Shallow Magma Storage Beneath Mt. Etna: Evidence From New Attenuation Tomography and Existing Velocity Models

Abstract

Determining the location and size of potential magma reservoirs is crucial to constrain the size of future eruptions or eruptive frequency. Magma accumulation and melt migration have been the focus of extensive research at Mt. Etna volcano. Recent geophysical imaging of Mt. Etna has shown the growing importance of several geological bodies in explaining the migration of eruptive materials inside the volcano. One such body, known as the High Velocity Body (HVB), is a highly consolidated structure located below the central-southern part of the volcano. The HVB has been observed in several tomography studies (Giampiccolo et al., 2020 and references therein) and is interpreted as a massive accumulation of intrusions within the sedimentary basement. In addition, new structural elements have been identified tomographically to the west and southwest of the main volcanic edifice (e.g., Díaz-Moreno et al., 2018 and references therein). Despite not being widely discussed and interpreted in studies based on travel time tomography, these bodies have been well resolved using other techniques. In addition, recent studies (Alparone et al., 2015;Barberi et al., 2016) have found a strong association between deep seismicity beneath Mt. Etna and these geological objects, indicating the need for further study. Apparent contradictions between older and newer tomographic images possibly reflect the increased sensitivity of new tomography techniques to rock heterogeneity

Small-Scale Volcanic Structures of the Aeolian Volcanic Arc Revealed by Seismic Attenuation

“…Etna volcano region. For these studies, two methodologies have been used: 1) the separation of the intrinsic attenuation (Qi −1 ) and scattering (Qs −1 ) contributions through the diffusion model (Wu, 1985) and its 2-D spatial representation (Ibáñez et al, 2020); and 2) a 3-D attenuation tomographic study (Castro-Melgar et al, 2021) using the coda normalization method (Aki, 1980). Therefore, we tested the resolution of both of these methods in this study.…”

“…Only shots generated with the maximum energy presented sufficient quality (based on the signal-to-noise ratio) to be used in tomographic structural models (both velocity and attenuation). Castro-Melgar et al (2021) found that the most energetic shots had an equivalent duration magnitude of up to 1.4, based on the magnitude scale of Havskov et al (2003) for volcanic regions. To this limitation we add a high content of background noise, which is typical of seismic signals in populated areas or on small islands (due to oceanic noise); as such, not all of the signals generated in the experiment were useful for this study.…”

“…Imaging volcanic structures remains a challenge for the seismological community, even when similar structures have been identified for multiple volcanoes using different methods (e.g., velocity and attenuation from active and passive seismic sources; Zandomeneghi et al, 2008;Zandomeneghi et al, 2009;Rawlinson et al, 2010;García-Yeguas et al, 2012;García-Yeguas et al, 2014;De Siena et al, 2014;Koulakov and Shapiro, 2015;Prudencio et al, 2015a;Prudencio et al, 2015b;De Siena et al, 2017;Prudencio and Manga, 2020;Gabrielli et al, 2020). In particular, high contrast heterogeneities and the identification of structural changes related to magma transport are challenging for these methods (e.g., Castro-Melgar et al, 2021;Giampiccolo et al, 2021). The quality of tomographic images depends strongly on the spatial distribution of both sources and receivers.…”

“…Various techniques have been proposed for modelling subsurface dynamics, including Deep Learning and Machine Learning (e.g., Titos et al, 2018;Bueno et al, 2019;Bueno et al, 2021;Martínez et al, 2021), satellite remote sensing (e.g., Ganci et al, 2020), among others (e.g., Saccorotti and Lokmer, 2021). However, tomographic analysis based on seismic velocity and attenuation remains one of the best tools because it can provide direct links between changes in wave-field properties and the physical conditions of the medium (Castro-Melgar et al, 2021). Obtaining tomographic images of the Aeolian Islands is complex, especially owing to the geographical dispersion and small sizes of the islands.…”

“…Finally, we directly compare the attenuation features of this region with the nearest volcanic complex, Mt. Etna, about which a number of recent studies have been published (Ibáñez et al, 2020;Castro-Melgar et al, 2021;Giampiccolo et al, 2021).…”