IGPP is pleased to invite you to join its Fall 2022 Seminar Series presentation featuring Cambridge University's Keith Priestley. Dr. Priestley's talk, "Anisotropic Structure of the Upper Mantle" will be available via Zoom on Tuesday, November 1, 2022, starting at 12:00pm. Zoom: https://ucsd.zoom.us/j/94029326670?pwd=QU5GZjFjYzNoVUwvYVdYR0s2WnNNUT09 Password: igpp
Time: 12:00 pm, Pacific Time
Location: Revelle 4000 (on-site with a zoom link)
Abstract: This study investigates the anisotropic structure of the Earth’s upper mantle and focuses on what the mantle anisotropy tells us about the dynamics of the oceanic mantle and the formation of the continents. The mantle anisotropic model is built from an analysis of more than 5x10^6 seismic waveforms, and the model is developed by jointly inverting for isotropic shear wave speed (Vs) and radial anisotoropy (ξ) along each path. The path-average Vs and ξ measurements are tomographically inverted for a 3D Vs and ξ model. Beneath the ocean basins, the average ξ increases from ~1.03 below the Moho, peaks at ~1.06 at ~150 km depth, decreasing to ~1 at ~250 km depth. The thickness of the ξ>1 layer increases slightly with the increasing age of the oceanic lithosphere. At >200 km and deeper below the East Pacific Rise and starting at somewhat greater depths beneath the slower spreading ridges, ξ<1. The Vs signature of the mid-ocean ridges vanishes at about 150 km depth while the ξ signature extends significantly deeper. At ~200 km and greater depths below most of the backarc basins of the western Pacific, ξ<1. Beneath the continents, the average ξ decreases from ~1.07 below the Moho to ~1 at ~200 km depth. However, there is a distinct difference between the active and stable parts of the continents. ξ beneath the active portions of the continents decreases from ~1.07 below the Moho to ~1 at ~200 km depth. However, ξ beneath the stable parts of the continents decreases from 1.06 below the Moho to ~0.98 at ~175 km depth before increasing to ~1.01 at ~275 km depth, then back to ~1 at ~350 km depth. The anisotropic structure of the upper oceanic mantle reflects recent oceanic spreading, whereas the anisotropic structure of the upper continental mantle reflects processes which formed the continental cores.