Geodynamically relevant anisotropic tomography

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Seismic tomography is one of the best tools for imaging the interior structure of the Earth, which is inaccessible by other means. Expanding these models to include anisotropy (i.e. directional dependence) of seismic velocities can more directly image the dynamic processes of the deep Earth. While many tomographic models including seismic anisotropy have been developed, there are few that invert for both strength and orientation of anisotropy in order to allow for direct comparison with geodynamic models, which make predictions about the patterns of mantle convection based upon assumptions of the mantle's viscosity and other rheological properties. The long term goal of this research is to develop global as well as more detailed regional models of seismic anisotropy that can both illuminate the dynamic processes of the mantle, as well as allowing for direct comparison with geodynamically predicted models. The objective of this application, which is the next step towards this long-term goal, is to test and apply a new approach of utilizing 3D finite-frequency modeling of surface wave data to model both the strength and best-fitting orientation of anisotropic seismic structure. We expect that this approach, when combined with finite-frequency modeling of shear wave splitting intensity data, will produce models which allow for direct comparison with geodynamical flow models, as well as allowing for anisotropic modeling of relatively sparse regional data. We plan to demonstrate the potential of this approach by pursuing the following specific aims. (1) Verify that the surface wave modeling method can accurately reproduce known models when applied to a large synthetic dataset calculated with known models of anisotropy. (2) Incorporate shear splitting intensity measurements into the model, expected to be complementary in terms of spatial sensitivity and relative sensitivity to different model parameters. (3) Apply the approach to a dataset from the Chile Ridge Subduction Project. This temporary deployment of broadband seismic instruments sampled a region of tectonic interest between 2004 and 2007, and the modeling of this relatively sparsely sampled region presents both a challenge and an opportunity to demonstrate the strengths of the proposed approach. The proposed work is innovative because it takes advantage of a new method of modeling surface wave data that has just been developed by the PI. This method is expected to allow for direct modeling of the strength and orientation of anisotropy beyond what has been traditionally obtained in anisotropic modeling. This approach is ideally suited for direct comparison with geodynamic predictions, allowing for a unique method of imaging the flow patterns of the Earth's mantle.This work will contribute to advancement of discovery and understanding while promoting teaching, training and learning through the training of at least one Ph.D. student, as well as potentially one or more Masters and undergraduate students, and the incorporation of such projects into class work. It will also supply for the enhancement of infrastructure for research and education, through the optimization of a new HPC cluster that will be used by other research groups. Finally, we expect the broad dissemination of results through presentation at international meetings and peer-reviewed journals. Computer codes developed in this research will be made available through the PI's website.