Abstract

This study is the case of groundwater development based on the geometrical fracture model of target area established only through geological fracture mapping technique. A fracture mapping of 9 km2, eastern Munsan, has been conducted to determine geological and hydrological factors for new water well placement in the Gyeonggi gneiss complex. Geophysical exploration was not applicable because of small restricted area and dense underground utilities at the site. Form line mapping on the basis of foliation orientation and rock type revealed a synform of NS fold axis bearing to the south. An EW geological cross-section passed through the site area shows a F2 synform as a double-wall ice cream spoon shape. Three regional faults of N20^oE, N30^oW and NS have been dragged into the site to help understand extensional fault paths. The N20^oE fault with dextral sense is geometrically interpreted as a western fault of two flexural conjugate type-P shear faults in the F2 synformal fold. The NE cross-section reveals that a possible groundwater belt in the western limb of superposed fold area is formed as a trigonal prism within 100 m depth of the intersectional space between the N20^oE fault plane
and the weakly sheared plane of transposed foliation. Another possible fault for water resource strikes N40^oE. Recommended sites for new water well placement are along the N20^oE and N40oE faults. As a result of fracture mapping, 145 ton/day of water can be produced at one well along the N20^oE fault line. Exploration of groundwater in the area is succeeded only using with geological fracture mapping and interpretation of geological cross-section, without any geophysical survey. Intersection of fault generated with the F2 synformal fold and foliation supply space of groundwater reservoir.

Keywords Fracture mapping, East Munsan, Groundwater well, Formline map Double-wall ice cream spoon shape, F2 synformal fold