River-Bottom DC Resistivity for 3-D Imaging in Seoul Subway Tunnel Site

B039 RIVER-BOTTOM DC RESISTIVITY FOR 3-D IMAGING IN SEOUL SUBWAY TUNNEL SITE Abstract 1 For site investigation related to planning Seoul subway tunnel construction river-bottom dipole-dipole resistivity survey was conducted in Han-River. In this case we need more precise subsurface information compared with bridge or mountain tunnel construction. We designed high density 3-D water-bottom resistivity exploration. In addition gradient cesium magnetic survey with DGPS-RTK boat system was also conducted. Before field survey we tried several numerical modeling to test the ability to detect two hidden parallel fracture in the 100Ωm rock body. The 3-D resistivity inversion results showed clear low