GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.1 GNGTS 2023 Here, two types of potential tsunami sources have been identified: on one side, five possible earthquake scenarios have been defined, based on the seismogenic structures known in the area, the historical and instrumental seismic data, and the general geodynamic model defined within the project. On the other side, geomorphological considerations and geophysical data analysis contributed to the individuation of three underwater landslide scenarios, located respectively in the study area’s northern, central and southern part. The tsunami simulation codes provide outputs that can be used to assess the impact of the flooding on coastal structures, allowing to estimate casualties and damages related to the tsunami scenarios. This latter task has been accomplished by the engineering component of the “H&RA Lacinia project” (ReLUIS, the Italian Network of the University Laboratories of Seismic Engineering). The scenarios deriving from the seismogenic faults with an inferred magnitude ranging from 6.0 to 6.9 Mw and located offshore Crotone provide the tsunami initial condition in terms of coseismic vertical displacement of the seafloor and the coast. In addition, the related seismic shaking may also contribute to landslide destabilization: such a trigger is parametrized in the model with the maximum peak ground acceleration affecting the landslide area. Landslide scenarios are placed in relatively deep water (from 400 to 1000 m sea depth), with volumes of less than 0.5 km 3 : for two of them, a slump behavior is prescribed (low run-out and deformation); for the remaining one a debris-flow-like motion has been defined (long run-out and high deformability). The application of the numerical routines described above produces tsunami propagation in the computational domain and an assessment of the wave impact on the coast. In this case study, it is found that no catastrophic waves are hitting the coast: in one of the landslide scenarios, the maximum water height can reach more than 3 m, localized over a short coastal stretch, while only two out of five earthquake scenarios are able to produce local maxima between 1.5 and 2 m. Coastal flooding is generally limited to the first inland cells, since the maximum waves hit the steepest coastline, whereas the flat coast (north of Crotone harbor) is affected by lower water elevations. Two features in the area may deserve further analysis: the first is the Crotone harbor, where the two sub-basins can give rise to resonance phenomena that can considerably enhance the effects of the incoming wave, causing possible damage to boats and facilities; the other is the mouth of water streams, especially the Neto river, about 10 km north of Crotone, and the Esaro river, just at the northern end of the Crotone harbor, in correspondence of which underwater morphology may cause tsunami energy focusing, and the presence of the water streams themselves fosters the tsunami inland penetration. References Gallotti G., Zaniboni F., Pagnoni G., Romagnoli C., Gamberi F., Marani M., Tinti S.; 2021. Tsunamis from prospected mass failure on the Marsili submarine volcano flanks and hints for tsunami hazard evaluation . Bulletin of Volcanology (2021) 83: 2. https://doi.org/10.1007/s00445-020-01425-0 .