We apply the Matrix Profile algorithm to 100 days of continuous data starting 10 days before the 2019 M 6.4 and M 7.1 Ridgecrest earthquakes from borehole seismic station B921 near the Ridgecrest aftershock sequence. We identify many examples of reversely polarized waveforms, but focus on one particularly striking earthquake pair with strongly negatively correlated P and S waveforms at B921 and several other nearby stations. Waveform-cross-correlation-based relocation of these events indicates they are at about 10 km depth and separated by only 115 m. Individual focal mechanisms are poorly resolved for these events because of the limited number of recording stations with unambiguous P polarities. However, relative P and S polarity and amplitude information can be used to constrain the likely difference in fault plane orientation between the two events to be 5–20°. We explore possible models to explain these observations, including low effective coefficients of fault friction and short-wavelength stress heterogeneity caused by prior earthquakes. Although definitive conclusions are lacking, we favor local stress heterogeneity as being more consistent with other observations for the Ridgecrest region.

中文翻译：

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反极性地震对加利福尼亚州 Ridgecrest 附近断层摩擦和应力非均质性的影响


我们将矩阵剖面算法应用于 2019 年 M 6.4 和 M 7.1 Ridgecrest 地震前 10 天，从 Ridgecrest 余震序列附近的钻孔地震站 B921 开始的 100 天连续数据。我们确定了许多反向极化波形的例子，但重点关注一个特别引人注目的地震对，在 B921 和附近的其他几个台站，P和S波形具有强负相关。这些事件基于波形互相关的重新定位表明，它们位于约 10 km 的深度，仅相距 115 m。由于具有明确 P 极性的记录站数量有限，因此这些事件的单个焦点机制解析不佳。然而，相对的 P 和 S 极性和振幅信息可用于将两个事件之间断层平面方向的可能差异限制为 5-20°。我们探索了可能的模型来解释这些观察结果，包括由先前地震引起的低有效断层摩擦系数和短波长应力异质性。尽管缺乏明确的结论，但我们赞成局部应力异质性，因为它与 Ridgecrest 地区的其他观测结果更一致。