Analysis of Ground Motion Amplification during Soil Liquefaction via Nonstationary Fourier Spectra

Abstract

In this study, the transient properties of dominant frequencies and their components during soil liquefaction were evaluated by the nonstationary Fourier spectra of the records at Kawagishi-cho during the Niigata-ken Chuetsu-oki earthquake in 1964, at Port Island during the Hyogoken-Nanbu earthquake in 1995, and at K-NET CHB024 during the 2011 off the Pacific Coast of Tohoku earthquake. The deterioration ratio of soil shear stiffness was calculated from the ratio of dominant frequencies at the beginning and the ending of the liquefaction process. The displacement profile was calculated through numerical integration of the acceleration record, and the shear strain was calculated from the relative underground displacement of Port Island from 0 to 83 m from ground level (GL-0m to GL-83m) to GL-83m. The deterioration ratio of shear stiffness was also evaluated by fitting the maximum shear strain to the G-γ relation, and the deterioration ratio was evaluated by the nonstationary spectrum was confirmed by the coincidence of both evaluated values. The property of the nonstationary Fourier spectra is confirmed from the analytical result to artificial design waves, which provide important information for revision of the design wave. The response property of pulse waves was analyzed by the response envelope spectra for the Ricker wavelet. The properties of dominant components in the artificial seismic wave for seismic design were compared with those of the measured seismic records.