To clarify the internal structure of the oceanic lithosphere-asthenosphere system, here we determine a new 3-D model of azimuthal anisotropic shear-wave velocity (Vs) down to ~200 km depth from the Juan de Fuca (JdF) mid-ocean ridge to the Cascadia subduction zone, by inverting newly measured teleseismic fundamental mode Rayleigh-wave phase and amplitude data at periods of 25–100 s. The JdF lithosphere is clearly imaged as a high-velocity anomaly from the ridge to the subduction zone. Distinct azimuthal anisotropies are revealed in the JdF lithosphere before and after its subduction. Obvious trench-normal fast-velocity directions (FVDs) exist in the JdF plate beneath the Pacific Ocean, whereas the subducting JdF slab beneath the Cascadia margin generally exhibits trench-parallel FVDs. We propose that the subduction-induced structure and mineral alignment in the JdF slab transform the fossil fabrics in the JdF plate formed at the mid-ocean ridge and altered during the plate motion and cooling.

中文翻译：

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俯冲作用改变了胡安德富卡板块的方位各向异性

为了阐明海洋岩石圈-软流圈系统的内部结构，我们在这里确定了一个新的方位各向异性剪切波速度 (Vs) 3-D 模型，从胡安德富卡 (JdF) 洋中脊深入至约 200 公里深度通过反演新测量的 25-100 秒周期的远震基模瑞利波相位和振幅数据，可以到达卡斯卡迪亚俯冲带。 JdF 岩石圈清晰地成像为从山脊到俯冲带的高速异常。 JdF 岩石圈在俯冲前后均显示出明显的方位各向异性。太平洋下方的 JdF 板块存在明显的海沟法线快速度方向（FVD），而卡斯卡迪亚边缘下方的俯冲 JdF 板片通常表现出与海沟平行的 FVD。我们认为，JdF 板块中俯冲引起的结构和矿物排列改变了 JdF 板块中在洋中脊形成并在板块运动和冷却过程中发生变化的化石结构。