On the Relationship Between Oceanic Plate Speed, Tectonic Stress, and Seismic Anisotropy

Abstract

Seismic radial anisotropy (the squared ratio between the speeds of horizontally and vertically polarized shear waves, (Formula presented.)) is a powerful tool to probe the direction of mantle flow and accumulated strain. While previous studies have confirmed the dependence of azimuthal anisotropy on plate speed, the first order control on radial anisotropy is unclear. In this study, we develop 2D ridge flow models combined with mantle fabric calculations to report that faster plates generate higher tectonics stresses and strain rates which lower the dislocation creep viscosity and lead to deeper anisotropy than beneath slower plates. We apply the SGLOBE-rani tomographic filter, resulting in a flat depth-age trend and stronger anisotropy beneath faster plates, which correlates well with 3D global anisotropic mantle models. Our predictions and observations suggest that as plate speed increases from 2 to 8 cm/yr, radial anisotropy increases by ∼0.01–0.025 in the upper 100–200 km of the mantle between 10 and 60 Ma.