Ground motion rotation for mainshock-aftershock sequences: Necessary or not?

This manuscript studies the effects of rotating mainshock-aftershock (MSAS) sequences to different orientations on the seismic performance of structures. A total of 222 recorded MSAS ground motions are additionally rotated the given angle away from the fault-parallel direction. Four different engineering demand parameters (EDPs) are used to quantify the seismic performance. The results indicate that the aftershock would change the critical angle of ground motions with respect to the mainshock, and the change in the critical angle can exceed 30°. The effect of ground motion rotation is significant for MSAS sequences, and can exceed 25% for all EDPs considered. The effects of aftershocks on the maximum and median EDPs over all rotation angles are generally comparable. Rotating MSAS sequences into the critical angle is necessary for seismic design and performance evaluation.