Probability of radial anisotropy in the deep mantle
Probability of radial anisotropy in the deep mantle
复制标题
地幔深部径向各向异性的概率
DOI：
10.1016/j.epsl.2008.03.041
复制
发表时间：
2008
影响因子：
5.3
通讯作者：
B. Kennett
中科院分区：
文献类型：
--
作者：
K. Visser;J. Trampert;S. Lebedev;B. Kennett
地球最上层的地幔是各向异性的，这是公认的，但在更深的地幔各向异性的观测一直比较模糊。径向各向异性，爱和瑞利波之间的差异，包括在顶部220公里的PREM，但没有共识是否各向异性存在低于该深度。基模表面波，通常使用的周期高达200秒，是敏感的结构在前几百公里，因此不提供信息的各向异性以下。然而，更高模式的表面波具有延伸到过渡区和过渡区以下的灵敏度，因此应该能够洞察更大深度处的各向异性，但它们非常难以测量。我们以前开发了一种新的技术来测量更高的模式表面波相速度一致的不确定性。这些数据在这里被用来构建概率密度函数的径向各向异性地球模型下降到约1500公里。在上地幔，我们得到一个更快的水平偏振剪切波速度的概率很高，可能与板块运动。然而，在软流圈和过渡区，我们发现了更快的垂直偏振剪切波速度的概率很高。在下地幔1500公里深处，我们没有看到明显的剪切波各向异性。这与实验室测量结果一致，实验室测量结果表明下地幔矿物是各向异性的，但LPO不太可能在中地幔的压力-温度条件下发展。
It is well established that the Earth's uppermost mantle is anisotropic, but observations of anisotropy in the deeper mantle have been more ambiguous. Radial anisotropy, the discrepancy between Love and Rayleigh waves, was included in the top 220 km of PREM, but there is no consensus whether anisotropy is present below that depth. Fundamental mode surface waves, for commonly used periods up to 200 s, are sensitive to structure in the first few hundred kilometers and therefore do not provide information on anisotropy below. Higher mode surface waves, however, have sensitivities that extend to and below the transition zone and should thus give insight about anisotropy at greater depths, but they are very difficult to measure. We previously developed a new technique to measure higher mode surface wave phase velocities with consistent uncertainties. These data are used here to construct probability density functions of a radially anisotropic Earth model down to approximately 1500 km. In the uppermost mantle, we obtain a high probability of faster horizontally polarized shear wave speed, likely to be related to plate motion. In the asthenosphere and transition zone, however, we find a high probability of faster vertically polarized shear wave speed. To a depth of 1500 km in the lower mantle, we see no significant shear wave anisotropy. This is consistent with results from laboratory measurements which show that lower mantle minerals are anisotropic but LPO is unlikely to develop in the pressure–temperature conditions present in the mid-mantle.