Estimation of Local Spectral Density of Seismogram by Orthogonal Hilbert-Huang Transform and Application of the Spectral Density

It is necessary to describe earthquake ground motion with local spectral density, which is time-dependent and can reflect the non-stationary characteristics. Firstly, the paper introduces the approach using HHT to estimate local spectral density, which makes the local spectral density estimation very convenient by HHT transform. Secondly, the approach using the orthogonal HHT to estimate local spectral density is provided in the paper as a complementarity of HHT. Comparisons of estimating precision and speed are carried out among orthogonal HHT, HHT, STFT and Multifilter. The study shows that orthogonal HHT is a universal method avoiding leakage of energy compared with conventional HHT. So it is an efficient method to estimate local spectral density. Thirdly, the study illustrates that the local power spectra estimated by orthogonal HHT are able to reveal the temporal-frequency energy distribution for earthquake recordings precisely and clearly. Finally, integrated with the orthogonal HHT estimating local spectral density of earthquake ground motion, time-dependent power spectra is used as target power spectrum and the trigonometric series is used to simulate record of non-stationary earthquake ground motion.