THE STUDY ON CONTRIBUTION COMPARISON BETWEEN DIRECT WAVE PLUS SINGLE SCATTERING WAVE AND MULTIPLE SCATTERING WAVE ON S WAVE ENVELOPE SYNTHESIZED BY MULTIPLE NON-ISOTROPIC SCATTERING THEORY

摘要

In this paper,based on Sato's non-isotropic scattering theory,a seismic wave density integral equation is improved by introducing a characteristic source time,which is used to define the initial impulse width at the source.Then,based on non-isotropic patterns derived from the inhomogeneous random media,a discrete wave-number method is used to solve the improved S wave energy density integral equation.And the S wave velocity envelope is obtained according to the relationship between energy density and velocity.Based on different non-isotropic scattering patterns,the effect of group of direct wave and single scattering term and multiple scattering terms on S wave velocity envelope is originally investigated.From the analysis result,the result from the group of direct wave and single scattering term match the whole velocity envelope of S wave pretty well at small hypocentral distance(less than 100km).Therefore,in this case,the multiple scattering terms can be neglected and the single scattering model can be used to simulate the S wave scattering process.With increasing of hypocentral distance,multiple scattering terms will be gradually dominated over the group of direct wave and single scattering term.Compared with results from backward and isotropic scattering pattern,the contribution of multiple scattering terms from forward scattering pattern grew more rapidly.And multiple scattering terms must be considered to model the whole S wave velocity envelope when the hypocentral distance is larger than 100km.Consequently,adaptability conditions of the single,multiple scattering theory are clarified,respectively.