A new parameter to empirically describe and predict the non-linear seismic response of sites derived from the analysis of Kik-Net database

Abstract

We evaluate the non-linear site response at the stations of the Japanese Kik-Net network by computing the ratio between the Fourier spectra of the recordings at the surface and at the downhole station. When the amplitude of the input signal increases, we observe a shift of the resonance peaks towards lower frequencies, characteristic of non-linear soil behavior. We propose a new parameter called fsp to characterize this shift. We observe that fsp is a good proxy for the shear modulus reduction by comparing fsp and the modulus reduction curve obtain by both laboratory test measurements and numerical approaches. The fsp is used to correct the linear site response and surface ground motion in frequency domain in order to take into account the non-linear soil behavior. We show that the procedure we established reduces the error in predicting the main frequency peak by 50% compared to an elastic evaluation of the site response during the 2016 Kumamoto earthquake (Mw = 7.1).