Exploring frequency-domain nonstationary of seismic ground motions using evolutionary power spectrum and Archimedean Copula functions

Abstract

In this paper, the frequency-domain nonstationarity of seismic ground motions is investigated using Archimedean Copula functions. To measure the nonstationarity of the ground motions, a group of nonstationarity indexes is introduced based on the evolutionary power spectral density. The values of the proposed nonstationarity indexes of 1034 seismic ground motion records are calculated and their distributions are obtained. The Gumbel, Clayton, and Frank Copula functions among the nonstationarity indexes and intensity measures of the ground motions are estimated from the Kendall rank correlation coefficients. The best-fit Copula functions are determined by minimizing these three estimated Copula functions and the empirical Copula function. The correlation among the nonstationarity indexes and intensity measures from the Copula functions indicates that the average frequency and bandwidth of the seismic ground motion tend to decrease with time increasing, and the ground motion with long duration tends to have remarkable low-frequency components. It is suggested that the nonstationarity of the ground motions may increase the seismic risk of civil engineering structures and could not be ignored in the structural design.