3-D Structure and Tectonic Interpretation of the Cascadia Crust and Subducting Slab from SHIPS and Earthquake Data

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Abstract for proposal EAR 0107138 (PH # 12x)Title: 3-D structure and tectonic interpretation of the Cascadia crust and subducting slab from SHIPS and earthquake dataPI's: Robert S. Crosson, Kenneth Creager University of WashingtonIn the Pacific Northwest, subduction of the Juan de Fuca plate beneath the margin of North America (Cascadia subduction zone) causes earthquakes on the plate boundary, as well as within both the continental crust and the subducting plate (slab). Seismic hazards are of particular concern in western Washington State owing to the concentration of population and earthquakes in this region. The hazard due to earthquakes in the subducting Juan de Fuca slab was underscored by the recent magnitude 6.8 earthquake of February 2001 in the southern Puget Sound region. To make progress in understanding the tectonic processes giving rise to earthquakes in this region, it is necessary to gain a better understanding of the structure of both the crust and upper mantle. Fortunately, recent seismic experiments using controlled sources of energy, such as the SHIPS (Seismic Hazards in Puget Sound) experiment, have provided extensive data which can be used to obtain high resolution images of seismic wave speed in the crust, as well as images of the subducting slab from reflections. In this project, we will combine data from several recent "active source" seismic experiments with extensive earthquake observations from the Pacific Northwest seismograph network (PNSN) to produce a high quality but large-scale model of P wave speed of the crust and upper mantle to a depth of 50-60 km. This model will be used to improve our knowledge of the locations of earthquake recorded by the PNSN, and also to accurately model reflected waves from the subducted slab in order to better understand the origin of slab earthquakes. We plan to provide an internet distribution site for our models and interpretations from this project.