JAPAN 297 JAPAN J Tazawa, Niigata University, Niigata, Japan ß 2005, Elsevier Ltd All Rights Reserved Introduction Japan, lying off the eastern coast of Eurasia, has an area of 377 819 km2; slightly larger than the United Kingdom, and comprises four major islands, Hokkaido, Honshu, Shikoku, Kyushu, and some thousands of smaller islands Honshu accounts for over 60% of the total area The Japanese Islands are about 3800 km long, ranging from Kunashiri (45Á33ÁN, 148Á45ÁE) to Yonakuni (24Á27ÁN, 122Á56ÁE) (Figure 1) The Japanese Islands consist of two arc-trench systems, the North-east Japan and South-west Japan Systems The NE Japan System, related to the subduction of the Pacific Plate, extends from the Chishima (Kuril) arc-trench to the Izu-Ogasawara (Bonin) arctrench, through the NE Japan Arc-Japan Trench The SW Japan System, related to the subduction of the Philippine Sea Plate, extends from the SW Japan Arc-Nankai Trough to the Ryukyu arc-trench Two back-arc basins, the Okhotsk Sea and the Japan Sea, are placed behind the NE Japan System Moreover, another new, weakly-developed convergent plate boundary (see Tectonics: Mountain Building and Orogeny) extends along the eastern margin of the Japan Sea from Sakhalin to central Honshu The Itoigawa-Shizuoka Tectonic Line (west border of the ‘Fossa Magna’) is considered to be the boundary between the North American Plate and the Eurasian Plate Thus Japan exhibits the interaction of four plates, the Pacific, North American, Philippine Sea, and Eurasian Plates Japan’s current tectonic setting has existed only since mid-Tertiary (Early Neogene) time Japan was born at the site of a trench, namely, a subduction zone bordering the eastern margin of North China (Sino-Korea) in the Early Ordovician (about 500 Ma) Since then, the Proto-Japan has experienced successive accretions, with episodic high-P/T metamorphism, thrusting, and large scale strike-slip faulting and therefore the geology of Japan is very complicated Geological exploration of Japan dates from the pioneer work of E Naumann in 1875–1885 He first described the geological features of the Japanese Islands, and proposed the ‘Fossa Magna’ and the Median Tectonic Line Between 1940 and 1960, T Kobayashi and M Minato put forward syntheses on the tectonic development of the Japanese Islands based on the Geosyncline concept In contrast to the classical syntheses, K Kanmera, A Taira, and T Kimura expressed their new progressive opinions in the 1970 to the 1980s, after the establishment of the Plate Tectonic theory In the early 1990s, three models of the tectonic framework of the Japanese Islands and its development were proposed: (i) the microcontinent model by K Ichikawa and others; (ii) the nappe model by Y Isozaki and S Maruyama; and (iii) the strike-slip model by J Tazawa Since then, an enduring controversy has continued between the three models In this article, the tectonic division and evolution of the Japanese Islands are based on the strike-slip model The ‘Economic Geology’ of the area is omitted, since most of the mines in Japan are no longer working Topography Japan is very mountainous, with mountains occupying about 71% of the total land area (Figure 2) Altogether, 532 of these mountains are over 2000 m high; Mt Fuji, the highest, rises to 3776 m The high mountains are concentrated in central Honshu, just west of the ‘Fossa Magna’, and form three echelon ranges, the Northern, Central, and Southern Japan Alps from north to south Other ranges coincide with the Palaeozoic to Mesozoic tectonic and regional metamorphic belts or the Quaternary volcanic belts Trenches are particularly deep along the Pacific Plate boundary, reaching about 7000 m in the Chishima and Japan Trenches, and 8000 m in the Izu-Ogasawara Trench The Nankai Trough along the Philippine Sea Plate is not as deep as a trench, being less than 6000 m The Japan Sea, one of the back-arc basins, is roughly divided into northern and southern parts: the Northern Japan Sea has a flat floor, the Japan Basin, of about 3500 m: the Southern Japan Sea has an uneven floor, with the Yamato Bank, Yamato Basin, Tsushima Basin, and Korean Plateau Volcanism About 200 Quaternary volcanoes, of which more than 60 are still active, occur in the Japanese Islands (Figure 3) These volcanoes are distributed in two belts, the East Japan and West Japan Volcanic Belts, and are related to the subduction of the Pacific Plate and the Philippine Sea Plate, respectively The East Japan Volcanic Belt extends parallel to the ChishimaJapan-Izu-Ogasawara trenches, from the Chishima Islands to the Izu-Ogasawara Islands, through Hokkaido and northern Honshu Mt Fuji, a typical