| A large number of studies show that there are many kinds of complex inhomogeneous structures with different scales in the earth medium.The deterministic physical model and the method will increase the complexity in the face of this kind of multi-scale inhomogeneous media.It is not possible to construct a deterministic medium model which describes the multi-scale heterogeneity information based on limited observations.Based on the statistical distribution theory,the stochastic medium model has obvious advantages in describing the characteristics of multi-scale inhomogeneity in the earth medium.However,it is not clear that any kind of stochastic medium model is closest to the small scale inhomogeneity in the crust.In the analysis of the wave field characteristics of random medium,due to the smoothness assumption of the finite difference numerical simulation method,it may lead to the high scattering attenuation coefficient of the random medium model.The article mainly includes:1?The basic theory and method of stochastic medium based on stochastic process and FFT transform model are summarized;2?The determination of the numerical fluxes of the boundary of the computational unit and the numerical scheme for the application of discontinuous finite element method to two-dimensional velocity stress elastic wave equation;3?Discuss the loading method of isotropic explosive source and absorbing boundary condition of perfectly matched layer;4?Estimation of inverse quality factor based on amplitude attenuation method;5?The correction of random medium model based on statistical distribution;6?Simulation of seismic wave propagation in random media based on discontinuous finite element method,include analysis of wave propagation and energy attenuation.The innovation of this paper lies in:The smoothness assumption of the finite difference method may make the estimation of the scattering attenuation coefficient higher.In this paper,the discontinuous finite element method is used to adapt to the complex medium.In the case of high disturbance level,it can still maintain high accuracy and stability.The method avoids the solution of large scale linear equations in the conventional finite element method and the advantages of the conventional finite element method.For example,it is easy to be extended to high dimensional condition and easy to improve accuracy.Since the computational equation contains only the data communication between adjacent cells,the method is easy to be parallelized.The following conclusions are obtained in this paper.1?In the random medium model,the scattering wave is the main reason for the long time vibration.2?In the random medium model,when the autocorrelation length is equal to or smaller than the seismic wave length and the seismic wave frequency is constant,the larger the autocorrelation length is,the higher the inverse quality factor is,the stronger the attenuation of seismic wave energy is.The autocorrelation length of the random medium model remains unchanged,with the increase of the frequency of seismic wave,the attenuation effect becomes stronger.3?The inverse quality factor of stochastic medium model is proportional to the variance of random medium model.When the perturbation level of the random medium model is lower(less than 0.01),the scattering attenuation of the medium can be neglected.4?Without considering the intrinsic attenuation of the medium,the range of the minimum scattering angle of the P wave is approximately 60°?90°. |
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