Assessing the statistical significance of electromagnetic anomalies in the ultralow frequency (ULF) range observed prior to earthquakes is a necessary step toward determining whether these perturbations constitute actual earthquake precursors. A statistical epoch analysis (SEA) was recently performed by Han et al. (2014, https://doi.org/10.1002/2014JA019789) to analyze earthquakes happening between 2001 and 2010 near the geomagnetic observatory of Kakioka, Japan; the authors found a significant number of anomalies 6 to 15 days prior to the earthquake day within 100 km from Kakioka, while no significant pre‐earthquake activity was observed for the farther region 100 to 216 km from the observatory. In this current paper, we describe the application of our independent software implementation of their method. Despite using a different outlier rejection scheme, we manage to approximate their results. Upon validation of our program, we conduct multiple sensitivity studies. First, we explore how different outlier rejection schemes impact the results. We then restrict the analysis to only mantle earthquakes, highlighting a marginally significant number of anomalies prior to the earthquake day. Next, we test a higher band‐pass filter than the one initially used but find no anomalous pre‐earthquake activity in this higher‐frequency band. We then use a different catalog to establish the list of qualifying “earthquake days” which also leads the anomalous pre‐earthquake episode to vanish, thus raising concerns about the robustness of the results. Finally, we apply the SEA to another time window, ranging from 2013 to 2018: No significant pre‐earthquake episode can be observed for this interval. We conclude our study by providing guidelines for upcoming work.

中文翻译：

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ULF范围内地震前电磁异常的统计分析

评估地震前观察到的超低频（ULF）范围内的电磁异常的统计意义是确定这些扰动是否构成实际地震前兆的必要步骤。Han等人最近进行了统计纪元分析（SEA）。（2014，https://doi.org/10.1002/2014JA019789）分析2001年至2010年日本柿木地磁观测站附近发生的地震；作者发现在地震发生前6至15天，距柿木冈100公里以内有大量异常，而在距天文台100至216公里的较远地区未观察到明显的地震前活动。在本文中，我们描述了应用我们自己的软件实现其方法的独立软件。尽管使用了不同的离群值拒绝方案，但我们设法估算了它们的结果。验证我们的计划后，我们将进行多项敏感性研究。首先，我们探索不同的离群值拒绝方案如何影响结果。然后，我们将分析限制为仅发生地幔地震，从而突出显示了地震发生前的异常异常现象。接下来，我们测试了比最初使用的滤波器更高的带通滤波器，但是在此更高的频段中没有发现异常的地震前活动。然后，我们使用不同的目录来建立合格的“地震日”列表，这也导致异常的地震前事件消失，从而引起人们对结果可靠性的担忧。最后，我们将SEA应用于另一个时间范围，从2013年到2018年：在此时间间隔内未观察到明显的地震前发作。我们通过为即将开展的工作提供指导来结束研究。