Near-Fault Forward Directivity Effect on the Estimation of Ground Motion Amplification Factors

Abstract

Near-fault forward directivity (NFFD) ground motions cause significant potential damage to civil infrastructure. Buildings at soil sites at which NFFD motions are expected might need probabilistic seismic hazard analysis (PSHA) for soil sites considering the NFFD effect. In the analysis, ground motion amplification factors (GMAFs) considering the NFFD effect are required. Thus, investigating the characteristics of GMAFs due to the NFFD effect is important. To achieve this objective, this paper performs probabilistic ground response analyses for two typical soil sites subjected to three ground motion suites, that is, NFFD motions, far-fault motions, and near-fault motions without pulses. The results indicate that pulse periods of NFFD motions significantly affect the characteristics of GMAFs, rendering mean GMAFs remarkably lower or higher than those of ordinary ground motions. This study also reveals that standard deviations of GMAFs are insensitive to types of input motions. By further investigating the influences of soil deposit on pulse periods, this study observes that the pulse periods tend to approach 1.5 times the fundamental period of the soil deposit after pulselike ground motions propagate through the soil deposit. This observation provides a useful clue to pulselike ground motion selection for soil sites.