Collaborative Research: Delineation of the Slab Geometry of the Cascadia Subduction Zone Using Broadband Teleseismic Waveform Analysis

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This proposal seeks funding to deploy 7 temporary broadband seismograph stations in a north-south profile at a longitude of about 123oW in western Washington for the purpose of recording teleseismic body waveforms. We intend to undertake a receiver function analysis of the recorded P-waves in order to delineate variations in the amplitude and timing of Ps conversions from the oceanic Moho of the subducted Juan de Fuca plate that are indicative of variations in the geometry of the subducted slab along its strike. Specifically, we will attempt to confirm and refine a working hypothesis recently proposed that suggests that the Juan de Fuca plate may be deformed in a broad arch centered in the vicinity of Puget Sound. This model explains certain aspects of the seismicity beneath this region as well as a number of other geological and geophysical observations. We have recorded teleseismic P-waveforms along an east-west profile at about 47oN latitude that demonstrates that the oceanic Moho of the Juan de Fuca plate has a characteristic signature in teleseismic receiver functions. Results from these earlier deployments are consistent with our arch model. Further refinements in this model will have important implications in terms of the tectonic evolution and earthquake hazards potential of the Cascadia Subduction Zone. This research represents a collaborative project between the University of Missouri-Columbia (T.J. Owens) and the University of Washington (R.S. Crosson).