How large an earthquake can Cascadia Subduction Zone produce?

The maximum magnitude potential compiled for Cascadia Subduction Zone is M9.2. That figure comes from the length and width of the fault area that could rupture at once, calibrated against its historical and paleoseismic record. It is an upper bound on what the structure can do, not a forecast of the next event.

Is Cascadia Subduction Zone overdue for an earthquake?

No fault is ever 'overdue' in the way the phrase suggests. Recurrence intervals are averages over a handful of past ruptures, not a schedule: the interval between two events on the same fault routinely varies by a factor of two or more. The elapsed time shown on this page is exactly that — how long it has been — and not a probability that a rupture is imminent.

How is the seismicity on this page selected?

Every earthquake listed sits within 25 km of the mapped trace of Cascadia Subduction Zone, measured as the distance to the nearest fault segment rather than to a bounding box. Events on a neighbouring structure therefore do not appear here, even when they are geographically close. The slip rate of 35–40 mm/yr and the rupture history are compiled from the published literature.

All fault systems

Subduction megathrust

Cascadia Subduction Zone

Pacific Northwest, United States and Canada

Plate boundary: Juan de Fuca ↔ North American

Length: 1,000 km
Mₘₐₓ potential: M9.2
Slip rate: 35–40 mm/yr
Recurrence interval: ~500 years

Time elapsed since the last known rupture

65%

326 years have passed against an average interval of about 500 years. Recurrence on a real fault is not a clock — this is elapsed time, not a probability of rupture.

Locking depth

10–30 km

The depth range over which the fault is locked and accumulating elastic strain. Below it the rock creeps aseismically; above it, strain is released in earthquakes.

Historical rupture sequence

1700M9.0Cascadia megathrust

Live seismicity within 25 km of the trace (last 30 days)

Loading seismicity along this fault trace…

Frequently Asked Questions (FAQ)

Verified scientific, operational, and emergency protocols

Cascadia Subduction Zone is a subduction megathrust system running roughly 1,000 km through Pacific Northwest, United States and Canada. The kinematics describe how the two sides move relative to each other, which governs both the shaking a rupture produces and whether it can displace the sea floor.