HTI介质方位转换波反射系数一阶扰动近似

First-order perturbation approximation of azimuth converted wave reflection coefficient of HTI media

人们根据不同研究目的对Zoeppritz方程进行了简化与近似,但各类近似方程在大入射角情况下,大多无法准确描述转换波振幅变化规律,且由于地震数据随方位变化,对于PSV波方位反射系数的研究也相对薄弱。为此,基于HTI介质反射/透射系数精确表达式,根据介质分解理论与扰动思想,在弱各向异性假设条件下,推导了PSV波反射系数近似表达式,通过正演模拟分析振幅随方位的变化特征,并讨论方位转换波反射系数对各向异性参数的敏感性。正演分析表明:①在小入射角时,反射系数方位特征不明显,各向异性参数变化几乎不影响反射系数;随入射角增大,反射系数随方位角变化特征愈加明显,反射系数受各向异性参数变化影响;②界面上、下介质各向异性参数差越大,反射系数随方位变化越明显;③γ(V)(与SH波垂直传播和水平传播速度差异相关)变化对反射系数影响最大,ε(V)(与准纵波垂直传播和水平传播速度差异相关)变化对反射系数影响最小,且各向异性参数变化对反射系数的影响与方位角有关。

Depending on separate research purpose,scholars simplified and approximated the Zoeppritz equation.However,most of the approximate equations cannot accurately describe the changing laws of the amplitude of PSV wave at a large incident angle.And due to seismic data changing with azimuth,research on the azimuth reflection coefficient of PSV wave is relatively weak.Based on the precise expression of the reflection/transmission coefficient of HTI media,according to the theory of medium decomposition and perturbation,and assuming weak anisotropy,we derived an approximate expression of the reflection coefficient of PSV wave,analyzed the amplitude azimuth through forward modeling,and discussed the sensitivity of azimuthal PSV reflection coefficient to anisotropic parameters.Forward modeling shows that:(1)At a small incident angle,the azimuth of the reflection coefficient is not obvious,and changes in anisotropic parameters have little effect on the reflection coefficient;however,as the increase of the incident angle,the characteristics of the reflection coefficient changing with the azimuth become more obvious,and the reflection coefficient is affected by the change of anisotropic parameters;(2)The greater the contrast between the anisotropic parameters of the media above and below an interface,the more obvious the reflection coefficient changes with azimuth;(3)γ(V)(related to the velocity difference in vertical and horizontal propagation of S-wave)has the greatest effect on the reflection coefficients,andε(V)(related to the velocity difference invertical and horizontal propagation of qP-wave)has the least effect on the reflection coefficient,and the effect of anisotropic parameters on the reflection coefficient is related to azimuth.