Abstract
Based on the structural contour maps drawn by the well lithological and circulation loss data during drilling, following characteristics of fractures in the Matsukawa geothermal reservoir can be pointed out:
1) The main reservoir is located in the three vertical fractures, Akagawa Fault (NE-SW direction).
Yunomori Fault (ENE-WSW direction) and Sumikawa Fault (NW-SE direction).
2) The above fractures correspond to the distribution of hydrothermal alteration mineral zones, distribution of low frequency waves and low signal noise ratio obtained from the reflective seismic survey.
3) A large quantity of geothermal fluids seem to be flowing up through the fractures.
4) Geochemically, geothermal fluids collected from wells are divided into two fracture groups, Akagawa and Yunomori Faults, and Sumikawa Fault.
