Global Imaging of the Mantle Transition Zone Using SS Precursors Shows Lower Mantle Convection Patterns that are Broadly Linked to Tectonics

Abstract Central to our understanding of mantle convection and inner Earth material transport is the mantle transition zone. Mantle transition zone thicknesses can reveal key constraints on the locations and degree of material transport between the upper mantle and lower mantle. Therefore, it's essential for our knowledge of geochemical reservoirs, hydration cycles, and the evolution of the Earth. We use SS precursors to image the mantle transition zone discontinuities using a newly developed method and seismic data from 1990–2021, providing excellent global data coverage. We also test a variety of different migration models. The major features are robust regardless of the choice of migration model. We find a thickened mantle transition zone (by 5–20 km) beneath subduction zones, coincident with the locations of high‐velocity anomalies from tomography models. The mantle transition zone is thinned by 5–10 km beneath oceans, although thinning is not necessarily focused beneath hotspot regions. The thinning and thickening also correspond to shear velocity anomalies that would be predicted for thermal perturbations. The 660 topographies are generally consistent with mantle transition zone thickness variations, whereas the 410 topographies do not show relationships with mantle transition zone thickness. This is likely because convection processes are more complex than simple vertical upwelling at hotspots and downwelling at subduction zones, and/or because material transfer at the 410 occurs at smaller lateral scales than resolved by our study.