In recent years, water analysis has been proposed as a method to extract the potential slopes of deep-seated landslides. Although this technique can be used to predict the site of groundwater spring by water analysis, it does not take into consideration changes in the characteristics of leaching ions due to bedrock condition. Therefore, in the current study, we conducted a leaching test on boring cores weathered under different conditions for differences in ion concentration. We found that ion concentration changed with sample core depth and fracture opening length. Ion concentrations increased at a fracture opening length of approximately 3 mm. From these results, we conclude that cracks and bedrock weathering can influence the dissolution of ions.

  To clarify landslide trigging mechanism of earthquakes, we investigate the effect of maximum acceleration, predominant period of earthquake acceleration wave and material property of ground. One-dimensional earthquake response analysis was performed in Yanagihara landslide of Niigata prefecture which showed relatively small strain increasing in pipe strain gages at the time of earthquakes. As a result of analysis using multiple earthquake acceleration waves with different maximum acceleration, the predominant period of earthquake acceleration wave and the own natural period of ground effect to strain increasing of the slope of landslide. S-wave velocity structure also effect to strain increasing. Analysis result shows good agreement with depth which showed maximum strain increasing by pipe strain gage measurement. Therefore, one-dimensional earthquake response analysis using investigation result of the S-wave velocity profile could be used for initial evaluation of strain increasing by earthquake in landslide.

  Although the effective rainfall method has been widely used for analyzing groundwater level fluctuation in landslide sites, few previous studies have applied the method to snow-cover area throughout a year. This study estimated snowmelt by a simple and easy way, and analyzed groundwater level fluctuation in a landslide site in snow-cover area throughout a year using the effective meltwater and/or rainwater (MR). The results suggested that the groundwater level can be reproduced using the effective MR, and that incorporating the effect of evapotranspiration can improve the accuracy.