1949 年 58 巻 6-7 号 p. 210-212
It is one of the most important pokicies, at present, to make direct connection with the resourceful Hokkaido and main land (Honshu) in order to promote its exploitation. As the route of the railway tunnel, we can lay out two routes ; one crosses the channel at its eastern cape of the Aomori Bay and the other at its western. The length of the each tunnel under the sea water is about 20 km., and the maximum depth of the water on the fatter route is about 80 m., shallower than the former. However all other conditions of the western route being favorable, we have been engaging in the investigations of the western route.
The tunnel has the steepest grade of 12.51/000 and is 38, km. long. To drive the tunnel, the ordinary system (mountain-tunnelling method) must be adopted because of the reason that the minimum depth of the water (about 160 m.) exceeds far the limit (about 40 m.) of pneumatic method. So, in order to avoid the leakage, the tunnel must pass through safety-zone in a considerable depth from the sea bottom. The Tertiary tuff is most desirable for its watertightness and easiness of tunnel-driving. The geological factors, the rock-properties (hardness and permeability), spouting water, fault and collapse etc. must be seriously, taken in consideration for the construction work. According to the plan, the geological survey, boring work and seismic prospecting have been carried on from 1946 to the present.
At Honshu side, seismic prospectings and the boring work (400 m.) were finished. But the boring work at Hokkaido side is now on half-way (132 m/200 m), and its remained Work and also the seismic prospecting on land and its subsidiary are intended to be carried out in 1949.
It is proved at present so far as investigated that Tertiary system composed of volcanic products (mainly tuff-breccia) develops largely at both of the subsidiary of Honshu and Hokkaido capes, and also under the sea bottom.