Simulation of ground motion scaling characteristics for the NGA-E Project

Strong motion simulations of ground motions for rock sites on 1D crustal models were used to guide the development of empirical models in the NGA-E Project by addressing various ground motion scaling issues. The simulation procedures were first tested against the recorded ground motions of six events, including the 1971 Imperial Valley, 1989 Loma Prieta, 1992 Landers, 1994 Northridge, 1995 Kobe, and 1999 Kocaeli earthquakes. The simulations were then used to examine the scaling of ground motion response spectra with magnitude, distance, and static stress drop (rupture area); rupture directivity effects, hanging wall / foot wall effects, and buried / shallow faulting effects. Uncertainty in the scaling of rupture area with magnitude is a key issue for the simulation of ground motions from large strikes-slip earthquakes. For constant stress drop scaling of strike-slip faults at periods of 1 second and less, the UNR simulations show magnitude scaling similar to the Sadigh et al (1997) model for M > 7, while the PEA and URS simulations show less scaling than the Sadigh model, and approach magnitude saturation. At periods longer than 1 second, the scaling of all three simulations is closer to the Sadigh model. Overall, magnitude scaling is stronger for the L model than for the constant stress drop model. Differences in results between the three simulation procedures appear to result from discrepancies in the representation of the earthquake source.