CAN THE LACK OF LAKE LOADING EXPLAIN THE EARTHQUAKE DROUGHT ON THE SOUTHERN SAN ANDREAS FAULT?

The last major rupture on the southern San Andreas Fault (SSAF) occurred in ca 1726. This ~300 year open interval is well beyond the observed quasiperiodic recurrence interval of ~150 years. The unexpectedly long open interval poses the question of whether or not there is a physical mechanism underlying the observed large ‘earthquake drought’ on the SSAF system. Recently refined paleoseismic evidence shows that variations in ancient Lake Cahuilla high-stands, a 236 km3 lake that loaded the SSAF with nearly 100 m of water, correlates with historical ruptures on the SSAF. Here, we build a fully coupled 3D poroelastic model of the SSAF system under the previous ~1000 year loading history of Ancient Lake Cahuilla to calculate Coulomb stress changes through time in the Salton Trough that contribute to the pre-existing tectonic loading (18 ± 1 mm/yr). We compute the spatiotemporal change in Coulomb stress with differing fault permeability structures to quantify the relative effect of elastic stress changes and pore pressure diffusion on the SSAF at depth through time. Our model demonstrates the effect of historical and present-day lake loading to quantify the modulation of the SSAF recurrence interval through time.