Long- and Short-Term Stress Interaction of the 2019 Ridgecrest Sequence and Coulomb-Based Earthquake Forecasts
Long- and Short-Term Stress Interaction of the 2019 Ridgecrest Sequence and Coulomb-Based Earthquake Forecasts
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DOI：
10.1785/0120200169
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发表时间：
2020-08
影响因子：
3
通讯作者：
S. Toda;R. Stein
中科院分区：
文献类型：
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作者：
S. Toda;R. Stein
我们首先探讨了南加州一系列回顾性地震相互作用。我们发现，在过去的150年里，4次Mw≥7级的冲击使Ridgecrest断层更接近破坏。研究了6.4和7.1级地震之间的34小时时间跨度，我们计算出6.4级地震使7.1级地震的震源震区更接近于0.7巴的破坏，而7.1级地震减轻了第一次地震带来的大部分周围应力。我们还发现，6.4级跨断层余震落在7.1级余震的应力阴影下时停止了余震。脊峰主震使加洛克断层120公里长的部分从0.2巴到10巴更接近破裂。这些结果促使我们引入对未来地震活动性的预测。大多数预测余震的尝试都使用统计衰减模型或库仑应力传递。统计方法需要简化关于余震空间分布及其衰减的假设；库仑模型对周围断层的几何形状作了简化的假设，我们在这里试图消除这些假设。我们在震源机制上执行库仑应力变化的速率状态实现，以捕获断层复杂性。在经过一段学习期对模型进行调整以提高预测能力后，我们进行回顾性预测以评估模型的预测能力。我们预测未来12个月发生Mw≥7.5的Garlock断层破裂的可能性为2.3%。如果这样的破裂发生在距离圣安地列斯断层45公里的范围内，我们计算得出，它将使圣安地列斯断层在莫哈韦剖面上破裂的可能性提高150倍。因此，我们估计未来12个月发生圣安德烈亚斯大地震的净概率为1.15%，约为其背景概率的3至5倍。
We first explore a series of retrospective earthquake interactions in southern California. We find that the four Mw≥7 shocks in the past 150 yr brought the Ridgecrest fault ∼1 bar closer to failure. Examining the 34 hr time span between the Mw 6.4 and Mw 7.1 events, we calculate that the Mw 6.4 event brought the hypocentral region of the Mw 7.1 earthquake 0.7 bars closer to failure, with the Mw 7.1 event relieving most of the surrounding stress that was imparted by the first. We also find that the Mw 6.4 cross-fault aftershocks shut down when they fell under the stress shadow of the Mw 7.1. Together, the Ridgecrest mainshocks brought a 120 km long portion of the Garlock fault from 0.2 to 10 bars closer to failure. These results motivate our introduction of forecasts of future seismicity. Most attempts to forecast aftershocks use statistical decay models or Coulomb stress transfer. Statistical approaches require simplifying assumptions about the spatial distribution of aftershocks and their decay; Coulomb models make simplifying assumptions about the geometry of the surrounding faults, which we seek here to remove. We perform a rate–state implementation of the Coulomb stress change on focal mechanisms to capture fault complexity. After tuning the model through a learning period to improve its forecast ability, we make retrospective forecasts to assess model’s predictive ability. Our forecast for the next 12 months yields a 2.3% chance of an Mw≥7.5 Garlock fault rupture. If such a rupture occurred and reached within 45 km of the San Andreas, we calculate it would raise the probability of a San Andreas rupture on the Mojave section by a factor of 150. We therefore estimate the net chance of large San Andreas earthquake in the next 12 months to be 1.15%, or about three to five times its background probability.