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Browsing by Subject "subduction"

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    Forearc Stresses in the Northern Cascadia Subduction Zone
    (2020-08) Rippke, Joseph
    We investigate the spatial variation in the state of stress in the overriding plate in the forearc region of northern Cascadia. The key forces that act on the forearc region are the plate coupling force, the northward push of the Oregon block, the gravitational collapse force on elevated topography, and buoyancy of the serpentinized mantle wedge. The latter two forces are expected to cause margin-normal tension at shallow depths in the inner forearc. In this study, we compile available earthquake focal mechanism solutions and determine spatial variations of stress orientation through focal mechanism inversion. The results indicate the maximum compressive stress axis is margin-normal in the outer forearc due to shear stress at the subduction interface and margin-parallel throughout the inner forearc with varying orientations of the intermediate and minimum compressive stress axes throughout the inner forearc, consistent with previous studies. Using a 3-D finite-element code for lithospheric deformation, we explore the effects of gravitational collapse force, the buoyancy of the serpentinized mantle wedge corner, the plate coupling force, the shape of the slab, and the Oregon push on the stress field. The results indicate the buoyancy of the serpentinized mantle wedge corner and the shape of the slab may be as important of contributors to the the state of stress in the inner forearc as the plate coupling force whereas the gravitational collapse force and the Oregon push have a minimal effect on the state of stress in the inner forearc.