Effect of soil layer structures on landslide area-depth relationships and frequencies : Case study on the 2022 Kaetsu and the 2014 Hiroshima and Tamba heavy rain disasters, and comparison with earthquake-induced landslides

Abstract

  We compared soil layer structures investigated using simplified dynamic cone penetration test with the relationship between landslide area and depth on slopes underlain by six types of geology where many landslides occurred by heavy rains in August 2022 in Kaetsu Region, Niigata Prefecture and in August 2014 in Hiroshima and Tamba Cities. The increase ratio in the landslide depth relative to the landslide area was considered to become larger as increasing in the thickness of the L-layer that is a hard soil layer located deeper than the potential failure layers (U- and M-layers) for shallow landslide, and the composition ratio of the L-layer in the all soil layer, and it was considered that the landslide frequency decreased. The thickness and composition ratio of the L-layer were large for many earthquake-induced landslides. The result suggests that estimating the soil layer structure without field surveys in the target geology (region) may be possible by determining the relationship between landslide area and depth using LiDAR topographic data.