Location and occurrence of the studied landslide. (a) Locations of the epicenter of the Eastern Iburi earthquake (red cross) and the study area. (b) 3D view of the hills near Atsuma after the earthquake (produced by data from the Geospatial Information Authority of Japan 2018a). (c) Close-up photograph of the studied landslide (taken on 6 September 2018; Geospatial Information Authority of Japan 2018b). (d) Striated mud on the collapsed slope (modified after Kameda et al. 2019). (e) Scarp measuring 2–3 m in height, which contains a stratigraphic sequence of volcanoclastic deposits (modified after Kameda et al. 2019). The slip surface material analyzed in this study was collected where the “clay layer” is in contact with the basement Neogene marine strata.