On estimating site damping with soil non-linearity from earthquake recordings

This study proposes an approach for estimating the damping factor of non-linear soil and its role in seismic wave responses at soil sites from earthquake recordings. In particular, the paper first reviews the Fourier-based approach to characterizing the dynamic features of soil sites in seismic ground motion and shows the deficiencies for assessing non-linear site amplification and damping. It then offers an alternative approach, i.e., the Hilbert-Huang transform (HHT) for non-linear and non-stationary data process, in addressing the non-linearity issues. This study focuses on discerning the signature of non-linear site damping from the general non-linear features in the motion that are typically shown in the frequency-dependent site amplification. As a result, the study proposes an HHT-based approach to estimate site damping with non-linear soil from earthquake recordings and to measure the influences in the motion at soil sites. With the use of recordings from the mainshock and aftershock of the 2001 Nisqually earthquakes, this study shows that the proposed approach is able to assess appropriately the site damping that can be used to estimate the influences of soil damping in non-linear site responses.