Parameter Uncertainty Analysis Of Stochastic Finite-fault Method And Its Application In Near-field Ground Motion Simulation

Due to the complexity of the source characteristics,propagation path,propagation medium,and site conditions,the earthquake ground motions are not accurately predictable and repeatable..Therefore,how to obtain reasonable seismic input is a problem worthy of attention in seismic design for major engineering structures.In this paper,stochastic finite fault method is used to simulate the near-field ground motion to solve the problem of complex source parameter setting and calculation efficiency.In order to solve the problems of stochastic uncertainty and cognitive uncertainty,the multi-scheme(multi-weight coefficient)design of parameters is adopted,and a parameter evaluation method of near-fault ground motion suitable for engineering application is established.Firstly,the effects of the uncertainty of source model parameters,path parameters and site parameters on the simulation results are analyzed.Then the ground motion simulation scheme and parameter evaluation method which can consider parameter uncertainty are established according to different sub-source dislocation modes.Finally,based on the actual engineering site,the seismic parameters of dam site considering the most credible earthquake are analyzed to discuss the application of method in complex site.The following main conclusions are obtained:(1)The stochastic finite fault method is used to simulate the near-field ground motion.It can not only describe the fault rupture source which is more in line with the real situation,consider the seismic wave path attenuation,site attenuation and other factors,but also has high computational efficiency.It can be used for the estimation of ground motion parameters in important engineering sites;(2)It is recommended that the number of acceleration time history generated by a single simulation,that is,the sample size is 30,which has no obvious correlation with the parameters setting of the source model;(3)In the ground motion simulation,the stress drop and the value of kappa have significant influence on results in the high-frequency larger than 1Hz.The variation rate of simulation results at different value increases with the increase of magnitude.Therefore,for the simulation of strong earthquakes,multiple values are adopted within a reasonable range for each parameter,which is a reasonable way to handle.In addition,for faults with smaller rupture,the slip on the fault can be set according to the single asperity model and arranged in the nearest position to the site to ensure the safety of simulation results;for faults with larger ruptures,the multi-asperity model can be used to set the slip amount of the fault,and the largest asperity is placed at the position closest to the site,while other asperity can be arranged reasonably on the fault.(4)The effects of parameters uncertainty on the simulation results are fully considered and a parameter estimation method for ground motion is established,which can consider the influence of different hypocenter on the site.The method includes setting the range and level of source parameters,path parameters and site condition parameters,establishing simulation scheme with multi-value level(multi-weight)for ground motion,establishing the principle and method of calculating the weight coefficient of each parameter,establishing parameter evaluation methods corresponding different earthquake hazad levels.(5)The site ground motion parameter evaluation method established in this paper is applied for actual engineering site-Xiluodu dam.The ground motion parameters of the dam site considering the maximum credible earthquake of different faults are obtained.The results show that the proposed method can take into account the complexity of seismogenic structure affecting the site.and The effects of different sources on the site and their contributions in different frequency bands can be analyzed by setting up a ground motion simulation scheme for each fault.Moreover,the multi-level and multi-risk parameter evaluation results can be obtained,which is convenient for the actual engineering to make decisions according to the importance of the structure.(6)Based on the Maltab platform,the program of “evaluation of site ground motion parameters considering different seismogenic structures” was written,and the interactive computing platform was built by integrating software based on Matlab GUI development environment.