Velocity Structure Modelling From Ambient Noise And Seismic Propagation Simulating In Xiluodu Earthquake Zone

In recent years,frequent earthquake occured,and the safety of hydraulic engineering,especially high dam seismic safety evaluation,is an important study direction for engineering practice research.The seismic load of the target area is the necessary prerequisite for the seismic safety evaluation of the high dam.The method of using the traditional seismic hazard to determine the seismic load is not enough,Such as the empirical attenuation relationship can not represent a single earthquake event characteristics.Therefore,This paper based on the spectral element method,constructs a3 D numerical model of the source-medium-site and performs large-scale calculation on the supercomputer to simulates the actual earthquake from the source excitation to the whole process,to obtain the seismic parameters required for the seismic evaluation of the site buildings.The construction of the propagation medium structure model is both the focus of the Seismology and the difficulties.This paper based on noise tomography is used to construct the 3D shear wave velocity structure of the upper and middle crust in the site area.The main contents are as follows:1.Using the ambient noise tomography to establish the 3D velocity structure within a wide range of areas on Xiluodu dam site.Through the cross-correlation calculation of the noise records between stations to extract empirical Green's function and inversion of the group velocity dispersion curve of each cycle to build the figures of the surface wave tomography.According to the dispersion curve,the vertical distribution of the shear wave velocity of the crust is obtained,and the wave velocity distribution of each point is integrated into the 3D shear wave velocity structure of the crust.According to Birch(1961)empirical relation,we can get a 3D crustal medium structure with S-wave velocity,P-wave velocity and density.2.By integrating the source model,the medium structure model and the terrain mesh model to constructed the large-scale terrain mesh model.The seismic source model is based on the point source model and the finite fault model.The medium model use the 3D crustal medium model based on the background noise imaging method.3.Based on the comprehensive numerical model to simulate the seismic propagation processes occurred on April 4 and August 16,2014 in Yongshan County.The simulation results show that the simulation results are in good agreement with the measured records,and the simulation results can meet the requirements of engineering seismic design.Using the finite fault model can improve the excitation frequency of the source,which makes the high frequency component fit better and reduce the error of the point source model with Incomplete high frequency component.4.Studying the influence factors of wave field simulation,the paper discusses the limited degree of fault segmentation on the result of simulation and the regularity and found limited fault segmentation can increase the source high frequency component.