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TitleMapping crustal stress and strain in southwest British Columbia
AuthorBalfour, N J; Cassidy, J F; Dosso, S E; Mazzotti, S
SourceJournal of Geophysical Research vol. 116, B03314, 2011, 11 pages,
Alt SeriesEarth Sciences Sector, Contribution Series 20100277
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia
NTS92E; 92F; 92G; 92H; 92I; 92J; 92K; 92L; 92M; 92N
AreaSouthwest British Columbia; Vancouver; Victoria; Vancouver Island
Lat/Long WENS-129.0000 -120.0000 52.0000 48.0000
Subjectstectonics; structural geology; continental crust; crustal studies; crustal structure; stress analyses; strain; strain analysis; structural features; tectonic interpretations; tectonic environments; tectonic zones; Cascadia Subduction Zone
Illustrationslocation maps; stereonets; ternary diagrams; graphs; plots
ProgramTargeted Hazard Assessments in Western Canada, Public Safety Geoscience
AbstractThis paper investigates the orientation and sources of stress in the forearc of the Cascadia subduction zone in southwest British Columbia, using Bayesian inversion results from focal mechanism data and comparing results with GPS derived short-term strain rates. The subduction margin in this region includes a change in orientation from N-S in Washington State to NW-SE in British Columbia. Over 1000 focal mechanisms from North American crustal earthquakes have been calculated to identify the dominant style of faulting, and ~600 were inverted to estimate the principal stress orientations and the stress ratio. Our results indicate the maximum horizontal compressive stress orientation changes with distance to the trench, from approximately margin-normal along the coast to approximately margin-parallel 100 - 150 km inland from the coast. Comparing stress orientations with GPS data, we relate the margin-normal stress direction to subductionrelated strain rates due to the locked interface between the North American and Juan de Fuca plates just west of Vancouver Island. Further from the margin the plates are coupled less strongly, and the margin-parallel maximum horizontal compressive stress in the North American Plate relates to the northward push of the Oregon Block, which is also observed in the horizontal shortening direction of the residual strain rates, after the subduction component is removed.