Cascadia subduction zone

The convergent boundary where the Juan de Fuca Plate and related oceanic plates descend beneath North America from northern California to British Columbia. Its shallow interface can lock between great earthquakes, creating a major earthquake and tsunami hazard.

Juan de Fuca Plate: An oceanic tectonic plate that subducts beneath North America along much of the Pacific Northwest coast. Its motion drives convergence across the Cascadia boundary.
1700 Cascadia earthquake: A great earthquake on the Cascadia subduction zone around January 26, 1700, inferred from geological and historical evidence. Its estimated rupture and date anchor assessments of Cascadia recurrence.
Cascadia Rising: A regional emergency exercise preparing Pacific Northwest agencies for a major Cascadia earthquake and tsunami. The exercise tests response plans against a plausible regional disaster.
Juan de Fuca Ridge: A mid-ocean ridge off the Pacific Northwest where new oceanic crust forms between the Pacific and Juan de Fuca plates. Crust formed here moves toward the Cascadia subduction zone.
Earthquake recurrence interval: The time between successive earthquakes on a fault or within a defined region. Cascadia’s irregular prehistoric record limits simple forecasts of the next great rupture.
Cascadia megathrust: The shallow fault interface between the subducting Juan de Fuca Plate and the overriding North American Plate. This locked interface stores strain that can be released in a great earthquake.
Ghost forest: A stand of dead trees preserved after sudden land subsidence or burial, often along tectonically active coasts. Cascadia ghost forests record coastal subsidence during past great earthquakes.
ShakeAlert: An earthquake early-warning system that detects seismic waves and sends alerts before stronger shaking arrives. Its alerts could provide limited warning after a Cascadia rupture begins.
Explorer Plate: A small oceanic plate off British Columbia, associated with the northern end of the Cascadia subduction system. Its boundary and motion complicate the northern geometry of Cascadia.
Cascadia slow-slip segmentation: The pattern by which slow-slip events occur in separate along-strike sections of the Cascadia interface. Segmentation may reveal whether neighboring fault sections interact or behave independently.

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