“There are many geological faults in the Japanese archipelago. They are classified as normal faults, reverse faults, or lateral faults according to the direction of movement. Faults found in the Tōhoku region (northeast Japan) are mainly reverse faults. Normal faults are not often seen in Japan outside of Kyūshū Island (southern Japan).
Mt. Chōkai has a distribution of normal faults characteristic of volcanoes.

The Araisawa fault on the west side of the mountain has a drop of up to 30 m. Its 2.5-km-long cliff (fault scarp) can be seen clearly on topographic maps.
The fault around Gassanmori is called the Gassanmori fault, and has a drop of up to 50 m and 1.5-km-long cliff.
Gassanmori seen from Ohama resembles Mt. Gassan (one of the Three Mountains of Dewa).”