Seismo Lab Brown Bag Seminar

Large earthquakes (M>7) frequently occur along the southern San Andreas fault (SSAF) with a quasi-periodic recurrence interval between about 116 and 221 years over the last millennia, except for the most recent long quiescence (>300 yrs). The SSAF locates beside ancient Lake Cahuilla that experiences periodic inundations and desiccations in historical time. Previous studies suggest a temporal correlation between Lake Cahuilla flooding and SSAF earthquakes, although a direct causal relationship is still in debate. In this study, we developed observationally constrained 3-dimensional fully dynamic earthquake cycle models to explore the influence of hydrologic perturbations associated with Lake Cahuilla on the SSAF earthquakes. We find that the perturbations from water loading, pore-pressure changes and nearby stepover fault movement all contribute to modulating cycle behaviors on the SSAF and perturbations applied at late interseismic stage tend to promote temporal correspondence between earthquakes and Lake Cahuilla high-stands although the simulated events in this study are not able to match all Lake Cahuilla water high-stands history. We also tested the hypothesis whether the prolonged earthquake interval since the last major event can be solely explained by the drought effect approximated through pore-pressure reduction and find an unfeasibly large pore-pressure reduction rate is required to prolong the earthquake interval from less than 200 yrs to more than 300 yrs.