10:45 AM - 12:15 PM
[HRE12-P06] Post-Middle Miocene fracture systems and deep-seated landslides in the Shimanto accretional complexes, in the Kumano-gawa basin, Kii Peninsula
Keywords:lineament, orthogonal joints, geologic constraints, accretionary complex
Many deep-seated landslides have occurred in the sedimentary rock area of the Shimanto accretionary complexes in the outer belt of southwestern Japan. As the geological constraints, in addition to the accretion-induced imbricated structure, it has been pointed out that the existence of fracture systems that crosses the imbricated structure is important. However, in the conventional geological maps, the representation of such fracture systems is limited and the description of outcrops is extremely poor.
In the Kumano River basin of the Kii Peninsula, accretionary complexes of the Late Cretaceous to Paleogene Shimanto Belts are widely distributed. In the Kumano River Basin,The rocks in the Kitayama River Basin, the left tributary of the Kumano River, has undergone extensive thermal metamorphism due to felsic igneous activity in the Middle Miocene, and have hardened (Hosono et al. , 2022).
In this study, the steep cliffs of the Kitayama River Basin were surveyed, and based on slope maps produced based on 5m DEM, aerial photographs, and outcrop observations, topographical characteristics were understood and lineament analysis of the fracture system was performed. As a result, after the thermal metamorphic event in the Middle Miocene, three fracture systems occurred in the order of formation: NW-SE and NE-SW orthogonal joint systems, NS and EW joint groups, and ENE-WSW strike-slip faults. The arrangement of these fracture systems shows a close positional relationship with the gravitational deformation of mountain slopes and the shapes of deep-seated landslides such as the Kuridaira.
In the Kumano River basin of the Kii Peninsula, accretionary complexes of the Late Cretaceous to Paleogene Shimanto Belts are widely distributed. In the Kumano River Basin,The rocks in the Kitayama River Basin, the left tributary of the Kumano River, has undergone extensive thermal metamorphism due to felsic igneous activity in the Middle Miocene, and have hardened (Hosono et al. , 2022).
In this study, the steep cliffs of the Kitayama River Basin were surveyed, and based on slope maps produced based on 5m DEM, aerial photographs, and outcrop observations, topographical characteristics were understood and lineament analysis of the fracture system was performed. As a result, after the thermal metamorphic event in the Middle Miocene, three fracture systems occurred in the order of formation: NW-SE and NE-SW orthogonal joint systems, NS and EW joint groups, and ENE-WSW strike-slip faults. The arrangement of these fracture systems shows a close positional relationship with the gravitational deformation of mountain slopes and the shapes of deep-seated landslides such as the Kuridaira.