南海トラフ
Otsuki, along with the coastline along Kochi prefecture, is close to the Nankai Trough, and experiences seismic activity related to the Nankai megathrust earthquakes. These earthquakes typically result in landslides, flooding, and tsunamis, in addition to damage from seismic activity. These earthquakes occur approximately 100–200 years apart, with the most recent earthquake occurring in 1946.