Response spectrum-oriented pulse identification and magnitude scaling of forward directivity pulses in near-fault ground motions

This paper presents a novel approach to identify the pulse-like motions in earthquake recordings that dominate the maximum structural responses over a wide period range. The identification method is based on the congruence relationship between the response spectrum and the dimensionless П-response spectrum established in this study through straightforward dimensional arguments of linear and bilinear SDOF oscillators subject to pulse-like ground motions. By evaluating the geometric match and dislocations of the П-response spectrum of a given waveform with the dimensional response spectrum in bi-logarithm plotting, one can identify the simple pulses and their parameters that match simultaneously the kinematic characteristics and the response spectrum of earthquake recordings that exhibit pulse-like features. The developed pulse identification method has been implemented in a computer program and applied successfully to detect the pulse-like motions in the PEER NGA strong motion database. Both velocity and acceleration pulses potentially due to forward directivity effects in near fault regions are identified. The identified velocity pulses show strong correlation with the seismological parameters. They are subsequently used in regression analysis to derive the empirical scaling laws that relate the directivity pulse parameters to the earthquake magnitude and rupture distance. The study confirms some magnitude scaling laws in literature and demonstrates the accuracy and efficiency of the proposed pulse identification method.