各向异性介质中地震波参数反演及其在隧道不良地质预报中的应用

Parameter inversion of seismic waves in anisotropic media and its application in bad geological prediction of tunnels

以HTI(horizontal transverse isotropy)介质中的动校正速度、慢度向量及走时方程为基础,通过坐标旋转,推导EDA(extensive dilatancy anisotropy)裂隙诱导介质中动校正速度的射线参数表达式;通过对地震广角反射勘探数据进行速度分析,获取动校正速度;基于拟牛顿法的最优化射线追踪法,确定地层界面最佳几何参数。研究结果表明:采用射线参数反演的速度与理论计算速度相对误差小于5%;利用动校正速度的各向异性特征可确定EDA介质的裂隙发育方位;通过射线追踪及多项式拟合可确定多层倾斜地层界面;当加入噪声时,反演的裂隙方位角和各向异性参数相对误差均在5%以内,加入高斯噪声后,裂隙方位角和各向异性参数相对误差均在10%以内,其余参数相对误差在5%以内;速度谱与衰减分析结果一致;裂隙走向反演结果误差为±5°;所提出的反演方法可应用于隧道裂隙发育及富水区预报,具有较高预报精度。

Based on normal moveout(NMO) velocity, the slowness vector and the travel time equation in the HTI (horizontal transverse isotropy) medium,the ray parameter expression of NMO velocity in the EDA(extensive dilatancy anisotropy) fracture induced medium was derived by axis rotating.The NMO velocity was obtained by velocity analysis of wide-angle seismic exploration data. The optimal ray tracing method based on quasi-Newton method was used to determine the optimal geometric parameters of the formation interface.The results show that the relative error between the velocity inversion and the theoretical velocity is less than 5%.The anisotropic characteristic of NMO velocity can be used to determine the fracture orientation of EDA medium. The ray tracing and polynomial fitting can be used to determine the multi-layer inclined formation interface. The inversion error of the fracture azimuth and anisotropy parameters using ray parameter inversion is within 5%, when Gaussian noise is added, the relative error of fracture azimuth and anisotropy is within 10%,and that of the other parameters is within 5%.The velocity spectrum is consistent with that of the attenuation analysis,and the error of the fracture orientation inversion is ±5°. The proposed inversion method can be applied in the prediction fracture development and water-rich areas of tunnel construction with high prediction accuracy.