Cascadia 3D P- and S-Wave Velocity Model for Ground Motion Simulations: Past, Present and Future

Date: 4/25/2019

Time: 06:00 PM

Room: Grand Ballroom

I review the Cascadia three-dimensional (3D) P- and S-wave velocity (Vp and Vs, respectively) model developed in support of ground motion simulations and earthquake hazards studies in the Pacific Northwest. I discuss the philosophy behind the model’s development, present the history and evolution of the model, describe its use and what I perceive as its key limitations. This model, which incorporates the Cascadia subduction zone, encompasses the region from about 40.2°N to 50°N latitude, and from about 122°W to 129°W longitude from mean sea level to 60 km depth. Development of the Cascadia model began in 2003 and evolved into the version described in Stephenson (2007). This presentation describes the updated version of Stephenson et al. (2017). EarthVision® modeling software was used throughout model development. The backbone of the velocity property volumes is a simplified geologic model consisting of: (1) continental sedimentary basins, (2) continental crust, (3) continental mantle, (4) oceanic sediments, (5) oceanic crust (including the subducting slab), and (6) oceanic mantle. The model volume incorporates bathymetry as part of the oceanic crust and oceanic sediments but does not incorporate topography. Vp and Vs within each of the geologic units are derived from published values. Currently, the model can support a subduction zone rupture in excess of 1000 km. I envision key updates to this Cascadia model will include full topography, a geotechnical (weathered) layer, and improved shallow Vs in basins that are not constrained by the needs of legacy software and hardware for 3D ground motion simulations. With the current development of the National Crustal Model (Boyd and Shah, 2016), it is plausible that future versions of this model may be directly integrated with that effort. In its current form, the existing Cascadia model can be considered to be a template for a community velocity model of the Cascadia region.

Presenting Author: William J. Stephenson

Authors