Development of Monitoring System to Understand Preparation Processes of Rainfall-Induced Landslides: －Estimation of Slip Surface and In-Situ Observation using Electromagnetic Methods－@@@－電磁気学的手法を用いた実斜面におけるすべり面の推定と実斜面観測システムの構築－

SUMMARY In order to mitigate landslide risks, monitoring of ground water is essential. Previous indoor experiments suggest that the self-potential approach has an advantage to establish the early warning system in performance to detect related signals and in cost. To evaluate results obtained from the previous indoor experiments, in situ measurements are required. To achieve this, we selected a test slope at Nishiikawa, Tokushima, Japan and we performed preliminary electrical resistivity exploration (ERT) and core-sampling. The results of ERT show that there are low resistive areas in shallow depth (<3 m). The core-sampling results also indicate that there exists the structure which corresponds to slip surface. In addition, anisotropy in magnetic susceptibility was examined and the samples around the estimated slip surface region provide the oblate ellipsoid characteristics. These results of ERT and core analyses are consistent and make convince the identification of the slip surface. Based on these preliminary results, we set up the in situ self-potential observation at the slope and started measurements.