Upper mantle slab under Alaska: contribution to anomalous core-phase observations on south-Sandwich to Alaska paths
Upper mantle slab under Alaska: contribution to anomalous core-phase observations on south-Sandwich to Alaska paths
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DOI：
10.1016/j.pepi.2020.106427
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发表时间：
2020-02-01
影响因子：
2.3
通讯作者：
Roecker, Steve
中科院分区：
文献类型：
--
作者：
Frost, Daniel A.;Romanowicz, Barbara;Roecker, Steve
作为相对于地球自转轴的路径取向的函数，观测到的内核敏感的PKPdf地震体波走时异常被解释为内核各向异性的证据。从南桑威奇群岛的地震到阿拉斯加地震台的路径显示出强烈的异常旅行时间，具有与各向异性的简单模型不兼容的大范围传播。在这里，我们评估了阿拉斯加海底强速度不均匀对PkPdf的旅行时间、到达方向和幅度的影响。我们通过一种新的、高分辨率的阿拉斯加下地幔层析成像模型，使用3D射线跟踪和2.5D波形建模。我们发现阿拉斯加下面的结构，特别是俯冲板块，反映在这些PKPdf观测的模式中，这可以被我们的模型复制。我们还在观测到的远震P波中发现了类似的模式，这同样可以用我们的平板模型来解释。我们的结论是，通常被归因于内核各向异性的旅行时异常中，至少有2 S是由于阿拉斯加下地幔的板片效应造成的。
Observations of travel time anomalies of inner core-sensitive PKPdf seismic body waves, as a function of path orientation with respect to the earth's rotation axis, have been interpreted as evidence of anisotropy in the inner core. Paths from earthquakes in the South Sandwich Islands to stations in Alaska show strongly anomalous travel times, with a large spread that is not compatible with simple models of anisotropy. Here we assess the impact of strong velocity heterogeneity under Alaska on the travel times, directions of arrival and amplitudes of PKPdf. We use 3D ray-tracing and 2.5D waveform modelling through a new, high-resolution tomography model of the upper mantle beneath Alaska. We find that the structure beneath Alaska, notably the subducting slab, is reflected in the patterns of these PKPdf observations, and this can be replicated by our model. We also find similar patterns in observed teleseismic P waves that can likewise be explained by our slab model. We conclude that at least 2 s of the travel time anomaly often attributed to inner core anisotropy is due to slab effects in the upper mantle beneath Alaska.