Mapping anelastic structures in the upper mantle - Applications to the hotspot tracks beneath the western United States

The Northwestern US has experienced a complicated intraplate volcanism over the past 20 Ma, which formed the Yellowstone hotspot tracks (dating back to 12 Ma) and the Newberry hotspot tracks (dating back to 10 Ma). These hotspot tracks are thought to be the surface expression of the interaction among the southwestward-moving North American Plate, a buoyant upwelling mantle plume, and the return flow induced by the subducting oceanic plate down to the west. However, details of the interaction are unclear and several hypotheses about the formation of the hotspot tracks remain debatable. A good knowledge of both seismic velocity and attenuation in this region can provide us useful constraints on the formation of the hotspots. In this study, we use a newly developed 3D full waveform attenuation inversion method to obtain a high resolution anelastic upper mantle structure in the western US. We apply the optimal fourth-order strong stability preserving Runge-Kutta method to solve the anelastic wave equation, and apply the scattering-integral method to calculate the velocity and attenuation sensitivity kernels. We incorporate waveforms of body waves and surface waves from the USArray Transportable Array to improve the lateral and vertical resolution of the inverted model. Since attenuation is largely related to temperature, partial melt and water content, our tomographic model will provide important constraints on temperature, which further helps determine the time-history of the hotspot tracks in the crust and lithospheric mantle and the complex interaction of the upwelling mantle plume, subduction-driven mantle flow, and the North American lithosphere.