2011 Volume 33 Issue 2 Pages 87-92
We have conducted gravity surveys at some areas in Fukuoka Prefecture, Japan. One of the purposes of the surveys is to reveal underground structure of non-volcanic hydrothermal systems. As the result of the gravity surveys at Yokote-Ijiri area in Fukuoka City, we concluded that one of the basement differences where some hot springs concentrate is a part of Kego Fault, and there is a permeable zone, which is like a fracture zone created by the past activities of the fault and acts as a path of hot spring water from the deeper side of the granitic body. And the survey result in Oto Town indicates an underground structure of the half graben, which is concerned with Tagawa Fault, with a strike of a north-south direction. It was concluded that Tagawa Fault is a likely target for the future hot spring well by comparison between the results of this gravity survey and the previous geological research. And the directional drilling should be adopted for the drilling of the future hot spring well because the dip of Tagawa Fault seems to be nearly perpendicular.
