The earthquake magnitude‐frequency distribution is characterized by the b‐value, which describes the relative frequency of large versus small earthquakes. It has been suggested that changes in b‐value after an earthquake can be used to discriminate whether that earthquake is part of a foreshock sequence or a more typical mainshock‐aftershock sequence, with a decrease in b‐value heralding a larger earthquake to come. However, the measurement of b‐value during an active aftershock sequence is strongly biased by short‐term incompleteness of the earthquake catalog and by data‐windowing, and these biases have the same direction as the proposed signal. Here I develop a new estimator of the b‐value that is insensitive to transient changes in catalog completeness and that does not require data windowing. The new estimator “b‐positive” is based on the positive‐only subset of the differences in magnitude between successive earthquakes, which are described by a double‐exponential (Laplace) distribution with the same b‐value as the magnitude distribution itself. The b‐positive estimator greatly improves the robustness of continuous b‐value measurements during active earthquake sequences, as well as in historical catalogs with unknown or variable completeness. The new estimator confirms some of the observations of Gulia and Wiemer (2019), although at a reduced level, showing a decrease and recovery of the b‐value during several recent foreshock sequences that cannot be attributed simply to measurement bias. However, the unbiased b‐value changes may be too subtle to use in a real‐time earthquake alarm system.

中文翻译：

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B正值：瞬态不完整目录中余震幅度分布的鲁棒估计

地震震级频率分布的特征是b值，它描述了大地震与小地震的相对频率。有人建议，地震后b值的变化可用于区分该地震是前震序列的一部分，还是更典型的主震-余震序列的一部分，而b值的减小预示着更大的地震将要来临。但是，活动余震序列中b值的测量受到地震目录的短期不完整性和数据窗口的强烈偏倚，并且这些偏倚与拟议信号的方向相同。在这里，我开发了b-的新估计量该值对目录完整性的瞬时变化不敏感，并且不需要数据窗口。新的估算器“ b阳性”基于连续地震之间震级差的仅正子集，该子集由双指数（拉普拉斯）分布描述，且b值与震级分布本身相同。所述b阳性估计器大大提高了连续的鲁棒性b -值测量活性地震序列期间，以及在具有未知或可变完整性历史目录。新的估算器证实了Gulia和Wiemer（2019）的一些观测值，尽管其水平有所降低，但显示出b的减少和恢复。不能仅归因于测量偏差的几个最近前震序列中的值。但是，无偏的b值变化可能太微妙，无法在实时地震报警系统中使用。