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| Northeast Honshu–Hokkaidō arc | |
|---|---|
| Name | Northeast Honshu–Hokkaidō arc |
| Region | Tohoku region, Hokkaidō |
| Country | Japan |
| Orogeny | Island arc |
| Length km | 800 |
Northeast Honshu–Hokkaidō arc is an island arc system in northern Honshu and Hokkaidō formed by subduction along the western Pacific margin. It links volcanic, seismic, and sedimentary provinces including the Ou Mountains, the Kitami Mountains, and the Daisetsuzan Volcanic Group, and lies offshore of the Japan Trench and the Kuril Trench. The arc has produced major eruptions, megathrust earthquakes, and long-term crustal growth that shaped regional basins such as the Mogami Basin and the Kushiro Plain.
The arc resides above the convergent boundary where the Pacific Plate subducts beneath the Okhotsk Plate, interacting with the Eurasian Plate margin near the Nankai Trough, the Itoigawa-Shizuoka Tectonic Line, and the Yamato Basin transform features. Key terranes and structural units include the Sakhalin Island-proximal accretionary prism, the Abukuma Highlands, and the Oga Peninsula metamorphic slices. Regional metamorphism and magmatism are recorded in formations such as the Tateyama Metamorphic Belt, the Kitakami Belt, and the Rishiri Volcanic Complex sequences. Interactions with the Eurasian Plate microblocks including the Izu–Bonin–Mariana Arc fragments influence forearc basins like the Akita Basin and backarc basins like the Shiribeshi Basin.
Volcanism along the arc is represented by stratocones, calderas, and lava domes exemplified by Mount Chokai, Mount Iwate, Mount Azuma, Mount Zao, Mount Komagatake (Hokkaido), and Mount Meakan. Large calderas such as Towada Caldera, Shikotsu-Toya Caldera system analogues, and the Kuttara Caldera-style depressions reflect explosive rhyolitic eruptions linked to crustal melting beneath the arc. Volcanic products record geochemical signatures comparable to those from Mount Fuji-adjacent arcs and the Kuril Islands volcanic front; mineral assemblages include andesite and dacite suites with accessory pyroxene and hornblende phases found in outcrops near Aomori and Sapporo. Hydrothermal manifestations occur at sites like Noboribetsu Onsen and Jozankei Onsen with sinter deposits analogous to Beppu systems.
The arc has generated historic megathrust events including analogues to the Great East Japan Earthquake of 2011 and earlier shocks rupturing along the Japan Trench and the Oki Islands-to-Nemuro segments. Notable seismic sequences affected ports such as Sendai, Hakodate, and Wakkanai, producing tsunamis that impacted coasts along the Pacific Ocean and the Sea of Japan. Paleoseismic evidence from trenching near Sanriku and radiocarbon-dated turbidites in the Joban and Boso basins document recurrence intervals tied to subduction slip on the Megathrust interface beneath the arc. Instrumental networks operated by Japan Meteorological Agency, Geological Survey of Japan, and international partners like USGS and IRIS monitor ongoing seismicity and slow-slip transients.
Arc evolution since the Cretaceous and Cenozoic involved sequential accretion of island arcs, oceanic plateaus, and continental fragments such as the Oshima Peninsula microblock and the Matsuyama Basin relics. Marine transgressions and regressions tied to global sea-level changes influenced deposition in the Sendai Bay and Funka Bay shelves. Fossil assemblages from strata near Mutsu and Kushiro record biogeographic shifts linked to migrations through the Bering Strait corridor and climate changes during the Pleistocene glaciations. Tectonic reorganization events associated with the opening of the Sea of Japan and clockwise rotation of the Japanese Archipelago microplates drove uplift recorded in uplifted marine terraces at Oga Peninsula and fault-bounded basins like the Yamagata Basin.
Relief across the arc includes glacially modified peaks in the Daisetsuzan Volcanic Group and fluvial valleys draining to estuaries at Morioka, Aomori Bay, and Ishikari Bay. Sedimentary systems comprise turbidite fans in the Japan Trench slope basins, deltaic sequences in the Kitakami River and Abukuma River catchments, and pyroclastic deposits forming thick ignimbrite sheets near Towada and Toya. Coastal geomorphology shows ria coastlines along Sanriku and barrier-bar systems near Fukushima and Ibaraki, with aeolian deposits on the Tanesashi Coast and fluvial terrace staircases in the Yamase River valleys.
Populated prefectures including Iwate Prefecture, Miyagi Prefecture, Akita Prefecture, and Hokkaidō Prefecture face volcanic hazards from eruptions of Mount Sakurajima-style ash fall, seismic shaking like the 2011 Tohoku earthquake, and tsunami inundation similar to events impacting Kesennuma and Ishinomaki. Mitigation measures employ monitoring by JMA, National Research Institute for Earth Science and Disaster Resilience, evacuation planning in municipalities such as Sendai City and Sapporo City, and engineered defenses along coasts at Ofunato and Rikuzentakata. Land-use policies coordinated with agencies like Ministry of Land, Infrastructure, Transport and Tourism and disaster education programs in schools and universities including Tohoku University and Hokkaido University aim to reduce risk from volcanic gas, lahars, landslides, and tsunami inundation.