Upper Mantle P-Wave Tomography beneath the Western United States from USArray and Global Data

The large volume of high quality data being collected by the USArray Transportable Array affords an excellent opportunity for high-resolution seismic imaging beneath the Western United States. Seismic tomography helps constrain mantle velocity structure and aids in the understanding of chemical and geodynamic processes at work. Using a combination of USArray and global travel-time data, we create a global tomography model of P wavespeed heterogeneity in the mantle. We perform a multi-scale inversion with resolution approaching that of regional tomography studies in the Western US, where dense USArray data is available. The scope and resolution of this technique allows us to investigate a broad suite of essential problems concerning the North American mantle lithosphere, including the nature major tectonic features such as the Yellowstone hotspot, the Sierran root, and the Cascadia subduction zone. The method gives evidence for differences in thickness and velocity anomaly of the mantle lithosphere between adjacent tectonic blocks, especially between the stable center of the continent and the more active west, which is vital for the understanding of lithospheric evolution. The inclusion of global data additionally allows us to image the mantle beyond the current extent of USArray in order to look at the fate of the subducted Farallon slab under the North America and its influence on overlying lithospheric features. We present the latest tomographic inversion, using USArray data through May 2008 and the interpretation of first-order features of the mantle lithosphere in the model.