To clarify the upper mantle structure and dynamics of the Kamchatka subduction zone, we conduct Rayleigh-wave phase-velocity azimuthal anisotropy tomography beneath Kamchatka using amplitude and phase data of teleseismic fundamental mode Rayleigh-waves at periods of 25–150 s. With the obtained anisotropic phase-velocity model, a 3-D azimuthal anisotropic shear-wave velocity (Vs) model is determined down to ∼300 km depth. Beneath Kamchatka, the subducting Pacific slab is clearly imaged as a dipping high-Vs zone on the south of the Shiveluch volcano at ∼57°N latitude, whereas this high-Vs zone is absent on the north of the volcano, suggesting that a slab edge exists in the region. Visible low-Vs anomalies are revealed around the slab edge. The subducting Pacific slab beneath Kamchatka generally exhibits a fast-velocity direction (FVD) of ∼NE-SW in the area south of ∼54°N latitude, whereas the dominant FVD in the slab rotates to ∼N-S or ∼NNW-SSE in the area of ∼54°–57°N latitude. The FVDs in the subducting Pacific slab are generally parallel to the Kamchatka trench, which may result from the shape-preferred orientation of stratified oceanic lithosphere. At shallow depths (<∼150 km), the low-Vs mantle wedge generally exhibits ∼ NW-SE FVDs, whereas ∼ E-W FVDs appear on the north of the slab edge, which form semi-toroidal FVDs around the slab edge. The semi-toroidal FVDs may reflect a combination of corner flow in the mantle wedge and toroidal mantle flow around the slab edge beneath Kamchatka, which may deform and heat or even melt the slab near its edge.

中文翻译：

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绘制堪察加半岛下方的太平洋板块边缘和环形地幔流

为了阐明堪察加俯冲带的上地幔结构和动力学，我们使用周期为 25-150 s 的远震基模瑞利波的振幅和相位数据，在堪察加下方进行了瑞利波相速度方位各向异性层析成像。使用所获得的各向异性相速度模型，可以确定3-D 方位角各向异性横波速度 ( V s) 模型，该模型可下至约 300 公里深度。在堪察加半岛下方，俯冲的太平洋板块被清晰地描绘为位于纬度~57°N 的 Shiveluch 火山南部的一个倾斜的高V s 带，而在火山北部没有这个高V s 带，这表明该区域存在板坯边缘。可见低Vs 异常在板边缘周围显露出来。堪察加半岛下方俯冲太平洋板块在纬度~54°N以南地区通常表现出~NE-SW的快速度方向（FVD），而板块中的主导FVD旋转到~NS或~NNW-SSE在约 54°–57°N 纬度的区域。俯冲太平洋板块中的 FVDs 通常平行于堪察加海沟，这可能是由分层海洋岩石圈的形状偏好取向造成的。在较浅的深度 (<∼150 km)，低Vs 地幔楔通常表现出 ~ NW-SE FVD，而 ~ EW FVD 出现在板块边缘的北部，在板块边缘周围形成半环形 FVD。半环形 FVD 可能反映了地幔楔中的角流和堪察加半岛下方板坯边缘周围的环形地幔流的组合，这可能使板坯在其边缘附近变形、加热甚至熔化。