EAPS Geophysics Seminar (12.571) – Maureen Long: New constraints on deep mantle dynamics from seismic anisotropy: What drives flow at the base of the mantle?

Title: New constraints on deep mantle dynamics from seismic anisotropy: What drives flow at the base of the mantle? Abstract: Mantle convection and its surface manifestation, plate tectonics, are fundamental to Earth’s evolution. Observations of seismic anisotropy, or the directional dependence of seismic wavespeeds, provide some of the most direct constraints on the pattern of convective flow in the Earth’s mantle. Seismic anisotropy analysis is routinely applied to study upper mantle processes, leading to fundamental discoveries about the patterns of flow in the upper mantle and the drivers of that flow. There is also convincing observational evidence for seismic anisotropy in the lowermost mantle; however, it has proven challenging to develop reliable frameworks for accurately measuring D” anisotropy and for interpreting these measurements in terms of mantle flow patterns. Despite the challenges, however, observations of lowermost mantle anisotropy have the potential to shed light on a number of fundamental unsolved problems relating to deep mantle structure and dynamics, such as the origin and evolution of large low shear velocity provinces (LLSVPs) and the role that subducting slabs play in lowermost mantle processes. This talk will describe a set of studies aimed at measuring and interpreting seismic anisotropy at the base of the mantle, using a combination of tools and approaches. These include the development of new strategies for measuring shear wave splitting due to D” anisotropy, the modeling of D” anisotropy using global wavefield modeling approaches, the incorporation of new results from mineral physics into the interpretation of D” anisotropy, and comparisons between geodynamic model predictions and seismic measurements. About this series: The EAPS Geophysics Seminar is a class for EAPS geophysics graduate students with a guest speaker approximately every two weeks. All members of the MIT community are welcome to attend the guest talks which are generally on Tuesdays at 10am in 54-209 and on Zoom. Titles and abstracts will be posted here when available. Contact Josh at jkastorf@mit.edu with any questions.