Seismic Azimuthal Anisotropy Beneath a Fast Moving Ancient Continent: Constraints From Shear Wave Splitting Analysis in Australia
Seismic Azimuthal Anisotropy Beneath a Fast Moving Ancient Continent: Constraints From Shear Wave Splitting Analysis in Australia
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DOI：
10.1029/2022jb025866
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发表时间：
2023-01
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影响因子：
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通讯作者：
Kailun Ba;Stephen S. Gao;Jian-Li Song;Kelly H. Liu
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文献类型：
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作者：
Kailun Ba;Stephen S. Gao;Jian-Li Song;Kelly H. Liu
澳大利亚地下的地震方位各向异性研究使用了地球上最古老和快速移动的大陆之一的PKS，SKKS和SKS相位的分裂来描绘软流圈流动和岩石圈变形。在116个地震台站共观测到511对高质量分裂参数。与非洲、东亚和北美的其他稳定大陆地区不同，在这些地区，空间一致的分裂参数占主导地位，在澳大利亚观察到的快速方向和分裂时间显示出复杂的模式，比正常的平均分裂时间略小0.85 ± 0.33 s。在北澳大利亚板块上，快速方向大多为N-S，与热点框架中的绝对板块运动（APM）方向平行。在南澳大利亚州南半球观测到的主要是NE-SW和E-W方向，它们垂直于岩石圈最大水平缩短方向。在澳大利亚东部，观测到的方位各向异性可以归因于APM引起的简单剪切或平行于造山带走向的岩石圈组构。所观察到的地震方位各向异性的空间变化，结合深度估计的结果，利用空间相干性的分裂参数和地震层析成像研究，表明方位各向异性在澳大利亚主要是有关简单的剪切在岩石圈和软流圈之间的流变过渡层。非APM平行各向异性可归因于岩石圈底部起伏对地幔流系统的调制，岩石圈组构的贡献程度在空间上是可变的。
Seismic azimuthal anisotropy beneath Australia is investigated using splitting of the teleseismic PKS, SKKS, and SKS phases to delineate asthenospheric flow and lithospheric deformation beneath one of the oldest and fast‐moving continents on Earth. In total 511 pairs of high‐quality splitting parameters were observed at 116 seismic stations. Unlike other stable continental areas in Africa, East Asia, and North America, where spatially consistent splitting parameters dominate, the fast orientations and splitting times observed in Australia show a complex pattern, with a slightly smaller than normal average splitting time of 0.85 ± 0.33 s. On the North Australian Craton, the fast orientations are mostly N‐S, which is parallel to the absolute plate motion (APM) direction in the hotspot frame. Those observed in the South Australian Craton are mostly NE‐SW and E‐W, which are perpendicular to the maximum lithospheric horizontal shortening direction. In east Australia, the observed azimuthal anisotropy can be attributed to either APM induced simple shear or lithospheric fabric parallel to the strike of the orogenic belts. The observed spatial variations of the seismic azimuthal anisotropy, when combined with results from depth estimation utilizing the spatial coherency of the splitting parameters and seismic tomography studies, suggest that the azimuthal anisotropy in Australia can mostly be related to simple shear in the rheologically transition layer between the lithosphere and asthenosphere. Non‐APM parallel anisotropy is attributable to modulations of the mantle flow system by undulations of the bottom of the lithosphere, with a spatially variable degree of contribution from lithospheric fabric.