This study addresses questions about the productivity of Cascadia mainshock–aftershock sequences using earthquake catalogs produced by the Geological Survey of Canada and the Pacific Northwest Seismic Network. Questions concern the likelihood that future moderate to large intermediate depth intraslab earthquakes in Cascadia would have as few detectable aftershocks as those documented since 1949. More broadly, for Cascadia, we consider if aftershock productivities vary spatially, if they are outliers among global subduction zones, and if they are consistent with a physical model in which aftershocks are clock‐advanced versions of tectonically driven background seismicity. A practical motivation for this study is to assess the likely accuracy of aftershock forecasts based on productivities derived from global data that are now being issued routinely by the U.S. Geological Survey. For this reason, we estimated productivity following the identical procedures used in those forecasts and described in Page et al. (2016). Results indicate that in Cascadia we can say that the next intermediate depth intraslab earthquake will likely have just a few detectable aftershocks and that aftershock productivity appears to be an outlier among global subduction zones, with rates that on average are lower by more than half, except for mainshocks in the upper plate. Our results are consistent with a clock‐advance model; productivities may be related to the proximity of mainshocks to a population of seismogenic fault patches and correlate with background seismicity rates. The latter and a clear correlation between productivities with mainshock depth indicate that both factors may have predictive value for aftershock forecasting.

中文翻译：

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卡斯卡迪亚余震序列的生产力

本研究使用加拿大地质调查局和太平洋西北地震台网制作的地震目录解决了有关卡斯卡迪亚主震-余震序列生产力的问题。问题涉及未来卡斯卡迪亚的中到大中深度板内地震的可探测余震数量与 1949 年以来记录的一样少的可能性。更广泛地说，对于卡斯卡迪亚，我们考虑余震发生率是否在空间上不同，如果它们是全球俯冲带中的异常值，如果它们与余震是构造驱动的背景地震活动的时钟先进版本的物理模型一致。这项研究的一个实际动机是根据美国地质调查局现在定期发布的全球数据得出的生产力评估余震预测的可能准确性。出于这个原因，我们按照这些预测中使用的和佩奇等人描述的相同程序来估计生产力。(2016)。结果表明，在卡斯卡迪亚，我们可以说下一次中等深度的板内地震可能只有少数可检测到的余震，余震生产力似乎是全球俯冲带中的一个异常值，其发生率平均低一半以上，除了用于上板的主震。我们的结果与时钟提前模型一致；生产力可能与主震与发震断层群的接近程度有关，并与背景地震活动率相关。后者以及生产力与主震深度之间的明显相关性表明，这两个因素可能对余震预报具有预测价值。