Estimation of Slip Surfaces Using the Results of Groundwater Logging in Fracture Zone Landslides

An essential part of the investigation of a landslide is the determination of the depth and geometry of the slip surfaces. However, it is rather difficult to locate the slip surfaces in stationary and/or very slow-moving landslides in tectonic-active regions such as Shikoku Island of West Japan. This paper tried using the results of salt logging obtained from two fracture zone landslides in Shikoku to find the distribution of groundwater flows which may locate in the location of sliding surfaces. In addition, the Equotip hardness value of borehole core samples, the magnetic susceptibility and numerical color values from digital imaging of borehole core samples were measured, and depth distribution graphs of these values were illustrated. It was shown that a relatively clear change in the measured Equotip value, magnetic susceptibility and numerical color values was observed near the location of sliding surfaces which reinforces the results from the groundwater logging.