In this study, we revisit the three largest historical earthquakes in California—the 1857 Fort Tejon, 1872 Owens Valley, and 1906 San Francisco earthquakes—to review their published moment magnitudes, and compare their estimated shaking distributions with predictions using modern ground‐motion models (GMMs) and ground‐motion intensity conversion equations. Currently accepted moment magnitude estimates for the three earthquakes are 7.9, 7.6, and 7.8, respectively. We first consider the extent to which the intensity distributions of all three earthquakes are consistent with a moment magnitude toward the upper end of the estimated range. We then apply a GMM‐based method to estimate the magnitudes of large historical earthquakes. The intensity distribution of the 1857 earthquake is too sparse to provide a strong constraint on magnitude. For the 1872 earthquake, consideration of all available constraints suggests that it was a high stress‐drop event, with a magnitude on the higher end of the range implied by scaling relationships, that is, higher than moment magnitude 7.6. For the 1906 earthquake, based on our analysis of regional intensities and the detailed intensity distribution in San Francisco, along with other available constraints, we estimate a preferred moment magnitude of 7.9, consistent with the published estimate based on geodetic and instrumental seismic data. These results suggest that, although there can be a tendency for historical earthquake magnitudes to be overestimated, the accepted catalog magnitudes of California’s largest historical earthquakes could be too low. Given the uncertainties of the magnitude estimates, the seismic moment release rate between 1850 and 2019 could have been either higher or lower than the average over millennial time scales. It is further not possible to reject the hypothesis that California seismicity is described by an untruncated Gutenberg–Richter distribution with a b‐value of 1.0 for moment magnitudes up to 8.0.

中文翻译：

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重温加州过去的大地震和长期地震发生率

在这项研究中，我们回顾了加利福尼亚州的三大历史地震，即1857年的特洪堡，1872年的欧文斯山谷和1906年的旧金山地震，以审查其公布的弯矩大小，并将其估计的振动分布与使用现代地面运动模型的预测结果进行比较（GMM）和地面运动强度转换方程式。目前公认的三级地震的震级估计分别为7.9、7.6和7.8。我们首先考虑所有三个地震的强度分布在一定程度上与估计范围上限附近的弯矩大小保持一致。然后，我们应用基于GMM的方法来估算历史大地震的震级。1857年地震的强度分布过于稀疏，无法对震级进行严格限制。对于1872年的地震，考虑到所有可用的约束条件，这表明这是一次高应力降落事件，其幅度上限由比例关系暗示，即高于矩震级7.6。对于1906年地震，根据我们对区域烈度的分析和详细的旧金山烈度分布，以及其他可用的限制条件，我们估计优选的震级为7.9，与基于大地测量和仪器地震数据的已发布估计一致。这些结果表明，尽管可能会高估历史地震震级，但公认的加利福尼亚最大的历史地震震级可能太低。鉴于震级估算的不确定性，1850年至2019年之间的地震矩释放率可能高于或低于千禧年时间尺度的平均值。不可能再拒绝这样的假设，即加利福尼亚地震活动是由不截断的Gutenberg-Richter分布描述的，其矩值最大为8.0的ab值为1.0。