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Earthquakes and Structures
  Volume 8, Number 6, June 2015, pages 1463-1480

Developed empirical model for simulation of time-varying frequency in earthquake ground motion
Ruifang Yu, Meiqiao Yuan and Yanxiang Yu

    This research aims to develop an empirical model for simulation of time-varying frequency in earthquake ground motion so as to be used easily in engineering applications. Briefly, 10545 recordings of the Next Generation Attenuation (NGA) global database of accelerograms from shallow crustal earthquakes are selected and binned by magnitude, distance and site condition. Then the wavelet spectrum of each acceleration record is calculated by using one-dimensional continuous wavelet transform, and the frequencies corresponding to the maximum values of the wavelet spectrum at a series of sampling time, named predominant frequencies, are extracted to analyze the variation of frequency content of seismic ground motions in time. And the time-variation of the predominant frequencies of 178 magnitude-distance-site bins for different directions are obtained by calculating the mean square root of predominant frequencies within a bin. The exponential trigonometric function is then use to fit the data, which describes the predominant frequency of ground-motion as a function of time with model parameters given in tables for different magnitude, distance, site conditions and direction. Finally, a practical frequency-dependent amplitude envelope function is developed based on the time-varying frequency derived in this paper, which has clear statistical parameters and can emphasize the effect of low-frequency components on later seismic action. The results illustrate that the time-varying predominant frequency can preferably reflect the non-stationarity of the frequency content in earthquake ground motions and that empirical models given in this paper facilitates the simulation of ground motions.
Key Words
    earthquake ground motion; time-varying frequency; non-stationarity of frequency; empirical models; envelope function
Ruifang Yu, Yanxiang Yu: Institute of Geophysics, China Earthquake Administration, Mingzu Daxue South Road No. 5, Haidian District, Beijing, 100081, China

Meiqiao Yuan: Huaian Guangan Seismic Safety Evaluation Technology Co. Ltd., Huaihai Road 254, Qinghe District, Huai\'an, Jiangsu, 223001, China

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