Seismic Imaging of The Cascadia Subduction Zone and Juan De Fuca Plate System Mantle Structure: A Bottom Up Approach to Subduction Dynamics

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dc.contributor.advisorToomey, Douglas
dc.contributor.authorBodmer, Miles
dc.date.accessioned2020-02-27T22:33:35Z
dc.date.available2020-02-27T22:33:35Z
dc.date.issued2020-02-27
dc.description.abstractI use seismic analysis of teleseismic data to constrain the isotropic and anisotropic mantle structure of the Cascadia subduction zone (CSZ). This work begins by estimating seismic anisotropy parameters beneath the Juan de Fuca (JdF) plate system using teleseismic shear wave splitting. I infer that mantle flow patterns beneath the JdF are heterogeneous and reflect the overlaying tectonic environment. Beneath the JdF plate, shear between the JdF plate and Earth’s deep interior entrains the mantle via viscous coupling with some evidence for secondary flow processes. In southern Cascadia, beneath the Gorda deformation zone, there is evidence for mantle reorganization due to plate fragmentation processes. Next, I investigate the isotropic structure of the JdF and CSZ through teleseismic tomographic imaging, utilizing an onshore-offshore P-wave dataset. I image two low-velocity anomalies beneath the subducting slab, interpreted to be localized upwellings and regions of increased buoyancy due to the presence of partial melt. I hypothesize that subslab buoyancy modulates the total shear force along the plate interface, influencing the distribution of megathrust segmentation, as evidenced by spatial correlations to plate locking and tremor density. I extend this model to investigate what influence subslab buoyancy has on forearc topography in Cascadia. We present a conceptual model in which subslab buoyancy modulates the slab dip angle and/or the degree of plate coupling, which in turn modulates the shear force on the megathrust interface. I suggest this variable shear coupling influences where uplift and forearc topography are most likely to develop and provides dynamic support for forearc topographic highs. Finally, I look at our onshore-offshore tomographic method, using synthetic modeling to show the influence that changes in elevation, crustal thickness, and local geology have on teleseismic delay times. I explore how these perturbations influence inversions and ways to correct for them, identifying artifacts and recommending a preferred methodology. This dissertation includes previously published and unpublished coauthored material.en_US
dc.identifier.urihttps://hdl.handle.net/1794/25247
dc.language.isoen_US
dc.publisherUniversity of Oregon
dc.rightsAll Rights Reserved.
dc.subjectCascadiaen_US
dc.subjectLandscape Evolutionen_US
dc.subjectMantle Deformationen_US
dc.subjectSeismic Anisotropyen_US
dc.subjectSeismologyen_US
dc.subjectSubduction Dynamicsen_US
dc.titleSeismic Imaging of The Cascadia Subduction Zone and Juan De Fuca Plate System Mantle Structure: A Bottom Up Approach to Subduction Dynamics
dc.typeElectronic Thesis or Dissertation
thesis.degree.disciplineDepartment of Geological Sciences
thesis.degree.grantorUniversity of Oregon
thesis.degree.leveldoctoral
thesis.degree.namePh.D.

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