[H-DS10] Geohazards in humid, tectonically active countries and their precursors

[HDS10-02] Estimation of subsurface structures in a landslide area with linear depressions

*Hikaru Osawa¹, Issei Doi², Noriyuki Arai², Ryoukei Azuma³, Takuma Watakabe¹, Yosuke Yamakawa⁴ (1.Forestry and Forest Products Research Institute, 2.Disaster Prevention Research institute, Kyoto University, 3.Osaka Institute of Technology, 4.University of Tsukuba)

Keywords:Gravitational slope deformation, Deep-seated landslide, Microtremor survey, Sasayama tectonic line

We conducted a geological survey, microtremor survey, and surface wave survey on a landslide with linear depressions, which is a characteristic terrain for a deep-seated landslide, to estimate the subsurface structure to clarify the cause of deep-seated landslides. Geological investigations revealed the presence of a high-angle fault at the terminal part of the landslide, with greenstone in the upper part and shale in the lower part, bordering the fault. As a result of microtremor surveys at five points along the longitudinal axis of the landslide, a low-velocity zone of about 360–640 m/s was detected. In combination with the results of the geological survey of the outcrop at the landslide terminus, the low-velocity zone was inferred to be a landslide-moving body.