GNGTS 2019 - Atti del 38° Convegno Nazionale

32 GNGTS 2019 S essione 1.1 Ground breaks broadly coincide with faults previously included in the database of capable faults (ITHACA database, http://sgi2.isprambiente.it/ithacaweb/viewer/ ), but in some places the newly formed breaks allowed to better define the fault trace. Rupture is arranged in several segments, trending N-S to NW-SE. Slip vectors show a dominant dip-slip component, with secondary dextral strike slip motion. We analyze the across-strike width along the entire rupture: the width can be either very narrow, with ruptures concentrated on a single strand, or distributed in up to 100-m-wide zones, including several en-echelon segments. Maximum vertical displacements reach 30 cm and right-lateral displacement 15 cm. We estimate the maximum intensity as IX on the ESI-07 scale (Michetti et al. , 2007). The comparison with topographic and subsurface factors allowed to evaluate the role of gravity and geological setting in driving shallow deformation. We found an influence of topography (elevation and slope) in the northernmost sector, whereas the overall pattern of deformation is controlled by slope and aspect of the top of basement lying below the volcanic deposits. Discussion and comparison with previous events. Typically, surface ruptures and environmental effects accompanying strong (Mw 4 to 5) earthquakes at Mt. Etna are clearly confined in a narrow belt around the causative fault. The 2018 earthquake is no exception, as testified by our original results and by macroseismic surveys (Quest WG, 2019). We compare the macroseismic field of the 2018 event with previous earthquakes that hit the Etnean region, in particular the 2002 Santa Venerina earthquake. In both cases, the very shallow focal depth favors a strong attenuation of intensity with distance. We argue that in such settings, surface faulting and other environmental effects can tightly define the trace of the causative fault and thus provide complementary information with respect to traditional macroseismic investigations: an integrated approach can foster a more comprehensive understanding of the extremely active volcano-tectonic settings of the Etnean region, and of similar areas affected by very shallow-focus earthquake ruptures, such as the Casamicciola sector at Ischia volcano (Nappi et al. , 2018). References Baratta M. (1894). Intorno ai recenti fenomeni endogeni avvenuti nella regione etnea agosto 1894. Boll. Soc. Geografica Italiana, Ottobre 1894. De Novellis, V., Atzori, S., De Luca, C., Manzo, M., Valerio, E., Bonano, M., et al. (2019), DInSAR analysis and analytical modeling of Mount Etna displacements: The December 2018 volcano-tectonic crisis. Geophysical Research Letters, 46, 5817–5827. https:// doi.org/10.1029/2019GL082467. Fig. 3 - Coseismic ground rupture (throw ca. 20 cm) in a field west of Fleri (via Nava), not far from the northwestern tip of the 2018 rupture.