Geology of Japan

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The island of Japan was separated from mainland Asia by back-arc spreading

The islands of Japan are primarily the result of several large ocean movements occurring over hundreds of millions of years from the mid-Silurian to the Pleistocene as a result of the subduction of the Philippine Sea Plate beneath the continental Amurian Plate and Okinawa Plate to the south, and subduction of the Pacific Plate under the Okhotsk Plate to the north.

Japan was originally attached to the eastern coast of the Eurasian continent. The subducting plates, being deeper than the Eurasian plate, pulled Japan eastward, opening the Sea of Japan around 15 million years ago.[1] The Strait of Tartary and the Korea Strait opened much later.

Japan is situated in a volcanic zone on the Pacific Ring of Fire. Frequent low intensity earth tremors and occasional volcanic activity are felt throughout the islands. Destructive earthquakes, often resulting in tsunamis, occur several times a century. The most recent major quakes include the 2011 Tōhoku earthquake and tsunami, the 2004 Chūetsu earthquake and the Great Hanshin earthquake of 1995. Hot springs are numerous and have been developed as resorts.

The geological features and bedrock composition of Japanese Islands

Geological history[edit]

Orogeny phase[edit]

The breakup of Rodinia about 750 million years ago has formed the Panthalassa ocean, with rocks that eventually became Japan sitting on its eastern margin. Since the early Silurian (450 million years ago)[2], the subduction of the oceanic plates has started and continue to today, forming roughly 400 km wide orogeny at the convergent boundary. Several (9 or 10) oceanic plates were completely subducted and their remains has formed paired metamorphic belts. Most recent completely subducted plate was Izanagi Plate 95 million years ago. Currently the Philippine Sea Plate is subducting beneath the continental Amurian Plate and Okinawa Plate to the south at speed 4 cm/year, forming Nankai Trough and Ryukyu Trench. The Pacific Plate is subducting under the Okhotsk Plate to the north at speed 10 cm/year. Early stages of subduction-accretion has recycled the continental crust margin several times, leaving the majority of modern Japanese archipelago composed of rocks formed in Permian period or later.

The topographical and tectonic maps of Japanese archipelago
Japanese archipelago relief (including submerged parts) 

Island arc phase[edit]

Around 23 million years ago, the now Western Japan was a coastal region of the Eurasia continent. The subducting plates, being deeper than the Eurasian plate, pulled parts of Japan which become modern Chūgoku region and Kyushu eastward, opening the Sea of Japan (simultaneously with the Sea of Okhotsk) around 15-20 million years ago, with likely freshwater lake state before the sea has rushed in.[3] Around 16 million years ago, in Miocene period, a peninsula attached to the eastern coast of the Eurasian continent was well formed. About 11 million years before present, the parts of Japan which become modern Tōhoku and Hokkaido were gradually uplifted from the seafloor, and terranes of Chūbu region were gradually accreted from the colliding island chains. The Strait of Tartary and the Korea Strait opened much later, about 2 million years ago. At the same time, a severe subduction of Fossa Magna graben have formed the Kantō Plain.[4]

Changes of land-forms of Japan over time
Japanese archipelago, Sea of Japan and surrounding part of continental East Asia in Early Miocene (23-18 Ma) 
Japanese archipelago, Sea of Japan and surrounding part of continental East Asia in Middle Pliocene to Late Pliocene (3.5-2 Ma) 
Japanese archipelago at the Last Glacial Maximum about 20,000 years ago, thin black line indicates present-day shorelines
  Vegetated land
  Unvegetated land
  Ocean
 

Current state[edit]

General information[edit]

Overall, the geological composition of Japan is poorly understood. Japanese islands are formed of several geological units parallel to the subduction front. The parts of islands facing oceanic plates are typically younger and display larger proportion of volcanic products, while the parts facing Sea of Japan are mostly heavily faulted and folded sedimentary deposits. In north-west Japan, the thick quaternary deposits make determination of the geological history especially difficult.[5]

Geological structure[edit]

The Japanese islands are divided into three major geological domains:

Research on Geology of Japan[edit]

The Geology of Japan is handled mostly by Geological Society of Japan (ja), with the following major periodicals:

Current geological hazards of Japanese Islands[edit]

Japan is in a volcanic zone on the Pacific Ring of Fire. Frequent low intensity earth tremors and occasional volcanic activity are felt throughout the islands. Destructive earthquakes, often resulting in tsunamis, occur several times a century. The most recent major quakes include the 2011 Tōhoku earthquake and tsunami, the 2004 Chūetsu earthquake and the Great Hanshin earthquake of 1995. Hot springs are numerous and have been developed as resorts.

See also[edit]

References[edit]

Further reading[edit]

  • Hashimoto, M., ed. (1990). Geology of Japan. Dordrecht: Kluwer Academic Publishers. ISBN 9780792309093. 
  • T. Moreno; S.R. Wallis; T. Kojima; W. Gibbons (eds.). Geology of Japan (Geological Society of London)(2015). ISBN 978-1862397439. 

by - (Author),

  • Takai, Fuyuji; Tatsurō Matsumoto; Ryūzō Toriyama (1963). Geology of Japan. University of California Press. 

External links[edit]

External image
Statistical map of location, size and depth of earthquakes near Japan