Evaluation of directionality in physics-based ground motion simulations of strike-slip earthquakes

Recent advances in engineering seismology and computing power have led to the development of realistic physics-based ground motion simulations. The use of these simulations for engineering applications requires that the ground motions exhibit characteristics consistent with those of recorded ground motions. While several studies have evaluated the intensity, frequency content, duration, and other characteristics of ground motion simulations for their possible use in engineering applications, few have focused on directionality. This article evaluates directionality in the response of single-degree-of-freedom oscillators when subjected to CyberShake Study 15.12 simulated ground motions from strike-slip earthquakes, by carefully comparing it to the directionality in recorded ground motions having the same style of faulting. Physics-based ground motion simulations at 334 stations from 5 different rupture variations in two large-magnitude earthquake scenarios on the Elsinore fault are evaluated. The orientation of maximum oscillator response and its spatial distribution are studied for each rupture. The orientation of maximum oscillator response is found to occur systematically close to the epicentral transverse orientation at all rupture distances, consistent with recent findings for ground motions recorded during strike-slip earthquakes. In addition, the orientation-specific spectral accelerations, when computed as a function of angular distance from the epicentral transverse orientation, are found to exhibit a variation consistent with the overall trend observed in records from the next-generation attenuation (NGA)-West2 database. However, the level of polarization at short periods in the simulated hybrid broadband waveforms used in this study is larger than that in recorded ground motions.