USGS earthquake-hazard maps describe regional ground-shaking models. They can help identify a question for a proposed or existing ADU, but they do not assess an individual lot, its foundations, or the safety of a building. A map result is a screening input for the next local code, site, or professional check—not a design value or approval.
Check the model before using the map
Record the map or data product, the location searched, the model edition or data-release variant, and the date of the lookup. Coverage and versions matter. USGS lists different model variants for the conterminous United States, Alaska, and Hawaii; do not assume that one map or file represents every U.S. territory or uses the same edition everywhere.
The revised 2023 50-state model data released on August 18, 2026 supersede earlier covered releases. The data identify variants including CONUS.2023.R1, CONUS.2023.R2, Alaska.2023.R1, and Hawaii.2021.R2. The variants are not interchangeable: the appropriate one depends on the location and intended application. If the map is used for design or code work, ask the local building official or qualified design professional which adopted code and model input apply.
Why a regional result cannot clear a parcel
USGS describes its maps as generalized information about areas, not an evaluation of a specific property. Local geology can amplify ground motion beyond what a regional map suggests. Site conditions such as subsurface material, depth to bedrock, groundwater, and slope can matter; for an existing structure, construction materials, number of floors, design, and retrofit history also affect an assessment.
The USGS does not perform private-property evaluations. Where the local authority, project, or professional identifies a need for site-specific work, arrange the appropriate geotechnical or structural assessment with a qualified professional. The necessary scope depends on the property, proposed work, applicable code, and local requirements; a national map does not establish when a particular project must commission a study.
A practical handoff
- Confirm the property location and select the current official model product for that region.
- Record its edition, data variant, lookup date, and stated limits.
- Ask the local building authority which code edition and seismic review apply to the proposed work.
- Have a qualified professional determine whether site or structural assessment is needed and interpret any results.
Do not use a regional hazard value to choose a foundation, design an ADU, or conclude that an existing unit is safe. Seismic screening supports due diligence; site-specific engineering and code compliance are separate decisions.