Estimation of Local Spectral Density of Non-Stationary Earthquake Ground Motion Based on Orthogonal HHT Theory

It is necessary to describe earthquake ground motion with local spectral density,which is time-dependent and can reflect the non-stationary characteristics.The paper presents a method to estimate local spectral density by adopting the Hilbert-Hung Transform(HHT).A comparative study is conducted on the results of traditional HHT,Multifilter and STFT with some numerical examples.Comparison results show that the orthogonal HHT has great advantages on local spectral density estimation due to its higher precision and faster speed over the Multifilter and STFT.With the orthogonal HHT method,leakage of energy can be avoided.The local spectral density derived in this paper is also adopted to study the energy of three earthquake records.A significant conclusion is drawn on the energy distribution and its variation.