Development of Highly Accurate Exploration System for Clarifying Fault Structures from Shallow to Deep Parts

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The purpose of this research project is to develop a highly accurate exploration system for clarifying fault structures from shallow to deep parts, by combining the four methods, satellite-image analysis, radioactive prospecting, electric resistivity sounding, and MT (m__-agnetot__-elluric) method. The main results are as follows.1. By the combination of lineaments from satellite images and digital elevation model data, orientations and geometries of the significant faults which act as conduits for transport of hydrothermal fluids to the ground surface could be identified for the geothermal field in the middle Kyushu.2. Three-dimensional resistivity distribution was clarified from 0 to 10-km depth by a combination of MT survey at lattice points, inversion analysis of apparent resistivity, and interpolation of the resistivity results. By applying it to the western side of Mt. Aso crater, two reservoirs were found along the fault in the elevation range -2000m to -3000m and estimated to be pillar shapes.3. MT survey was applied to structural analysis of fracture zones in deep parts of the Futagawa fault, an active fault along the southern edge of Kumamoto plain. The resistivity distributions estimated by this inversion analysis show clearly the low resistivity zones smaller than 10 Ω-m at all the lines, which imply that the Futagawa fault is accompanied with largely fractured zones by repetitive tectonic events. These zones are found to be located from the 1- to 7-km depths with 200- to 1000-m widths.4. The deep structures, which were estimated by the satellite-image analysis and MT survey, corresponded to the characteristics detected by the electric sounding and radon prospecting data.