CONTEMPORARY DEFORMATION AND KINEMATICS OF THE YELLOWSTONE HOTSPOT AND ITS EFFECT ON THE WESTERN U.S. FROM GPS, SLIP RATES, AND EARTHQUAKES

Contemporary deformation of the western U.S. was modeled based on a compilation of ~2500 GPS velocities 200 Late Quaternary fault slip rates, using both a tectonic block formulation and a finite element continuum methodology. Modeling reveals a notable regional clockwise regional rotation of velocities, with deformation accommodated at fault zones characterized by high strain rates that divide the western U.S. into microplate tectonic blocks. These fault zones correlate with earthquake belts and are associated with increased seismic hazard. The Yellowstone-Snake River Plain volcano-tectonic system (YSRP) is specifically examined to resolve local kinematics and the role of the Yellowstone hotspot in regional tectonic deformation. Locally high extension rates of 2.5 ± 0.4 mm/yr at the Yellowstone Plateau exceed average southwest motion of the eastern Snake River Plain (ESRP) of 1.8 ± 0.1, suggesting contraction between these two areas. Long-term GPS monitoring from 1987 to 2009 indicates that extension rates across the Yellowstone Plateau vary from ~2 to 4 mm/yr and correlate with cycles of caldera uplift and subsidence, so that Yellowstone Plateau extension is strongly influenced by crustal volcanic processes. Comparison of deformation rates between the ESRP and adjacent portions of the Northern Rocky Mountains and Basin-Range indicates minor differential motion less than 0.5 mm/yr between the ESRP and the Rocky Mountains at the northern boundary, and no differential motion at the south boundary of the ESRP. Southwest motion of the YSRP can be attributed to tensional stresses from the topographic swell associated with the buoyant Yellowstone hotspot. Volcanic reworking of the YSRP lithospheric structure through underplating, melting, and intrusion of a mid-crustal sill introduce a negative load, contributing to topographic subsidence, southwest motion, and lower stresses of the ESRP.