Comparison of equivalent linear and nonlinear methods in seismic analysis of liquefiable site response due to near-fault incident waves: a case study

In this paper, the one-dimensional ground response of a near-fault earthquake is compared by two methods. An equivalent linear method based on total stress modeling in frequency domain and a nonlinear method based on effective stress modeling in time domain. DEEPSOIL. V5 software is used based on the latest achievements and various techniques in both solution domains. LNG port project in Assaluyeh, situated south of Iran, is considered as a real liquefiable site. Due to the lack of the real near-fault recorded data at the project site, the simulated method is used in order to create the artificial earthquake. In order to evaluate the real behavior of the site response due to near-fault incident waves, three near-fault acceleration time histories are selected. In addition, the spectrum responses are compared with spectral acceleration schemes being presented by some legitimate codes such as 2800 and UBC97. The study indicates that the pulse in the horizontal component of acceleration perpendicular to the fault plane affects severely the liquefiable ground response of the near-fault earthquake. The results of the nonlinear modeling of the soil with excess pore water pressure build up in time domain are extremely different from those of frequency domain responses established based on the equivalent linear method. In addition, because of the inherent linearity of the equivalent linear analysis leading to spurious resonances in ground responses, the peak ground acceleration in time domain is lower than frequency domain.