M 6.8 - 210 km SW of Port McNeill, Canada

Tectonic Summary

Over the course of 43 minutes on October 22, 2018 a series of M6.6, M6.8 and M6.5 earthquakes occurred off of Vancouver Island, Canada. These earthquakes occurred as a result of strike-slip faulting at shallow depths on the boundary or within the interior of the Explorer microplate. Focal mechanism solutions for the earthquakes indicate rupture occurred on either a near-vertical right-lateral northwest-southeast striking fault, or along a near-vertical left-lateral northeast-southwest striking fault. The tectonics of the Pacific margin of North America between Vancouver Island and south-central Alaska are dominated by the northwest motion of the Pacific plate with respect to the North America plate at a velocity of approximately 50 mm/yr. Convergence between the northern extent of the Juan de Fuca plate (also known as the Explorer microplate) and North America plate dominate the regional tectonics. The Explorer Ridge along the western side of the Explorer plate and the Sovanco Fracture Zone to the south define the boundary between the Pacific and Explorer plates. To the east, the Explorer plate subducts beneath the North American Plate. Eastward of the Sovanco Fracture Zone the Nootka fault separates the Explorer plate from the Juan de Fuca plate. As a result of these forces the Explorer plate is internally deformed and faulted and can produce diffuse seismicity away from its boundaries. Although a larger earthquake cannot be ruled out, previous sequences of large, closely spaced events in this region have not resulted in larger events, including a M 6.6 and M 6.4 in 2008 that were separated by an hour.

The Explorer microplate is heavily deformed by internal dextral faulting, experiencing frequent moderate-sized earthquakes. Within approximately 70 km of these earthquakes, 11 earthquakes of M 6 or greater have occurred since 1951. The largest previous recorded earthquake in this region was a M 6.8 event that occurred on December 17, 1980.

Explorer plate seismicity, M6.0 or larger earthquakes since 1918. The recent M6.6, M6.8 and M6.5 earthquakes are shown as yellow circles, older earthquakes in shown as grey circles.