| Obtaining strong earthquake records near the hydraulic engineering site is the precondition for seismic safety analysis of engineering structures.However,there is still a lack of strong earthquake records near the project site.Therefore,considering the influence of seismic source and propagation medium on synthetic ground motion becomes the main way to solve this problem.Due to insufficient knowledge of smallscale inhomogeneity in crustal media,in the current seismic synthesis technology,the small-scale inhomogeneity in the propagation medium is often ignored or simplified as isotropic scattering process to describe the interaction between seismic waves and heterogeneous bodies,which leads to large deviation between synthetic ground motion and observed records.In order to describe the scattering process of high-frequency seismic waves more realistic,the anisotropic scattering theory is introduced into the composite source model in this thesis.The role of small-scale inhomogeneity in crustal medium is simulated by isotropic scattering theory and anisotropic scattering theory,respectively.Meanwhile,there is no scattering process in the medium is also considered to synthesize ground motion.Then the influence of scattering on ground motion is analyzed.Taking the actual observed records of Northridge Mw6.7 earthquake and Jiuzhaigou Ms7.0 earthquake as examples,the influence laws of different seismic wave scattering modes on ground motion are compared and analyzed,and the best seismic wave scattering modes in Northridge and Jiuzhaigou areas are given.The main conclusions are as follows:(1)Consideration of seismic wave scattering process can increase ground motion duration and oscillation.Oscillation increases with increasing scattering intensity.The forward scattering oscillates more strongly than the isotropic and the backward scattering.There are strong oscillations in observed seismic waves,so considering scattering can make the simulation results closer to the observed values.Compared with the Northridge area,the seismic hypocentral distance of selected stations in Jiuzhaigou area is longer,and the oscillation of acceleration time history is more significantly affected by scattering.(2)Compared with the simulation results without considering scattering,the peak ground acceleration simulated based on isotropic scattering process is closer to the observed value.The peak ground acceleration error of Northridge earthquake can be reduced by17.0% and Jiuzhaigou earthquake can be reduced by 29.9% at most and that of Jiuzhaigou earthquake can be reduced by 29.9%.(3)When the scattering intensity is the same,compared with the results of isotropic scattering and backward scattering modes,the peak ground acceleration simulated based on the forward scattering modes are the closest one to the observed value,especially for the exponential forward scattering mode.When the scattering mode is exponential forward scattering,the peak ground acceleration error of Northridge earthquake can be reduced by 6.8% and Jiuzhaigou earthquake can be reduced by 16.2% at most.This shows that the influence of scattering on peak ground acceleration is more obvious in the area with longer hypocentral distance.(4)In the Fourier spectrum,the consideration of scattering can improve the simulation of ground motion in the high frequency band(greater than 1Hz).The results of exponential forward scattering simulation in different scattering models are closer to the observed values. |
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