When most Americans think about earthquake risk, they picture California. But USGS data tells a more complex story: 39 states face moderate to high seismic hazard, and the financial consequences of buying in a high-risk zone without proper due diligence can be devastating.
Understanding Seismic Hazard Zones
The USGS National Seismic Hazard Model (NSHM) maps ground motion probability across the entire United States. The key metric is Peak Ground Acceleration (PGA) — expressed as a fraction of g (gravitational acceleration) — at a 2% probability of exceedance in 50 years (the standard engineering benchmark, roughly equivalent to a 2,500-year return period).
| PGA Value | Hazard Level | States/Regions |
|---|---|---|
| > 0.5g | Very High | Coastal CA, parts of OR/WA, AK, HI |
| 0.2–0.5g | High | Inland CA, Cascadia subduction zone, New Madrid Seismic Zone |
| 0.1–0.2g | Moderate | Parts of WA, OR, ID, MT, UT, NV, WY, SC, TN, MO, IL, IN |
| 0.05–0.1g | Low-Moderate | Mid-Atlantic, Intermountain West, Southeast |
| < 0.05g | Low | Gulf Coast, Great Plains, upper Midwest |
High-Risk Regions Beyond California
The New Madrid Seismic Zone
Stretching across parts of Missouri, Tennessee, Kentucky, Arkansas, and Illinois, the New Madrid Seismic Zone produced three of the largest earthquakes in US history in 1811-1812 (estimated Mw 7.5-8.0). A repeat of those events today would affect an area 20x larger than the 1906 San Francisco earthquake, due to the efficiency of Eastern rock in transmitting seismic waves.
Cities at significant risk include: Memphis, TN; St. Louis, MO; Little Rock, AR; Evansville, IN; and Paducah, KY. Very few residential structures in this region are seismically retrofitted.
Cascadia Subduction Zone
The Cascadia subduction zone off the coasts of Oregon, Washington, and Northern California is capable of producing Mw 9.0+ megathrust earthquakes. The last full-rupture event was in January 1700. A repeat would generate catastrophic shaking throughout the Pacific Northwest plus a large tsunami affecting coastal communities.
Portland and Seattle — both growing tech hubs — face significant risk. Many older unreinforced masonry (URM) buildings in both cities remain unretrofitted despite known vulnerability.
Charleston, South Carolina
In 1886, Charleston experienced one of the most damaging earthquakes in US history east of the Rockies (Mw ~7.0). The Charleston seismic zone remains active, and the region's aging building stock has minimal seismic reinforcement.
How the NRI Calculates Earthquake EAL
FEMA's National Risk Index uses USGS hazard data to estimate Expected Annual Loss from earthquakes at the census tract level. The methodology accounts for:
- Hazard — PGA probability curves from the NSHM
- Exposure — Building inventory value at risk
- Vulnerability — Building fragility by construction type and age
The resulting EAL figure represents the annualized probabilistic loss from earthquake damage to buildings in the tract. For homebuyers, this translates directly to: if I hold this property for 30 years, what is the present value of expected earthquake damage?
A tract with $10,000/year earthquake EAL has a 30-year NPV risk cost of approximately $154,000 (at 5% discount rate). This cost is invisible in the listing price but very real in ownership economics.
Building Codes and Retrofit Costs
Earthquake resilience is largely a function of when a building was constructed relative to local code adoption milestones:
| Construction Era | Risk Level | Notes |
|---|---|---|
| Pre-1933 | Very High | No seismic requirements; URM common |
| 1933–1971 (CA) | High | Basic requirements; soft-story wood frames common |
| 1971–1994 (CA) | Moderate | Post-Sylmar improvements; pre-Northridge connections |
| Post-1994 (CA) | Low-Moderate | Significant improvements post-Northridge |
| Post-2015 (Seattle/Portland) | Improving | New mandatory retrofit programs for URMs |
Soft-story buildings — multi-unit wood-frame structures with open parking at ground level — are especially vulnerable. Los Angeles has mandated retrofit of ~13,500 such buildings since 2015. Seattle has begun a similar program for its ~1,100 URMs. If you're buying a pre-1980 multi-unit property in a seismically active area, a structural engineering inspection is non-negotiable.
Retrofit costs typically range:
- Cripple-wall retrofit (wood frame): $3,000–$8,000
- Soft-story retrofit (multi-unit): $60,000–$200,000+
- URM seismic upgrade: $50,000–$300,000+
These costs should factor into purchase price negotiations and your long-term capital expenditure budget.
What Earthquake Insurance Actually Covers
Homeowner's insurance does not cover earthquake damage. A separate earthquake insurance policy is required. Key facts:
- Availability: CEA (California Earthquake Authority) for CA residents; private markets in other states (thin coverage in many)
- Deductibles: Typically 10-25% of dwelling coverage — a $500,000 home faces a $50,000-125,000 deductible before insurance pays
- Premiums: $800-$5,000+/year depending on location, construction, age
- Coverage gaps: Most policies exclude contents, additional living expenses, and non-structural damage in low tiers
In practice, earthquake insurance has low take-up rates (fewer than 15% of CA homeowners carry it) partly because high deductibles make it function more like catastrophic coverage than practical protection. Budget accordingly.
The Bottom Line
Earthquake risk is underpriced in most US real estate markets outside California. The NRI's tract-level EAL data quantifies exactly how much of that risk you're absorbing at any specific address. Use the data before you negotiate, not after you're on the hook for a mortgage.
Check your target county's earthquake EAL on RiskBeforeBuy's free risk calculator, and factor the 30-year NPV cost into your maximum bid.