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The islands of Japan
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
Amurian Plate
and Okinawa Plate to the south, and subduction of the Pacific Plate under the Okhotsk Plate to the north.

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

Japan
Japan
is situated in a volcanic zone on the Pacific Ring of Fire
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
2011 Tōhoku earthquake and tsunami
, the 2004 Chūetsu earthquake
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

CONTENTS

* 1 Geological history

* 1.1 Orogeny phase * 1.2 Island arc phase

* 1.3 Current state

* 1.3.1 General information * 1.3.2 Geological structure

* 2 Research on Geology of Japan
Japan
* 3 Current geological hazards of Japanese Islands * 4 See also * 5 References * 6 Further reading * 7 External links

GEOLOGICAL HISTORY

OROGENY PHASE

The breakup of Rodinia about 750 million years ago has formed the Panthalassa ocean, with the some rocks which eventually become Japan sitting on its eastern margin. Since the early Silurian (450 million years ago) , 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
Izanagi Plate
95 million years ago. Currently the Philippine Sea Plate is subducting beneath the continental Amurian Plate
Amurian Plate
and Okinawa Plate to the south at speed 4 cm/year, forming Nankai Trough
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

Around 23 million years ago, the now Western Japan
Japan
was a coastal region of the Eurasia
Eurasia
continent. The subducting plates, being deeper than the Eurasian plate, pulled parts of Japan
Japan
which become modern Chūgoku region
Chūgoku region
and Kyushu
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. Around 16 million years ago, in Miocene
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
Japan
which become modern Tohoku and Hokkaido
Hokkaido
were gradually uplifted from the seafloor, and terranes of Chūbu region
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
Kantō Plain
.

CHANGES OF LAND-FORMS OF JAPAN OVER TIME

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

Japanese archipelago, Sea of Japan
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

General Information

Overall, the geological composition of Japan
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
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.

Geological Structure

The Japanese islands are divided into three major geological domains:

* Northeastern Japan, north of Tanakura fault (which had high volcanic activity 14-17 million years before present )

* 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
Japan
is further subdivided into several metamorphic belts stretched along Japan
Japan
Median Tectonic Line . The parts of Japan north of Japan
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
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 * Sambagawa orogenic belt * Chichibu orogenic belt * Sambosan orogenic belt * Beppu–Shimabara graben

RESEARCH ON GEOLOGY OF JAPAN

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

* The Journal of the Geological Society of Japan
Japan
(ja) - since 1893 * Geological Studies (地質学論集) - since 1968 * Geological Society of Japan
Japan
News (日本地質学会News) - since 1998

CURRENT GEOLOGICAL HAZARDS OF JAPANESE ISLANDS

Japan
Japan
is situated in a volcanic zone on the Pacific Ring of Fire