Three‐dimensional P wave azimuthal anisotropy in the lithosphere beneath China
Three‐dimensional P wave azimuthal anisotropy in the lithosphere beneath China
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DOI：
10.1002/2014jb010963
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发表时间：
2014-07
期刊：
影响因子：
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通讯作者：
Zhouchuan Huang;Pan Wang;Dapeng Zhao;Liangshu Wang;Mingjie Xu
中科院分区：
文献类型：
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作者：
Zhouchuan Huang;Pan Wang;Dapeng Zhao;Liangshu Wang;Mingjie Xu
利用剪切波（SKS）分裂测量对东亚上地幔的地震各向异性进行了广泛研究，这为该地区的地幔动力学提供了重要信息。然而，SKS测量的垂直分辨率较差，因此其解释通常不唯一。在这项工作中，我们使用了1563个地震台站记录的34036次本地地震的大量走时数据，以确定中国下方岩石圈的第一个三维P波方位各向异性模型。我们的结果表明，快速波速方向（FVDs）通常与地表地质特征相关，例如造山带、活动断层和构造边界的走向。在上地壳中，在诸如青藏高原等广泛受压的区域，FVDs与最大水平应力（σH）垂直，而在走滑剪切带（如喜马拉雅山西部和东部构造结）中，它们与σH大致平行。P波各向异性的FVDs与SKS分裂测量的比较表明，在青藏高原下方，岩石圈的地震各向异性对SKS分裂观测有显著贡献。相比之下，在中国东部，岩石圈中的P波FVDs与SKS分裂测量结果不同，这表明SKS分裂主要是由中国东部下方更深的地幔（如软流圈和地幔过渡带）的各向异性引起的。这些新的结果为东亚岩石圈变形和地幔动力学提供了重要的新信息。
Seismic anisotropy in the upper mantle beneath East Asia has been studied extensively using shear wave (SKS) splitting measurements, which have provided important information on mantle dynamics in this region. However, SKS measurements have poor vertical resolution, and so their interpretations are usually not unique. In this work we use a large number of traveltime data from 34,036 local earthquakes recorded by 1563 seismic stations to determine the first model of 3‐D P wave azimuthal anisotropy in the lithosphere beneath China. Our results show that the fast velocity directions (FVDs) are generally correlated with the surface geologic features, such as the strikes of the orogens, active faults, and tectonic boundaries. The FVDs in the upper crust are normal to the maximal horizontal stress (σH) in regions with extensive compression such as the Tibetan Plateau, whereas they are subparallel to σH in strike‐slip shear zones such as the western and eastern Himalayan syntax. The comparison of the FVDs of P wave anisotropy with SKS splitting measurements indicates that beneath the Tibetan Plateau the seismic anisotropy in the lithosphere contributes significantly to the SKS splitting observations. In contrast, in east China the P wave FVDs in the lithosphere are different from the SKS splitting measurements, suggesting that the SKS splitting is mainly caused by the anisotropy in the deeper mantle such as the asthenosphere and the mantle transition zone under east China. These novel results provide important new information on the lithospheric deformation and mantle dynamics in East Asia.