After a large earthquake, it is quite important to estimate strong ground motions at the site of damaged port structures to analyze damage mechanism and to determine restoration policy. Although several strong motion records were successfully obtained at damaged ports during the 2011 Great East Japan Earthquake Disaster (Takahashi et al., 2011), the records do not necessarily represent strong ground motions at the site of structural damage, because, according to recent knowledge, site effects can vary significantly within a relatively small area, even within a port. Thus, in this study, microtremor measurements and aftershock observations were conducted at damaged ports and strong ground motions were estimated based on the observation results. First, microtremor observations were conducted densely within the ports to reveal the gross distribution of the site effects. In particular, microtremor characteristics at the strong motion stations and at the sites of structures were compared to know whether the strong motion records represent the strong ground motions at the sites of structures. Then, if the strong motion records do not represent the strong ground motions at the sites of structures, aftershock observations were carried out to reveal the site effects at the sites of structures. Furthermore, strong ground motions at the sites of structural damage were estimated based on the site effect replacement method. The results of the study can be summarized as follows:
1) Gross distribution of the site effects within the ports were revealed at 8 ports where microtremor observations were conducted.
2) At 7 ports (9 points), detailed site effects were revealed based on aftershock observations.
3) Strong ground motions during the 2011 Great East Japan Earthquake Disaster were estimated at 4 ports (6 points) based on the site effect replacement method.