Investigation of the shallow subsurface geological structures using the ground penetrating radar; An Example of the Omagari-Toyotomi fault, northern Hokkaido

Yasue, Kenichi; Niizato, Tadafumi  ; Chiba, Akihiko*

Information about shallow subsurface geological structures, about 10m in depth, is useful for the estimation of a detailed position and an activity of fault, and discovery of concealed fault, and so on. We carried out the GPR (ground penetration radar) exploration to clarify the subsurface geological structure around the area where the Omagari-Toyotomi Fault was estimated. In addition, we carried out an interpretation of aerial photograph, topographical and geological investigations, and drawing up of detail counter maps. Study sites are Kaishin and Hokushin districts in the Horonobe Town, northern Hokkaido. We used the GPR with antennas of 25 MHz and 100 MHz frequencies on the alluvial surface and the lower river terrace surface. GPR profiles show the thickness of the alluvium and the terrace deposit, the distribution of the basement rock, and the structure in the alluvium. The results of this study show that GPR exploration is an effective tool to investigate the shallow subsurface geological structure in the area where the fault topography would be altered by periglacial phenomena and man-caused effects.