High‐frequency decay of Fourier spectra of strong motion acceleration and nonlinear site response

Abstract

We examine how the decay of high‐frequency amplitudes of Fourier spectra of strong earthquake ground acceleration (described in seismological literature by the slope parameter κ $\kappa $) depends on the soil and geological site conditions at the recording stations in the Los Angeles metropolitan area. Then, we introduce a Gedanken numerical experiment, in which we analyze nonlinear wave motion in shallow soil and show that it also leads to similar decay of the high‐frequency spectral amplitudes. The results of both of our studies are consistent with the interpretation that the decay of high‐frequency Fourier spectra of strong motion acceleration, described by κ $\kappa $, occurs at the recording site near the ground surface.

City-scale buildings damage estimation based on broadband physics-based ground motion simulation of 2021 Ms 6.4 Yangbi, China, earthquake

“…Historical earthquakes have observed evident nonlinear site effects and its impact on structures, such as 1989 Loma Prieta and 1994 Northridge earthquakes (Chin and Aki, 1991; Field et al, 1997). In addition, numerical studies show that soil nonlinearities may cause significant amplification or de-amplification in peak ground accelerations depending on the soil properties and shaking intensity (Gicev and Trifunac, 2022; Pitarka et al, 2013; Zhang et al, 2022). Therefore, site corrections should be performed in order to incorporate the site amplification or de-amplification effects.…”