3D imaging of geological structure by R-VSP utilizing vibrations caused by shaft excavation at the Mizunami Underground Research Laboratory in Japan

Matsuoka, Toshiyuki; Hodotsuka, Yasuyuki; Ishigaki, Koichi*; Lee, C. H.*

We carried out R-VSP using vibrations caused by blasting for the shaft excavation and drilling of the borehole investigation in the horizontal research galleries of the MIU, and examined the applicability of this method to imaging of geological structures around underground facilities, such as boundary between sedimentaly rocks and basal granite, fault and fracture zone in basal granite. As the results, the reflective events that seemed to correspond with sedimentary layers, the unconformity between sedimentaly rocks and granite, and fracture zone in granite could be confirmed by reflection profiles using the conventional VSP data processing and Seismic interferometry. From data processing by Image Point transform, the distribution of three faults, that are correspondent with the current geological model constructed from investigation data in the MIU project, could be detected.