DEVELOPMENT OF A 3D VELOCITY AND DENSITY MODEL FOR THE CASCADIA SUBDUCTION ZONE AND PRELIMINARY FINITE-DIFFERENCE MODELING RESULTS

We have developed a three-dimensional velocity and density model of the Cascadia Subduction Zone geographically covering the region from latitudes 42° to 49°, longitudes –121° to –126°, and depths to 60 km. The basic model has been derived from published data interpretations obtained in an extensive geological and geophysical literature search. Information from topographic and bathymetric databases, and both published and unpublished tomographic results are also incorporated. The current basic model consists of oceanic and continental mantle, oceanic and continental crystalline crust, and accretionary oceanic sediment. Simplified Seattle and Everett sedimentary basins have also been integrated into the model (based on the gravity inversion results of R. Blakely, USGS), as have the Tacoma and Portland basins. P- and S-wave velocity as well as density vary both vertically and laterally within assigned geologic units. The model is currently being developed in proprietary software (EarthVision®), but it can be easily ported to formats used by many numerical modeling routines. As such, we envision this model as a possible template for a Cascadia community earth model. Preliminary finite-difference subduction zone modeling shows the effects of the sedimentary basin structures on ground motion.