Ching-Ying Tsou

Testing a failure surface prediction and deposit reconstruction method for a landslide cluster that occurred during Typhoon Talas (Japan)

The reconstructions of failure surfaces, prior to potential landslides or after their releases, landslide deposits or other palaeotopographic features are important for hazard and erosion assessment. The volumes involved in the landslide and failure surfaces constrain the propagation of a landslide, and the knowledge of the past topography helps to understand these hazards. Some methods exist to characterise landslide geometry, but these methods usually require monitoring information. This study 15 tries to assess the validity of the Sloping Local Base Level (SLBL) method for this purpose. Two sets of airborne LiDAR digital elevation models (DEMs) of the Kii peninsula (Japan) are used: the first one was acquired before Typhoon Talas, and the second one was acquired after. A total of 70 deep-seated landslides occurred during this event between 2 and 5 September 2011. This study shows that the SLBL method is efficient using either the slope deformations identifiable on the DEM before the 20 release of the landslide or a reliable 2.5D failure surface created by using both DEMs. In addition, this method allows the reconstruction of eroded deposits and buried valleys. Most of the volumes estimated are within ±35% of the estimation made by Chigira et al. (2013), and the coefficients of expansion range from 10 to 25%. These results show the considerable sensitivity of the landslide volume estimations and demonstrate the need for an efficient and fast tool to reconstruct potential landslide geometries or histories. 25