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The 3D Seismic Azimuthal Anisotropies and Velocities in the Eastern Tibetan Plateau Extracted by an Azimuth‐Dependent Dispersion Curve Inversion Method
Tectonics ( IF 4.2 ) Pub Date : 2020-04-18 , DOI: 10.1029/2019tc005747
Chuntao Liang 1, 2 , Zhiqiang Liu 2 , Qian Hua 3 , Liang Wang 2 , Ningbo Jiang 2 , Jing Wu 4
Affiliation  

An azimuth‐dependent dispersion curve inversion (ADDCI) method is applied to Rayleigh waves to extract 3D velocity and azimuthal anisotropy. The synthetic tests show that the ADDCI method is able to extract azimuthal anisotropy at different depths. The errors of the fast propagation direction (FPD) and the magnitude of the anisotropy (MOA) are less than 10° and 1–2%, respectively. The 3D anisotropic model shows large variations in the FPDs and MOAs with depth and blocks; strong contrasts are observed across major faults, and the average MOA in the crust is approximately 3%. The FPDs are positively correlated with the GPS velocity direction and the strikes of regional faults in most of the blocks. The low‐velocity zones (LVZs) in middle to lower crust are widely observed in the Songpan‐Ganze terrane, the north Chuan‐Dian block, and surprisingly in the Huayingshan thrust and fold belt. The LVZs in middle crust are also positively correlated with a region of low velocities in the uppermost mantle. These observations may suggest that large‐scale deformation is coupled vertically from surface to uppermost mantle. Crust shortening by the pure shearing process, which involves the thrusting and folding of the upper crust and the lateral extrusion of blocks, may be the major mechanism causing the growth of the eastern Tibetan Plateau.

中文翻译:

方位角相关的色散曲线反演方法提取青藏高原东部3D地震方位各向异性和速度

将与方位角有关的色散曲线反演(ADDCI)方法应用于瑞利波,以提取3D速度和方位各向异性。综合测试表明,ADDCI方法能够提取不同深度的方位各向异性。快速传播方向(FPD)的误差和各向异性的大小(MOA)的误差分别小于10°和1-2%。3D各向异性模型显示,FPD和MOA随深度和块而变化很大;在主要断层之间观察到强烈的对比,地壳中的平均MOA约为3%。FPD与大多数区块中的GPS速度方向和区域断层走向正相关。在川北断块的松潘—甘泽地层中,普遍观测到中低地壳的低速带(LVZ)。令人惊讶的是在华鹰山冲断褶皱带。中地壳中的LVZs也与最上地幔中低速区域呈正相关。这些观察结果可能表明,大范围的变形是从地表到最高地幔垂直耦合的。通过纯剪切过程缩短地壳,这涉及上地壳的推挤和折叠以及块体的横向挤压,可能是导致青藏高原东部生长的主要机制。
更新日期:2020-04-18
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