Tha an Tsugaru Strait air an ear agus an iar necks, an dà chuid timcheall air 20 km (12 mi) tarsainn. A 'chiad sgrùdaidhean a chaidh a dhèanamh ann an 1946 a' sealltainn gun 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. Chaidh an iar necks a thaghadh, le a cho-theachdan fàbharach airson tunneling. The geology of the undersea portion of the tunnel consists of volcanic rock, pyroclastic rock and sedimentary rock of the period involved excavation. By August 1982, less than 700 meters of the tunnel remained to be excavated. 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. The Tsugaru Strait has an eastern neck up to 200 meters (
Inntrigeadh agus mearachdan igneous