Abstract 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.

中文翻译：

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内核地震波时间变化的成因

摘要 高质量波形双峰已经证实了内核 (IC) 地震相位的时间变化。然而，时间变化的性质仍然存在争议。我们使用大量波形双峰数据集系统地研究了 IC 折射 (PKIKP) 和反射 (PKiKP) 波的时间变化。我们使用了非 IC 参考相位（主要是 SKP），这消除了时间变化来自何处的歧义。我们发现时间变化总是从折射的 PKIKP 开始，并且旅行时间变化与 PKIKP 的相关性更好。反射 PKiKP 的变化很容易被强且随时间变化的 PKIKP 和尾波序列污染，因此不是 IC 边界变化的可靠指标。结合之前的观察，我们得出结论，时间变化主要（如果不是全部）来自 IC 内部和 IC 表面变化，因为可以排除之前建议的唯一来源。IC 的微分旋转移动其异构最上层结构是对时变 IC 波起源的最简单和最合理的解释。每年大约 0.05-0.1° 的旋转速率可能会出现年代际波动，可以协调来自体波、IC 散射和正常模式数据的所有时间变化观测。