Evaluation of strongest ground motions under strike-slip rupture for the Luding and Imperial Valley earthquakes

Abstract

Strong ground motions can yield serious disasters to engineering structures and geotechnical slopes in the vicinity of surface rupture. In this work, based on 189 sets of strong motion records from the Mw6.6 Luding and Mw6.5 Imperial Valley strike-slip earthquakes with similar magnitudes, the strongest horizontal ground motions are obtained via the rotation technique, and the spatial motion distributions, seismic spectra and attenuation characteristics under similar focal mechanisms are analysed. Our research results indicate that the characterization parameters of ground motion are correlated with the degree of earthquake damage in high-intensity regions. The pulse-like ground motion generated by the unilateral rupture of the strike-slip seismic fault is stronger and the directional effect is more obvious than that generated by the bilateral rupture. Although the peak acceleration and peak ratio of the strongest ground motion in the Imperial Valley and Luding earthquakes are similar, the Arias intensity is formed by energy accumulation in the former is approximately three times that in the latter. The high-amplitude response velocities of the Luding and Imperial Valley earthquakes are elliptical around the epicenter and zonally distributed along the fault at the front end of the rupture, respectively. The spectral value and characteristic period of the velocity pulse of the Imperial Valley earthquake are significantly greater than those of the Luding earthquake, and the spectral value of the near-fault pulse-like ground motion exceeds the seismic design code for the basic earthquake within the local natural vibration period, which also increases the seismic design requirements for engineering structures in medium and long periods. The study of strong ground motions of strike-slip rupture fault not only contributes to quickly formulating corresponding disaster relief plans for seismic events but also provides valuable data support for future seismic risk analyses and earthquake disaster prevention.