Finite-frequency Imaging of the Mantle Transition Zone Discontinuities

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Due to increased pressure, minerals in the Earth’s subsurface undergo major phase transitions in the mantle transition zone at depths of about 410 km and 660 km. Processes in the Earth's mantle transition zone provide important constraints on the mass exchange between the shallower upper mantle and the deeper lower mantle. Those are dynamic processes that are responsible for plate tectonics, earthquakes and volcanoes. This research takes advantage of a new seismic imaging theory and data collected by seismic stations around the world to map the structure of the mantle transition zone. This research aims to advance understanding of mantle dynamics with focuses on major subduction zones (where massive oceanic plates subduct into the deep mantle) as well as volcanic hotspots in global oceanic regions. High-resolution images of the mantle transition zone will be made available to the broader Geosciences community for future multidisciplinary studies. Hands-on course projects and labs based on this research will be developed and implemented in undergraduate teaching, and a graduate student will be supported and trained. Slab pull is generally considered as the dominant force that drives the global movement of tectonic plates. This convection mode is well constrained in the upper mantle but the convection pattern in the mid mantle is more speculative. This research will build a global dataset of finite-frequency travel time measurements of SS precursors to image the global structure of the 410-km and 660-km discontinuities based on Born sensitivities calculated in the framework of traveling-wave mode coupling. Finite-frequency receiver function measurements at GSN and USArray stations will be used as complementary datasets to improve regional resolution beneath continents. The new high-resolution MTZ discontinuity models will be analyzed together with published seismic wave speed and anisotropy models to advance fundamental understanding of Earth processes in the mantle transition zone, with focus on the structure and dynamics of stagnant slabs in subduction zones as well as thermal and compositional variations beneath oceanic hotspots.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.