Cascadia Subduction Zone: The 1700 Earthquake and Future Risk
The Cascadia subduction zone is the plate boundary off the Pacific Northwest coast where the Juan de Fuca plate sinks beneath the North American plate, running about 700 miles from northern California to British Columbia. Its last great earthquake struck at about 9 p.m. on January 26, 1700, with an estimated magnitude of 8.7 to 9.2. The USGS puts the chance of another magnitude 9 on Cascadia in the next 50 years at 10 to 15 percent.
Where is the Cascadia subduction zone?
The Cascadia subduction zone lies offshore of northern California, Oregon, Washington and southern British Columbia. The USGS says the Juan de Fuca plate is thrust, or subducts, beneath the North American plate there. In southern Oregon and northern California, the USGS fact sheet calls the subducting plate the Gorda plate.
Oregon’s Office of Emergency Management describes Cascadia as a 700-mile fault that runs from northern California up to British Columbia, about 70 to 100 miles off the Pacific coast. The USGS earthquake catalog describes the zone as about 1,100 km long.
The two largest earthquakes in the USGS catalog for the United States, in Alaska in 1964 and in Cascadia in 1700, both came from subduction zones. Our guide to what causes a tsunami explains why this type of fault can also lift the seafloor and start a tsunami.
What happened on January 26, 1700?
On the evening of January 26, 1700, a great earthquake ruptured the Cascadia subduction zone. The USGS fact sheet gives an estimated magnitude between 8.7 and 9.2, and the USGS catalog lists it as magnitude 9.0. According to the USGS, scientists identified it by combining First Nations and Native American oral histories, tree-ring dating, coastal geology and written records of a tsunami in Japan.
| Evidence | What it shows |
|---|---|
| Ghost forests | Dead western red cedars and buried Sitka spruce stumps stand in tidal marshes of southern Washington, Oregon and northern California. Tree rings show a last growing season of 1699, so the land dropped suddenly before the 1700 growing season. |
| Sand sheets | Layers of sea sand that taper inland show a tsunami arrived soon after the land subsided. |
| Sand-filled cracks | Signs of liquefaction show the subsidence came with strong shaking. |
| Japanese records | Towns on Japan’s Pacific coast wrote about destructive waves on January 27 and 28, 1700, with no earthquake felt locally. Wave heights in Japan were estimated at 2 to 5 meters (7 to 16 feet). |
| Oral histories | First Nations and Native American accounts describe violent shaking at night, coastal flooding and villages destroyed. |
The Japanese records fix the time. According to the USGS catalog entry for the 1700 Cascadia earthquake, the waves struck two Japanese towns on the same day and hour, which pins the earthquake to about 9 p.m. local time on January 26 in Cascadia. Because no one in Japan felt shaking first, the event became known as the “orphan tsunami.”
How often does Cascadia produce great earthquakes?
Cascadia has a record of large earthquakes going back about 10,000 years. The USGS Fact Sheet 2025-3050, first posted September 19, 2025, calls it the most paleoseismically well-constrained subduction zone in the world. That evidence includes coastal land-level change, tsunami deposits, landslides, liquefaction and turbidites, which are underwater sediment flows on the continental margin and in inland lakes.
The USGS fact sheet makes these points about recurrence:
- At least 19 great (magnitude 8 or larger) megathrust earthquakes have ruptured most of the Cascadia coastline over the past 10,000 years.
- The USGS National Seismic Hazard Model uses a recurrence interval of about 500 years for full-margin, magnitude 9 ruptures.
- In southern Cascadia, partial ruptures of about magnitude 8 may occur every 800 to 1,000 years. Combined with full ruptures, that gives an overall recurrence of about 300 to 350 years in the south.
- Very few small or moderate earthquakes have been observed on the Cascadia megathrust itself.
What is the chance of the next big Cascadia earthquake?
The USGS gives Pacific Northwest earthquake chances over 50 years, about the lifetime of a typical building. The two figures for a magnitude 9 come from different methods: one treats each year as equally likely, and the other accounts for the time since 1700.
| Earthquake type (USGS Fact Sheet 2025-3050) | Chance in the next 50 years |
|---|---|
| Full-margin Cascadia megathrust, about M9 | 10% (time-independent) to 15% (time-dependent) |
| M8 or larger in southern Cascadia, full or partial rupture | About 30% (time-dependent) |
| Deep (intraslab) M6.5 or larger, Puget Sound region | 85% |
| Shallow crustal M6.5 or larger, Puget Sound region | 17% |
| M6.5 or larger on the Seattle Fault Zone | 5% |
State agencies use their own wording. Oregon’s Office of Emergency Management states that there is about a 37 percent chance of a megathrust earthquake of magnitude 7.1 or larger on Cascadia in the next 50 years. The same page estimates five to seven minutes of shaking along the coastline in a Cascadia earthquake. The Oregon and USGS figures describe different earthquake sizes, so they are not directly comparable.
What other earthquakes threaten the Pacific Northwest?
Cascadia’s megathrust is one of three earthquake types in the region, according to the USGS. Based on USGS recurrence estimates, the other two produce magnitude 6.5+ events more often.
Deep (intraslab) earthquakes happen inside the sinking Juan de Fuca plate, typically 40 to 60 km (25 to 40 miles) down. They are most common beneath Puget Sound. Examples include the 1949 magnitude 6.8 Olympia, 1965 magnitude 6.5 Seattle and 2001 magnitude 6.8 Nisqually earthquakes. Our guide to earthquake depth covers how deep events are classified.
Shallow crustal earthquakes happen on faults within about 30 km (20 miles) of the surface. Paleoseismic studies document a magnitude 7.5 to 7.8 Seattle Fault earthquake in 923 to 924 C.E. In western Oregon, the USGS lists the 1873 magnitude 6.8 Brookings and 1993 magnitude 5.6 Scotts Mills earthquakes.
How can you follow earthquakes and tsunami messages in Cascadia?
- See our live lists of USGS earthquakes in Oregon and Washington for the last 24 hours, 7 days and 30 days.
- Check our page of the latest NTWC and PTWC tsunami messages; the official source is tsunami.gov. Our guide to tsunami alerts explains warnings, advisories and watches.
- Learn how ShakeAlert early warnings reach phones in our ShakeAlert guide.
Oregon’s Office of Emergency Management advises residents to be “2 Weeks Ready,” because people may be without services and assistance for at least two weeks after a major disaster. For local guidance, follow your county emergency managers and the National Weather Service. Our pages show official data only and do not issue warnings.
Bottom line
Cascadia is a roughly 700-mile subduction zone off northern California, Oregon, Washington and British Columbia. Its last great earthquake, on January 26, 1700, is dated by ghost forests, tsunami sands and Japanese records. The USGS estimates a 10 to 15 percent chance of another magnitude 9 within 50 years, while deep earthquakes under Puget Sound are far more likely in the same period.
FAQ
When was the last Cascadia earthquake?
The last great Cascadia earthquake struck at about 9 p.m. on January 26, 1700. The USGS estimates its magnitude at 8.7 to 9.2.
How big could the next Cascadia earthquake be?
A full-margin rupture would be about magnitude 9, according to the USGS. Partial ruptures of about magnitude 8 are also in the geologic record, especially in southern Cascadia.
Which states would a Cascadia earthquake affect?
The USGS lists northern California, Oregon and Washington, along with southern British Columbia in Canada. These are the areas where Cascadia earthquakes have caused damage in the past.
How long ago was the last great Cascadia earthquake?
As of November 2026, it was 326 years ago. The USGS hazard model uses an average of about 500 years between full-margin ruptures, but individual intervals in the geologic record vary.