Identifying Optimal Intensity Measures for Predicting Damage Potential of Mainshock-Aftershock Sequences

Large earthquakes are followed by a sequence of aftershocks. Therefore, a reasonable prediction of damage potential caused by mainshock (MS)-aftershock (AS) sequences is important in seismic risk assessment. This paper comprehensively examines the interdependence between earthquake intensity measures (IMs) and structural damage under MS-AS sequences to identify optimal IMs for predicting the MS-AS damage potential. To do this, four categories of IMs are considered to represent the characteristics of a specific MS-AS sequence, including mainshock IMs, aftershock IMs (i.e., IMMS and IMAS, respectively), and two newly proposed IMs through taking an entire MS-AS sequence as one nominal ground motion (i.e., IM1MS-AS), or determining the ratio of IMAS to IMMS (i.e., IM2MS-AS), respectively. The single-degree-of-freedom systems with varying hysteretic behaviors are subjected to 662 real MS-AS sequences to estimate structural damage in terms the Park-Ang damage index. The intensities in terms of IMMS, IMAS, and IM1MS-AS are correlated with the accumulative damage of structures (i.e., DI1MS-AS). Moreover, the ratio (i.e., DI2MS-AS) of the AS-induced damage increment to the MS-induced damage is related to IM2MS-AS. The results show that IM2MS-AS exhibits significantly better performance than IMMS, IMAS, and IM1MS-AS for predicting the MS-AS damage potential, due to its high interdependence with DI2MS-AS. Among the considered 22 classic IMs, Arias intensity, root-square velocity, and peak ground displacement are respectively the optimal acceleration-, velocity-, and displacement-related IMs to formulate IM2MS-AS. Finally, two empirical equations are proposed to predict the correlations between IM2MS-AS and DI2MS-AS in the entire structural period range.