Properties of a recent 3D S-wave velocity

Properties of a recent 3D S-wave velocity Earth model showing (a) the power spectrum of velocity variations as a function of angular degree (inversely proportional to spatial scale) and depth; red is high power, blue is low power. Shear velocity anomalies at (b) 600-km depth, (blue is fast, red is slow; scale range is ± 2%), and at (c) 2800-km depth (scale range is ± 3%). Largespatial- scale (angular degree 2) patterns dominate at both of these depths, likely due to accumulations of slabs near 600 km and the presence of two large lowshear- velocity provinces under Africa and the Pacific and a continuous ring of higher than average velocities beneath the circum-Pacific near 2800-km depth. The unexpected dominance of very large-scale structure with anomalous seismic velocities indicates the importance of thermo-chemical convection in the mantle (Image courtesy of B. Kustowski, G. Ekström, and A. Dziewonski.)


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