Abstract
Submarine geological surveys in the area of the seikan tunnel have being carried out from 1946, by various methods, dredging of sea bottom, sonic logging, seismic survey, under sea drilling and the others. The geological structure of this area is shown at Fig. 1, 2, 3. Sea bottom contains so many faults at which are various fracturs and crushed rocks, that water may leak into the tunnel frequently during the excavation.
F 50, one of theirs submarine faults, which is the nearest from the shore of Hokkaido have been excavated excavated at 1969 in the Yoshioka (Hokkaido site of Seikan tunnel) research tunnel. From conclusion of various surveys, we assumed F-50 would be 50m in width in research tunnel and practically it was 100m in width. But structures of F 50 were almost collect.
