[H-DS05] Landslides and related phenomena

[HDS05-04] New insights of geological structures for Oya-kuzure and Shichimenzan-kuzure landslides

*Masahiro Chigira¹, Ching-Ying Tsou², Osamu Yokoyama³ (1.Fukada Geological Institute, 2.Faculty of Agriculture and Life Science, Hirosaki University, 3.Japan Conservation Engineers and Co. Ltd)

Keywords:Landslides, Slate, Toppling, Buckling

Oya-kuzure in the upstream of the Abe River was induced by 1707 Hoei earthquake and
Shichimenzan-kuzure to its north was induced by 1854 Ansei-Tokai earthquake and previous earthquakes. Chigira (1992) inferred that Shichimenzan kuzure occurred at a ridge-top depression made by the normal faulting due to toppling of slate. However, inside the landslide scar was too dangerous to get in at that time so observation was made from far. The landslide scar of Oya-kuzure was also dangerous to get in and to investigate the geological structure there. Last year, we observed geological structures of both the landslide scars using an UAV. We found several faults (probably normal faults) and intense crushing of rocks in the scar of Shichimenzan-kuzure. In the Oya-kuzure scar, we found toppling of slate in the east and buckling of slate in the west, which both preceded and prepared for the 1707 catastrophic landslide.

Chigira, M. (1992). Long-term gravitational deformation of rocks by mass rock creep. Engineering Geology, 32, 157-184.