A simulation-based nonlinear site amplification model for ground-motion prediction equations in Japan

In this manuscript we present a nonlinear site amplification model for ground-motion prediction equations (GMPEs) in Japan, using a site period-based site class and a site impedance ratio as site parameters. We used a large number of shear-wave velocity profiles from the Kiban-Kyoshin network (KiK-net) and the Kyoshin network (K-NET) to construct the one-dimensional (1D) numerical models. The strong-motion records from rock-sites in Japan with different earthquake categories and taken from the Pacific Earthquake Engineering Research Center dataset were used in this study. We fit a set of 1D site amplification models using the spectral amplification ratios derived from 1D equivalent linear analyses. Parameters of site impedance ratios for both linear and nonlinear site response were included in the 1D model. The 1D model could be implemented into GMPEs using a new proposed adjustment method. The adjusted site amplification ratios retain the nonlinear characteristics of the 1D model for strong motions and match the linear amplification ratio in GMPE for weak motions. The nonlinearity of the present site model is reasonably similar to that of the historical models, and the present site model could satisfactorily capture the nonlinear site response in empirical data.