The goal of the project is to develop a better model of the three-dimensional variations in seismic shear velocity in Earth's mantle as well as to explore the implications of the seismic model for flow in the mantle. The seismic model will be improved by use of a semi-automatic approach to measuring delay times of all S and multi-bounce S waves as well as ScS and all multi-bounce ScS waves. SKS and SKKS waves will also be used. A second aspect of the work will be to use a nonlinear waveform inversion on seismic data that propagate through the upper mantle to extract travel time delays and paths through the mantle for data sensitive to the upper mantle. The investigators will also conduct joint inversions of the seismic data and geodynamic data (gravity field and topography) to test different hypotheses for the flow regime within the mantle. The connection between seismic velocity and observable geodynamic data, such as the Earth's gravity field, depends on the viscosity of the mantle, the density to velocity scaling, as well as the nature of any flow barriers in the mantle. We will run joint inversions for a range of models to see what types of models are most consistent with the observed seismic data as opposed to non-unique seismic models. This work will have a broad impact on all areas of earth science concerned with the physical and chemical nature and evolution of Earth including mineral physics, geodynamics, and geochemistry. The project will also support the graduate education of two students.
