Slow earthquakes are slow fault slip events. Quantifying and monitoring slow earthquake activity characteristics are important, because they may change before large earthquakes occur. Statistical seismicity models are useful for quantifying seismicity characteristics. However, no standard statistical model exists for slow earthquake activity. This study used a high-quality catalog of low-frequency earthquakes (LFEs), a type of slow earthquake, in the Nankai subduction zone from April 2004 to August 2015 and conducted the first comparison of existing statistical LFE activity models to determine which model better describes LFE activity. Based on this comparison, this study proposes a new hybrid model that incorporates existing model features. The new model considers the LFE activity history in a manner similar to the epidemic-type aftershock sequence (ETAS) model and represents the LFE aftershock rate (subsequent LFE occurrence rate) with a small number of model parameters, as in the Omori–Utsu aftershock law for regular earthquakes. The results show that the proposed model outperforms other existing models. However, the new model cannot reproduce a feature of LFE activity: the sudden cessation of intense LFE bursts. This is because the new model superimposes multiple aftershock activities and predicts extremely high seismicity rates during and after the LFE bursts. I suggest that reproducing and successfully predicting the sudden cessation of intense LFE bursts is critical for the further improvement of statistical LFE activity models. In addition, the empirical equations formulated in this study for the LFE aftershock rates may be useful for future statistical and physical modeling of LFE activity.

Graphical Abstract

中文翻译：

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低频地震活动统计模型比较

慢地震是慢断层滑动事件。量化和监测慢震活动特征很重要，因为它们可能在大地震发生之前发生变化。统计地震活动模型对于量化地震活动特征非常有用。然而，慢地震活动不存在标准统计模型。本研究使用了2004年4月至2015年8月南开俯冲带低频地震（LFE）（一种慢地震）的高质量目录，并对现有统计LFE活动模型进行了首次比较，以确定哪种模型更好描述 LFE 活动。基于这种比较，本研究提出了一种融合现有模型特征的新混合模型。新模型以类似于流行病型余震序列（ETAS）模型的方式考虑LFE活动历史，并用少量模型参数表示LFE余震率（随后的LFE发生率），如大森宇津余震定期地震法。结果表明，所提出的模型优于其他现有模型。然而，新模型无法重现 LFE 活动的一个特征：强烈的 LFE 爆发突然停止。这是因为新模型叠加了多次余震活动，并预测 LFE 爆发期间和之后的极高地震活动率。我认为，重现并成功预测强烈 LFE 爆发的突然停止对于统计 LFE 活动模型的进一步改进至关重要。此外，本研究中为 LFE 余震率制定的经验方程可能对未来 LFE 活动的统计和物理建模有用。

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