Canada

Canada extends across some of the most geologically diverse territory on Earth, and while much of the country rests on ancient stable cratons, its western and eastern margins host significant seismic hazard from fundamentally different tectonic processes. British Columbia faces the most immediate and severe threat from the Cascadia Subduction Zone, where the Juan de Fuca Plate slides beneath the North American Plate at approximately 4 centimetres per year. In a broad sense, the entire Vancouver Island and southern British Columbia region is locked in an accumulating stress cycle that periodically releases in giant megathrust earthquakes. Farther north along the Queen Charlotte Fault — the Canadian segment of the transform boundary between the Pacific and North American plates — right-lateral strike-slip motion generates large shallow [[fault]] earthquakes. In eastern Canada, the St. Lawrence and Ottawa River valleys follow ancient rifted margins and failed rift arms, reactivated periodically by [[seismic-wave]]-generating events tied to postglacial isostatic rebound as the crust slowly rises after the removal of Pleistocene ice sheets.

The geological archive of Cascadia megathrust events is written in coastal stratigraphy rather than written history. Ghost forests of dead western red cedar trees drowned by sudden land subsidence, tsunami sand sheets deposited far inland, and native oral traditions describing great shaking and ocean flooding all point to recurring great earthquakes at the Cascadia [[subduction-zone]]. The most recent full-margin Cascadia rupture occurred on 26 January 1700, generating a [[tsunami]] that reached the coasts of Japan with a [[magnitude]] now estimated at 9.0 to 9.2. The interval between such full-margin ruptures averages around 200 to 500 years, suggesting the region is well within the window for the next event. In terms of recorded history, the 1700 event predates European seismological observation on the Pacific Coast. In eastern Canada, the 1663 Charlevoix-Kamouraska earthquake (magnitude estimated at 7.0) remains the largest historic event in the St. Lawrence region; the 1935 Timiskaming earthquake (magnitude 6.2) and the 1988 Saguenay earthquake (magnitude 5.9) caused significant damage in Quebec. Nunavut and the Arctic experienced a notable magnitude 6.1 event in 2015. British Columbia's recorded history includes the 1918 Haida Gwaii (Queen Charlotte Islands) earthquake (magnitude 7.0) and the 1949 event (magnitude 8.1), one of the largest strike-slip earthquakes ever recorded.

Canada's tectonic setting combines three fundamentally distinct regimes. The stable Precambrian Canadian Shield — rocks up to four billion years old — forms a vast, low-seismicity nucleus covering most of central Canada. Around its edges, the Appalachians in the east record the ancient collision of North America with Africa during the Paleozoic, leaving behind a legacy of east-trending faults susceptible to rare but significant reactivation. The Western Cordillera is entirely different: an accreted collage of exotic terranes — oceanic crust, island arcs, and continental fragments — welded onto the western margin of the continent during Mesozoic and Cenozoic time. The current [[subduction-zone]] represents the latest chapter of this ongoing accretion. Preparedness has advanced significantly in recent decades; Natural Resources Canada operates the National Seismograph Network, and the joint Canadian-American development of ShakeAlert-type [[early-warning]] technology for the Cascadia zone remains an active research priority.