The strength of radial anisotropy can effectively reveal vertical or horizontal material flow, which may provide significant dynamic implications. The South China Block (SCB) is a classic laboratory to study strong deformation under compression from the surroundings. We construct a radially anisotropic 3-D shear-wave model of the entire SCB using multimode surface wave tomography with a lateral resolution of 2.0°. Distinctive structural contrasts are revealed in the S-wave velocity anomalies in the Cathaysia Block and the Yangtze Craton. In the Cathaysia Block, a low-velocity anomaly becomes evident with increasing depth, particularly in the V_SH model. The Yangtze Craton is, however, characterized by a high-velocity anomaly, especially in the Sichuan Basin, where the high-velocity feature can extend down to a depth of 300 km. Interestingly, an abrupt change in radial anisotropy is observed beneath the Sichuan Basin, with positive radial anisotropy (faster V_SH) in the uppermost mantle and negative radial anisotropy (faster V_SV) at depths from 80 to 250 km. The lower negative anisotropic layer may reflect the directional arrangement of constituent materials caused by eastward compression and erosion of mantle flow under the Tibetan Plateau. In addition, remarkable negative radial anisotropy is found in the asthenosphere beneath Hainan Island and its surroundings. The features beneath Hainan Island and its surroundings may be related to the Hainan mantle plume in the Cenozoic.

中文翻译：

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多模面波层析成像的异常径向各向异性及其对华南地区上地幔动力学的影响

径向各向异性的强度可以有效地揭示垂直或水平物质流，这可能会产生重要的动态影响。华南地块（SCB）是研究环境压缩下的强变形的经典实验室。我们使用横向分辨率为 2.0° 的多模表面波断层扫描构建了整个 SCB 的径向各向异性 3-D 剪切波模型。华夏地块和扬子克拉通的横波速度异常显示出明显的构造对比。在华夏地块，随着深度的增加，低速异常变得明显，特别是在V _SH模型。然而，扬子克拉通以高速异常为特征，特别是在四川盆地，高速特征可向下延伸至 300 km 深度。有趣的是，在四川盆地下方观察到径向各向异性的突然变化，在最上地幔具有正径向各向异性（较快V _{SH ）和负径向各向异性（较快}V _SV) 在 80 至 250 公里的深度。下部负各向异性层可能反映了青藏高原下地幔流向东压缩和侵蚀造成的成分物质的定向排列。此外，海南岛及其周边软流圈具有显着的负径向各向异性。海南岛及其周围的地貌特征可能与新生代的海南地幔柱有关。