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Earthquake Fault Zones and Seismic Hazards When Buying in California

By Matthew Martinez, Founder, CEO & Managing Broker, Diamond Real Estate Group. California DRE #01869679.

An Alquist-Priolo Earthquake Fault Zone is a regulatory zone the California Geological Survey draws around the surface traces of active faults, meaning faults that have ruptured in the last 11,000 years. The zones average about a quarter mile wide. Inside one, a new building for human occupancy can’t be placed over an active fault and generally must sit at least 50 feet from it, and a seller must disclose the zone to a buyer. A separate state map, the Seismic Hazard Zones, covers ground that could liquefy or slide in a strong earthquake.

Both maps show up on the Natural Hazard Disclosure statement in most California sales. This guide explains what each zone means for an existing house and for new construction, which duties fall on the seller, how older homes are handled, and what buyers in the Bay Area and North Bay should check during escrow. It reflects the statutes and agency pages we reviewed in October 2026.

Two state earthquake zones, two different questions

	Earthquake Fault Zone	Seismic Hazard Zone
Law	Alquist-Priolo Earthquake Fault Zoning Act, Public Resources Code section 2621 and following	Seismic Hazards Mapping Act, Public Resources Code section 2690 and following
Hazard mapped	Surface fault rupture along active faults	Liquefaction and earthquake-induced landslides
Rule for new projects	Geologic investigation by a state-licensed geologist; no occupied building over an active trace; setback generally 50 feet	Geotechnical report defining the hazard before the city or county approves the project, unless waived
At sale	Disclosed under section 2621.9, usually on the Natural Hazard Disclosure statement	Reported on the Natural Hazard Disclosure statement
Where to look	The Geological Survey’s EQ Zapp map shows both by address

A “Yes” on either line doesn’t mean a house is unsafe or can’t be insured. It tells you what kind of expert to call and what questions to ask before you remove contingencies. Our natural hazard disclosure guide explains the full report.

How the Alquist-Priolo Act works

The Geological Survey says the Act was created after the 1971 San Fernando earthquake to reduce losses from surface fault rupture. Its Special Publication 42 records that the law was signed on December 22, 1972, and took effect on March 7, 1973. Shaking is a separate problem that building codes address; this law deals with the ground itself tearing along a fault. The survey maps the zones, and cities and counties apply them through their permitting.

Before permitting a covered project in a zone, the city or county requires a geologic investigation, prepared by a state-licensed geologist, showing that buildings won’t straddle an active fault. The Geological Survey notes that local agencies may adopt rules stricter than state law.

Which projects are covered

Section 2621.6 defines a “project” as a land division that contemplates buildings for human occupancy, or a structure for human occupancy. It carves out a single-family wood-frame or steel-frame home of no more than two stories that isn’t part of a development of four or more homes, and homes on lots whose geologic reports were already approved at subdivision. So under state law alone, one custom house on an existing lot may not trigger the Act, though a city or county can still require a fault study.

Section 2621.7 adds exemptions that matter for existing buildings: alterations worth no more than 50 percent of the structure’s appraised value, conversion of an existing apartment complex into condominiums, and certain seismic retrofits of older building types such as soft-story wood frames. None of those exemptions removes the seller’s disclosure duty.

What the seller must disclose

Under Public Resources Code section 2621.9, the seller’s agent, or the seller if there’s no agent, must tell a prospective buyer that the property is “located within a delineated earthquake fault zone.” The duty applies if the seller or agent actually knows, or if the state’s map covering the property has been provided to the city or county and notice posted at the county recorder, assessor and planning offices.

In most sales the disclosure is made on the Natural Hazard Disclosure statement under Civil Code section 1103.2. If the official map is too imprecise for a reasonable person to tell whether the property is inside the zone, the agent must mark “Yes” unless a report verifying the property is outside the zone is attached. The disclosure does not limit any other duty the seller or agent has to disclose known facts.

What a “Yes” does and doesn’t tell you

A zone line marks a band around mapped fault traces, not the trace itself. Most of a zone’s area is not on a fault. To learn where the trace runs relative to the house, ask the seller and the city or county for any geologic investigation filed for the parcel or the subdivision, and consider a consultation with an engineering geologist during your investigation period.

Seismic Hazard Zones: liquefaction and landslides

The Seismic Hazards Mapping Act covers ground failure. Public Resources Code section 2697 makes a geotechnical report a condition of approval: in a mapped seismic hazard zone, the city or county must obtain one that defines and delineates the hazard before it approves a project. It may waive the report if it finds no undue hazard based on studies of nearby sites with similar soils, and it must send a copy of each approved report to the State Geologist within 30 days.

For a buyer, a liquefaction or landslide zone is a reason to look at the foundation, drainage, retaining walls and any past movement. Our post on geotechnical reports for hillside homes explains when to order one, and our guide to San Francisco hazard maps shows how the liquefaction zones fall across the city.

Fault zones in Diamond’s markets

Fault zones are drawn quadrangle by quadrangle, and the maps are revised as new studies come in. Napa is a recent example. The South Napa earthquake of August 24, 2014 led the Geological Survey to issue a new official fault zone map for the Napa quadrangle, and the county’s GIS copy of that map is dated January 11, 2018. The county’s metadata says the map supports permitting and real estate disclosure, does not show every fault that could rupture, and is no substitute for site-specific geologic investigation. Our Browns Valley neighborhood guide describes what that means on the ground there.

Elsewhere in the Bay Area and North Bay, don’t rely on a listing description or a general fault map. Look up the exact address on EQ Zapp, read the Natural Hazard Disclosure, and ask the local planning department whether any parcel-specific fault study exists.

Older homes: the Homeowner’s Guide to Earthquake Safety

Government Code section 8897.1 adds a duty for older houses. When a dwelling of one to four units built before 1960 with conventional light-frame construction is sold, the seller must give the buyer the state’s Homeowner’s Guide to Earthquake Safety and complete an earthquake hazards disclosure “as soon as practicable before the transfer.” Court-ordered, foreclosure and fiduciary transfers, such as sales by a trustee or estate, are among the listed exemptions.

Section 8897.2 lists the weaknesses the seller must disclose if the seller actually knows of them and they are material:

No anchor bolts securing the sill plate to the foundation.
Perimeter cripple walls that aren’t braced.
First-story walls that aren’t braced.
A perimeter foundation of unreinforced masonry.
Unreinforced masonry walls.
A habitable room or rooms above a garage.
A water heater that isn’t anchored, strapped or braced.

The seller must also disclose known corrective work on those items. The statute asks about the seller’s knowledge; it doesn’t require the seller to inspect or strengthen anything. Our page on California point-of-sale requirements lists this alongside the other statewide sale items.

What to have inspected

Ask your home inspector to look specifically at foundation bolting, cripple walls, chimney condition, the water heater and any rooms over a garage. Where there’s doubt, a structural engineer can scope a retrofit and estimate cost before you negotiate. For the smaller fixes inside the house, such as water heater straps, cabinet latches and anchoring tall furniture, see our home safety essentials checklist. For apartment buildings, local soft-story ordinances add their own rules; see our guide to seismic retrofits for multifamily property.

Earthquake insurance

The California Earthquake Authority says that in most cases earthquake damage isn’t covered by a homeowners policy. CEA policies are sold only through participating residential insurers, so you buy one through your home insurer or agent. Coverage includes the dwelling, personal property, loss of use, emergency repairs and a building code upgrade amount.

Dwelling deductibles range from 5 to 25 percent. CEA limits homes with a dwelling limit over $1 million, and pre-1980 raised-foundation homes without a verified retrofit, to the 15, 20 or 25 percent options. It offers premium discounts of up to 25 percent for older houses that have been properly retrofitted. Get quotes during escrow; our guide to homeowners insurance during escrow covers timing.

A buyer’s checklist

Look up the address on EQ Zapp before you write an offer, and note any fault, liquefaction or landslide zone.
Read the Natural Hazard Disclosure and the seller’s disclosures for fault and seismic entries and any known earthquake repairs.
Ask for prior reports. Geologic or geotechnical reports filed for the parcel or subdivision, and permits for any retrofit.
Inspect the structure for bolting, bracing and water heater strapping, and bring in a structural engineer if needed.
Plan any new construction with the city or county early, since a fault or seismic zone can require studies before permits. Our post on buying a teardown covers rebuild planning.
Price earthquake insurance and compare deductibles before your contingencies expire.

Diamond may refer you to partners we work with, such as inspectors, engineers and insurance agents; you’re free to choose any provider. This is general information, not legal or engineering advice; an engineering geologist or structural engineer should evaluate a specific site and building, and a real estate attorney can answer disclosure questions.

Questions people ask

What is an Alquist-Priolo Earthquake Fault Zone?

It’s a regulatory zone the California Geological Survey maps around active faults, those that have ruptured in the last 11,000 years. Zones average about a quarter mile wide, and new occupied buildings can’t be placed over an active fault inside them.

Can I buy a house in an earthquake fault zone?

Yes. The zone triggers disclosure and rules for new projects; it doesn’t prohibit owning or selling an existing home. Check where the fault trace runs relative to the house and what reports exist.

Can I build a new house in an earthquake fault zone?

Often, but not over an active fault, and typically with a setback of about 50 feet. Under state law a single two-story-or-less wood-frame home not in a development of four or more isn’t a covered project, but local rules may still require a geologic study.

How do I find out if a property is in a fault zone?

Search the address on the Geological Survey’s EQ Zapp map, and read the Natural Hazard Disclosure statement, which reports both earthquake fault zones and seismic hazard zones.

What is the Homeowner’s Guide to Earthquake Safety?

It’s the state booklet a seller must give the buyer of a one-to-four-unit, light-frame home built before 1960, along with an earthquake hazards disclosure of known weaknesses such as missing anchor bolts or an unbraced water heater.

Does homeowners insurance cover earthquakes?

Usually not. The California Earthquake Authority says most homeowners policies don’t cover earthquake damage; a separate earthquake policy, such as one from CEA through a participating insurer, is needed.

What’s the difference between a fault zone and a seismic hazard zone?

A fault zone maps where the ground could rupture along an active fault. A seismic hazard zone maps where soil could liquefy or slopes could slide in strong shaking. They come from different laws and trigger different studies.

If you’re buying in an area with fault or seismic zones and want help reading the reports, contact Diamond Real Estate Group. Our home buying process guide covers the rest of escrow, including flood zones and fire hazard zones.

Sources & notes

Last reviewed October 2026 by Matthew Martinez.