Abstract
Reflection and transmission(R/T)responses characterize the propagation and energy distribution of incident and reflected waves on both sides of an interface which is crucial for imaging,amplitude variation with offset(AVO),and seismic inversion techniques.Subsurface media are typically characterized by anisotropy which can have a significant impact on the R/T response,even at small incident angles.Currently,anisotropic media problems including reflection,transmission,and inversion are generally discussed under a weak anisotropy assumption.However,this assumption is no longer valid in cases of large angles where anisotropy enhancement exacerbates the error of the conventional R/T coefficient approximation.An R/T coefficient approximation method for strong VTI media was proposed based on the assumption of weak-contrast of the media.In contrast to the conventional approach,which simplifies the phase velocity and polarization in an anisotropic background,the phase velocity and polarization at the weak-contrast interface of the elasticity and anisotropy parameters were approximated using a combi-nation of the anisotropic background and perturbation terms.Specifically,a first-order approximation of the R/T coefficients for the VTI media characterized by elastic and anisotropic parameters was derived using Cramer's law to invert the anisotropic background matrix,avoiding the assumption of weak anisotropy.Subsequently,the exact solution of the Zoeppritz equations was used to correct the isotropic part,improving the accuracy of the R/T coefficients at interfaces with high-velocity contrast.Modeling tests on four classes of typical interfaces showed that the derived equations can be degraded to the Aki approximation in isotropic media,while exhibiting high accuracy in strong VTI media.Uncertainty analyses showed that a linear approximation that facilitates seismic inversion can be obtained by taking the S-to P-velocity ratio and anisotropy parameters in the coefficient terms a priori.
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