Tuvè, Tiziana

Seismic wave attenuation is a key feature of seismic wave propagation that provides constraints on the composition and physical state of the medium within the Earth. We separated intrinsic and scattering attenuation coefficients for the shallow crust and lower crust/upper mantle in the Mt. Etna area. For this purpose, the Multiple Lapse Time Window Analysis (MLTWA) was applied to two groups of earthquakes, well separated in depth. We also studied the spatial variation of the attenuation parameters by dividing the study area into four sectors around Etna. The results show an effective homogeneity of the propagation characteristics inside Etna and, in particular, some lateral variations and minor variations with depth. We observe that structural discontinuities and lithology control scattering losses at all frequencies, with higher scattering in the shallow crust. The intrinsic absorption shows no sensitivity to the presence of these main geological structures and is quite uniform for different depths. Furthermore, compared to the northern sector of the volcano, the southern one shows stronger scattering attenuation at low frequencies. This pattern correlates well with the high seismic activity along most of Etna’s active tectonic structures and ascending magmatic fluids that characterize this sector of the volcano. Although we only discuss the differences in the ‘‘average’’ scattering and inelastic properties of the investigated volumes, the results of this study are very informative about the characteristics of each region. Moreover, they suggest that a future study is necessary, providing a more detailed picture of the spatial distribution of seismic attenuation in the study area, through a 3D inversion of the attenuation parameters estimated along the single source-receiver paths.

This work presents the first results of the PANACEA project regarding the assessment of different volcano-related hazards at Mt. Etna (lava and pyroclastic flows, tephra fallout and earthquakes) by exploiting data deriving from the volcano’s history with accurate physical–mathematical models. Volcano-related hazards are distributed differently on Etna—from the deserted summit area down to the densely populated flanks—but must be considered together for long-term territorial planning.

Descrizione degli effetti di invertibilità e risentimento del terremoto del 18/05/2023, ML 3.2

In questo lavoro viene descritta la sismicità, collegata agli eventi vulcanotettonici, registrata dalle stazioni della Rete Sismica Permanente dell’INGV – Osservatorio Etneo (OE) nell’area vulcanica del Monte Etna dall’1 gennaio al 31 dicembre 2020. Nel periodo di riferimento la rete sismica gestita dall’INGVOE risulta costituita da un centinaio di stazioni i cui segnali sismici sono trasmessi in tempo reale al CUAD (Centro Unificato Acquisizione Dati) di Catania dove vengono acquisiti e trasferiti in continuo alla Sala Operativa dell’Osservatorio Etneo. Nel corso del 2020 sono stati registrati 3604 terremoti, di cui 2287 localizzati dal Gruppo di Lavoro Analisi Dati Sismici dell’OE (GLAOE), secondo gli standard definiti per la compilazione del catalogo strumentale nell’ambito delle attività di monitoraggio previste all’interno dell’Accordo Quadro INGV – Dipartimento Protezione Civile (DPC) 20122021 (Allegato A). Le profondità focali degli eventi analizzati sono comprese tra 1.6 e 35 km circa, mentre la magnitudo locale (ML) risulta compresa tra 0.2 e 3.7; la magnitudo di completezza (MC) del risultante catalogo è pari a 1.2 (± 0.01), valore quindi del tutto confrontabile con quello stimato per il 2017 e il 2019, ma superiore di 0.1 unità rispetto a quello stimato per il 2018. Sono 15 gli eventi con ML ≥ 3.0 registrati nel corso del 2020, la maggior parte dei quali appartenenti alle 11 sequenze sismiche che sono state individuate per lo stesso anno. La sequenza sismica più importante sia per numero di eventi (21) sia per energia rilasciata (valore massimo ML = 3.7), è stata registrata il 31 dicembre a partire dalle 19:59 (UTC) e ha interessato il medio versante meridionale dell’edificio vulcanico, poco a nord del centro abitato di Ragalna.

DESCRIZIONE DEGLI EFFETTI DI AVVERTIBILITA' E RISENTIMENTO DEL TERREMOTO DELL'08122022, ML 4.1

Descrizione degli effetti di avvertibilità e risentimento del terremoto del 04/12/2022, ML 4.6

Three dimensional attenuation images of Mt Etna volcano obtained by the analysis of Q-coda from local volcano-tectonic earthquakes are presented in this work. Seismic sources are confined inside the Etna structure with a maximum focal depth of 35 km below the sea level. The space distribution of the attenuation values was calculated by using 3-D weighting functions derived by the sensitivity kernels of Pacheco & Snieders and approximated by a polynomial interpolation, represented in the maps by using a backprojection method. Data were analyzed in four bands with central frequency placed at 1.5, 3, 6 and 12 Hz, respectively. We observed a frequency dependence of Q-coda with values that range from 55 at 1.5 Hz to 218 at 12 Hz. Q-coda space distribution in the Etna area shows almost uniformity in the average attenuation in the first 35 km below the surface. The images were derived with a resolution of 5 km. We observe as one of our main conclusions that Q-coda attenuation space anomalies are correlated with the areas of highest structural heterogeneities and are distributed along the well-known tectonic structures which characterize the crust in Mt Etna region. Previous and numerous velocity and attenuation images describing the structure of Mt Etna support our main conclusion: high Q-coda volumes almost coincide with the zones marked by high velocity and relative low total attenuation for direct waves.

In recent years, new approaches for developing earthquake rupture forecasts (ERFs) have been proposed to be used as an input for probabilistic seismic hazard assessment (PSHA). Zone- based approaches with seismicity rates derived from earthquake catalogs are commonly used in many countries as the standard for national seismic hazard models. In Italy, a single zone- based ERF is currently the basis for the official seismic hazard model. In this contribution, we present eleven new ERFs, including five zone-based, two smoothed seismicity-based, two fault- based, and two geodetic-based, used for a new PSH model in Italy. The ERFs were tested against observed seismicity and were subject to an elicitation procedure by a panel of PSHA experts to verify the scientific robustness and consistency of the forecasts with respect to the observations. Tests and elicitation were finalized to weight the ERFs. The results show a good response to the new inputs to observed seismicity in the last few centuries. The entire approach was a first attempt to build a community-based set of ERFs for an Italian PSHA model. The project involved a large number of seismic hazard practitioners, with their knowledge and experience, and the development of different models to capture and explore a large range of epistemic uncertainties in building ERFs, and represents an important step forward for the new national seismic hazard model.

Sono analizzati ed elaborati i dati dei rilievi macrosismici relativi ai terremoti verificatisi in Sicilia nel periodo 2014­2018. Si tratta di eventi che hanno provocato effetti macrosismici di rilievo e/o danneggiamento per la maggior parte localizzati nell’area etnea, cui si aggiungono alcuni terremoti di magnitudo moderata verificatisi nei settori ibleo e eoliano. I dati sono stati raccolti e elaborati secondo il protocollo del gruppo operativo QUEST (QUick Earthquake Survey Team) dell’INGV, e successivamente parametrizzati secondo gli standard adottati per la compilazione del catalogo CPTI e della banca dati macrosismica DBMI.

3D earthquake locations, focal mechanisms and stress tensor distribution in a 16- month interval covering the 2018 Mt. Etna flank eruption, enabled us to investigate the relationship between magma intrusion and structural response of the volcano and shed light on the dynamic processes affecting the instability of Mt. Etna. The magma intrusion likely caused tension in the flanks of the volcano, leading to significant ground deformation and redistribution of stress on the neighbouring faults at the edge of Mt. Etna's unstable sector, encouraging the ESE sliding of the eastern flank of the volcano. Accordingly, FPSs of the post-eruptive events show strike slip faulting mechanisms, under a stress regime characterized by a maximum compressive σ1, NE-SW oriented. In this perspective, any flank eruption could temporarily enhance the sliding process of both the southern and eastern flanks of the volcano.