Three-dimensional seismic slope stability assessment with the application of Scoops3D and GIS: a case study in Atsuma, Hokkaido

Background The 2018 Hokkaido Eastern Iburi earthquake (Mj 6.7, Mw 6.6), occurred on the 6th of September 2018 and triggered thousands of landslides in pyroclastic fall deposits. The triggered landslides caused destructive damages to the structures and resulted in serious causalities. Hundreds of earthquakes persisted after the mainshock and the Iburi region is of high possibility to suffer major earthquakes in the future. An effective method to assess the seismic slope stability is of great importance for the disaster prevention and mitigation in the Iburi region. Results Based on the isopachs of different pyroclastic fall deposits mantled in the study area, GIS was employed to process the input soil layers and construct the 3D domain. By applying different horizontal pseudo-acceleration coefficients in the Scoops3D program, the factor-of-safety maps of eight cases were obtained. After validating by the coseismic landslide inventory, the performance of the computed results was evaluated. Conclusions A horizontal pseudo-acceleration coefficient between 1/2 and 2/3 of PHGA is suitable for seismic slope stability assessment in pyroclastic fall deposits. The catastrophic Tomisato landslide and Yoshinoya landslide were correctly predicted. Scoops3D proves to be an effective and efficient method for guiding disaster mitigation and management.