The 2018 Mount Etna Earthquake (Mw 4.9): Depicting a Natural Model of a Composite Fault System From Coseismic Surface Breaks

Abstract

Current volcano-tectonic models of Mount Etna in eastern Sicily, Italy (Figure 1) are mostly based on geometric and kinematic analyses of the ground effects due to active deformation (e.g., coseismic fracturing and creep;

Surface Faulting of the 26 December 2018, Mw5 Earthquake at Mt. Etna Volcano (Italy): Geological Source Model and Implications for the Seismic Potential of the Fiandaca Fault

“…This rotation produces an increase of the normal faulting component southward along strike, as observed also by Romagnoli et al. (2021). In this frame, the slip vectors measured in the field, such as those at the tensional fractures, can be misleading since they are mainly related to outcrop‐scale, local stress field orientation and are not representative of the PDZ kinematics (e.g., Figure 5c).…”

“…In compliance with the Poisson's ratio of basalts (Figure 11c) calculated for the study area (Aloisi et al, 2011), these divergence vectors produce wrench-dominated transtension (key area of Figure 7) and extension-dominated transtension (key areas of Figures 5 and 6) (Figure 11d), where the minimum principal extension axis switches from the horizontal orientation to the vertical one. This rotation produces an increase of the normal faulting component southward along strike, as observed also by Romagnoli et al (2021). In this frame, the slip vectors measured in the field, such as those at the tensional fractures, can be misleading since they are mainly related to outcrop-scale, local stress field orientation and are not representative of the PDZ kinematics (e.g., Figure 5c).…”

“…Such pressure-ridges, when present, are located at the stepover of the en-échelon, left-stepping ruptures. Locally, a kinematic partition of the slip components is present (see also Romagnoli et al, 2021), with tensional open fractures coupled with normal faults generally set at the top of the main fault escarpment, and strike-slip ruptures set at the base (Figure 4c). Some of the tensional fractures at the top of the scarp also accommodate local extension due to bulging.…”

“…With a rupture length of 7.5 km and displacements up to 50 cm in throw and 35 cm in strike (right‐lateral), together with significant extensional components (30–45 cm in heave), the M w 5.0 2018 earthquake was the most significant event in terms of extent and complexity of the surface rupture observed in the Etna region in the past 70 years. The relevance of the phenomenon attracted several research groups who worked simultaneously in the field soon after the earthquake and analyzed the event and its tectonic significance from different perspectives (Monaco et al., 2021; Romagnoli et al., 2021; Tortorici et al., 2021; Tringali et al., 2022). Among these, the EMERGEO Working Group—the emergency INGV team for mapping the geological effects of earthquakes (https://www.ingv.it/emergeo/)—undertook a detailed survey to collect field data and observations before their evidence could be modified or concealed by weathering or man‐made interventions.…”