Research On Source Spectrum And Key Parameters Of Stochastic Finite-fault Simulation Technique

The stochastic finite-fault technique is the most important tool for simulating the near-field ground motion in the field of seismic engineering.It is one of the most important data sources for seismic design input,and can provide a certain basis for the post disaster rescue and reconstruction of the target area.Severe earthquake damage has forced governments to pay more attention to disaster prevention and mitigation.Near-field ground motion prediction has become a key problem to be solved in the field of earthquake engineering.In the ground motion simulation,the source spectrum is one of the most important factors,which has an important influence on the simulation results.The corner frequency is the reflection of the frequency components in the source soectrum,which determines the distribution of the frequency components in the synthetic result.In the stochastic simulation method,the corner frequency can not well reflect the uneven distribution of slip on the fault plane and the impact of rupture velocity.Based on this,this paper studies the corner frequency,high-frequency scaling factor and other important input parameters in the source spectrum,and studies the method of predicting the hybrid source model and discusses the sensitivity of key parameters.The main research work and conclusions are as follows:(1)The finite fault hybrid source model of Jiuzhaigou earthquake is simulated and its reliability is verified.Based on the concept of the kinematic source model,the global and local source parameter sequences of 30 sets of the Jiuzhaigou earthquake are generated by using mathematical theory and empirical or semi-empirical as well as semi-theoretical statistical relationships.The minimum residual principle is used to select the response spectra estimated by the target points in different directions.It is considered to find the source model with the smallest residual error with the average value as the final simulation source model of the Jiuzhaigou earthquake.Finally,six near-field stations of the Jiuzhaigou earthquake are simulated by using the stochastic finite-fault method based on the optimal source model to verify its reliability.(2)The sensitivity of some input parameters is discussed and some suggestions are given.Based on the research work of scholars at home and abroad,this paper discusses the influence of ground motion path duration on simulation results,and puts forward some suggestions for engineering simulation.Secondly,the sensitivity of parameters such as the buried depth of the upper edge,pulse percentage and stress drop are analyzed.The results show that the upper edge depth and pulse percentage have little influence on the simulation results,but the stress drop value has a great influence.Only when the stress drop of the random source models is larger than that of the inverted source model can we get more consistent simulation results.The proposed values of these parameters can provide theoretical basis for the selection of parameters in engineering ground motion simulation.(3)This paper systematically introduces the theoretical basis of the stochastic point-source method and the significance and calculation method of important parameters.Fistly,it introduces the stochastic finite-fault method based on static corner frequency(Model 1)and dynamic corner frequency(Model 2).The advantages,disadvantages,and applicable conditions of the two methods are analyzed.Finally,the two models with high-frequency scaling factors are used to simulate the near-field records of the 1994 Northridge earthquake in the United States.The simulation results of the two models are adjudged in terms of model deviation,acceleration response spectra,model standard deviation,and absolute error.Finally,the influence of earthquake duration on the peak ground acceleration is analyzed.In this paper,the development history of corner frequency is briefly introduced,the characteristics of dynamic corner frequency are analyzed,and its defects and deficiencies are introduced emphatically.(4)A corner frequency considering the non-uniformity of fault layers is proposed,and the rupture velocity is introduced into the calculation of corner frequency.Finally,the near-field station records of the Northridge and Jiuzhaigou earthquakes are simulated by the improved stochastic finite-fault method.In this paper,the formula for calculating corner frequency is comprehensively analyzed,and the limitation of considering the rupture velocity as a fixed value in the past is removed.A source model with variable rupture velocity is proposed.Simultaneously,based on the previous research results,the calculation of far-field received energy is improved.Finally,the improved stochastic finite-fault approach is used to simulate the near-field strong motion records of the Lushan earthquake,and its effectiveness is verified.