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TitreMapping crustal stress and strain in southwest British Columbia
AuteurBalfour, N; Cassidy, J; Dosso, S E; Mazzotti, S
SourceAmerican Geophysical Union Fall Meeting, abstracts volume; 2010 p. 1
Séries alt.Secteur des sciences de la Terre, Contribution externe 20100164
RéunionAGU Fall Meeting 2010; San Francisco; US; décembre 13-17, 2010
Mediapapier; en ligne; numérique
Sujetsétudes de la croûte; structure de la croûte; détermination des contraintes; déformation; analyse des déformations; déformation; séismologie; Zone de subduction de Cascadia ; tectonique; géophysique
ProgrammeÉvaluations ciblées des dangers dans l'Ouest du Canada, Géoscience pour la sécurité publique
Résumé(disponible en anglais seulement)
This paper investigates the orientation and sources of stress in the forearc of the Cascadia subduction zone in southwest British Columbia using stress orientations from focal mechanism data and comparing the results with GPS strain rates. The northern section of the Cascadia subduction zone experiences crustal earthquakes in the overriding North American Plate with recorded magnitudes up to ~7.5. Overall, these events have a shorter recurrence interval than megathrust earthquakes and pose a significant hazard to major population centres, such as Vancouver, Victoria and Seattle. The subduction margin in this region includes a change in orientation from N - S in Washington State to NW - SE in British Columbia and involves a complex region of deformation above a bend in the subducting Juan de Fuca plate. We combine new stress results with seismicity and local tectonics to determine regional stresses that control faulting in the North American crust. 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 three principal stress orientations and stress ratio. Our results indicate the maximum horizontal compressive stress orientation changes with distance from the trench from margin-normal along the coast to margin-parallel 100 - 150 km inland from the margin. Comparing stress orientations with GPS data, we relate the margin-normal stress direction to subduction-related strain rates due to the locked interface between the North America and Juan de Fuca plates just west of Vancouver Island. Further from the margin the plates are less coupled and the margin-parallel maximum horizontal compressive stress in the North America plate relates to the northward push of Washington and Oregon, which is also observed in the horizontal shortening direction of the residual strain rates with the subduction component removed.