Use of Probabilistically Generated Scenario Earthquakes in Landslide Hazard Zonation: A Semi-qualitative Approach

Abstract

Seismically induced landslide hazard zonation is a difficult task owing to the lack of globally recognized statistical or distribution-free methods. This is mainly attributed to the deficiency in seismically induced landslide inventories, which is further ascribed to the rarity of these extreme events. Yet, considering their astounding socio-economic impacts, researchers have been trying to establish frameworks for multi-hazard integration. In this context, an endeavour has been made in this present study to discuss a plausible approach of seismically induced landslide hazard zonation, where probabilistically generated scenario earthquakes are integrated with conventional models of landslide susceptibility zonation. The study presents a case study for a part of the lower Himalayan region, considering the frequency of earthquakes and landslide swarms observed in this area. Due diligence is required in selecting an appropriate earthquake intensity measure (IM) parameter for such multi-hazard integration, and after careful consideration, peak ground acceleration (PGA) characteristic of the scenario earthquakes is used. For the study area, six preparatory landslide causative factors are identified, and the PGA parameter is considered as the landslide triggering factor. The results of multi-hazard integration show that the potential of earthquake-induced landslides is quite real, particularly in the Himalayas. It is observed that there is a paradigm shift of landslide hazard zones from very low to very high under seismic conditions. For a scenario earthquake with a 10% exceedance probability in 50 years, almost 50% of the study area falls under the zone of very high landslide hazard. These observations emphasize that consideration of earthquakes in assessing actual or future landslide hazard levels is a more practical approach, particularly in the seismically active mountainous regions. The chapter presents a simple yet effective framework for integrating earthquake and landslide hazards.