The goal of this research is to derive new constraints for the depth distribution of seismic anisotropy in the crust and upper mantle. Seismic anisotropy is an indicator of deformation in the mantle, and the ability to separate signals from different depths, such as from the lithosphere versus the asthenosphere, allows new insights into the distribution of deformation with depth, and therefore into the nature of plate-mantle coupling and the driving forces of plate tectonics. There are several techniques to detect seismic anisotropy, such as measurements of shear wave splitting, P wave polarization anomalies, and Pn azimuthal velocity variations. These phases have different depth sensitivities for anisotropy, so that the combination of all measurements provides new constraints on vertically varying anisotropy. In addition, shear wave splitting and P wave polarization anomalies have shown to be frequency dependent in vertically varying anisotropic media, but a quantification of this effect that can be applied to observations has yet to be developed. The first part of this project is to quantify the differences in depth sensitivity between different body wave methods and the frequency dependent behavior, through numerical forward modeling and measurements on synthetic data. The second part is the application of the resulting benchmarks to data from the Global Seismic Network. In terms of broader impacts, these results will provide new tools and insights relevant to plate-mantle interaction to seismologists, geodynamicists, and the wider community. The resulting analysis guidelines may be especially useful for datasets anticipated from the EarthScope program. Linking seismic anisotropy more quantitatively to geodynamics will foster interdisciplinary research. Graduate students are involved in directly related projects.
