大岳― 八丁原地熱地域の断層と応力場

抄録

The strike and dip of fractures such as slickensides, hydrothermal veins and joints, found in drillcores from the Otake-Hatchobaru geothermal area have been estimated after measuring the thermo-remant magnetism of the cores with an astatic magnetmeter. The results show that most of the slickensides and veins dip southward, though their strikes vary considerably from NW-SE to NE-SW. In addition, the analysis of slickensides has revealed that the NW-SE trending faults basically are of left-handed strike slip type, while the NE-SW ones are of light-handed one. It is inferred that both kinds of faults were originally formed by the ENE-WSW compressional stress fields whose minimum stress axis dip NNW with moderate angles. Recently, the normal stress fields, whose intermediate stress axis tends NW-SE, have probably made the NW-SE trending fault planes open and permeable so that they have become the present breeding faults.