## 3 Study Area and Historical Events  
On 28 December 2020, the Tyrrhenian coastline of the Campania region (Figure 1) was struck by a severe sea storm, due to a deep Mediterranean low and related cold front, moving from NW to SE. Particularly, the Gulf of Naples was heavily involved during this sea storm. The recorded wind gusts caused widespread damages to coastal infrastructures, especially because of the action of associated huge sea waves. The Gulf of Naples represents a marginal basin of the south-eastern sector of the Tyrrhenian Sea (Figure 1c). It is characterized by a complex bathymetry, including two deep canyons, and submerged volcanic structures [18]. The southern limit of the Bay is formed by the Sarno River plain and the Sorrento peninsula, represented by the carbonate reliefs of the Lattari Mountains (Figure 1c). The entire coastal area, from Pozzuoli to Naples, Pompei and Sorrento is heavily urbanized and inhabited by ca. 1.5 million of people that cause an intense anthropic pressure to coastal and marine environments [36; 37]. Despite this high anthropic impact, the coastal part of the Gulf of Naples is characterized by the occurrence of habitats with high natural value [38] and numerous coastal archaeological sites [39; 40]. In this sector, the former beaches and natural environments have been lost due to urbanization and the shorelines are stabilized with revetments and seawalls. The waterfront construction was necessary to protect local houses and the several economic and touristic activities along this coastal zone. The morphology of Naples coastal sector is mainly characterized by volcanic landforms with the Campi Flegrei caldera hills to the north-west and the Somma-Vesuvius volcanic complex to the east, minor coastal plains associated with fluvial processes (e.g., the Sebeto plain), and erosive traces of wave action (cliffs, erosion terraces), resulting in alternating small bays and cliffed promontories [40]. Depositional sequences of volcaniclastic deposits, reworked by alluvial and/or colluvial processes, are present in the coastal plain of Chiaia [41]. This area is characterized by an overall subsidence in the last 4000 years with a prevailing prograding/aggrading trend due to the sedimentary input coming from the hillslopes and significant anthropic pressure [40; 41]. In the near high rocky coast sector, the Neapolitan Yellow Tuff (NYT) unit crops out along the paleo cliffs of the Pizzofalcone promontory and Castel dell'Ovo islet (Figure 3a). The study site is located along the Chiaiaia coastal segment of the Naples seafront between Castel dell'Ovo and Mergellina, particularly at Via Partenope, the area most intensely hit by the storm (Figure 1d). The dominant waves mainly come from the SW sector with fetches less than 400 nautical miles for the Gulf of Naples. The medium wave height generally ranges between 0.9 and 2.2 m, although heights of up to 4.7 m have been recorded, especially during the winter. These values may double with a critical wave height of 7.4-8.4 m if we consider the recording data in a period of 50 years for the widest fetch [42]. Extreme waves characteristics evaluated for Via Caracciolo and Via Partenope sectors and for T = 100 years (T = return period) present a significant wave height H\({}_{8}\) =2.55-2.91 m for the wave exposure angle 165\({}^{\circ}\)-225\({}^{\circ}\)N [42]. Concerning storm surge processes triggered by extreme swells, local authorities (e.g., Autorita di Bacino Nord Occidentale della Campania) [43] evaluated H\({}_{8100}\) = 2.91 m and the \"Run up\" R\({}_{100}\)= 3.95 m a.s.l. over coastal infrastructures for T = 100 years. The local marine setting, where waves propagate before affecting the seawall of Via Partenope, is characterized by an articulated seafloor morphology and by the occurrence of Castel dell'Ovo islet. In front of \"Castel dell'Ovo\", the water depth is greater than \(-10\) m up at ca. 150 m off the tuff cliff, and this depth almost reaches the base of the Castel dell'Ovo western basin (Figure 3a).