A three‐dimensional radially anisotropic model of shear velocity in the whole mantle

SUMMARY We present a 3‐D radially anisotropic S velocity model of the whole mantle (SAW642AN), obtained using a large three component surface and body waveform data set and an iterative inversion for structure and source parameters based on Non‐linear Asymptotic Coupling Theory (NACT). The model is parametrized in level 4 spherical splines, which have a spacing of ∼ 8°. The model shows a link between mantle flow and anisotropy in a variety of depth ranges. In the uppermost mantle, we confirm observations of regions with V SH > V SV starting at ∼80 km under oceanic regions and ∼200 km under stable continental lithosphere, suggesting horizontal flow beneath the lithosphere. We also observe a V SV > V SH signature at ∼150–300 km depth beneath major ridge systems with amplitude correlated with spreading rate for fast‐spreading segments. In the transition zone (400–700 km depth), regions of subducted slab material are associated with V SV > V SH , while the ridge signal decreases. While the mid‐mantle has lower amplitude anisotropy (<1 per cent), we also confirm the observation of radially symmetric V SH > V SV in the lowermost 300 km, which appears to be a robust conclusion, despite an error in our previous paper which has been corrected here. The 3‐D deviations from this signature are associated with the large‐scale low‐velocity superplumes under the central Pacific and Africa, suggesting that V SH > V SV is generated in the predominant horizontal flow of a mechanical boundary layer, with a change in signature related to transition to upwelling at the superplumes.