[H-DS07] Landslides and related phenomena

[HDS07-06] Development of uphill-facing scarps along high angle faults by flexural toppling

*Osamu Yokoyama¹, Masahiro Chigira² (1.Japan Conservation Engineers & Co., Ltd., 2.Fukada Geological Institute)

Keywords:Uphill-facing scarp, Flexural toppling, Deep-seated gravitational slope deformation, High-angle fault, GPS, UAV

Uphill-facing scarps or counter scarps are typical surface expressions of deep-seated gravitational slope deformations and are commonly created by flexural toppling. However, their evolution mechanisms are not well-understood, because their internal structures cannot be observable in detail. In addition, their development rates are extremely slow and are difficult to measure. Aka-kuzure (landslide), which is located upstream of the Oi River in the Cretaceous accretionary complex, is studied for the internal structures and development rates of uphill-facing scarps. The internal structure of the DGSD with uphill-facing scarps is exposed on the landslide scar, which was observed using UAV in 3D. Slope displacement rates were monitored for three fixed points using GPS for the time intervals of 20 years. As a result, we observed the internal structure of a gravitationally deformed slope that has been toppled with uphill-facing scarps. Uphill-facing scarps were found to be the extensions of geological faults, along which displacement occurred during toppling. Surface displacements by the toppling were 64 mm downslope for 18 years. The average displacement rate was 0.4 cm per year.