Site effects based on time varying horizontal-to vertical spectral ratio

Abstract

Horizontal to vertical spectral ratio (HVSR) based on seismic ground motion is an important index to study site conditions and dynamic characteristics (seismic effect). Due to the influence of the vertical dynamic amplification effect of the site, the Fourier spectral ratio calculated according to the surface motion and downhole motion is quite different from that of the horizontal and vertical ground motion in the case of strong vibration input. However, our recent research shows that when considering the time-varying characteristics of ground motion, the time-varying surface-downhole spectral ratio and time-varying HVSR are almost the same. Based on this discovery, the time-varying HVSR is used to study the dynamic characteristics of the site (site effect). First, a new method for calculating the natural period and damping ratio of the site is proposed. Secondly, based on tremendous strong motion records, the prediction formulas of natural period and damping ratio are studied. Finally, the effects of various influencing factors on the natural period and damping ratio are compared. The results of this paper can provide a basis for selecting and synthesizing appropriate ground motions in structural seismic design.