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, also Median Tectonic Line (MTL), is Japan's longest fault system. The MTL begins near
Ibaraki Prefecture is a Prefectures of Japan, prefecture of Japan located in the Kantō region of Honshu. Ibaraki Prefecture has a population of 2,871,199 (1 June 2019) and has a geographic area of . Ibaraki Prefecture borders Fukushima Prefecture to the north, ...
, where it connects with the
Itoigawa-Shizuoka Tectonic Line , also Ito Shizu Sen (糸静線) is a major fault on Honshu island that runs from the city of Itoigawa, Niigata Prefecture, through Lake Suwa to the city of Shizuoka in Shizuoka Prefecture. It is often confused with the Fossa Magna (Great Fis ...
(ISTL) and the
Fossa Magna Fossa Magna is a great rift lowland in Japan. It is often confused with Itoigawa-Shizuoka Tectonic Line. However, Itoigawa-Shizuoka Tectonic Line is a line; Fossa Magna is an area. Fossa Magna is Latin for "great crevasse". This name was given by ...
. It runs parallel to Japan's volcanic arc, passing through central Honshū to near Nagoya, through
Mikawa Bay Mikawa Bay (Landsat photo) Mikawa Bay (三河湾 ''Mikawa-wan'') is a bay to the south of Aichi Prefecture, Japan, surrounded by Chita Peninsula to the west and Atsumi Peninsula to the east and south. Its area is approximately 604 km2. Pollu ...
, then through the
Inland Sea An inland sea (also known as an epeiric sea or an epicontinental sea) is a continental body of water which is very large and is either completely surrounded by dry land or connected to an ocean by a river, strait, or "arm of the sea". An inland se ...
from the
Kii Channel The , also called the Kii Strait, is a strait separating the Japanese island of Shikoku from the Kii Peninsula on the main island of Honshū. This strait connects the Inland Sea with the Pacific Ocean. The name of the strait derives from Ki ...
and
Naruto Strait is a strait between Awaji Island and Shikoku in Japan. It connects Harima Nada, the eastern part of the Inland Sea and the Kii Channel. A famous feature of the strait is the Naruto whirlpools. Ōnaruto Bridge, the southern part of the Kobe-A ...
to
Shikoku is the smallest of the four main islands of Japan. It is long and between wide. It has a population of 3.8 million (, 3.1%). It is south of Honshu and northeast of Kyushu. Shikoku's ancient names include ''Iyo-no-futana-shima'' (), '' ...
along the
Sadamisaki Peninsula The is the westernmost part of the island of Shikoku, covered by the town of Ikata, Ehime Prefecture and home to the Ikata Nuclear Power Plant. It is sometimes referred to as the "Misaki Peninsula." This landmass juts out in a straight line fro ...
and the
Bungo Channel The is a strait separating the Japanese islands of Kyushu and Shikoku. It connects the Pacific Ocean and the Seto Inland Sea on the western end of Shikoku. The narrowest part of this channel is the Hōyo Strait. In the English-speaking world, t ...
and
Hōyo Strait The is the strait at the narrowest part of the Bungo Channel in Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the ...
to
Kyūshū is the third-largest island of Japan's five main islands and the most southerly of the four largest islands ( i.e. excluding Okinawa). In the past, it has been known as , and . The historical regional name referred to Kyushu and its surround ...
. The sense of motion on the MTL is right-lateral strike-slip, at a rate of about 5–10 mm/yr.Okada, A., On the Quaternary faulting along the Median Tectonic Line, in ''Median Tectonic Line'' (in Japanese with English abstract), edited by R. Sugiyama, pp. 49–86, Tokai Univ. Press, Tokyo, 1973. This sense of motion is consistent with the direction of oblique convergence at the
Nankai Trough The is a submarine trough located south of the Nankaidō region of Japan's island of Honshu, extending approximately offshore. The underlying fault, the ''Nankai megathrust,'' is the source of the devastating Nankai megathrust earthquakes, wh ...
. The rate of motion on the MTL is much less than the rate of convergence at the
plate boundary Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...
, making it difficult to distinguish the motion on the MTL from interseismic elastic straining in GPS data.


History

The upper part of the Japanese islands was created at the edge of the Eurasian plate 180 million years ago. Then, 50 million years later, the lower part was created at the southern part of the Yangtze continent. The lower part then rode on the Izanagi plate and moved to the upper part. These islands were joined into one and formed the Japanese islands 70 million years ago. The boundary line between the upper part and lower part is the MTL.


Seismic activity

The most important part of the MTL is called which is an
active fault An active fault is a fault that is likely to become the source of another earthquake sometime in the future. Geologists commonly consider faults to be active if there has been movement observed or evidence of seismic activity during the last 10,0 ...
and considered hazardous. It is separated into six regions defined by the most recent seismic activities. Although the MTL is a less seismically active region than others, earthquakes with magnitudes of 6 to 7 have occurred. The oldest known activity occurred about 3000 years ago, and the most recent in the 16th century. It is expected that seismic activities will continue in the future. The boundaries of the regions are still being discussed, so the regions are not well defined. #East edge of
Kongō Range The is a mountain range on the borders of Nara and Osaka Prefectures on the island of Honshū in the southwest of central Japan. The range separates the Osaka Plain and the Nara Basin, and forms a natural place for the boundary between the pre ...
(between Osaka Prefecture and Nara Prefecture) #*Expected magnitude of earthquake: 6.9 #*Probability of earthquake: 0 to 5% within 30 years #*Most recent activity: From 2000 years ago to the 4th century #South edge of Izumi Mountains (between Osaka Prefecture and Wakayama Prefecture) #*Expected magnitude of earthquake: 7.6 to 7.7 #*Probability of earthquake: 0.07 to 14% within 30 years #*Most recent activity: In the 7th to 9th century #Kitan Strait (between Wakayama Prefecture and Hyōgo Prefecture) – Naruto Strait (between Hyōgo Prefecture and Tokushima Prefecture) #*Expected magnitude of earthquake: 7.6 to 7.7 #*Probability of earthquake: 0.005 to 1% within 30 years #*Most recent activity: 3100 to 2600 years ago #Sanuki Mountains (between Kagawa Prefecture and Tokushima Prefecture) – Eastern part of north edge of Ishizuchi mountains (between Ehime Prefecture and Kōchi Prefecture) #*Expected magnitude of earthquake: 8 #*Probability of earthquake: 0 to 0.4% within 30 years #*Most recent activity: In the 16th century #North edge of Ishizuchi mountains (between Ehime Prefecture and Kōchi prefecture) #*Expected magnitude of earthquake: 7.3 to 8 #*Probability of earthquake: 0 to 0.4% within 30 years #*Most recent activity: In the 16th century #Western part of south edge of Ishizuchi mountains – Iyonada (Between Ehime Prefecture and Kōchi Prefecture – southern part of Seto inland sea) #*Expected magnitude of earthquake: 8 or above #*Probability of earthquake: 0 to 0.4% within 30 years #*Most recent activity: In the 16th century..


Notable earthquakes

The
Great Hanshin earthquake The , or Kobe earthquake, occurred on January 17, 1995, at 05:46:53 JST (January 16 at 20:46:53 UTC) in the southern part of Hyōgo Prefecture, Japan, including the region known as Hanshin. It measured 6.9 on the moment magnitude scale and had ...
of 1995 occurred on the
Nojima Fault is a fault that was responsible for the Great Hanshin earthquake of 1995 (Kobe Quake). It cuts across Awaji Island, Japan and it is a branch of the Japan Median Tectonic Line which runs the length of the southern half of Honshu island. The fa ...
, a branch of the MTL. Approximately 6,434 people lost their lives; about 4,600 of them were from Kobe. It caused approximately ten trillion yen ($100 billion) in damage, 2.5% of Japan's GDP at the time.


Regions


Chūbu

The MTL goes from
Shizuoka Prefecture is a prefecture of Japan located in the Chūbu region of Honshu. Shizuoka Prefecture has a population of 3,637,998 and has a geographic area of . Shizuoka Prefecture borders Kanagawa Prefecture to the east, Yamanashi Prefecture to the northea ...
to
Nagano Prefecture is a landlocked prefecture of Japan located in the Chūbu region of Honshū. Nagano Prefecture has a population of 2,052,493 () and has a geographic area of . Nagano Prefecture borders Niigata Prefecture to the north, Gunma Prefecture to the ...
. At Nagano prefecture, it lies between the Ina mountains and the Akaishi mountains. Then, it goes to Chino-shi, the northern part of Nagano prefecture.


Kantō

The MTL goes from Shimonita in
Gunma Prefecture is a prefecture of Japan located in the Kantō region of Honshu. Gunma Prefecture has a population of 1,937,626 (1 October 2019) and has a geographic area of 6,362 km2 (2,456 sq mi). Gunma Prefecture borders Niigata Prefecture and Fukushima ...
to the Hiki hill district in
Saitama Prefecture is a landlocked prefecture of Japan located in the Kantō region of Honshu. Saitama Prefecture has a population of 7,338,536 (1 January 2020) and has a geographic area of 3,797 km2 (1,466 sq mi). Saitama Prefecture borders Tochigi Prefecture ...
, and then continues down to the
Kantō Plain The is the largest plain in Japan, and is located in the Kantō region of central Honshū. The total area of 17,000 km2 covers more than half of the region extending over Tokyo, Saitama Prefecture, Kanagawa Prefecture, Chiba Prefecture, ...
. In the central Kanto Plain, boring tests have shown that the MTL lies 3000 meters beneath ground level in Saitama Prefecture. It is not clear where the MTL goes from there, but it is thought that it passes beneath Kashima or Ōarai on the Pacific coast in
Ibaraki Prefecture is a Prefectures of Japan, prefecture of Japan located in the Kantō region of Honshu. Ibaraki Prefecture has a population of 2,871,199 (1 June 2019) and has a geographic area of . Ibaraki Prefecture borders Fukushima Prefecture to the north, ...
.


Kinki

The MTL passes south of Awaji Island as it crosses the
Kii Channel The , also called the Kii Strait, is a strait separating the Japanese island of Shikoku from the Kii Peninsula on the main island of Honshū. This strait connects the Inland Sea with the Pacific Ocean. The name of the strait derives from Ki ...
from Shikoku to the
Kii Peninsula The is the largest peninsula on the island of Honshū in Japan. It is named after the ancient Kii Province. Overview The area south of the “ Central Tectonic Line” is called , and is home to reef-like coral communities which are amongst ...
. On the
Kii Peninsula The is the largest peninsula on the island of Honshū in Japan. It is named after the ancient Kii Province. Overview The area south of the “ Central Tectonic Line” is called , and is home to reef-like coral communities which are amongst ...
, it passes north of the Kinokawa River, from
Wakayama Wakayama may refer to: *Wakayama Prefecture, a prefecture of Japan *Wakayama (city) Wakayama City Hall is the capital city of Wakayama Prefecture in the Kansai region of Japan. , the city had an estimated population of 351,391 in 157066 househol ...
on the west coast past Gojō in
Nara Prefecture is a prefecture of Japan located in the Kansai region of Honshu. Nara Prefecture has a population of 1,321,805 and has a geographic area of . Nara Prefecture borders Kyoto Prefecture to the north, Osaka Prefecture to the northwest, Wakayama P ...
(where the river is called the Yoshino River) to
Mie Prefecture is a prefecture of Japan located in the Kansai region of Honshu. Mie Prefecture has a population of 1,781,948 () and has a geographic area of . Mie Prefecture is bordered by Gifu Prefecture to the north, Shiga Prefecture and Kyoto Prefecture to ...
on the east coast. There is an active shear zone north of the river in the southern foothills of the Izumi Mountains, which separate
Wakayama Prefecture is a prefecture of Japan located in the Kansai region of Honshu. Wakayama Prefecture has a population of 944,320 () and has a geographic area of . Wakayama Prefecture borders Osaka Prefecture to the north, and Mie Prefecture and Nara Prefecture ...
from
Osaka Prefecture is a Prefectures of Japan, prefecture of Japan located in the Kansai region of Honshu. Osaka Prefecture has a population of 8,778,035 () and has a geographic area of . Osaka Prefecture borders Hyōgo Prefecture to the northwest, Kyoto Prefecture ...
. East of Nara Prefecture, shear zones along the MTL are less active. The MTL takes a northern turn and passes along the eastern foothills of the
Kongō Range The is a mountain range on the borders of Nara and Osaka Prefectures on the island of Honshū in the southwest of central Japan. The range separates the Osaka Plain and the Nara Basin, and forms a natural place for the boundary between the pre ...
, connecting to the shear zone along the east side of the Ikoma Mountains between Nara Prefecture and Osaka Prefecture.


Kyushu

The MTL is known to pass through the region between Kunisaki Peninsula and Saganoseki Peninsula in
Ōita Prefecture is a prefecture of Japan located on the island of Kyūshū. Ōita Prefecture has a population of 1,136,245 (1 June 2019) and has a geographic area of 6,340 km2 (2,448 sq mi). Ōita Prefecture borders Fukuoka Prefecture to the northwest, Kumam ...
. However, because the
Ōno River Ōno River The is a river that originates in Ōita Prefecture, Japan. After running through the southern and central portions of Ōita Prefecture, it runs through the eastern part of Kumamoto Prefecture and the northern part of Miyazaki Prefectu ...
basin south of Ōita is covered by late
Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...
sedimentary rock, the geological continuity in the westward direction is unclear. According to one theory, the MTL may turn south around the Ōno River, connecting Usuki in Ōita Prefecture to the
Yatsushiro is a city located in Kumamoto Prefecture, Japan. Geography Located at the geographic center of Kyushu, Yatsushiro City is situated on the aptly named Yatsushiro Sea in between Kumamoto and Ashikita City. Climate Yatsushiro has a humid subtro ...
tectonic line in
Kumamoto Prefecture is a Prefectures of Japan, prefecture of Japan located on the island of Kyūshū. Kumamoto Prefecture has a population of 1,748,134 () and has a geographic area of . Kumamoto Prefecture borders Fukuoka Prefecture to the north, Ōita Prefecture to ...
. According to another theory, it may connect Ōita directly to the Kumamoto tectonic line.


Shikoku

After crossing the
Hōyo Strait The is the strait at the narrowest part of the Bungo Channel in Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the ...
from Kyushu to Shikoku, the MTL passes north of the
Sadamisaki Peninsula The is the westernmost part of the island of Shikoku, covered by the town of Ikata, Ehime Prefecture and home to the Ikata Nuclear Power Plant. It is sometimes referred to as the "Misaki Peninsula." This landmass juts out in a straight line fro ...
to land at Iyo on the west coast of
Ehime Prefecture is a prefecture of Japan located on the island of Shikoku. Ehime Prefecture has a population of 1,342,011 (1 June 2019) and has a geographic area of 5,676 km2 (2,191 sq mi). Ehime Prefecture borders Kagawa Prefecture to the northeast, Toku ...
. It continues eastward past the city of Saijō and along the foothills of the Ishizuchi Range. From Miyoshi in
Tokushima Prefecture is a prefecture of Japan located on the island of Shikoku. Tokushima Prefecture has a population of 728,633 (1 October 2019) and has a geographic area of 4,146 km2 (1,601 sq mi). Tokushima Prefecture borders Kagawa Prefecture to the north, E ...
it passes along the northern side of the
Yoshino River The Yoshino River (吉野川 ''Yoshino-gawa'') is a river on the island of Shikoku, Japan. It is long and has a watershed of . It is the second longest river in Shikoku (slightly shorter than the Shimanto), and is the only river whose watershe ...
until it arrives at the city of
Tokushima is a prefecture of Japan located on the island of Shikoku. Tokushima Prefecture has a population of 728,633 (1 October 2019) and has a geographic area of 4,146 km2 (1,601 sq mi). Tokushima Prefecture borders Kagawa Prefecture to the north, E ...
on the east coast of the island. There are active shear zones to the north of the MTL: north of Iyo and, in eastern Shikoku, along the southern foothills of the
Sanuki Mountains The are a mountain range running along the southern border of Kagawa and the northern border of Tokushima prefectures on the island of Shikoku, Japan. The highest peak is at 1059.9 m.


Museum

There is a museum dedicated to the tectonic line in Oshika-mura, Nagano Pref.
You are very welcome to the Oshika museum of Japan Median Tectonic Line.
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References

{{Authority control Geology of Japan Seismic faults of Japan Strike-slip faults