Abstract
Many aftershocks were observed in the Pacific coast of Tohoku Earthquake. In view of this fact, aftershocks should be paid attention, although it is ignored in conventional design. In this paper, the effect of aftershocks to buildings is discussed focusing on energy input. From cumulative energy spectrum, it is elucidated that aftershocks recorded this time have enough energy to bring certain level of damage. P-delta effect degrades the strength of the buildings. Therefore, buildings damaged after main shock can be brought significant incremental deformation by small energy of aftershocks.
