Application of Audiofrequency Magnetotelluric Method in Ogiri Geothermal Field, Southwestern Japan

Abstract

The audiofrequency magnetotelluric (AMT) method was applied in 2004, for detailed investigation of the reservoir in the Ogiri geothermal field, southern Kyushu, southwestern Japan, by Nittetsu Kagoshima Geothermal Co., Ltd. (NKG). The AMT stations were arranged with an interval of about 150 m on a grid array whose size was approximately 2.5 km x 2.5 km. The number of AMT stations was 66. This survey was targeting an eastern expansion of the currently producing geothermal reservoir. There had been conducted several stages of MT surveys in the same area by the New Energy and Industrial Technology Development Organization (NEDO), NKG and Geological Survey of Japan (GSJ) before. This report presents a trial of three-dimensional (3D) inversion of the AMT data, together with those existing MT data.