KINEMATICS AND GEODYNAMICS OF THE INTERMOUNTAIN REGION: WASATCH FAULT TO THE YELLOWSTONE PLATEAU

GPS data from Wasatch Front and Yellowstone were analyzed to obtain contemporary velocities and strain rates, quantifying the distribution of deformation in these seismically active areas and then combining the velocities with other GPS data to characterize deformation in the Intermountain region. The deformation budget is assessed by comparing the moment release rate sfrom GPS-measured strain rates, representing total moment release, historic seismicity, representing contemporary moment release from seismic slip on faults, and Late Quaternary fault slip rates, representing accumulated moment from fault loading of the Wasatch fault. These calculations reveal significant moment deficits that are attributed to aseismic volcanic deformation in the Yellowstone Plateau and potential multi-fault loading at the Wasatch Front. Dislocation models are constructed for plausible geometries of the Wasatch fault zone and compared to deformation data. The horizontal GPS velocity data are integrated into models of Intermountain deformation and used to constrain horizontal stress models based on lithospheric density structure. The kinematic modeling demonstrates a regional tectonic clockwise rotation in the direction of deformation, with deformation accommodated at fault zones between microplate tectonic blocks, while the dynamic modeling demonstrates the importance of lithospheric structure in producing the body stresses that drive deformation. For the eastern Basin-Range and Wasatch Front, tensional stresses and regional extension are produced by dynamic topography: thinned crust and buoyant mantle supporting anomalously high elevations. For the Yellowstone-Snake River Plain volcanic system, tensional stresses at the Yellowstone Plateau are produced by the 600-km wide, 300-m high topographic swell associated with the Yellowstone hotspot and augmented by local deformation related to the mid-crustal Yellowstone magma reservoir.