GNGTS 2019 - Atti del 38° Convegno Nazionale

200 GNGTS 2019 S essione 1.3 Indeed, recent studies have highlighted that SSEs occur close to zones of frictional transition from velocity strengthening to velocity weakening (e.g. Rubin, 2011; Segall et al. , 2010) therefore providing useful information on fault zone properties. The rapid increase of continuous GPS (CGPS) stations has allowed to detect a large number of SSEs worldwide. The large majority of SSEs has been observed at convergent plate boundaries and, in some cases, they are associated with seismic tremor (e.g. Dragert et al. , 2004). SSEs have been detected also at Mt. Etna from the continuous GPS stations covering the eastern flank of the volcano (see Palano 2016 and references therein for additional details). Here, we improved results reported in Palano (2016) by extending in time the SSE catalog and therefore providing additional constraints on their causative mechanism. Mt. Etna background. Mt. Etna is a basaltic Quaternary volcano located on the east coast of Sicily (South Italy) at the front of the Apennine-Maghrebian chain (AMC). The volcano developed over the last 500 ka over metamorphic and sedimentary rocks (belonging to the AMC) on its western and northern slopes and over Quaternary plastic clays (accumulated along the Gela-Catania Foredeep at the front of AMC; Branca and Ferrara, 2013). The different geomechanical properties of outcropping rocks coupled with the inhomogeneous long-term updoming of the volcano have produced a major morphological difference between the eastern flank (dominated by the presence of a 17 km-wide horseshoe-shaped depression) and the other flanks (formed by paleovalleys), resulting into a complex basement topography (Branca and Ferrara, 2013). Such a complex basement topography drives a large-scale seaward motion of the eastern flank of Mt. Etna as clearly documented since the early 1980s (e.g. Borgia et al. , 1992). At the surface, the unstable sector is defined by a 25 km-wide horseshoe-shaped depression which, encompassing the sedimentary one, is bounded by the “NE Rift - Pernicana fault” and by the “South Rift - Mascalucia - Tremestieri - San Gregorio - Acitrezza fault system”, on its NW and SW margin respectively. In addition, the presence of compressional structures (e.g. folds) at the toe of the continental margin as well as a prominent ESE lineament (hereinafter ESEL), with prevailing right-lateral transpressive kinematics, located northward of Catania Canyon, has recently been observed on the Etnean offshore (Gross et al. , 2015). Furthermore, active tectonics also occurs over the unstable sector and is distributed on a number of shallow faults such as the Timpe, the Santa Tecla, and the Santa Venerina faults. The Timpe faults consist of a 20 km long and 5 km wide belt of mainly NNW to N extensional structures with well-developedmorphological scarps; the Santa Tecla and Santa Venerina faults consist of two near parallel faults, which have a NW-SE trend and are characterized by right- lateral slips coupled with minor normal components (Fig. 1). Fig. 1 - Simplified tectonic map of Mt. Etna and its eastern off-shore. Sites managed by INGV and ISPRA are reported as black and blue dots, respectively. The dark-gray line indicates the coastal line. Abbreviations are as follows: PF, Pernicana fault; TFS, Timpe Fault system; SVF, Santa Venerina fault; STF, Santa Tecla fault; AF, Acicatena fault; TF, Trecastagni fault; MTF, Mascalucia-Tremestieri fault; ESEL, ESE lineament.