Earthquake Risk

Earthquake risk in the United States is concentrated in the West Coast, the Pacific Northwest, and a handful of inland zones near the New Madrid and Wabash Valley seismic zones. The USGS National Seismic Hazard Maps are the authoritative federal source; the peak ground acceleration (PGA) value they publish for any lat/lon drives the design loads in modern building codes and is the input to the Risk Before Buy earthquake score.

Earthquake is the hazard with the highest severity-to-frequency gap. A major event in a high-PGA zone happens every 100 to 300 years; the median property owner experiences no earthquake during their holding period. That asymmetry is why earthquake insurance take-up in California — the most exposed state — is roughly 10%. The deductible structure (typically 10 to 20 percent of dwelling value) is a further friction, as is the fact that earthquake coverage is excluded from standard homeowners policies and must be purchased as an endorsement or stand-alone policy through the California Earthquake Authority or a private carrier.

For properties in moderate and high PGA zones, three signals matter most: vintage (pre-1980 construction often needs retrofitting), foundation type (raised, post-and-pier, or unreinforced masonry are the most vulnerable), and soil (liquefaction-prone alluvial and fill soils amplify shaking). A licensed structural engineer is the right professional for a deeper property-level review; the free Risk Before Buy snapshot returns the USGS PGA at the parcel coordinates.