17:15 〜 18:30
[HTT30-P02] Subsurface structure of dolines on the Akiyoshi-dai Plateau, Japan: An approach from electrical resistivity tomography
キーワード：カルスト地形、電気探査、土層厚
Distribution of soil thickness was estimated based on 2-D electrical resistivity tomography (ERT) in more than 10 solution dolines on Akiyoshi-dai plateau in Yamaguchi Prefecture, Japan. The 2-D ERT revealed a transition zone of resistivity values that increase with depth. The upper layer of the transition zone (< 400 Ω·m) was identified as soil on the basis of the result of cone penetration tests. The lower layer immediately below the soil was considered as epikarst, which is composed of fractured limestone with soil. Soil thickness was maximized at the bottom or at the lower slope of dolines. In addition, mean soil thickness at the bottom increases with increasing the size of source area of doline. Soil creep accumulates the larger amount of soil into the bottom of the doline with larger source area. In contrast, soil thickness at the bottom was smaller in dolines with larger ratio of rock exposure (pinnacles) probably due to the limited amount of soil. Although the estimated shape of soil-epikarst boundary was similar to the shape of the ground surface for most slopes, the boundary was not flat for the bottoms of most dolines. The inclined soil-epikarst boundaries below bottom of doline may be a key to solve the development process of dolines in Akiyoshi-dai plateau.