The area in the Tohoku district where Neogene mudstone is distributed is well known as a typical place with high frequency of rock-slides.
The study of the overfolded structure and the anomalous sedimentary structure of the mudstone in the westernmost part of the Ou mountains has revealed that they have generated a gravity folded structure.
This means that the rise of the sediment on the sea bottom and volcanic activities owing to the crustal uplift during the Miocene and the early Quarternary brought about the Ou mountains, and it can be considered to be a geological factor in the recent landslides. In the area in question rock-slides subsequently took place due to the climate, topography, and volcanic activities during the Pleistocene and the early Alluvium.
These facts show that the recent landslides have a close connection with the ancient landslides during the Miocene.
