Collaborative Research: High Resolution Imaging of Deep Mantle Structure and Dynamics Using USArray Data

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USArray Transportable Array (TA) and Backbone Array data will be used in high-resolution seismic analyses of deep mantle structure and processes, building on exciting results obtained using data from the initial 5 years of EarthScope deployment. Arizona State University and University of California, Santa Cruz, researchers will extend their collaboration, analyzing teleseismic earthquake signals that traverse the deep mantle in three sub-regions: beneath the southern U.S.-Gulf of Mexico-Central America-Caribbean, under the eastern and central Pacific, and beneath Alaska and the northern Pacific. Waveform stacking, Born-scattering migration, shear-wave splitting and 2.5D/3D waveform modeling procedures will be applied to broadband P and S arrivals, exploiting the density and spatial aperture of the USArray data coverage to resolve fine-scale structures. As the TA progressively moves eastward, special effort will be focused on the mid- and deep mantle beneath Central America and the Gulf of Mexico, where tomographic models indicate a tabular high velocity structure extending through the lower mantle and spreading broadly in the D" region, putatively associated with the Farallon slab and the long history of subduction beneath North America. The velocity gradients, structural continuity, structural fabric, and spatial extent of this feature will be examined using combined travel time and migration methods, with 2.5D and 3D synthetic seismogram modeling being used to quantify the elastic and anisotropic structure. Corresponding downwelling structure deep beneath the subduction zone under Alaska will be analyzed, and the two convergent zone regions will be compared to the eastern Central Pacific structure where there is an abrupt lateral transition from a chemically-distinct large low shear velocity province to adjacent higher velocity structure in the D" region. Continued collaborations with mineral physics and geodynamic colleagues will allow us to explore connections between shallow and deep structures in the mantle and their dynamic implications for tectonics and evolution of the North American continent.