GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.2 GNGTS 2023 A seismological analysis of the November 26, 2022, Casamicciola Terme (Ischia Island) debris flow N.A. Pino 1 , S. Carlino 1 , S. Danesi 2 1 INGV Sezione di Napoli, IT 2 INGV Sezione di Bologna, IT Landslides, debris flow, and mud flow are frequent occurrences, in particular in volcanic environments. At Ischia Island, these events are often disastrous and represent a dramatic, constant threat and a major source of risk. The last one happened on November 26, 2022, and caused the death of 12 persons and considerable damage, when a massive wave of mud – coming from Mt. Epomeo and triggered by an exceptional rainfall – inundated the area of Casamicciola, in the northern sector of the island. There are clues indicating that the event was composed by several, successive surges. However, no specific monitoring system designed for this kind of process exists on the island, and very scarce direct witness accounts are available, also because the landslide occurred very early in the morning (about 05:00 AM, local time), thus, a reconstruction of the sequence of events is not easy. Nevertheless, a full comprehension of the way the debris flow developed can be very useful to help in mitigating the effects of likely future occurrences and in setting up a monitoring system, possibly oriented to early warning. Although developed for recording transient seismic waves generated by earthquakes in tectonic as well as in volcanic areas, seismic stations can provide important, quantitative, information also on any event, natural and anthropic, somehow able to generate either high frequency or extremely slow ground oscillations. Moreover, the recording obtained at some modern seismometers can even be processed to determine static ground displacement and ground tilt. For instance, landslide- (e.g., Pino et al., 2004) and tsunami-generated seismic waves (e.g., Pino and Boschi, 2009) can be analysed to provide information on the source and – in particular for modern broadband instruments – very slow post-seismic crustal relaxation (Pino, 2012) can be reconstructed by processing seismic recordings, allowing the analysis of crust rheological parameters. Based on the above considerations and in the light of published observations and results of experiments on the seismic signals of controlled landslides and debris flow, we analyse the recordings of the INGV seismic stations located on Ischia Island (Fig. 1), attempting to deduce