起伏地形大地电磁二维反演

Two-dimensional magnetotelluric inversion of topography

为了适应地形起伏的实际地质情况,开展带地形的最小二乘二维反演研究。鉴于大地电磁(MT)反演的不适定问题,引入Tikhonov的正则化方法,从而获得关于总目标函数的方程,利用光滑约束最小二乘法求解总目标函数方程。由于正则化因子值与反演精度以及稳定性相关,采用主动约束平衡方法获取最优化的正则化因子,以确保反演精度和稳定性都达到最佳。与此同时,利用电磁场互易定理以节省反演迭代过程求解雅可比矩阵的计算时间。构建了若干地质构造模型进行试算,分别讨论TE、TM模式以及二者联合模式的反演结果,并与前人研究工作对比以说明本文方法的反演效果。

In order to simulate the actual geological conditions,the authors present the least squares inversion by incorporating topography into a forward model. In consideration of an ill-posed inverse problem of MT,the authors introduce Tikhonov regularization to obtain the equation of the total objective function and utilize smoothness-constrained least-squares inversion to solve the total objective function. As the regularized factor controls resolution and stability of the inverse problem,the authors put forward active constraint balancing（ ACB） to obtain an optimized regularized factor that balances the resolution as well as the stability of the inversion process.Meanwhile,for the purpose of speeding up the calculation of the field Jacobian for 2-D magnetotelluric inversion,the principle of electromagnetic reciprocity is applied. Finally,the authors discuss the inversion results of TE mode,TM mode and joint inversion of TE and TM mode using some synthetic models,in comparison with some of previous work.