Quantitative Research On Parameter Uncertainty Of Stochastic Finite Fault Method

The stochastic finite fault method is a ground motion simulation method developed based on the stochastic theory.Due to the complexity of the source model,the seismic wave propagation mode and the propagation medium,the parameter values in the ground motion simulation are random and uncertain.In order to promote the application of the stochastic finite fault method in engineering practice,this paper conducts a quantitative study on the parameters that have a great influence on the results in the ground motion simulation.Firstly,the influence of the uncertainty of source model,path and site parameters on ground motion simulation results is analyzed,and the targets to be quantified are selected,namely stress drop,high-frequency attenuation coefficient of local ground motion,and upper and lower wall effects.Then,based on different research objectives,a reasonable ground motion simulation scheme is designed;finally,with the parameter mean value as the relative target,the ground motion simulation results(peak ground acceleration and acceleration response spectrum)are expanded for the values of each parameter.analysis research.The following main conclusions were reached:(1)Different values of stress drop have a greater impact on the simulation results of ground motion.Therefore,for the simulation of large earthquakes,it is a more reasonable way to use multiple value levels for stress drop within a reasonable range.(2)During large earthquake simulation,the mean value of stress drop can be taken as 30 bar,40 bar or 50 bar,and the corresponding standard deviation can be estimated according to 20%of the mean value.The ground motion simulation results show that when the stress drop is taken according to the mean value,plus/minus 1 times,2 times and 3 times the standard deviation,the simulated ground motion peaks change by about 15%compared with the mean stress drop calculation results.,30%and 45%,and obtained the spectral acceleration values corresponding to different periods corresponding to the quantification range of the mean result.(3)The value of kappa has obvious correlation with local site conditions.In this paper,the least squares method is used to perform regression analysis on 546 high-frequency attenuation coefficients of different site conditions,and a relationship model between the local site high-frequency attenuation coefficient mean and site average shear wave velocity VS30 is established.After the applicability analysis of the model It shows that the model constructed in this paper can approximate the high-frequency attenuation effect of ground motion.(4)In practical engineering applications,kappa can be taken according to the following suggestions,that is,when the average shear wave velocity VS30 of the site is less than 500m/s,the mean value of kappa can be taken between 0.029s-0.038s,and the corresponding standard deviation can be taken as 30%of the mean;when changing in the range of[500-1500]m/s,the mean value of kappa can be between 0.017s-0.038s,and the corresponding standard deviation can be taken as 20%of the mean;when VS30 is greater than 1500 m/s,the mean value of kappa can be between 0.010s and 0.017s,and the corresponding standard deviation can be taken as 15%of the mean.(5)The value of kappa has a significant effect on the high frequency part greater than 1Hz.When the mean value of kappa is between 0.01 and 0.08s,if the standard deviation is estimated according to 20%of the mean value,the ground motion peak value obtained by simulation will change by about 10%compared with the calculation result of the mean value of kappa,and the spectral acceleration value with a period of 0.02s will change by about is 20%,when the period is greater than 0.2s,the change of kappa value has a negligible effect on the simulation results.(6)The ground motions obtained by the simulation have obvious up-down and down-board effects.Relative to the same distance from the seismic fault,the calculated spectral acceleration values of the ground motion in the upper wall in the range of 0.02s to 6s are basically larger than the calculation results of the lower wall,but the influence of the high frequency part is relatively significant.