Earthquake Risk in the US: How FEMA Scores It and How to Prepare

Earthquakes are the National Risk Index’s second-largest hazard by expected loss — roughly $26 billion per year nationally — despite being rare. That combination is exactly what makes them tricky to think about: a county can go a century without a damaging quake and still carry enormous risk, because when the ground finally moves under a modern city, losses arrive all at once and uninsured. The 1994 Northridge earthquake, a magnitude 6.7 under suburban Los Angeles, caused over $20 billion in damage in about twenty seconds.

What counts as earthquake risk

The NRI’s earthquake hazard (code ERQK) covers ground shaking from fault rupture — the primary killer of buildings — along with the liquefaction and ground failure that shaking triggers. (Earthquake-caused tsunamis and landslides are booked under their own NRI hazards.)

US earthquake risk is not just the San Andreas. The Cascadia Subduction Zone off Oregon and Washington can produce magnitude-9 events — the last one, in January 1700, dropped the coastline and sent a tsunami to Japan. The New Madrid Seismic Zone produced some of the strongest quakes in US history (1811–12) under what is now Missouri, Tennessee, and Arkansas. Salt Lake City sits on the Wasatch Fault; Charleston, SC was devastated in 1886; Alaska has more large quakes than the rest of the country combined; and Hawaii, Puerto Rico (2020), and even Oklahoma (induced seismicity) round out the map.

How the NRI measures it

FEMA combines each county’s exposure (building value and population), annualized earthquake frequency derived from USGS National Seismic Hazard Model probabilities, and historic loss ratios into an Expected Annual Loss, scored 0–100 relative to all counties. For a hazard this rare, the “annualized” framing matters: a county expecting one severe quake per 200 years with $200B exposed can carry a $1B-class EAL even if nobody alive has felt a big one there.

Where the risk concentrates

3,137 counties record measurable earthquake risk, but the top is emphatic: Los Angeles County, CA leads the nation (score 100, ~$4.6 billion expected annual loss — the largest single county-hazard number in the entire index outside flooding). The Bay Area follows — Alameda (~$1.35B) and Santa Clara (~$1.19B) counties — with Orange County, CA and King County, WA (Seattle, ~$1.2B) completing the top five. High ratings continue through the Puget Sound, Portland, Salt Lake City’s Wasatch Front, Memphis and the New Madrid zone, Charleston, Anchorage, and Honolulu.

How to read your county’s score

Earthquake risk is about when your buildings were built as much as where they stand. Modern seismic codes (roughly post-1994 in the West) perform well; the dangerous stock is older: unreinforced masonry, pre-1980 concrete, “soft-story” apartments over open parking, and houses not bolted to their foundations. If your county rates High or Very High, the questions are: What vintage is your home? Is it bolted and braced? Does your city have a mandatory retrofit program (LA, San Francisco, and Seattle do)? And crucially — do you have earthquake insurance? Standard homeowners policies exclude earthquake entirely; in California only about 10–15% of homeowners carry it.

What actually reduces the risk

• Bolt and brace. For wood-frame houses, a foundation bolt-and-cripple-wall-brace retrofit costs a few thousand dollars, prevents the most common catastrophic failure (sliding off the foundation), and is subsidized in California (Earthquake Brace + Bolt).
• Kill the soft story. Living above open parking or storefronts in an older building is the highest-risk residential situation; retrofits add steel frames or shear walls.
• Secure the interior. Strap the water heater (fire + water loss), anchor tall furniture and TVs, use museum putty and cabinet latches. Most injuries are from falling objects, not collapsing buildings.
• Drop, Cover, Hold On — under a table, not in a doorway, and do not run outside during shaking; facades kill. Practice via the annual Great ShakeOut.
• Get early warning. The ShakeAlert system delivers seconds of warning via the MyShake app and wireless alerts in CA, OR, and WA — enough to drop, stop surgery, or slow a train.
• Prepare for two weeks on your own. A Cascadia or San Andreas event will overwhelm response capacity; water (1 gal/person/day), a gas shutoff wrench, and out-of-state contact plans are the standard kit.

Sources

• USGS Earthquake Hazards Program — hazard maps and real-time data
• FEMA NRI earthquake methodology
• ShakeAlert earthquake early warning
• Ready.gov earthquake preparedness