Nonlinear Response Potential of Mainshock-Aftershock Sequences from Japanese Earthquakes

A large mainshock triggers numerous aftershocks, exposing evacuees and residents to significant risk and hampering building reoccupation and restoration activities in a post-disaster situation. It is thus important to take into account the seismic effects of mainshock-aftershock (MSAS) sequences, not just those of mainshocks. To assess the nonlinear damage potential caused by aftershocks, this study investigates the effects of aftershocks on peak ductility demand of inelastic single-degree-of-freedom systems using real as well as artificial MSAS sequences. The real sequences are constructed from the K-NET and KiK-net databases for Japanese earthquakes. Comparison of peak ductility demand due to real mainshock events alone and real MSAS sequences renders empirical assessment of the aftershock impact on peak ductility demand. Moreover, time-history data of artificial MSAS sequences are generated based on the generalized Omori's law and suitable aftershock record selection procedure that takes into account key characteristics of aftershock records (magnitude, distance, and site classification). The validity of artificially generated MSAS sequences is evaluated by comparing probabilistic characteristics of peak ductility demand caused by artificial sequences with those caused by real sequences. The results indicate that peak ductility demands from real and artificial sequences are similar; thus, artificial sequences can be substituted for real sequences. Such calibration is particularly useful when an extensive data set of real MSAS sequences is not available.