水平单轴应力与横波反射系数

地球物理勘探中,地下应力的估测是非常重要的.本文利用应力诱导的弱各向异性的各向异性参数, 借助已有的具有水平对称轴横向各向同性介质顾及高阶小量的横波反射系数近似公式,针对下介质为各向同性受单轴应力作用情况随应力的增加求取应力精度降低的问题,从横波反射系数近似公式的推导出发,联合SH波与SV 波反射系数给出新的改进的单轴应力与横波反射系数的直观表达式;计算并对比了受单轴应力作用的各向同性介质的横波近似和严格的反射系数,并利用理论得到的横波反射系数对应力进行了估值.结果表明,利用改进后横波反射系数与应力的直观表达式, 当应力增加时,应力估值精度有了明显的改善,这为利用横波反射数据直观估测应力提供理论依据.

Relationships between uniaxial stress and S-wave reflection coefficients

The investigation of subsurface stress is most important for geophysical exploration. This paper analyzed relationships between uniaxial stress and S-wave reflection coefficients based on the known weak-anisotropy approximations for the anisotropic parameters in stressed media and the reflection coefficients in anisotropic media. We proposed a new simple relationship to improve the estimation accuracy of larger uniaxial stress for an interface between an isotropic overburden and an anisotropic medium induced by horizontal uniaxial stress. The approximate S-wave reflection coefficients are compared with the exact ones in stressed media by numerical calculations, and the improved direct relationships between uniaxial stress and S-wave reflection coefficients are used to estimate the magnitude of stress. The results show the simple formulations given in this paper are stable and useful except degree is close to zero, and the error of uniaxial stress estimated from S-wave become smaller than before when uniaxial stress is more than 5 MPa. Therefore, the improved direct relationships between uniaxial stress and S-wave reflection coefficients will be helpful to estimate the magnitude of stress.