## 2 Geological Background  
### The Tyrrhenian Sea  
The Tyrrhenian Sea (Western Mediterranean; Figure 1A), is a small extensional back-arc basin formed due to the subduction of the Ionian lithosphere beneath the Calabrian Arc in the broader context of the Africa-Eurasia convergence [25], which led to widespread volcanism that is characterized by high heat flow values (>150 mW m\({}^{-2}\)) [26], thin crust (averaging 7 km) and lithosphere (averaging 30 km) [27; 28], a youthful oceanic crust [29; 30] and the emplacement of several seamounts with huge, and partially still active, hydrothermal events [31].  
The initiation of the Tyrrhenian Sea's opening occurred approximately 11 million years ago, marked by an extension oriented from east to west. During this phase, extensive extension prevailed in the northern region, while rift activity dominated the western portion of the southern region [32], leading to the creation of oceanic crust in the Southern Tyrrhenian area and the development of the Vavilov ocean-like basin (Figure 1A). Subsequently, a transition to extension directed from east to east-southeast occurred concurrently with frontal accretion in the Southern Apennines thrust belt. This shift primarily impacted the Southeastern Tyrrhenian Sea and resulted in the formation of the Marsili ocean-like basin (1.8 to 0.2 million years ago) [30]. This huge extension led to widespread volcanism across the Tyrrhenian Sea and its adjacent coasts [33].  
The Aeolian Archipelago consists of seven islands (Stromboli, Panarea, Vulcano, Liplari, Salina, Alicudi, and Filicudi) and several seamounts (Figure 2) with a strong volcano-structural control [34; 35] and arranged in a ring-like formation, located at the southern edge of the Tyrrhenian Sea [36]. This area lies just a few tens of kilometers from the northern coast of Sicily and the southwestern coast of Calabria. The archipelago's location, structure, and geochemical makeup, along with the region's deep seismic activity, suggest that the volcanic activity in the Aeolian Archipelago is due to a subduction zone [37; 38]. Volcanic activity in the Aeolian island arc started around 1 million years ago on continental crust (Figure 1A).  
The Palinuro Volcanic Chain (PVC), approximately 90-100 km long, consists of 15 volcanoes aligned in an east-west direction, with heights up to 3200 m above the surrounding seafloor [39]. The presence of calderas (to the west), fracture systems, and canyons provides evidence of instability [40; 41]. Additionally, the PVC is influenced by hydrothermal activity that can weaken volcanic rocks [42; 43]. Lower seismicity, possibly related to hydrothermal activity, has also been detected [44]. Different styles of volcanism are clearly visible, grouped into three sectors that differ in morphologic characteristics [40], including  
Figure 2: Map of the seamounts of the Tyrrhenian Sea.  
cones, calderas, and structurally controlled volcanic features [45], and located at depths ranging \(-\)84/\(-\)2600 m below sea level.  
Marsili Seamount MS refers to the spreading ridge of the Marsili back-arc basin [46]. The most recent activity of MS, estimated to have occurred around 2-3 thousand years ago, was linked to a vent in the central-northern part of the volcano responsible for the last explosive eruption [47, 48]. Today, the volcano is active, with shallow seismic activity and hydrothermal emissions [49]. Its actual morphology represents the surface expression of different ridge segments controlled by the larger-scale spreading processes and by the local occurrence of an active hydrothermal field [50, 51].