Validation Against NGA Empirical Model of Simulated Motions for M7.8 Rupture of San Andreas Fault

Abstract eng:
As part of a loss-estimation and emergency response planning exercise for a major earthquake on the San Andreas fault east of Los Angeles (ShakeOut), ground motions were simulated for a specific Mw 7.8 scenario rupture. The simulation uses a hybrid procedure in which short period components of shaking are computed semi-stochastically and long period components are computed through a deterministic calculation. The simulation considers both heterogeneous fault rupture and wave propagation through the crust and the sedimentary basins in and around Los Angeles. We compare these simulated motions to predictions of empirical ground motion prediction equations developed through the Next Generation Attenuation (NGA) project. We find that high frequency components of the simulated ground motion attenuate more rapidly with distance than the empirical model, whereas long-period components are roughly similar. The average residuals of the simulated event (i.e., event terms), which are expressed in natural log units, range from approximately -0.6 at short periods (near PGA) to approximately 0.8 at long periods (approximately 2- 4 sec). Those values of event terms are generally within the scatter of event terms from actual earthquakes used in the development of the NGA equations.

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