二维块状结构大地电磁快速反演

The fast magnetotelluric inversion of 2-D block structure

同济大学海洋与地球科学学院,上海 200092

School of Ocean& Earth Science, Tongji University, Shanghai 20092, China

利用大地电磁快速松弛反演法(RRI)中求偏导数的方法,结合二维块状地质模型建模法,提出了一种块状地质单元边界的快速二维反演方法。该方法的基本原理是,采用二维有限元法进行正演计算,通过一组修正系数把RRI法计算的一维偏导数转化为二维偏导数,并且在偏导数矩阵中只保留对本测点模型参数的偏导数,忽略对其它测点参数的偏导数,形成一个近似雅可比矩阵。在每一次反演迭代中只需要做一次有限元法正演就可以求出近似偏导数矩阵,与常规的采用互易定理的反演方法相比,反演的时间大为缩短。3个模型的试算实例表明,该快速二维反演方法能够使反演稳定地收敛到真实模型附近。

A new fast magnatotelluric 2-D inversion method has been developed, which utilizing the same method as that of rapid relax inversion (RRI) to calculate the partial derivatives of apparent resistivity with respect to model parameter and presented the model structure of Catherine de Groot-Hed-lin and Steven Constable.An approximate 2-D Jacobian is got through transforming the RRI partial derivatives to 2-D partial derivatives and ignoring the byway derivatives.Each of inversion iteration needs forward only one.The method is extremely fast comparing with the inversion method using reciprocity. Finally some synthetic models are calculated to test the method.