High-resolution susceptibility mapping of seismically induced landslides on Ischia island: the 2017 earthquake case study

Ischia island represents the westernmost portion of the Phlegraean Volcanic District (Campania Region, Italy) and is characterized by the presence of Mt. Epomeo, a giant centrally located resurgent volcanic horst. This horst is controlled by fault systems and magmatic dynamics able to generate recurrent seismicity. Such seismicity, associated with the presence of volcanic terrains with different degrees of erodibility, makes Ischia highly subjected to several ground instability phenomena such as landslides. This multidisciplinary study aimed to map the seismically induced landslide susceptibility of the island, taking into account the M_d 4.0 earthquake that occurred on August 21, 2017, as a reference seismic event. Eight parameters were isolated as relevant predisposing factors for landslide occurrence and combined, through GIS elaborations, to compute a numerical index (SNAP index) that quantified the seismically induced landslide susceptibility for each 5 × 5 m area. The resulting map, through five classes of susceptibility, highlights that the highest exposed areas are mainly localized along the N–NW flanks of Mt. Epomeo, involving mainly the municipality of Casamicciola Terme. Moreover, the map is discussed considering the spatial distribution of historical and recent seismically induced ground effects, an ERT field survey carried out on significant test sites, and the displacement map obtained by 2015–2022 InSAR data.