Geology of Japan#Island arc phase

File:Japan separation.png.]]

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 Philippine and Pacific plates descended beneath the Asian plate into the eastward flow of the asthenosphere.{{Cite journal |last=Tatsumi |first=Yoshiyuki |last2=Otofuji |first2=Yo-Ichiro |last3=Matsuda |first3=Takaaki |last4=Nohda |first4=Susumu |date=1989-09-10 |title=Opening of the Sea of Japan back-arc basin by asthenospheric injection |url=https://www.sciencedirect.com/science/article/abs/pii/0040195189902837 |journal=Tectonophysics |volume=166 |issue=4 |pages=317–329 |doi=10.1016/0040-1951(89)90283-7 |issn=0040-1951}} This change in pressure from the asthenosphere pushing back on the subjected plates pulled Japan eastward off of Asia in the process of back-arc extension. This opened up the Sea of Japan around 15 million years ago.{{cite web|url=http://shinku.nichibun.ac.jp/jpub/pdf/jr/IJ1501.pdf|author=Barnes, Gina L.|title=Origins of the Japanese Islands: The New "Big Picture"|publisher=University of Durham|year=2003|access-date=August 11, 2009|archive-url=https://web.archive.org/web/20110428043510/http://shinku.nichibun.ac.jp/jpub/pdf/jr/IJ1501.pdf|archive-date=April 28, 2011|url-status=dead}} 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 per century. The most recent major quakes include the 2024 Noto earthquake, the 2011 Tōhoku earthquake and tsunami, the 2004 Chūetsu earthquake, and the Great Hanshin earthquake of 1995.

File:Geological map Japan basement.png

Geological history

=Orogeny phase=

File:Japan_Relief_Map_of_Land_and_Seabed.png

The breakup of Rodinia about 750 million years ago formed the Panthalassa ocean, with rocks that eventually became Japan sitting on its eastern margin.{{Cite journal |last=Wakita |first=Koji |date=2013-08-10 |title=Geology and tectonics of Japanese islands: A review – The key to understanding the geology of Asia |url=https://www.sciencedirect.com/science/article/pii/S1367912012001642 |journal=Journal of Asian Earth Sciences |series=Geological Evolution of Asia |volume=72 |pages=75–87 |doi=10.1016/j.jseaes.2012.04.014 |bibcode=2013JAESc..72...75W |issn=1367-9120}} In the Early Silurian (450 million years ago),{{cite journal|url=http://www.earth.sinica.edu.tw/papers/1547.pdf|author=Bor-ming Jahn|author-link1=Bor-ming Jahn|title=ACCRETIONARY OROGEN AND EVOLUTION OF THE JAPANESE ISLANDS—IMPLICATIONS FROM A Sr-Nd ISOTOPIC STUDY OF THE PHANEROZOIC GRANITOIDS FROM SW JAPAN|journal=American Journal of Science|publisher=American Journal of Science, Vol. 310, December, 2010, P. 1210–1249, DOI 10.2475/10.2010.02|year=2010|volume=310|issue=10|pages=1210–1249|doi=10.2475/10.2010.02|bibcode=2010AmJS..310.1210J|s2cid=129989718|access-date=October 10, 2017|archive-url=https://web.archive.org/web/20170809233914/http://www.earth.sinica.edu.tw/papers/1547.pdf|archive-date=August 9, 2017|url-status=dead}} the subduction of the oceanic plates started, and this process continues to the present day, forming a roughly 400 km wide orogeny at the convergent boundary. Several (9 or 10) oceanic plates were completely subducted and their remains have formed paired metamorphic belts. The most recent complete subduction of a plate was that of the Izanagi Plate 95 million years ago. Currently the Philippine Sea Plate is subducting beneath the continental Amurian Plate and the Okinawa Plate to the south at a speed of 4 cm/year, forming the Nankai Trough and the Ryukyu Trench. The Pacific Plate is subducting under the Okhotsk Plate to the north at a speed of 10 cm/year. The early stages of subduction-accretion have recycled the continental crust margin several times, leaving the majority of the modern Japanese archipelago composed of rocks formed in the Permian period or later.

=Island arc phase=

Around 23 million years ago, 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.{{cite web|url=http://shinku.nichibun.ac.jp/jpub/pdf/jr/IJ1501.pdf|author=Barnes, Gina L.|title=Origins of the Japanese Islands: The New "Big Picture"|publisher=University of Durham|year=2003|access-date=August 11, 2009|archive-url=https://web.archive.org/web/20110428043510/http://shinku.nichibun.ac.jp/jpub/pdf/jr/IJ1501.pdf|archive-date=April 28, 2011|url-status=dead}} Around 16 million years ago, in the 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.{{cite web|url=http://www.glgarcs.rgr.jp/intro/history_p4.html|publisher=glgarcs.rgr.jp|title=Formation history of the Japanese Islands (4) -- GLGArcs|access-date=July 16, 2017|archive-url=https://web.archive.org/web/20171201032559/http://www.glgarcs.rgr.jp/intro/history_p4.html|archive-date=December 1, 2017|url-status=dead}}

{{Gallery

|title=Changes of land-forms of Japan over time

|width=200 | height=210

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|File:Sea of Japan Early Miocene map.svg

|Japanese archipelago, Sea of Japan and surrounding part of continental East Asia in Early Miocene (23–18 Ma)

|File:Sea of Japan Pliocene map.svg

|Japanese archipelago, Sea of Japan and surrounding part of continental East Asia in Middle Pliocene to Late Pliocene (3.5-2 Ma)

|File:Japan glaciation.gif

|Japanese archipelago at the Last Glacial Maximum about 20,000 years ago, thin black line indicates present-day shorelines

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=Current state=

==General information==

Overall, the geological composition of Japan is poorly understood. The 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 a larger proportion of volcanic products, while the parts facing the Sea of Japan are mostly heavily faulted and folded sedimentary deposits. In northwest{{vague|date=August 2024}} Japan, the thick Quaternary deposits make determination of the geological history especially difficult.{{cite web|url=https://www.gsj.jp/en/education/geomap-e/geology-e.html|publisher=gsj.jp|title=Geology of Japan｜Geological Survey of Japan, AIST｜産総研地質調査総合センター / Geological Survey of Japan, AIST |access-date=July 16, 2017}}

==Geological structure==

The Japanese islands are divided into three major geological domains:

Northeastern Japan, north of {{ill|Tanagura fault|ja|棚倉断層}} (which had high volcanic activity 14–17 million years before present{{cite web|url=https://confit.atlas.jp/guide/event-img/jpgu2016/SGL36-P01/public/pdf?type=in|publisher=confit.atlas.jp|title=Yurie SAWAHATA, Makoto Okada, Jun Hosoi, Kazuo Amano, "Paleomagnetic study of Neogene sediments in strike-slip basins along the Tanagura Fault|access-date=July 16, 2017}})
Idosawa Fault
Senya Fault
Hidaka Mountains
Kitakami Mountains
Ōu Mountains
Central Japan, between Tanakura fault and Itoigawa-Shizuoka Tectonic Line.
Fossa Magna graben
Tanna Fault
Bōsō Hill Range
Southwestern Japan, south of Itoigawa-Shizuoka Tectonic Line. The Southwestern Japan is further subdivided into several metamorphic belts stretched along Japan Median Tectonic Line.{{cite web|url=http://www.geo.arizona.edu/geo5xx/geo527/Japan/|author=connelly@geo.arizona.edu|publisher=geo.arizona.edu|title=Southwest Japan|access-date=July 16, 2017|archive-url=https://web.archive.org/web/20171010155307/http://www.geo.arizona.edu/geo5xx/geo527/Japan/|archive-date=October 10, 2017|url-status=dead}} The parts of Japan north of Japan Median Tectonic Line ("Inner Zone") contains many granitoid fragments dating from Paleogene to Cretaceous period intruding the older material, while south of the line ("Outer Zone") is mostly accretionary complexes of Jurassic period or younger.
Urasoko fault
Fukozu Fault
Neodani Fault
Nojima Fault
Hida orogenic belt (Hida Mountains and Ryōhaku Mountains)
Sangun orogenic belt
Maizuru orogenic belt
Tanba-mino orogenic belt
Ryoke orogenic belt
Shimanto orogenic belt[http://sp.lyellcollection.org/content/10/1/5.full.pdf A. Taira, H. Okada, J. H. McD. Whitaker & A. J. Smith, The Shimanto Belt of Japan: Cretaceous-lower Miocene active-margin sedimentation]
Sambagawa orogenic belt{{cite web|url=https://www.mindat.org/loc-9910.html|publisher=mindat.org|title=Sanbagawa belt (Sambagawa metamorphic belt), Shikoku Island, Japan |access-date=July 16, 2017}}
Chichibu orogenic belt{{cite web|url=http://www.geo.arizona.edu/geo5xx/geo527/Japan/chichibu/index.html|publisher=geo.arizona.edu|title=Chichibu belt from geo.arizona.edu|access-date=July 16, 2017|archive-url=https://web.archive.org/web/20171205123927/http://www.geo.arizona.edu/geo5xx/geo527/Japan/chichibu/index.html|archive-date=December 5, 2017|url-status=dead}}
Sambosan orogenic belt
Beppu–Shimabara graben

Research

The Geology of Japan is handled mostly by {{ill|Geological Society of Japan|ja|日本地質学会}}, with the following major periodicals:

{{ill|The Journal of the Geological Society of Japan|ja|地質学雑誌}} - since 1893
{{Nihongo|Geological Studies|地質学論集}} - since 1968
{{Nihongo|Geological Society of Japan News|日本地質学会News}} - since 1998

Geological hazards

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 2024 Noto earthquake, the 2011 Tōhoku earthquake and tsunami, the 2004 Chūetsu earthquake and the Great Hanshin earthquake of 1995.

References

External links

[https://www.gsj.jp/en/ Geological Survey of Japan – English homepage]
[https://www.jstage.jst.go.jp/browse/geosoc Geological Journal of Japan – English homepage]

{{external media

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| image1 =[http://static2.businessinsider.com/image/4d7a0d2649e2ae5e5a0e0000/japan-map.jpg Statistical map of location, size and depth of earthquakes near Japan]

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National Archives of Japan: [https://web.archive.org/web/20090223201416/http://jpimg.digital.archives.go.jp/kouseisai/category/emaki/tatoroyama_no_ki_e.html Tatoroyama no ki, survey of limestone cave in Mount Tatoro in Kozuke Province, 1837 (Tenpo 8).]