It is well known that the predominant period of earthquake ground motion differs from place to place. If the predominant period of earthquake ground motion is known at the site of construction, the engineer can design the structure so that the natural period of the structure do not coincide with the predominant period of earthquake ground motion, thereby mitigating the possible damage to the structure due to earthquakes.
　In Japanese ports, earthquake ground motions have been observed since 1960's. The network covers 60 important ports around Japan. Retrieving information on the predominant period of earthquake ground motion will be very beneficial to the future construction in Japanese ports.
　Having this in mind, a comprehensive list of the predominant periods of earthquake ground motion at the observation sites at the ground surface in Japanese ports was developed based on the Fourier spectra of the major records. The list is provided as a table within the report, with all of the Fourier spectra studied in the appendix.
　To investigate the effects of the shallow soil layers on the predominant period, the transfer function based on PS logging was compared with the predominant period from the ground motion records. It was found that, although the predominant periods shorter than about one second coincide with the peaks of the transfer function, the predominant periods longer than about one second cannot be explained as effects of the shallow soil layers. Therefore, the predominant periods longer than about one second seem to be the effects of deeper soil layers.