Origin of temporal changes of inner-core seismic waves
Origin of temporal changes of inner-core seismic waves
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DOI：
10.1016/j.epsl.2020.116267
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发表时间：
2020-07
影响因子：
5.3
通讯作者：
Yi Yang;Xiaodong Song
中科院分区：
文献类型：
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作者：
Yi Yang;Xiaodong Song
用高质量的波形偶线证实了核内地震震相的时间变化。然而，时间变化的性质仍有争议。利用大量的波形偶数据，系统地研究了IC折射波（PKIKP）和反射波（PKIKP）的时间变化。我们使用非IC参考相位（主要是SKP），这消除了时间变化的模糊性。我们发现，时间的变化总是开始于折射PKIKP和旅行时间的变化相关性更好的PKIKP。反射PKiKP的变化很容易被强的和时变的PKIKP和尾波波列污染，因此不是IC边界变化的可靠指标。结合以前的观察，我们得出结论，时间上的变化主要（如果不是全部）来自IC内部和IC表面的变化作为唯一的来源之前建议可以排除。IC的差异旋转移动其异质最高结构是对时变IC波起源的最简单、最合理的解释。每年0.05-0.1°的自转速率和可能的年代际波动可以调和体波、IC散射和简正波的所有时间变化观测。
Temporal changes of inner-core (IC) seismic phases have been confirmed with high-quality waveform doublets. However, the nature of the temporal changes is still controversial. We investigated systematically the temporal changes of IC refracted (PKIKP) and reflected (PKiKP) waves with a large data set of waveform doublets. We used non-IC reference phase (mainly SKP), which eliminated ambiguity where the temporal changes come from. We found that the temporal changes have always started at refracted PKIKP and the travel time changes correlate better with PKIKP. Changes in reflected PKiKP can be easily contaminated by the strong and time-varying PKIKP and coda wave trains and therefore are not reliable indicators for IC boundary changes. Combining with previous observations, we conclude that the temporal changes come mostly (if not all) from the IC interior and IC surface changes as the sole source suggested previously can be ruled out. The differential rotation of the IC shifting its heterogeneous uppermost structures is the simplest and most reasonable explanation for the origin of the time-varying IC waves. A rotation rate of about 0.05-0.1° per year with possible decadal fluctuation can reconcile all temporal change observations from body waves, IC scattering, and normal mode data.