Tha an Tsugaru Strait air an ear agus an iar necks, an dà chuid timcheall air 20 km (12 mi) air feadh. A 'chiad sgrùdaidhean a chaidh a dhèanamh ann an 1946 a' sealltainn gu robh an ear necks suas ri 200 meatair (656 troighean) domhainn le volcanic geology. An iar necks bha a 'char as àirde doimhneachd de 140 meatair (459 troighean) agus geology a' gabhail a-steach sa mhòr-chuid de rocainnean sedimentary an Neogene ùine. An iar necks a chaidh a thaghadh, le a cho-theachdan fàbharach airson a bhith a 'tuinnleachadh. The geology of the undersea portion of the tunnel consists of volcanic rock, pyroclastic rock, and sedimentary rock of the sedimentogene period. The first contact between the two sides was in 1983. The Tsugaru Strait has an eastern and western necks, both approximately 20 km (12 mi) across. How did initial surveys undertaken in 1946 indicate that the eastern neck was up to 200 meters (656 troighean) deep with volcani
200 gu h-àrd