Numerical Simulation Of Ground Motions Correlated To The Known Site

Earthquake is one of the most serious natural disasters by human beings,and historically,the loss of life and property caused by the earthquake is too numerous to mention.At present,it is difficult to synthesize the ground motion whose power spectrum is consistent with the target power spectrum.And most of the engineering method to simulate seismic fields of each ground motion coherence is simply using coherence function,which often does not tally with the actual situation due to lacking of physical basic.Although the seismic field can be accurately simulated by using the seismic method,it is difficult to be widely used because of its high computational cost.In order to solve the problems in engineering method and seismological methods in the synthetic earthquake field,this paper presents a new method for the simulation of ground motions correlated to the known site,which makes the synthesized seismic field power spectrum consistent to the known site,and the coherence of synthetic ground motion is reasonable.This paper considers seismic waves as superposition of body waves and surface waves from the perspective of studying the dispersion curves of given sites,and studies the propagation characteristics of body waves and surface waves in layered semi-infinite space media.The dispersion curve of the site surface waves is calculated by the generalized reflection-transmission coefficient method.And the method to calculate body wave propagation velocity is determined.The results show that for the surface wave,if the phase velocity and the wave number are independent in the propagation process,no dispersion occurs;otherwise,the dispersion occurs.For body waves,no dispersion occurs during the propagation.The surface wave dispersion curve of El-Centro wave is calculated by MATLAB programming,and the surface wave dispersion law of El-Centro wave and the velocity of wave propagation are obtained.Under the premise of obtaining the dispersion curve by theoretical calculation,on the basis of synthesizing of ground motion by normal mode superposition,this paper first studies the influence of each wavelet on the synthetic wave amplitude spectrum when the composite wave is synthesized by the superposition of each wavelet,and determines the main factors that affect the amplitude spectrum of the composite wave.And then,by studying the nonstationary of the ground motion,this paper determines a parameter that describes the non-stationary characteristic of the ground motion.Finally,a model is established to synthesize the ground motions correlated to the known site.The results show that the factors that influence the oscillatory characteristics of the amplitude spectrum of the composite ground wave are mainly wavelet amplitude,wavelet arrival time,wavelet phase and so on.Among them,wavelet amplitude determines the absolute value and the overall shape of the composite amplitude spectrum;the wave packet arrival time is the main factor that influences the oscillation characteristic of the synthesized amplitude spectrum and determines the oscillation rate;the wavelet phase determines the horizontal position of the composite amplitude spectrum.Phase difference spectrum is an important parameter to describe the nonstationary characteristics of ground motion.If introduced into the model of synthetic ground motion,the model can be used to synthesize ground motions with non-stationary information of known field.The wavelet packet and the amplitude of the wavelet are introduced into the model proposed in this paper,which makes the amplitude spectrum of the model consistent to the known ground motion,and also the power spectrum;The phase difference of the known ground motion is introduced into the model so that the phase difference spectrum of the combined ground motion is consistent with the phase difference spectrum of the known ground motion to ensure that the synthetic ground motion and the known ground motion waveform are similar;The coherence of different field points is regarded as the result of the frequency dispersion of the surface wave and the wave propagation distance,which is more in line with the physical reality.The example of the El Centro seismic fields shows that not only is the power spectrum of the ground motions synthesized by the proposed method in this paper consistent to the known site,but also the coherence is reasonable.Therefore,the method to synthetic seismic motions proposed in this paper is reasonable,practical and can be used for engineering analysis.