oa Three-Dimensional Magnetotelluric Inversion Using Generalized RRI Method

To handle the real geological environment, 3-D MT inversion studies has been developed by many researchers (Madden et al, 1989; Mackie et al, 1993). The method to calculate 3-D Frechte derivative takes enormous computational time and computer memory, while the RRI method (Smith and Booker, 1991), the approximate one, provides reasonable solution with less computing resource. But it may be liable to the static shift. The method discussed here is expanding the RRI method into the local 3-D area. We have developed a generalized method based on a locally three dimensional analysis to improve the computational efficiency and stability of inversion. The developed algorithm has been realized in the GRRI3D code, which has been tested on synthetic 3-D MT data. The case study includes interpretation of 3-D MT su1'vey conducted in the Minami-kayabe area located in the southern part of Hokkaido, Japan.