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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. [ABSTRACT FROM AUTHOR]

Magmatic intrusions, eruptions and flank collapses are frequent processes of volcano dynamics, inter-connected at different space and time scales. The December 2018 recrudescent episode at Mt. Etna is an exemplary case where a sudden intrusive event culminated with a short eruption, intense seismicity and a shallow large strike-slip earthquake at the edge of the eastern sliding flank. Here, we show that high resolution velocity models and transient changes of VP and VP/VS resolve the magma intrusion through a dyke and local stress increase at the base of the unstable flank, inducing the collapse. Episodic brittle faulting occurs at the edge of the sliding sector, locally contributed by high fluid pressure. The feedback between magma ascent, stress changes and flank collapse is driving the volcano dynamics, with processes ranging from long term to transient episodes. [ABSTRACT FROM AUTHOR]

The mechanism of seismic attenuation for shear waves was studied through the separate measure of the intrinsic dissipation and scattering coefficients. A modified version of the Multiple Lapse Time Window Analysis (MLTWA) was applied to about 5000 local earthquakes with magnitude 1.5 ≤ Ml ≤ 4.8 occurred in the period 2006–2017 in both the tectonic (Peloritani Mountains and Hyblean Plateau) and volcanic (Aeolian Islands and Mt Etna) areas of eastern Sicily. Observed data, processed via direct Fourier Transform instead of the filtering and averaging procedures utilized in the ordinary MLTWA technique, were fit to the correspondent Paasschens solution of the Energy Transport model in 3D. Model parameters B 0, the seismic albedo, and Le , the extinction length, in turn associated with the intrinsic (Qi) and scattering (Qs) quality factors for S waves, are thus obtained from the fit in the frequency bands centred at 1.5, 3, 6 and 12 Hz. Finally, the corrections to these estimates in case of an opaque layer (the crust) overlying a uniform and transparent mantle, were applied in order to obtain more realistic estimates of the seismic attenuation in the areas investigated. Obtained results are first interpreted in terms of the characteristics of each domain and then compared by the same point of view with a huge set of measurements of the same parameters carried out in other tectonic and volcanic domains through the world. Results show how the rock heterogeneity characterizes the tectonic domain and determines the value of total attenuation coefficient, which, on the other hand, is a crucial parameter in the estimation of the seismic hazard. [ABSTRACT FROM AUTHOR]

In this study, we derived the first 3-D P-wave seismic attenuation images (QP) as well as new 3-D VP and VP/VS models for the crust in southeastern Sicily. We used a large data set of local seismic events occurring in the time span 1994-2013. The results of this tomographic study have important implications on the seismic behaviour of the region. Based on velocity and attenuation images, we identified distinct volumes characterized by different fluid content, which correlate well with seismicity distribution. Moreover, the obtained velocity and attenuation tomographies help us to provide a more complete picture of the crustal structure of the area. High VP, high QP and high VP/VS values have been obtained in the crustal basement, below a depth of 8 km, and may be interpreted as due to the presence of serpentinized peridotites. Accordingly, the new model for the degree of serpentinization, retrieved from VP values, shows that the basement has an average serpentinization value of 96 ± 3 vol.% at 8 km, decreasing to 44 ± 5 vol.% at about 18-20 km. Our joint interpretation of geophysical and petrophysical evidence suggests that the nature and composition of the Hyblean upper lithosphere may differ from accepted and longestablished geological models, which consider this lithospheric block a continuation of the Africa continental plate. [ABSTRACT FROM AUTHOR]

Several seismic tomographic studies have been carried out to outline the intricate interplay between tectonics and magma uprising at Etna volcano. Most of these studies assume a seismically isotropic crust. Here we employ a novel methodology that accounts for the anisotropic structure of the crust. Anisotropy patterns are consistent with the Etna structural trends, unveiling the depth extent of fault segments. A high‐velocity volume, deepening toward the northwest, identifies the subducting foreland units that appear to confine a low‐velocity anomaly, interpreted as the expression of magmatic fluids within the crust. A discontinuity, likely tectonic in origin, affects the subducting units and allows magma transfer from depth to the surface. This structural configuration may explain the presence of such a very active basaltic strato‐volcano within an atypical collisional geodynamic context. Plain Language Summary: [In our study, we investigate the complex relationship between tectonics and magma ascent at Etna volcano. Unlike previous research, we consider the anisotropic nature of the crust, meaning its properties vary depending on direction. Using our innovative methodology, we have uncovered patterns aligned with Etna fault segments, revealing their depth and distribution. We have identified the presence of magma fluids within the crust and potential pathways for its uprising. Our results provides an explanation for the emplacement of the very active Etna basaltic volcano within an unusual collisional geodynamic setting.] Key Points: This study conducts the first P‐wave anisotropic tomography using local earthquakes recorded in the area of Etna volcanoThe tomography resolves three‐dimensional (3D) isotropic and anisotropic structures beneath the volcanoAnisotropy reveals geological features providing valuable insights into the interplay between tectonic deformation and volcanic activity [ABSTRACT FROM AUTHOR]

We present a new three‐dimensional (3D) image of attenuation beneath Mt. Etna volcano based on the coda normalization method. Mt. Etna is an ideal natural laboratory for the application of new or unconventional tomography techniques owing to high levels of seismicity spanning a wide range of epicentral distances and depths. We retrieved seismic waveforms from the database generated in the 2014 TOMO‐ETNA seismic experiment and performed a joint interpretation of tomographic and geophysical inversion models to better constrain interpretations of the volcanic structure. We compared the attenuation tomography results with seismic inversion models (two P wave seismic models and a 3D coda wave seismic attenuation model) and the literature to highlight and interpret structural elements and their impact on the volcano dynamics. We created a new image of the inner structure of Mt. Etna that will help to constrain present and future volcanic behavior. In particular, we focused on magma storage below the summit area and identified a large high‐attenuation volume that is characterized by physical properties compatible with the presence of magma and other fluids. The existence of such a large volume of magma in the shallow crust below Mt. Etna has implications for the eruptive potential of the volcano. Plain Language Summary: Mount Etna, Italy, is one of the world's most active volcanoes and presents an almost constant state of activity. To correctly interpretate potential volcanic hazards, there is a need to better understand the complex inner structure of the volcano. To this end, Mt. Etna is an ideal natural laboratory for the application of new or unconventional tomography techniques. We analyzed seismic attenuation, which measures the loss of energy of the seismic waves, to obtain a three‐dimensional attenuation model of Mt. Etna. We compared our attenuation tomography results with other geophysical data in order to interpret key structural elements and their impact on volcano dynamics. We identified a large volume below the summit area that is compatible with the presence of magma and other volcanic fluids, highlighting the continued eruptive potential of the volcano. Key Points: Three‐dimensional attenuation images over the first 10 km below Etna volcano obtained by coda normalization methodAttenuation images show partial melt body below Etna volcanoJoint interpretation of different models confirm the high heterogeneity below Etna volcano [ABSTRACT FROM AUTHOR]