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Research Highlights, Unveiling the Mysteries of a Large Fault That Cuts Across Japan

Geological Survey of Japan

Unveiling the Mysteries of a Large Fault That Cuts Across Japan

NAGAMORI Hideaki, NAKAZAWA Tsutomu, TAKEUCHI Makoto
Research Institute of Geology and Geoinformation
FURUKAWA Ryuta
Research Institute of Earthquake and Volcano Geology

Geological map of southwestern part of Niigata Prefecture, Itoigawa, published

The "Itoigawa" geological map showing the southwestern part of Niigata Prefecture has been published. This completes the geological maps that include the northernmost part of the Itoigawa-Shizuoka Tectonic Line (ISTL). As a result, the Itoigawa area was revealed to have experienced sudden uplift activity since one million years ago.

Geological outline map of the Itoigawa area

The mysteries of a large fault that cuts across Japan, which were previously unknown

Japanese geology differs greatly across the ISTL boundary. The northern Fossa Magna region on the east side of the northernmost part of ISTL is thought to be significantly uplifted, but when or how this uplift occurred was not known. In addition, this is a valuable area where various rocks dating from 400 million years ago to the present can be seen, and it has been certified as a World Geopark. However, there are also steep mountains, so it is a difficult area to survey and there were no detailed geological maps.

Photo: Geological map of southwestern part of Niigata Prefecture, Itoigawa,

What the geology of the Itoigawa area tells us

Geological surveys clarified the types, distribution, and geological structures of the strata. The origins of the Itoigawa area geology were understood as a result of investigating the precise division and formation age of each stratum. It was found that the west and east sides of the northernmost part of ISTL deformed in conjunction, and that km-order uplift has occurred since one million years ago. It was also revealed that the northernmost area that includes the Itoigawa area is not the boundary between the Eurasian plate and North American plate.

Prepare further geological maps, and continue geological surveys

The cause and process of the uplift in the Shirouma-dake, Kotaki, and Itoigawa areas that include the northernmost part of ISTL will be clarified.

Photo: NAGAMORI Hideaki, FURUKAWA Ryuta, NAKAZAWA Tsutomu

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