Usuki-Yatsushiro Tectonic Line

Japanese: 臼杵‐八代構造線 - うすきやつしろこうぞうせん

...The prefecture's name was later changed to Kumamoto Prefecture in 1976, and remains so to this day.
[Nature of Central Kyushu]
The Usuki-Yatsushiro Tectonic Line, which divides southwestern Japan into the inner and outer belts, runs east to west through the center of the prefecture. To the north of this line, i.e. the inner belt, lies Mount Aso in the east and the Chikuhi mountain range in the north, and in the northwest, rivers such as the Kikuchi River, Shirakawa River, Midorikawa River, and Kuma River flowing from the mountains to the east, north, and south form the Kikuchi (Tamana) Plain, Kumamoto Plain, and Yatsushiro Plain along the Ariake Sea coast, and the Kikuka Basin opens up in the middle reaches of the Kikuchi River.

From the Median Tectonic Line

...In Shikoku and the western Kii Peninsula, the Upper Cretaceous Izumi Group is distributed in the southern part of the Ryoke Metamorphic Belt, and mylonite (Kashio mylonite) develops on its southern edge from the eastern Kii Peninsula to the Chubu region. In Kyushu, the zonal arrangement of the Ryoke and Sanbagawa Metamorphic Belts is disordered, and Cenozoic volcanic rocks are widely distributed, making the location of the Median Tectonic Line unclear. However, this tectonic line passes through the northern side of the Saganoseki Peninsula, enters the distribution area of the Upper Cretaceous Onogawa Group, and is thought to merge with the Usuki-Yatsushiro Tectonic Line, which crosses central Kyushu from east-northeast to west-southwest and was named by Nagakatsu Yabe (1925) near Mt. Sobo. The Median Tectonic Line appears as a ductile shear zone on the southern edge of the acid igneous activity area of the late Mesozoic era, and fault movement along it has continued intermittently to the present day. ...

*Some of the terminology that refers to the Usuki-Yatsushiro Tectonic Line is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…その後76年県名を熊本県に再改称し，今日に至っている。【坂本一登】
［九州中央部の自然］
　西南日本を内･外帯に分ける中央構造線の臼杵（うすき）‐八代構造線が，県の中央を東西に走っている。この線の北側つまり内帯には，東部に阿蘇山，北部に筑肥（ちくひ）山地が横たわり，北西部に東，北，南の山地から流れる菊池川，白川，緑川，球磨（くま）川などの河川が，有明海沿岸に菊池(玉名)平野，熊本平野，八代平野を形成し，菊池川中流域に菊鹿盆地が開けている。…

【中央構造線】より

…四国と紀伊半島西部の場合は領家変成帯の南部に上部白亜系和泉層群が分布し，紀伊半島東部から中部地方にかけてはその南縁部にミロナイト(鹿塩（かしお）ミロナイト)が発達する。九州では領家，三波川両変成帯の帯状配列が乱れ，しかも新生代の火山岩類が広く分布しているため，中央構造線の位置が不明確になるが，この構造線は佐賀関半島の北側を通って上部白亜系大野川層群の分布域に入り，祖母（そぼ）山付近で矢部長克が命名(1925)した九州中央部を東北東～西南西に横断する臼杵（うすき）‐八代構造線に合流するものと考えられる。中央構造線は中生代後期の酸性火成活動域の南縁における延性剪断帯として出現し，これに沿う断層運動は断続的ながら現在までつづいている。…

※「臼杵‐八代構造線」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典第２版について | 情報

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