| Abstract: | Surveys on the Seikan Tunnel began in 1946. Survey items included a detailed geological survey of the land on both the Honshu and Hokkaido sides; the creation of an undersea topographical map based on echo sounding techniques; and a general study of the geological structure of the undersea portion, carried out by seismic prospecting. A detailed undersea geological map has been edited chiefly by dredging and sonic prospecting. Carrying out offshore survey proved rather difficult, however, due to the water depth in the Tsugaru Straits, the fast tidal currents and the adverse weather conditions. Nonetheless, the results of the survey generally agreed with the actual geological conditions in terms of geographical formation sequence, major structure distribution, etc. In addition, the survey results were particularly effective in presenting the major geological features of primary importance, while greatly assisting in choosing the most appropriate design and construction work that followed. |
