Multiple Landslides in an Area Draped in Volcanic Matters: The Dual Impacts of Rains and Earthquakes

The devastating 2018 Hokkaido Eastern Iburi Earthquake, with a moment magnitude (Mw) of 6.7, inflicted significant damage in the eastern part of Hokkaido, Japan, resulting in the tragic loss of 41 lives, with landslides accounting for 36 fatalities. The mountainous epicentral regions experienced a high number of landslides, primarily induced by the movement of tephra strati originating from eruptions associated with Shikotsu Caldera, Mt. Tarumae, and Mt. Eniwa. The combined intensity of the earthquake and the accumulation of rainfall played crucial roles in initiating these landslides. To gain comprehensive insights into the dynamics of this event, we utilized the Multi-Scale Simulator for the Geo-Environment (MSSG) to simulate the spatial and temporal patterns of rainfall from August 6 to September 5, 2018. Our simulation results were effectively validated against observed data from weather stations operated by the Japan Meteorological Agency (JMA) in the epicentral area. Impressively, the simulation accurately captured the intricate variations in rainfall, taking into account the influence of the region's mountainous terrain. Notably, our findings revealed a noteworthy relationship: as the peak ground acceleration (PGA) increases, the required threshold of rainfall for triggering landslides decreases. This study enhances our understanding of the complexities surrounding landslide dynamics in earthquake-prone areas and contributes to improved disaster preparedness and mitigation efforts.