Widespread Deformation at the Base of the Mantle Linked to Subducted Slabs

Abstract In Earth’s deepest mantle (D″), shear wave speeds can vary with propagation and vibration direction of the wave because of convection-driven mantle deformation, a phenomenon known as seismic anisotropy. Although D″ anisotropy has been mapped globally at long wavelengths (>4000 km laterally) in tomographic inversions, models exhibit disagreements at smaller scales (100s to 1000s of kilometers). Here, we present 70,000 differential splitting SKS-SKKS and PKS–SKKS measurements from a global seismic dataset that samples nearly 75% of Earth’s D″ layer, predominantly in the highest seismic wave speed regions. Anisotropy is found in about two-thirds of our sampled area, almost tripling the area where seismic anisotropy has been investigated at short wavelengths. Although the overall distribution is complex, lowermost mantle deformation is frequently detected in locations associated with putative deeply subducted slabs, thereby linking D″ deformation processes to the subduction of tectonic plates. In these colder, slab-dominated regions, the observed pervasive seismic anisotropy is consistent with the crystallographic preferred orientation of postperovskite as a significant contributor.