Dendrochronological analysis of the Usubetsu-gawa Landslide movement with special reference to hydrogeological structure of mass movement blocks

We examined that the integration of the two methods- Dendrochronological analysis and hydrogeological survey-can be effective measures to grasp the phenomenon of landslide with a view to preventing landslide disasters.For this study, the Usubetsu-gawa landslide in Sapporo, northern Japan, was selected as the study site. Firstly, we investigated mass movement history by way of compression wood analysis to identify the activity of small blocks that were divided in the landslide area to take account of geomorphic conditions. Secondly, we conducted hydrogeological survey to estimate the movement of each landslide blocks. The survey shows that the area has a single block which has suffered from many repeated slide action, that is, a highly active landslide block can be divided from other lower active landslide blocks.The findings suggest that compression woods analysis is a reliable method to identify active landslide blocks and priority landslide blocks, which must be of vital importance for the prevention of landslide disaster . In addition, through hydrogeological survey, some blocks are assumed highly active within harder weathering zone or in the area where the effective stress was notably declined by precipitation. The assumption was proved to be reliable by the findings of machine observation . It shows the possibility of estimating the movement of each landslide block through hydrogeological survey.It can be said that the integration of the two survey methods is effective in order to grasp the landslide phenomenon for the prevention of landslide disaster in the landslide area with unknown slide action frequency.