Generally speaking, the so-called seismic exploration was usually executed on the earth surface, and the geological structure of deep rocks was to be assumed from the data of geological survey and the result of the seismic explorations on the points of the earth surface.
However, in such case of the exploration at the site for the underground power station which is 600 meters deep from the surface, it is necessary to get more accurate results.
In this paper, the writer described the fact that the geological condition of such deep rocks and the influence of Isegami Fault, which is the main faults in this region, were concluded from the well to well seismic measurements, utilizing those holes drilled to the depth of 600 meters at the triangular position. The distance between those wells was about 200 meters, and those deep well geophones, whese diameter were 40 mm, could bear the water pressure of 80 kg/cmm2. The cables connecting those wells were especially designed with 14 pieces (6 elements) using steinless wire in order to bear enough the tensile strength of 800gr.
Reasonably accurate records were obtained by shooting 100 to 200 gr primer charges in one well bottom.
