资源环境科技发展态势分析平台

The anisotropic fabric of the oceanic mantle lithosphere is often assumed to parallel paleo-relative plate motion (RPM). However, we find evidence that this assumption is invalid beneath the Juan de Fuca (JdF) plate. Using travel times of seismic energy propagating through the topmost mantle, we find that the fast direction of P wave propagation is rotated 18 degrees +/- 3 degrees counterclockwise to the paleo-spreading direction and strikes between Pacific-JdF relative and JdF absolute plate motion (APM). The mean mantle velocity is 7.85 +/- 0.02 km/s with 4.6% +/- 0.4% anisotropy. Synthesis of the plate-averaged Pn anisotropy signal with measurements of Pn anisotropy beneath the JdF Ridge and SKS splits across the JdF plate suggests that the anisotropic structure of the topmost mantle continues to evolve away from the spreading center to more closely align with APM. We infer that the oceanic mantle lithosphere may record the influence of both paleo-RPM and paleo-APM.