UPDATED FAULT SLIP RATES FOR SOUTHERN CALIFORNIA BASED ON RECENT ADVANCES IN TERRESTRIAL COSMOGENIC NUCLIDE METHODS

Probabilistic models of earthquake hazard rely on Quaternary fault slip rates to characterize likely future fault activity. Terrestrial cosmogenic nuclides (TCNs), such as Beryllium-10, are commonly used in fault slip-rate studies to determine the ages of offset surfaces. Two recent advances in the treatment of TCN ages necessitate reinterpretation of previously published datasets: (1) refinement and calibration of physics-based models of TCN production (Phillips et al., 2014); and (2) a new mechanistic model for TCN clast age populations based on landslide recurrence (Prush and Oskin, submitted). We have updated fault slip-rates in southern California and the Eastern California Shear Zone by recalculating production rates for Beryllium-10 datasets and modeling surface clast age distributions using these new methods. We find that the impacts of these new models lead to opposing outcomes. New production rates are lower, increasing individual clast ages. However, our clast-age population model tends to reduce overall surface ages, despite increased individual clast ages. This occurs due to the assignment of the scatter of ages to the interplay of landslides and background erosion, rather than as a result of post-depositional modification of the target surface. The net effect of these models on slip rate varies on a site-by-site basis. In the majority of cases, our preliminary results suggest that the net effect on fault slip rate estimates throughout California will be limited.