Ground Motion Simulation Of Stochastic Finite Fault With Non-stationary Phase

To realize a reasonable simulation of ground motion,it is necessary to take into account the amplitude and phase non-stationary characteristics of the actual ground motion.As the current mainstream ground motion simulation method: the stochastic finite fault method is widely used to simulate ground motion in sparsely recorded areas with the characteristics of not relying on fine underground wave velocity structure,less undetermined parameter and fast calculation speed.Since this method uses stationary white noise as an approximation of the actual ground motion phase,it fails to account for the non-stationary characteristics of the actual phase,which may cause the accuracy of the simulated ground motion amplitude spectrum and response spectrum to be inconsistent.At the same time,the method also has the problem of inconsistency between high-frequency and low-frequency ground motion simulation accuracy.This paper conducts research on the above two points,and the research contents and results are as follows:(1)Establishment of an equivalent group velocity model: According to the concept of envelope delay,the different computing methods of envelope delay are compared,the phase differential method given by Boore is used to analyze the average envelope delay of earthquakes of magnitude 6-7 in China.And found that the average envelope delay of most earthquakes has the characteristics of high-frequency energy arrives first,low-frequency energy arrives later,and the time difference between high and low frequency energy increases with the increase of distance and magnitude.Using the relationship between propagation velocity of narrow-band packet energy and envelope delay,the equivalent group velocity model is established.Based on the model,the calculation of the non-stationary phase of the ground motion and the method of ground motion simulation are briefly described.By simulating typical non-stationary ground motion,the rationality of the method is verified,and the application of the method in the simulation of regional non-stationary ground motion is discussed.(2)The relation between the frequency nonstationary characteristic of ground motion and quality factor Q in stochastic simulation method: Based on the recognition of the time difference between high and low frequency energy,the generalized standard linear body(GSLS)constitutive relationship model is used to fit the collected domestic and foreign quality factors,and the group velocity of different frequency waves is calculated from the generalized standard linear body parameters,to analyze the high-low frequency energy to the time difference caused by the quality factor.Through analysis,it is found that: Q is not the main cause of the frequency non-stationary characteristics of the ground motion,that is,the Q value in the stochastic simulation method only includes a very small part of the frequency non-stationary information of the ground motion.(3)Effects of different source spectral function models and source models on stochastic finite fault simulation results: First,based on the simulation method of random finite fault ground motion,the influence of different source spectral function models on the simulation results is discussed.At the same time,based on different source models,the ground motion simulation results of Japan's northeast region on March 11,2011 were reproduced,and it was obtained that the improved source mode can effectively improve the inconsistency between the high-frequency and low-frequency ground motion simulation accuracy.The improved source model takes into account the relationship between the stress drop and the sub-source dislocation.The fault is represented by a background rupture zone at a low dislocation level and a strong rupture zone at a high dislocation level,but the former uses a low stress drop in the simulation and the latter uses a high stress drop.In addition,combined with the non-stationary phase represented by the average equivalent group velocity model calculated from the Kik-net station ground motion records of magnitude 7 to 9 in Japan,the ground motions in the northeastern region of Japan with non-stationary characteristics are simulated.Finally,the Kumamoto and Hokkaido ground motions in Japan were simulated by considering different source spectrum models,and the application of the source spectrum model in the stochastic finite fault method was discussed.(4)Application of stochastic finite fault ground motion simulation taking into account non-stationary phase.Taking the Lushan earthquake as an example,by absorbing the existing improved results of the current stochastic finite fault method,the application of the improved method in ground motion simulation is discussed.In order to ensure the accuracy of the obtained high-frequency and low-frequency ground motion simulation,two types of improvement measures are introduced:(1)Retain the dynamic change of the corner frequency of the sub-source with the fault rupture,and introduce the improved source spectrum model of Wang Guoxing in 2015 to replace the Brune function model;(2)The source model which takes into account the relationship between stress drop and sub-source dislocation is considered.At the same time,a non-stationary phase based on equivalent group velocity is introduced to compensate for the lack of non-stationary characteristics of the ground motion frequency in the simulated records.By comparing and analyzing the simulation results of the original stochastic finite fault method and the improved method,it is found that: The simulated record and the measured record obtained by the improved method can maintain good consistency in time history and response spectrum,and the simulated time history is closer to the real record;The improved method effectively avoids the inconsistency between high frequency and low frequency ground motion simulation accuracy;The improved stochastic finite fault method is still difficult to apply to the ground motion simulation of stations with significant terrain effects.The above findings are based on the broadband seismic simulation results of the Lushan earthquake,and their generality needs further analysis and demonstration.