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

• Published in: Geophysical research letters 2022-08, Vol.49 (15), p.e2022GL097795-n/a
• Main Authors: Kendall, E., Faccenda, M., Ferreira, A. M. G., Chang, S.‐J.
• Format: Article
• Language: English
• Subjects: Anisotropy; Asthenosphere; Deformation; Direction; geodynamic modeling; Mathematical models; Numerical models; Numerical prediction; oceanic lithosphere; Olivine; Plate motion; Plate tectonics; Plates; S waves; Seismic activity; Strain; Stresses; Tectonic processes; Tectonics; Texture; Two dimensional flow; upper mantle; Vertical polarization; Viscosity
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL097795

Seismic radial anisotropy (the squared ratio between the speeds of horizontally and vertically polarized shear waves, ξ=VSH2VSV2 $\xi =\frac{{{V}_{SH}}^{2}}{{{V}_{SV}}^{2}}$) 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. Plain Language Summary The asthenosphere is host to a plethora of tectonic processes and therefore is subject to large deformation. During deformation such as from plate motion, grains of olivine, the main rock‐forming mineral in the asthenosphere, rotate into a preferred direction parallel to the deformation, developing a texture that can be measured seismically. We present seismic observations which indicate the dependence of the strength of this texture on plate speed. We also use numerical models to predict the development of olivine texture for varying plate speeds, which are highly coupled. Our results suggest that faster plates induce higher tectonic stresses and strain rates and therefore generate deeper textures. Key Points Faster oceanic plates produce higher tectonic stresses, lower dislocation creep viscosities, and therefore deeper radial anisotropy As plate speed increases from 2 to 8 cm/yr, recovered ξ increases by ∼0.01–0.025 in the upper 100–200 km of the mantle between 10 and 60 Ma The observed flat depth‐age trend in radial anisotropy tomography models is likely due to strong regularization