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TitleGreat earthquakes on Canada's West Coast: a review
AuthorHyndman, R D; Rogers, G C
SourceCanadian Journal of Earth Sciences vol. 47, issue 5, 2010 p. 801-820,
Alt SeriesEarth Sciences Sector, Contribution Series 20090196
PublisherNRC Research Press
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia
NTS92B; 92C; 92E; 92F; 92G; 92H; 92I; 92J; 92K; 92L
AreaVancouver; Victoria; Seatle; Canada; United States
Lat/Long WENS-128.0000 -120.0000 51.0000 47.0000
Subjectstectonics; geophysics; earthquakes; earthquake studies; earthquake risk; earthquake mechanisms; earthquake magnitudes; earthquake catalogues; subduction
Illustrationslocation maps; photographs; cross-sections; block diagrams; plots; profiles
ProgramNational-Scale Geohazard Assessments, Public Safety Geoscience
AbstractThe first Lithoprobe transect in 1984 across Vancouver Island had primary objectives to define the structure associated with subduction and constraints on the potential for great thrust earthquakes. The Lithoprobe results and the comprehensive multidisciplinary data collection and analyses that followed provide compelling evidence for past great earthquakes along the Cascadia subduction zone from Vancouver Island to northernmost California, and for present elastic strain build up toward future great events. There is evidence of sudden coastal subsidence up to 2 m and of deep-sea turbidite deposits indicating strong shaking from huge earthquakes at irregular intervals averaging about 500 years, the last in 1700. Precision geodetic measurements define the present buckling of the coastal region, diagnostic of elastic strain accumulation on a locked thrust fault. The landward extent of rupture and, therefore, shaking at coastal cities is constrained by (i) the pattern of elastic strain buildup, (ii) the estimated temperatures on the fault, (iii) the updip limit of episodic tremor and slip (ETS), (iv) the downdip change in reflection character of the thrust, and (v) the magnitude of coastal subsidence in the most recent, 1700, and previous great events. The major earthquakes are very large, M9, rupturing most of the Cascadia margin, but mainly offshore, limiting somewhat the shaking at inland cities but producing large tsunamis. The ETS that occurs at intervals of just over a year appears to involve slow slip on the subduction thrust downdip of the rupture zone that increases stress on the locked zone and may indicate time varying potential for great events.