Abstract
Electromagnetic (EM) methods have been often used for geothermal exploration because resistivity is a physical property sensitive to temperature and the state of fluids, and because EM methods such as MT, CSAMT, and TEM are applicable to geothermal investigations over depths of several kilometers. In geothermal exploration, it is required to estimate the regional structure of a geothermal system including the geothermal reservoirs, heat sources, and geothermal fluids. The resistivity structure calculated from EM data shows only the distribution of resistivity, and therefore, it is necessary to interpret this as a geological structure. This paper describes a method for the estimation of a regional geothermal system based on EM exploration. It focuses on how the regional resistivity structure of a geothermal system can be interpreted and introduces two case studies of EM surveys in the Ogiri geothermal area of Kagoshima and the Toyoha geothermal area of Hokkaido in Japan.
