hazard.
- 5
Map tools are a starting point. Local permit files, recorded reports, and parcel studies can matter more.
- 6
Disclosure, insurance, lending, and permits can each treat the map differently.
Official sources
Where to confirm this
Use the source that matches the part you need. Current forms, fees, deadlines, maps, and local decisions can change after this guide is reviewed.
Earthquake-zone maps are regulatory starting points, not parcel-specific legal advice or earthquake predictions. Check the official CGS map, local planning or building office, recorded reports, disclosure documents, and current law for the exact parcel.