Tsunami risk management for crustal earthquakes and non-seismic sources in Italy

Abstract

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.

The Sensitivity of Tsunami Impact to Earthquake Source Parameters and Manning Friction in High-Resolution Inundation Simulations

“…On the other hand, in regions where the tectonic setting is more complex, the dominant tsunamigenic structures are less well known, and the tsunamigenesis and hazard is consequently subject to much larger uncertainty. Examples of such complex areas include for instance eastern Indonesia and the Philippines (Løvholt et al, 2012b;Horspool et al, 2014), the Caribbean (Parsons and Geist, 2008;Harbitz et al, 2012), and the Mediterranean Sea (Lorito et al, 2008;Selva et al, 2016;Basili et al, 2021;Lorito et al, 2021;Selva et al, 2021). This large source uncertainty poses a challenge for modelling the hazard, with accurate and efficient numerical modelling required for simulating tsunami generation, propagation, and inundation.…”

Source Characteristics and Exacerbated Tsunami Hazard of the 2020 Mw 6.9 Samos Earthquake in Eastern Aegean Sea

“…The 2020 Samos earthquake occurred in a tectonically active region prone to damaging earthquakes (e.g., Armijo et al., 2003; Flérit et al., 2004; Sternai et al., 2014). Located in the back‐arc extension zone of the SE Aegean Sea, the Samos earthquake is likely due to the reactivation of a normal fault with a north‐south tension axis—the main source of previous earthquakes in the area (Hancock, 1987; Selva et al., 2021; Yılmaz et al., 2000; Yilmaz & Karacik, 2001).…”

“…Such progressive slab retreat together with other tectonic activities, such as tearing (Jolivet et al, 2013;Meng et al, 2021;Sternai et al, 2014), may be responsible for the frequent earthquakes and volcano eruptions along the small plate boundaries, for example, the Santorini volcano eruption 3,650 years ago, the 1956 Mw 7.7 Amorgos earthquake, the 2017 Mw 6.6 Bodrum-Kos earthquake, and the 2020 Mw 6.9 Samos earthquake. Both the 2020 Samos and the 2017 Bodrum-Kos earthquakes may be related to upper crustal extension caused by the rollback of the subducting African Plate (Meng et al, 2021;Selva et al, 2021). Additionally, Coulomb stress change on the nearby faults segments induced by past earthquakes, as demonstrated in Bulut et al (2021) and Chousianitis and Konca (2021), and substantial increase on the fault segments, south of Izmir, caused by the 2020 Samos earthquake have brought active faults around Sığacık and Kuşadası Bays closer to rupture (Chousianitis & Konca, 2021).…”

“…Field surveys immediately following the mainshock (Doğan et al., 2021; Kalogeras et al., 2020; Papadimitriou et al., 2020; Triantafyllou et al., 2021) confirmed that the tsunami triggered by the earthquake was the largest event in eastern Mediterranean since the 9 July 1956 tsunami generated by the Mw 7.7 earthquake in Amorgos (Selva et al., 2021). The tsunami wave heights exceeded 3 m at many surveyed locations (Figure 1c) along the near‐field coast in western Turkey (Doğan et al., 2021) and northern Samos Island in Greece (Triantafyllou et al., 2021).…”

The enigmatic 1693 AD tsunami in the eastern Mediterranean Sea: new insights on the triggering mechanisms and propagation dynamics

“…The Mediterranean Sea experienced several tsunami events, as testified by historical records and geological evidence. The geodynamic activity of the Mediterranean basin has determined the occurrences of tsunami that have been related to seismic and non-seismic sources 1 – 3 . The non-seismic or mixed seismic/non-seismic sources have also recently generated significant tsunamis in the Mediterranean, such as that generated by a landslide at Stromboli in 2002 4 – 8 , and that related to the Mw 7.1 earthquake and submarine landslide of the Strait of Messina in 1908 9 – 12 .…”