Three Dimensional Electromagnetic Prospecting System for Deep Crust Structure

点击翻译按钮获取中文摘要

The purpose of this study was constructing an appropriate survey system to image three dimensional (3D) subsurface resisitivity structure using the magnetotelluric (MT) method.We developed the data processing scheme involving the robust stacking method based on the "M parameter" estimation, the impedance estimation method using Singular Value Decomposition of the data matrix and impedance smoothing method based on the Hirbert transformation between phase and impedance. We have verified the effectiveness of these techniques.We also developed a high accuracy 3D EM modeling scheme based on the staggered grid finite difference method. We tried to improve the condition of a large size coefficient matrix to easily solve and have overcome the problem of high resistivity contrast model and topography model in this scheme. The 3D inversion scheme based on the ABIC constrained smoothness least square method was modifying to apply a actual field data.We carried out MT survey at 25 sites distributed like a grid in the Nakatonbetsu area, Northern Hokkaido as a demonstrative research for the survey system developed in this research. We used MTU5 wide band MT survey machine and obtained electric and magnetic field data at 40 frequencies in the range of 380-0.00055 Hz. To obtain lower frequency data, we carried out MT observation using the fluxgate type magnetometer over two months. A reasonable 3D resistivity structure was imaged but the result suggested that we need further study to improve the resolution at deeper part