GNGTS 2019 - Atti del 38° Convegno Nazionale

168 GNGTS 2019 S essione 1.3 defined tectonic structures at Mt. Etna, bordering the northern limit of the sliding eastern flank of the volcano. In this work, we performed a careful analysis of seismicity and focal mechanisms collected during about 1-yr interval encompassing the 2018 eruption (October 2017-February 2019) for the purpose of: i ) characterizing and interpreting the space-time evolution and kinematics of the seismicity; ii ) giving insights into the stress field; iii ) investigating the relationship between the eruption and the dynamic of the southern and eastern flanks of the volcano. Data analysis and results. A total of 3200 seismic events with M L ≥1.1, recorded in just over a year (October 2017-February 2019) by the INGV-OE seismic permanent network deployed in the Mt. Etna area, were used as data source for this study (Gruppo Analisi Dati Sismici, 2019). Specifically, we calculated 3D locations of the events (Fig. 1) and computed 77 fault plane solutions (FPSs) of the most energetic events (M L ≥2.3). The computed FPSs show mainly strike slip faulting (62%) over most of the region during the pre- and post-eruptive periods, normal dip-slip ruptures (29%) during the eruptive period, only a few events (9%) are of reverse faulting type. Interestingly, the P (maximum compression) axes of the focal mechanisms, particularly those related to the pre-eruptive period (white in Fig. 2), are arranged radially with respect to a probable pressurization sector, located to the south of the Central Craters. Following, a standard numerical technique (Gephart and Forsyth, 1984) has been applied to invert the 77selected FPS and determine the principal stress axes (σ 1 , σ 2 , σ 3 ). The results of the present study gave new insights about the dynamic processes affecting the instability of Mt. Etna edifice and provide important information for any hazard evaluation deriving from these processes. In particular, the unrest was heralded few months before the beginning of the eruption, as shown by the distribution of hypocenters, P-axes radially oriented around a probable pressurization sector to the south of the Central Craters and σ 1 W-E oriented. During the eruption the magma intrusion caused significant ground deformation and redistribution of stress on the neighboring faults. After the eruption both the space-time distribution of most energetic earthquakes, following a temporal anti-clock wise rotation, and a σ 1 trending NE-SW shed light on the dynamic processes affecting the instability of Mt. Etna volcano. In this perspective any flank eruption could temporarily enhance the sliding process of both the southern and eastern flanks of the volcano. References Bonforte A., Guglielmino F. and Puglisi G.; 2019: Large dyke intrusion and small eruption: The December 24, 2018 Mt. Etna eruption imaged by Sentinel-1 data . Terra Nova, 1-8, https://doi 10.1111/ter.12403. Fig. 2 - Horizontal projections of P-axes before (white lines), during (red lines) and after (blue lines) the eruption (see text for details); yellow dashed lines show the location of the modelled sources by Bonforte et al. (2019).