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Upper mantle slab under Alaska: Contribution to anomalous core-phase observations on south-Sandwich to Alaska paths
Physics of the Earth and Planetary Interiors ( IF 2.3 ) Pub Date : 2020-02-01 , DOI: 10.1016/j.pepi.2020.106427
Daniel A. Frost , Barbara Romanowicz , Steve Roecker

Abstract 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.

中文翻译:

阿拉斯加下的上地幔板块:对南桑威奇到阿拉斯加路径异常核心相观测的贡献

摘要 对内核敏感 PKPdf 地震体波走时异常的观测,作为相对于地球自转轴的路径方向的函数,已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的站点的路径显示出强烈的旅行时间异常,传播时间大,与简单的各向异性模型不兼容。在这里,我们评估了阿拉斯加下强烈的速度异质性对 PKPdf 的旅行时间、到达方向和振幅的影响。我们通过阿拉斯加下方上地幔的新型高分辨率断层扫描模型使用 3D 射线追踪和 2.5D 波形建模。我们发现阿拉斯加下方的结构,尤其是俯冲板块,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,这同样可以通过我们的平板模型来解释。我们得出结论,通常归因于内核各向异性的旅行时间异常中至少有 2 s 是由于阿拉斯加下方上地幔中的板片效应造成的。
更新日期:2020-02-01
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