ShakeOut-D: Ground motion estimates using an ensemble of large earthquakes on the southern San Andreas fault with spontaneous rupture propagation



[1] We simulate ground motion in southern California from an ensemble of 7 spontaneous rupture models of large (Mw7.8) northwest-propagating earthquakes on the southern San Andreas fault (ShakeOut-D). Compared to long-period spectral accelerations from the Next Generation Attenuation (NGA) empirical relations, ShakeOut-D predicts similar average rock-site values (i.e., within roughly their epistemic uncertainty), but significantly larger values in Los Angeles and Ventura basins due to wave-guide focusing effects. The ShakeOut-D ground motion predictions differ from those of a kinematically parameterized, geometrically similar, scenario rupture: (1) the kinematic rock-site predictions depart significantly from the common distance-attenuation trend of the NGA and ShakeOut-D results and (2) ShakeOut-D predictions of long-period spectral acceleration within the basins of the greater Los Angeles area are lower by factors of 2–3 than the corresponding kinematic predictions. We attribute these differences to a less coherent wavefield excited by the complex rupture paths of the ShakeOut-D sources.