Hydrologic loads can stimulate seismicity in the Earth’s crust¹. However, evidence for the triggering of large earthquakes remains elusive. The southern San Andreas Fault (SSAF) in Southern California lies next to the Salton Sea², a remnant of ancient Lake Cahuilla that periodically filled and desiccated over the past millennium^3,4,5. Here we use new geologic and palaeoseismic data to demonstrate that the past six major earthquakes on the SSAF probably occurred during highstands of Lake Cahuilla^5,6. To investigate possible causal relationships, we computed time-dependent Coulomb stress changes^7,8 due to variations in the lake level. Using a fully coupled model of a poroelastic crust^9,10,11 overlying a viscoelastic mantle^12,13, we find that hydrologic loads increased Coulomb stress on the SSAF by several hundred kilopascals and fault-stressing rates by more than a factor of 2, which is probably sufficient for earthquake triggering^7,8. The destabilizing effects of lake inundation are enhanced by a nonvertical fault dip^14,15,16,17, the presence of a fault damage zone^18,19 and lateral pore-pressure diffusion^20,21. Our model may be applicable to other regions in which hydrologic loading, either natural^8,22 or anthropogenic^1,23, was associated with substantial seismicity.

水文负荷可以刺激地壳的地震活动¹。然而，引发大地震的证据仍然难以捉摸。南加州的南圣安德烈亚斯断层 (SSAF) 毗邻索尔顿海²，索尔顿海是古代卡维拉湖的遗迹，在过去的千年里定期充水和干燥^3,4,5。在这里，我们使用新的地质和古地震数据来证明过去 SSAF 上的六次大地震可能发生在卡韦拉湖的高位期间^5,6。为了研究可能的因果关系，我们计算了由于湖水位变化而导致的随时间变化的库仑应力变化^{7,8 。}使用多孔弹性地壳的完全耦合模型^9,10,11覆盖在粘弹性地幔^12,13上，我们发现水文负荷使 SSAF 上的库仑应力增加了数百千帕，断层应力率增加了 2 倍以上，这可能足以引发地震^7,8。^{非垂直断层倾角14,15,16,17}、断层破坏区^18,19和横向孔隙压力扩散^20,21的存在增强了湖泊淹没的不稳定效应。我们的模型可能适用于其他区域，其中水文负荷（自然^8,22或人为^1,23）与大量地震活动相关。