Abstract

Ultra-low velocity zones (ULVZs) are wide and thin regions of greatly reduced seismic velocities that lie on the core-mantle boundary. They may play a role in whole mantle dynamics; as passive tracers or more actively feeding into or anchoring plume hotspots. While individual ULV Zs have been found near and far from hotspots, the largest ULV Zs appear to be found near the hotspots with the highest buoyancy flux and most extreme isotopic ratios. However, a unified global distribution of ULV Zs is still debated. As well as this, questions remain about the origin and composition of ULV Zs. I will talk about my work using postcursory energy to the seismic phase Sdiff to produce a self-consistent global map of ULV Zs in order to analyse their potential relationship with both plumes and other deep mantle features. This phase has previously been used to locate and model the 3D structure of ULV Zs on an individual basis, and its long diffracted portion makes it particularly well-suited to studying large areas of the core-mantle boundary.