3-D synthetic modelling and observations of anisotropy effects on SS precursors: implications for mantle deformation in the transition zone
3-D synthetic modelling and observations of anisotropy effects on SS precursors: implications for mantle deformation in the transition zone
复制标题
SS 前体各向异性效应的 3-D 综合模拟和观测：对过渡带地幔变形的影响
DOI：
10.1093/gji/ggab529
复制
发表时间：
2022
影响因子：
2.8
通讯作者：
Maguire, Ross R.
中科院分区：
文献类型：
--
作者：
Huang, Quancheng;Schmerr, Nicholas C.;Beghein, Caroline;Waszek, Lauren;Maguire, Ross R.
地球的地幔过渡带（MTZ）在上地幔和下地幔之间的热和成分相互作用中起着关键作用。地震各向异性提供了有关地幔变形和整个 MTZ 动力学的有用信息。然而，MTZ 中的地震各向异性很难通过表面波或剪切波分裂测量来约束。在这里，我们通过 3D 合成建模研究体波方法（SS 前体）对各向异性的敏感性，并将其应用于实际数据。我们的研究表明，SS前兆可以区分源自三个深度的各向异性：浅上地幔（80-220 km）、深上地幔410 km以上和MTZ（410-660 km）。综合分辨率测试表明，SS 前兆信号可以解析 3% 的方位各向异性，其中数据具有平均信噪比 (SNR = 7) 和足够的方位覆盖。为了研究区域敏感性，我们将叠加和反演方法应用于两个密集采样区域：日本俯冲带和夏威夷热点周围的中太平洋区域。我们在日本俯冲带附近的 MTZ 中发现了显着的各向异性 (15.3 ± 9.2%) 和垂直于海沟的快速方向 (93° ± 5°) 的证据。我们将方位各向异性归因于中国东北部俯冲板片内剪切变形引起的玄武岩材料的晶粒尺度形状优选取向。在太平洋中部研究区域，没有检测到 MTZ 各向异性，尽管建模表明数据覆盖范围应该允许我们解析至少 3% 的各向异性。因此，夏威夷地幔柱在 MTZ 中没有产生可检测到的方位各向异性。
The Earth's mantle transition zone (MTZ) plays a key role in the thermal and compositional interactions between the upper and lower mantle. Seismic anisotropy provides useful information about mantle deformation and dynamics across the MTZ. However, seismic anisotropy in the MTZ is difficult to constrain from surface wave or shear wave splitting measurements. Here, we investigate the sensitivity to anisotropy of a body wave method, SS precursors, through 3-D synthetic modelling and apply it to real data. Our study shows that the SS precursors can distinguish the anisotropy originating from three depths: shallow upper mantle (80–220 km), deep upper mantle above 410 km, and MTZ (410–660 km). Synthetic resolution tests indicate that SS precursors can resolve3 per cent azimuthal anisotropy where data have an average signal-to-noise ratio (SNR = 7) and sufficient azimuthal coverage. To investigate regional sensitivity, we apply the stacking and inversion methods to two densely sampled areas: the Japan subduction zone and a central Pacific region around the Hawaiian hotspot. We find evidence for significantVSanisotropy (15.3 ± 9.2 per cent) with a trench-perpendicular fast direction (93° ± 5°) in the MTZ near the Japan subduction zone. We attribute the azimuthal anisotropy to the grain-scale shape-preferred orientation of basaltic materials induced by the shear deformation within the subducting slab beneath NE China. In the central Pacific study region, there is a non-detection of MTZ anisotropy, although modelling suggests the data coverage should allow us to resolve at least 3 per cent anisotropy. Therefore, the Hawaiian mantle plume has not produced detectable azimuthal anisotropy in the MTZ.