Japan was originally attached to the eastern coast of the
Eurasian continent. The subducting plates, being deeper than the Eurasian plate, pulled Japan eastward in the process of
back-arc extension, opening the
Sea of Japan around 15 million years ago.[1] The
Strait of Tartary and the
Korea Strait opened much later.
The breakup of
Rodinia about 750 million years ago formed the
Panthalassa ocean, with rocks that eventually became Japan sitting on its eastern margin.[2] In the
Early Silurian (450 million years ago),[3] 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.[4] 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.[5]
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
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 north-west Japan, the thick
quaternary deposits make determination of the geological history especially difficult.[6]
Geological structure
The Japanese islands are divided into three major geological domains:
Northeastern Japan, north of
Tanakura fault [
ja] (which had high volcanic activity 14-17 million years before present[7])
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 2011 Tōhoku earthquake and tsunami, the 2004 Chūetsu earthquake and the Great Hanshin earthquake of 1995.