What was the biggest earthquake in US history?

The magnitude 9.2 Prince William Sound, Alaska earthquake of March 28, 1964 — the largest recorded in US history and the second-largest ever measured worldwide.

Which US state has the most large earthquakes?

Alaska, by a wide margin. It sits on the highly active boundary between the Pacific and North American plates and records far more magnitude 6.0+ events than any other state, including several above magnitude 8.

Does a state with no recorded M6+ quake have no earthquake risk?

No. Many states experience smaller, still-damaging earthquakes, and some — like Missouri near the New Madrid Seismic Zone — have a history of rare but very large events. The absence of an M6+ event in a recent catalog reflects the data window, not zero risk.

Earthquake risk by region in the US (USGS data)

Earthquake risk in the US is highly uneven. Using the USGS earthquake catalog for magnitude 6.0+ events since 1900, here is where the big ones actually happen.

The answer first

Alaska is by far the most seismically active US state, recording far more large earthquakes than anywhere else — including the magnitude 9.2 Prince William Sound earthquake of 1964, the largest in US history. California, Hawaii, and the Pacific Northwest (Washington and Oregon) follow. Most of the central and eastern US has lower seismic activity, but not zero — a few regions, like the New Madrid zone, carry rare but serious risk.

Largest recorded US earthquakes (M6+)

Magnitude	Year	Region
9.2	1964	Prince William Sound, Alaska
8.6	1946	Unimak Island, Alaska
8.6	1957	Andreanof / Atka, Alaska
8.2	1938	Alaska
8.2	2021	Alaska Peninsula

Alaska’s dominance is not a quirk of the data — it sits squarely on the active boundary between the Pacific and North American plates. Each state profile lists its strongest attributed earthquakes; see Alaska and California for examples.

Why the West shakes most

The highest seismic hazard tracks plate boundaries and active fault systems:

Alaska — the Aleutian subduction zone produces the largest US earthquakes and tsunamis.
California — the San Andreas and related faults make it the most earthquake-aware state in the lower 48.
Pacific Northwest — the Cascadia Subduction Zone off Washington and Oregon is capable of a magnitude 9 event.
Hawaii — volcanic and flank earthquakes accompany active volcanism.
Nevada, Utah, Idaho, Montana — the Intermountain West has significant fault activity.

”No M6+ event” is not “no risk”

Our state pages attribute USGS magnitude-6.0+ events to states by parsing the event location. If a state shows no such event, that means none in this catalog named it — not that it has no earthquake risk. Two important caveats:

Smaller earthquakes (magnitude 4–5) can still cause damage and occur in most states.
The New Madrid Seismic Zone (around Missouri, Arkansas, Tennessee, Kentucky) produced some of the largest known central-US earthquakes in 1811–1812, before instrumental records — a reminder that the central US is not seismically quiet.

We say so explicitly rather than implying zero risk; see our methodology for how attribution works and its limits.

Earthquakes and FEMA declarations

Large earthquakes can trigger FEMA disaster declarations, though they are a small share of the total compared with fire, storms and floods — see which states have the most disasters. California’s record, for instance, includes a handful of earthquake declarations alongside its many wildfire declarations.

HazardMap is not affiliated with or endorsed by the USGS. Earthquake data is a USGS public-domain catalog summarised here for general information only — not seismic-hazard or safety advice. For authoritative hazard maps, consult the USGS National Seismic Hazard Model.