INVESTIGATION OF SITE EFFECTS AT DAMAGED PORTS DURING THE 2011 GREAT EAST JAPAN EARTHQUAKE DISASTER

Abstract

 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. 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. At 7 ports (9 points), detailed site effects were revealed based on aftershock observations.
2) At Ofunato Port, it is estimated that the site effects are significantly different between the berthing facilities and the strong motions stations. The site effects for the berthing facilities were newly estimated based on aftershock records.
3) At Ishinomaki Port, the site effects at the berthing facilities are close to those at the K-NET strong motion station except for the Hibarino berth (-13m), the deepest berth in the port. The site effects for the Hibarino berth were newly estimated based on aftershock records.
4) According to the overall results, peak values of microtremor H/V spectra and those of site amplification factors are more or less correlated to each other.