The Survey of the Omagari fault using Audio frequency Magnetotelluric method in Horonobe research project for the Subsurface Environment

Matsuo, Koichi*; Negi, Tateyuki*; Yokoi, Koichi*; Takahashi, Takeharu*; Teshima, Minoru*

The present document is to report the results of geophysical survey by electromagnetic method around a site proposed for the Horonobe Underground Research Program at Horonobe-cho, Hokkaido by the Japan Nuclear Cycle Development Institute. Remote-reference AMT(Audio-frequency magnetotelluric) method was carried out at 59 stations over 4 km2 in the area of Hokushin in Horonobe-cho. Two dimensional and three dimensional resistivity inversion analysis was carried out and the resistivity structure from the surface to 1,000m below sea level became clear. The resistivity structure was studied by comparing geological structure presumed from existing geological information. Resistivity contour lines extends NNW-SSE trend in plan of resistivity that is coincident with geological structure. The resistivity distribution was good agreement with existing electrical resistivity log data. At 500m below sea level, the resistivity of South-West part from presumed Omagari-fault was ranges from 1 to 3 ohm-m, and that of North-East part is ranges from 3 to 7 ohm-m.