||Shunji Sasaki and Hideshi Kaieda
||stress inversion, microseismic event, induced seismicity, fault plane solution, regional stress state, HDR
||World Geothermal Congress
||Advanced Technologies (HDR, Magma, Geopressure)
||The stress field around the Hijiori HDR geothermal energy site, Yamagata, Japan, was estimated by inverting the focal mechanism solutions of microseismic events induced during the various experiments. The stress inversion results show the maximum and intermediate principal stresses are in the direction inclining about 45? eastward and westward, respectively, from the vertical direction. The minimum principal stress orientation is nearly horizontal and trends north - south. The stress ratio indicates a value as small as 0.1. According to the results of the present study, the stress field in the Hijiori HDR site is in a state in which the maximum principal stress is almost equal to the intermediate principal stress.