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

Abstract

Abstract. Reconstructions of failure surfaces (prior to potential landslides or after their release), landslide deposits, or other palaeotopographic features are important for hazard and erosion assessment. The volumes involved in landslide and failure surfaces constrain the propagation of a landslide, and knowledge of the past topography helps us to understand these hazards. Some methods exist to characterise landslide geometry, but these methods usually require monitoring information. This study 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 release of the landslide or a reliable 2.5-D failure surface created by using both DEMs (the 2.5-D corresponds to a surface which has only one z value for each x–y coordinate; in other words, no true vertical topography or overhang can be represented perfectly). In addition, this method allows for 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 considerable sensitivity to the parameters used for the reconstruction of the landslide volume estimations and demonstrate the need for an efficient and fast tool to reconstruct potential landslide geometries or histories.

Landslide Scarp Assessments by Means of an Ellipse-Referenced Idealized Curved Surface

“…For approximating the 3D failure surface, Jaboyedoff et al (2004) and Jaboyedoff et al (2009) proposed the Sloping Local Base Level (SLBL) method to construct a curved surface, of which the second derivative along the down-slope direction remains constant. The SLBL technique has been tested against landslides triggered by Typhoon Talas in Japan, where reasonable agreements (±35%) were achieved (Jaboyedoff et al, 2019). For studying the 3D stability of stratovolcano edifice, Reid et al (2000) and Reid et al (2001) suggested a spherical failure surface for analyzing the slope stability by using the LEM without considering the internal/local structures.…”

“…However, the complex composition, spatial geological structure, and hydrological variations lead the determination of a precise failure surface on the natural slopes in mountain areas to a highly challenging task, especially when the field data are incomplete. Hence, the determination/prediction of a landslide failure surface and estimation of the associated volume of released mass are with a high degree of uncertainty (e.g., Jaboyedoff et al, 2019;Yeh et al, 2021).…”

Analysis of the Influence of Structural Geology on the Massive Seismic Slope Failure Potential Supported by Numerical Modelling

“…The volume balance of pre and post-failure state of the slope (considering a bulking factor of 15%, i.e., volume expansion during collapse; cf. Jaboyedoff et al [64]) was established in its 3D geomodel. Here, a 2D section was extracted from the latter and used as input profile in UDEC.…”

How 3d volcanic stratigraphy constrains headscarp collapse scenarios: the Samperre Cliff case study (Martinique Island, Lesser Antilles)

“…Both can be determined from the surface envelope separating the stable and unstable materials, and corresponding to potential rupture surfaces. This envelope can be deduced from the extent of the landslide on the topography and relative simple geometric considerations, provided the subsurface is homogeneous (Jaboyedoff et al, 2019(Jaboyedoff et al, , 2020. The determination of the landslide extent is a problem by itself: it can be inferred, for instance, from field observations or records of surface displacements (e.g.…”

“…InSAR acquisition for displacement measurements does not yield conclusive results in densely vegetated areas). Besides, in volcanic context, simple geometric considerations linking the rupture surface to the extent of the unstable mass may not be applicable either (Jaboyedoff et al, 2019(Jaboyedoff et al, , 2020: the volcanic formations below the surface are often not homogeneous and can display complex geometries. In these conditions where relatively few data are available but stakes require a quantified hazard assessment, how can we estimate the surface envelope of an unstable mass, from which the unstable volume can be quantified?…”