Finite Plate Model of Western United States Tectonics

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The purpose of this project is to understand how continents deform, how the deformation is spatially distributed, and how decade-scale GPS-derived velocities relate to long-term geologic fault slip rates. The active tectonics of the western United States is represented by a finite number of elastic-plastic, lithospheric plates, or blocks, and the angular velocities of and internal strain rates within those entities are estimated by inversion of GPS velocities, earthquake slip vector azimuths, and fault slip rates. The method formally takes into account the elastic deformation of the Earth so that the long-term deformation that includes the slip rates on faults can be separated from the short-term deformation that may be largely elastic. The block inversion is interfaced with a finite element code so that more realistic finite-thickness plate models can be used to go beyond the half-space approximations used to date. The work is leading to improvements in (1) estimates of fault slip rates that can be used to improve earthquake hazard models, (2) understanding of how geodetic and geologic fault slip rates are related and the roles of viscoelastic and finite-thickness plate models, (3) crustal block rotation rates that provide information about driving mechanisms, and (4) approaches to modeling large-scale deforming regions. Furthermore, this project will to lead to an improved understanding of the tectonics of the western United States, how continents deform in general, and how geodetic and geologic data, that commonly sample different time scales, are related. The work will lead to an increased understanding of earthquake potential in the western United States and will further understanding of how modern geodetic data, such as those to be collected by the EarthScope Plate Boundary Observatory, will contribute in a practical way to seismic hazard risk maps.