Time-dependent ground motion amplification characteristics at reclaimed land after the 1995 Hyogoken Nambu Earthquake

Two sets of borehole array records obtained from the Great Hanshin Earthquake, as well as its fore and after shocks, are investigated. One of the stations is located at Port Island in Kobe City, where severe liquefaction occurred and the records from the main event include the typical phenomena of liquefaction. The other station is located at Rokko Island in Kobe City, where the liquefaction phenomenon was not predominant as it was at Port Island. The non-linear ground motion amplification, depending on the level of input ground motion as well as its spectral characteristics, is carefully investigated. Two numerical techniques for seismic response ground analysis are applied for these stations: one is the frequency-dependent equivalent linearization technique for frequency domain analysis, and the other is the effective stress-based liquefaction analysis. The discussion is focused on the amplification characteristics of these two reclaimed lands, depending on their reclamation history. The time-dependent amplification ratio for peak ground motion and spectral contents is demonstrated, caused by the recovery of soil rigidity due to the decrease in excess pore water pressure after the main event.