Correlation of Spectral Acceleration Values of Mainshock-Aftershock Ground Motion Pairs

This study examines the statistical correlation between the spectral accelerations of mainshock-aftershock ground motion pairs in the NGA-West2 ground motion database. Aftershock spectral accelerations are found mildly correlated with their mainshock counterparts for closely-spaced periods of vibration and weakly correlated over the rest of the period range. We further investigate for potential differences between the inter-period correlations of mainshock and aftershock spectral accelerations, finding no substantial evidence to support the use of different models for the two cases. Furthermore, the impact of different rupture scenario parameters on correlation is also examined and discussed. The derived correlation estimates are expected to aid in aftershock seismic hazard assessment and/or in record selection for risk assessment applications by using the mainshock spectral ordinates to obtain better predictions for the aftershock ground motion.