A multi-hazard perspective in the analysis of earthquake-induced landslides: the case of Ischia Island

Italy is one of the countries most exposed to natural risks. The entire territory is characterized by intrinsic fragility derived from its unique morphologic, geologic, seismic, and hydrogeological features. This fragility is further exacerbated by actions resulting from relentless climate change, influencing both the intensity and frequency of meteoric hazards, as well as anthropogenic pressure associated with the rapid and unregulated growth of urban environments. The transition from conventional single-hazard evaluation to multi-hazard approaches is of outstanding importance to address this complexity and account for the possible combination of predisposing factors, preparatory phenomena, and triggering events that can induce cascading effects. In this study, a multi-hazard approach was adopted to evaluate earthquake-induced landslides on the volcanic island of Ischia. A careful analysis of the peculiar predisposing factors was carried out, highlighting the key role of the volcanic origin of the island in characterizing its hazard. The combination of these predisposing factors and some specific preparatory factors results in a variable but still high susceptibility of the island territory to triggering events such as extreme rainfall and strong-motion earthquakes. This susceptibility was evidenced by the results of a probabilistic assessment of seismically induced slope displacements carried out with reference to the northwestern part of Ischia Island, which was recently hit by an earthquake. Specific demand hazard curves, expressed in terms of the annual rate of exceedance of permanent earthquake-induced slope displacements, were produced, considering the influence of the seasonal variability of the pore pressure regime. These curves can provide valuable support in detecting action priorities in vulnerability reduction and effectively addressing mitigation strategies.