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Destructive tsunamis are most often generated by large earthquakes occurring at subduction interfaces, but also other "atypical" sources—defined as crustal earthquakes and non-seismic sources altogether—may cause significant tsunami threats. Tsunamis may indeed be generated by different sources, such as earthquakes, submarine or coastal landslides, volcano-related phenomena, and atmospheric perturbations. The consideration of atypical sources is important worldwide, but it is especially prominent in complex tectonic settings such as the Mediterranean, the Caribbean, or the Indonesian archipelago. The recent disasters in Indonesia in 2018, caused by the Palu-Sulawesi magnitude Mw 7.5 crustal earthquake and by the collapse of the Anak-Krakatau volcano, recall the importance of such sources. Dealing with atypical sources represents a scientific, technical, and computational challenge, which depends on the capability of quantifying and managing uncertainty efficiently and of reducing it with accurate physical modelling. Here, we first introduce the general framework in which tsunami threats are treated, and then we review the current status and the expected future development of tsunami hazard quantifications and of the tsunami warning systems in Italy, with a specific focus on the treatment of atypical sources. In Italy, where the memory of historical atypical events like the 1908 Messina earthquake or the relatively recent 2002 Stromboli tsunami is still vivid, specific attention has been indeed dedicated to the progressive development of innovative strategies to deal with such atypical sources. More specifically, we review the (national) hazard analyses and their application for coastal planning, as well as the two operating tsunami warning systems: the national warning system for seismically generated tsunamis (SiAM), whose upstream component—the CAT-INGV—is also a Tsunami Service Provider of the North-eastern Atlantic, the Mediterranean and connected seas Tsunami Warning System (NEAMTWS) coordinated by the Intergovernmental Coordination Group established by the Intergovernmental Oceanographic Commission (IOC) of UNESCO, and the local warning system for tsunamis generated by volcanic slides along the Sciara del Fuoco of Stromboli volcano. Finally, we review the state of knowledge about other potential tsunami sources that may generate significant tsunamis for the Italian coasts, but that are not presently considered in existing tsunami warning systems. This may be considered the first step towards their inclusion in the national tsunami hazard and warning programs. [ABSTRACT FROM AUTHOR]

We investigate the 24–27 December 2018 eruption of Mount Etna occurred from fissures located on the volcano eastern flank and accompanied by a seismic swarm, which was triggered by the magma intrusion and continued for weeks after the end of the eruption. Moreover, this swarm involved some of the shallow volcano‐tectonic structures located on the Mount Etna flanks and culminated on 26 December with the strongest event (ML 4.8), occurred along the Fiandaca Fault. In this work, we analyze seismological data and Sentinel‐1 Differential Interferometric Synthetic Aperture Radar (DInSAR) measurements, the latter inverted through analytical modeling. Our results suggest that a dike source intruded, promoting the opening of the eruptive fissures fed by a shallower dike. Moreover, our findings indicate that the activation of faults in different sectors of the volcano may be considered as a response to accommodate the deformations induced by the magma volumes injection. Key Points: We investigate the ground displacements and the 3D source geometry of the December 2018 Mount Etna (Italy) volcano‐tectonic crisisDInSAR data obtained from SAR data pairs collected by Sentinel‐1 have been inverted through analytical modelingOur results suggest the presence of two volcanic sources: a shallow dike and a deeper one associated with a long‐term seismic swarm [ABSTRACT FROM AUTHOR]

Abstract: The causative source of the first damaging earthquake instrumentally recorded in the Island of Ischia, occurred on 21 August 2017, has been studied through a multiparametric geophysical approach. In order to investigate the source geometry and kinematics we exploit seismological, Global Positioning System, and Sentinel‐1 and COSMO‐SkyMed differential interferometric synthetic aperture radar coseismic measurements. Our results indicate that the retrieved solutions from the geodetic data modeling and the seismological data are plausible; in particular, the best fit solution consists of an E‐W striking, south dipping normal fault, with its center located at a depth of 800 m. Moreover, the retrieved causative fault is consistent with the rheological stratification of the crust in this zone. This study allows us to improve the knowledge of the volcano‐tectonic processes occurring on the Island, which is crucial for a better assessment of the seismic risk in the area. [ABSTRACT FROM AUTHOR]

Over the past few years the assessment of the earthquake potential of large continental faults has increasingly relied on field investigations. State-of-the-art seismic hazard models are progressively complementing the information derived from earthquake cat- alogues with geological observations of active faulting. Using these observations, however, requires full understanding of the relationships between seismogenic slip at depth and surface deformation, such that the evidence indicating the presence of a large, potentially seismogenic fault can be singled out effectively and unambiguously. We used observations and models of the 6 April 2009, Mw 6.3, L'Aquila, normal faulting earthquake to explore the relationships between the activity of a large fault at seismogenic depth and its surface evidence. This very well-documented earthquake is representative of mid-size yet damaging earthquakes that are frequent around the Mediterranean Basin, and is somehow paradigmatic of the nature of the associated geologic evidence along with observational difficulties and ambiguities. Thanks to available high-resolution geologic, geodetic and seismological data aided by analogue modeling, we reconstructed the full geometry of the seismogenic source in relation with surface and sub-surface faults.We find that the earthquake was caused by seismogenic slip in the range 3-10 km depth, and that the slip distribution was strongly controlled by inherited discontinuities. We also contend that faulting was expressed at the surface by pseudo-primary breaks resulting from coseismic crustal bending and by sympathetic slip on secondary faults. Based on our results we propose a scheme for hierarchizing normal faults through which all surface occurrences related to faulting at depth can be interpreted in the frame of a single, mechanically coherent model. Appreciating such complexity is crucial to avoid severe over- or under-estimation of the local seismogenic potential. [ABSTRACT FROM AUTHOR]

We present a marine palaeoseismology analysis of a dense network of very high resolution seismic profiles along the Gondola Fault Zone (GFZ), a right-lateral, E–W-striking, active fault system in the Adriatic foreland. This case-study aims to show how time and space variations in the activity of a dominantly right-lateral fault system can be assessed using the vertical component of slip. The GFZ has been investigated for a length of 50 km. It includes two parallel subvertical fault sets and two main anticlines. The late Middle Pleistocene to Holocene vertical component of displacement along the fault is bell-shaped, suggesting that in the long-term the fault zone acts as a single, kinematically coherent structure. Slip rates are 0–0.18 mm a−1 and vary temporally on individual segments. This variability is consistent with a model in which individual fault segments rupture independently during earthquakes with magnitudes up to 6.4 and 1.3–1.8 ka recurrence intervals. [ABSTRACT FROM AUTHOR]