The Southern Apennines-Northern Calabrian boundary is a region marked by lithological heterogeneity, complex geodynamics and tectonics and prone to significant seismic hazard. This sector is part of a complex geodynamic system, where Africa-Eurasia convergence, Ionian subduction and slab retreat coexist. Its structure and seismic activity derive from extensive lithospheric heterogeneity and fluid-related processes, both of which are poorly constrained. Here, we present a novel application of seismic attenuation and scattering tomography of the area at a regional scale. We estimated seismic wave attenuation and scattering for the Southern Apennines-Northern Calabria region using a data set of 1581 waveforms related to 95 M >= 3.0 earthquakes that occurred between 2004 and 2024 and were recorded at 32 stations. We constrained the heterogeneous properties and fluid saturation of the Southern Apennines-Northern Calabrian region by mapping P-wave Peak Delays and inverting coda-normalized energies for total attenuation (1/Q). Results consistently reveal different seismic energy dissipation mechanisms between the two domains, reflecting their different characteristics in terms of Peak Delay and attenuation patterns. The Southern Apennines exhibit high Peak Delay values at all depths and almost no remarkable total attenuation anomalies, consistent with weakly consolidated, fractured sedimentary sequences and limited fluid content. Nevertheless, at a depth of 5.4 km, a relatively high attenuation pattern is detectable, likely linked to the presence of less cohesive and potentially fluid-saturated units. Conversely, Northern Calabria shows low Peak Delay and high attenuation in the investigated depth range, reflecting wave propagation through coherent crystalline rocks with significant fluid circulation, likely favoured by overpressurized materials or active migration pathways. The spatial correlation between high attenuation, low-seismic velocities and thermal anomalies shows that fluids modulate seismic wave behaviour, providing new constraints on the crustal structure and seismotectonic segmentation of the region. The joint interpretation of our results with other geophysical models and responses highlights the complex interplay between lithology, tectonics and fluid dynamics across this critical segment of the central Mediterranean.

The city of Messina, southern Italy, is characterized by high seismic hazard and complex near-surface conditions. Messina has been repeatedly struck by destructive earthquakes over the last centuries, most notably the M7.1 event of 1908, which caused near-total destruction. Reconstructions following these earthquakes generated thick and laterally non-uniform anthropogenic deposits (rubble and debris) that, combined with vertically heterogeneous stratigraphy, might pose significant challenges for accurate subsurface characterization and site response analysis. In this study, we performed integrated geophysical surveys in the historical center of Messina, focusing on the area surrounding the Cathedral, where urban stratigraphy is strongly influenced by both natural and anthropogenic processes. Ambient noise data were analyzed using the Horizontal-to-Vertical Spectral Ratio technique to estimate fundamental resonance frequencies and delineate major impedance contrasts. Active and passive surface-wave methods, including Multichannel Analysis of Surface Waves and array-based approaches, were employed to retrieve shear-wave velocity profiles at different depths. The combined results allowed the identification of key stratigraphic interfaces, the recognition of laterally variable anthropogenic fills and deposits, and the estimation of the main discontinuities within the uppermost layers. These findings demonstrate the effectiveness of a multi-method approach in resolving shallow subsurface complexity in highly urbanized areas. The outcomes provide essential input for seismic microzonation, site response modeling, and hazard mitigation strategies in one of the most seismically vulnerable urban environments of the central Mediterranean.

In February-March 2025 a seismic sequence occurred in the western sector of the Aeolian Archipelago (Southern Tyrrhenian Sea, Italy), a seismotectonic complex region located along the Africa-Eurasia plate boundary and mainly controlled by their NW-trending convergence. The seismicity, located similar to 20 km south of Alicudi Island and similar to 40 km north of the coast of Sicily, started on February 7 with an earthquake of magnitude Mw 4.7 that was followed in the next month by 42 events with local magnitudes between 1.2 and 3.4. Notwithstanding its moderate energy, this recent seismicity offers a unique opportunity to investigate seismogenic processes in a region for which a seismic potential of similar to M7 or even more has been suggested and a relevant data paucity mainly related to its offshore location was widely recognized. We tackle the limitations of not-optimal network configuration, by designing an ad-hoc approach, which integrates different advanced techniques. Specifically, we combine Bayesian methodology for accurate absolute hypocentre locations, machine learning techniques for detection of weaker events, distance geometry solvers for relative locations and a probabilistic inversion tool for source mechanism estimation. Our analysis led us to strongly enrich the data set of detected earthquakes, and to define the causative source of the 2025 sequence as a NE-SW trending N-dipping thrust faulting structure. The proposed source agrees with the regional seismogenic stress field and with the structural architecture of the southern Tyrrhenian portion of the Africa-Eurasia plate margin by also adding new constraints in a sector where no known fault segments were previously reported. This study provides new insights on seismogenic processes in the investigated area, while proving the effectiveness of the employed combined approach for characterizing seismogenic sources in poor network configurations.

Devastating earthquakes continue to surprise scientists, especially when they exhibit unexpected characteristics, such as the 2023 doublet of Mw>7.5 earthquakes in a day along the same fault system in eastern Türkiye. These earthquakes struck the East Anatolian Fault, a major >600 km long tectonic boundary, separating the Anatolian, Arabian, and Eurasian plates, resulting in approximately 60,000 fatalities in Türkiye and Syria and causing more slip than expected. Occurrences of temporally and spatially close earthquakes are hence rare and unmissable opportunities to advance our understanding of active fault mechanics and regional hazard. Such superevents could be part of a supercycle, wherein the likelihood of a large earthquake is determined by accumulated strain rather than time since past earthquakes. To advance our understanding of multiple earthquakes along fault systems and hence of seismic supercycles, we compare tectonic and seismological features of the two 2023 earthquake sequences near Pazarcik and Elbistan with those of the two previous Mw≥6.1 sequences, which occurred in 2010 and 2020, respectively, near Elâzığ along the northeastern East Anatolian Fault. We examined the four strong sequences along the East Anatolian Fault within a multimillennial context of historical seismicity and discovered progressively younger and nonuniform earthquakes moving southwestward. This pattern corresponds to a general progression and dispersion of seismic ruptures southwestward and we use it as a proxy to understand the mechanism of at least two major supercycles identified over the last two millennia. The supercycles evolved from the northeast spreading southwestward with an increasing number of earthquakes. Earthquakes to the northeast are spatially and kinematically well channelized along the main fault, efficiently translating slip toward the southwest, where dispersed and kinematically nonuniform earthquakes are triggered by the push from the northeast, until a new supercycle restarts from the northeast. Insights from recent events offer a crucial framework for interpreting past supercycles and enhancing seismic hazard assessment, providing essential guidance for future mitigation strategies.

An accurate re-evaluation of the instrumental magnitude has been performed for the 28 December 1908 Messina Straits earthquake (Southern Italy), one of the most destructive events ever recorded in the Mediterranean region. Despite the crucial importance of this earthquake for seismic hazard assessment, magnitude values reported in the literature show a wide range of variability, reflecting the inherent uncertainties typical of early instrumental data. This variability suggests the need of a rigorous revision of data and methods used for magnitude estimation. With this purpose, we (1) conducted a comprehensive collection and critical analysis of analog seismograms and station bulletins available for the 1908 event, and (2) rigorously applied the most recently revised approaches for determining body- and surface-wave magnitudes of historical events, also following the recommendations of the International Association of Seismology and Physics of the Earth’s Interior. We present the re-estimation of the body-wave magnitude “mB” using the original Gutenberg–Richter formula, and the surface-wave magnitude “Ms” employing both the “Moscow–Prague” formula and the approach proposed by Abe and Noguchi in 1983. Moreover, this study represents the first instance in which data from undamped instruments have been incorporated into reassessment of this magnitude. The results of our analysis suggest a more reliable final magnitude range between 6.9 and 7.0 for the 1908 earthquake and also emphasize the importance of using consistent and rigorous methodologies in historical seismic research for contributing to more accurate assessments of seismic hazard evaluations.

We present a new 3D overall model of Vp, Vs and Vp/Vs for the Mount Etna (southern Italy), the largest and most active volcano in Europe. We applied the LOTOS code (Koulakov, BSSA 2009) to a dataset of ~4600 crustal earthquakes that occurred in the study area during the last 26 years (Totaro et al., SciRep. 2024). The selected dataset, representing the longest time-interval ever analyzed for Mt. Etna, allowed us to characterize the volcano velocity structure getting over possible singularities due to specific eruptive phases. We estimated and jointly interpreted P- and S-wave velocity patterns together with the Vp/Vs ratio, particularly effective to discriminate the presence of groundwater, gas, and melts and thus very precious for volcano investigations (Kuznetsov et al., Geosciences 2017; Vargas et al., SciRep. 2017; Totaro et al., SciRep. 2022). The obtained 3D seismic velocity patterns allowed us to add further details on already known anomalies and to identify new previously undetected ones. Focusing on the latter, at the shallowest layer we highlight the presence of two high Vp/Vs volumes, located in close correspondence with low resistivity areas (Siniscalchi et al., JVGR 2010, JGR-SE 2012), that can be associated to underground aquifers generated by meteoric water penetrating the volcano edifice. Moreover, a high Vp/Vs anomaly characterized by intense seismic activity has been clearly detected along the eastern flank of Mt. Etna representing a volume of strongly fractured sedimentary rocks through which a large amount of fluids may rise. Finally, on the western side, a high Vp/Vs area with very low seismicity is detectable. The achieved velocity patterns may suggest fluid accumulation, probably not associated to the volcanic activity, even if further investigations are necessary to better solve and understand this previously unknown anomalous region. In conclusion, our study furnished a comprehensive velocity model that, encompassing specific volcanic phases and allowing a joint interpretation of Vp, Vs and Vp/Vs patterns, provides a more complete modelling of the main features of Mt. Etna.

In the western Mediterranean, the subduction of the Tethyan ocean has progressively come to an end, following the intervening continent-continent collision. Compressional deformation connected with the ongoing Africa (AF) – Eurasia (EU) convergence has therefore progressively resumed mostly along the southern passive margins of the Mediterranean back-arc basins. The use of geodetic, seismological, and pre-existing tectonic data recorded between the Gulf of Cadiz and the Ionian Sea helps to trace this nascent AF-EU boundary and constrain its kinematics. Based on these data, this plate boundary is detected, kinematically defined, and compared with the previously identified boundaries in the same region. The nascent boundary is articulated and formed by variably oriented inherited structures. It is characterized by a discrepancy between the general motion of Africa with respect to Eurasia and the local contractional/compressive axes deduced from geodetic and seismic data. The oblique convergence along the nascent boundary matches that recorded in other instances of subduction initiation elsewhere, but the average convergence rate equal to 5 mm/yr in the Mediterranean seems currently too small for such a subduction initiation. Based on the assumption of a future northward tectonic vergence (i.e., Eurasian foreland), the Tyrrhenian, Algerian, and Betic salients, the Oran and Fès recesses, and the Ionian, Trans-Alboran, and Gibraltar transfer zones are identified along the nascent boundary. The latter zones connect salients and recesses through strike-slip displacements. The Algerian offshore hosts a long segment of the boundary characterized by locally increased seismic rate and actual northward vergence that would suggest this area being the first nucleus of subduction initiation in the western Mediterranean.

The scientific community has become increasingly aware of the importance of preserving and recovering historical seismic data, also because of their possible use in combination with modern techniques of analysis. Seismograms coming from the analog recording era cover more than 100 yr of seismic activity and may have a great relevance, especially for seismic risk evaluations in regions struck by destructive events in the past centuries but characterized by minor activity in the last decades. In this study we used analog seismograms to investigate an earthquake of presumed magnitude 5.7 that occurred in 1947 in central Calabria, south Italy, a high-seismic risk region framed in a complex geodynamic setting led by northwest-trending Nubia-Eurasia convergence and southeastward Ionian slab rollback. According to seismic catalogs, the 1947 is the only M > 5.5 earthquake instrumentally recorded in an area where the presence of the lateral edge of the Ionian slab has been suggested and an intense debate is still open concerning possible existence, and proper location, of a subduction-transform edge propagator (STEP) fault zone. To study this earthquake, we selected 15 medium- to long-period analog seismograms with related instrumental parameters, and we proceeded with vectorization process and proper waveform corrections. A technique specifically developed for time-domain moment tensor computation through waveform inversion of analog seismograms has been applied to the digitized recordings. The moment tensor solution estimated for the 1947 earthquake indicates strike-slip mechanism, focal depth of 28 km and M-w 5.1. The obtained hypocentral depth and left-lateral kinematics on about west-northwest-east-southeast-oriented fault fit well with the local seismotectonic framework and are compatible with STEP fault activity in central Calabria, furnishing a new seismological constraint to the debate concerning slab edge kinematics. Moreover, the presented analysis is useful for sharing with the scientific community new data and methodological issues related to historical seismogram management.

The two Mw > 7.5 earthquakes that struck the East Anatolian Fault (EAF), Türkiye, in 2023 caused more slip than expected, indicating that they were potentially part of a supercycle, in which the occurrence probability of a large earthquake is determined by accumulated strain rather than time since the last large earthquake. Here, we show two potential supercycles along the EAF, analyzing earthquakes from the last two millennia. Within each supercycle, seismic ruptures originated in the northeast and progressively spread southwestward with an increasing number of earthquakes until a new supercycle began with another large earthquake in the northeast. To understand the supercycle behavior, we analyze the aftershock sequences of the four most recent Mw≥6.1 mainshocks (2010-2023). This series of earthquakes progressed southwestward, characterized by an increasing diversity of focal mechanisms and a heightened dispersion of epicenters across a branched seismotectonic environment. Earthquakes in the northeast exhibit spatial and kinematic channeling along the master fault surface, effectively transferring slip southwestward and there potentially triggering dispersed and heterogeneous earthquakes. This spatiotemporal pattern seems connected with varying levels of a presumably-innate property of fault sections or regions, ruling the process of seismic slip channeling, which could also explain the behavior of long-term supercycles.

We present a new seismotomography investigation providing a 3-D overall model of Vp, Vs and Vp/Vs for Mt. Etna, the largest and most active volcano in Europe. We estimated and jointly evaluated P- and S-wave velocity patterns together with the Vp/Vs ratio, particularly useful to discriminate the presence of groundwater, gas, and melts and thus very precious for volcano investigations. We applied the LOTOS software to similar to 4600 crustal earthquakes that occurred in the Etnean area during the last 26 years, the longest time-interval ever analysed for Mt. Etna. This wide dataset has allowed us to characterize the volcano velocity structure getting over possible singularities due to specific eruptive phases. Our results further refined the high velocity body widely recognized in the south-eastern sector of Mt. Etna by furnishing new clues on the possible former magma pathways. Moreover, the obtained 3D seismic velocity model depicted new anomalies revealing the presence of: (i) two shallow underground aquifers in the northern Etnean sector; (ii) a volume of strongly fractured rocks filled of fluids along the eastern flank; (iii) a quite deep region of probable fluid accumulation apparently not linked to the volcanic activity in the western sector.

We present an overall analysis of the recent seismic activity occurred in the Adriatic Sea region, a strongly debated sector of the Mediterranean area, where several authors have proposed different models of plate configuration and kinematics. In the past, seismic investigations of this marine area have been strongly hampered by non-optimal network geometries, but data quality increase and recent methodological improvements lay the groundwork to attempt more accurate analyses including proper evaluations of result reliability. On these grounds, we investigated the seismic activity of the last decades by means of new hypocenter locations, wave-form inversion focal mechanisms and seismogenic stress fields. We used the Bayloc non-linear probabilistic al-gorithm to compute hypocenter locations for the most relevant seismic sequences by carefully evaluating location quality and seismolineaments reliability. We also provided an updated database of waveform inversion focal mechanisms including original solutions estimated by applying the waveform inversion method Cut And Paste and data available from official catalogs. Then, focal mechanism solutions have been used to estimate seismogenic stress fields through different inversion algorithms. Seismic results indicate a relevant degree of fragmentation and different patterns of deformation in the Central Adriatic region. In particular, our analyses depicted two NW-SE oriented, adjacent volumes: (i) a pure compressive domain with NNE-trending axis of maximum compression characterizes the northeastern volume where the seismic activity occurs on W-to-NW oriented seismic sources; (ii) a transpressive domain with NW-trending axis of maximum compression charac-terizes the southwestern sector where thrust faulting preferentially occurs on ENE-to-NE oriented planes and strike-slip faulting on E-W ones. Joint evaluation of seismic findings of the present study and kinematic models proposed in the literature indicates just in the Central Adriatic region the presence of a broad deformation zone, accommodating a still evolving fragmentation of the Adriatic domain in two blocks rotating in opposite di-rections. On these grounds, the obtained results not only furnish new seismological evidence supporting the "two-blocks model" proposed by previous authors, but they also provide additional constraints, useful for better un-derstanding and modeling the seismotectonic processes occurring in the Adriatic region.Data availability: Data used in the present study were collected from catalogs and bibliographic sources indicated in detail in the article. Waveform inversions performed in this study used data available in the database EIDA, http://orfeus-eu.org/webdc3/ (accessed February 2022)

The seismic activity occurred in the last decades in the Adriatic Sea region has been investigated by means of new hypocenter locations, waveform inversion focal mechanisms and seismogenic stress fields. After a preliminary evaluation of seismic distribution, the Bayloc non-linear probabilistic algorithm has been used to compute hypocenter locations for the most relevant seismic sequences and to carefully evaluate location quality and seismolineaments reliability. We also provided an updated database of waveform inversion focal mechanisms integrating data available from official catalogs with original solutions we properly estimated by applying the waveform inversion method Cut And Paste. This database has been used to compute seismogenic stress fields through different inversion algorithms. The seismic activity, mainly concentrated in the Central Adriatic region, indicates high fragmentation and different patterns of deformation. In particular, our results highlighted the presence of two NW-SE oriented, adjacent volumes: (i) the northeastern one, characterized by pure compressive domain with NNE-trending axis of maximum compression, and mainly W-to-NW oriented seismic sources; (ii) the southwestern one, characterized by a transpressive domain with NW-trending axis of maximum compression, where thrust faulting preferentially occurs on ENE-to-NE oriented planes and strike-slip faulting on E-W ones. We jointly evaluated seismic findings of the present study and kinematic models proposed in the literature for the Central Adriatic region. The present analysis, furnishing new seismological results provide additional constraints useful for better understanding and modeling the seismotectonic processes occurring in the Adriatic Sea region.

Extensive ambient noise measurements have been carried out in the historical centre of Messina (Sicily, South Italy) and the related HVSR results showed a clear variation of the fundamental peak frequency in the range between 0.4 Hz and 1.6 Hz. This frequency variation is detected across a NW-SE segment, and it can be imputed to a strong lateral heterogeneity of the sediment cover going from southwest to northeast of the study area. Moreover, we carried out a detailed geological field survey and analysis of land surface morphology based on topographic maps and DTM data that allowed us to detect the NW-trending fault, never documented in literature, crossing the historical centre of Messina. Geologic observations indicate clearly normal faulting and activity of this fault is documented at least until Middle Pleistocene, with likely prosecution during Upper Pleistocene.The detected NW-trending fault is roughly perpendicular to the strike of the main structural system of the Straits of Messina framework to which the major earthquake of 1908 (M 7.1) is imputed. Therefore, deeper future investigations for appropriate framing into the local geodynamic context and for evaluation of its eventual prosecution in the offshore area are necessary.In this preliminary study we identify structural discontinuities and faults which may represent new sources of hazard in a town exposed to very high seismic risk in Italy.

Analysis of seismic noise measurements shows a clear change of the Site Resonant Frequency across a NW-SE segment cutting the historic center of the town of Messina. This change indicates strong lateral heterogeneity of the sediment cover going from southwest to northeast across the segment and suggests the existence of a fault never reported by previous investigators, oriented differently from the NNE-SSW main structural system which is widely believed to have produced the magnitude 7.1 earthquake of 1908. Additional evidence of such a NW-SE fault has been obtained by surface geology and analysis of morphological and Digital Terrain Model data. Geologic observations clearly indicate normal faulting but are not able to identify eventual strike-slip components. Activity of this fault is documented at least until Middle Pleistocene, with likely prosecution during Upper Pleistocene. The new detected fault requires deeper investigation in the near future for evaluation of its real extent and present dynamics including eventual seismogenic attitude.

We have investigated the seismicity occurred during 2000-2021 in the area of Messina, the town which suffered greatest loss of human lives over the territory devastated by the magnitude 7.1 earthquake of December 28, 1908. We have found that most of recent activity was located beneath the historical centre of the town, in and near the very peculiar sickle-shaped harbor zone which prompted the Greek colonizers in the VII Century B.C. to give Messina the old name of “Zancle”(“Sickle” in the ancient Greek language). Extracting from the whole dataset (consisting of hundred earthquakes of maximum magnitude 3.8) the data relative to a small sequence of 28 events concentrated in a few days at the end of 2013, and performing high-quality Bayesian hypocenter locations of these events, we have found very clear epi-hypocentral trends suitable for comparison with the local structural scenario. The joint analysis of seismic, geological and geomorphological data including morphobathymetric curves of the sea bottom in the study area, has brought us to propose that the small sequence in question (and probably most of activity recorded during the whole 22-years period) may have been generated by internal dynamics of a local horst/graben system, the position of which (i) appears to correspond to one of the minor horsts documented in the Messina Strait basin area and (ii) is very close to the upper edge of the 1908 earthquake blind source reported in the Database of Individual Seismogenic Sources of the Italian National Institute of Geophysics and Volcanology.

The Calabrian Orogenic Arc (COA) is affected by active extensional and strike-slip tectonics as documented by the presence of N-S and NE-SW trending intra-montane basins bordered by faults, whose slip has caused many destructive earthquakes during the last millennium. By focusing on the central sector of the COA (Sila Massif) through the analysis of new seismological and geodetic datasets, we observed some relevant differences (e.g., seismic activity and hypocentral depths, faulting style, geodetic strain, vertical rates) between its western and eastern sector. The transition between the two sectors occurs in the area of the Lakes Fault, a NW-SE striking and west-dipping fault indicated as the causative source of the 8 June 1638 M 6.8 earthquake. By modelling the available geodetic data, we inferred a dislocation plane whose geometry and kinematics (a prevalent dip slip component coupled with minor left-lateral strike-slip) is compatible with the real fault reported in literature. This fault only accounts for a small amount of the deformation across northern COA and divides the seismically more active western sector from its eastern counterpart with appreciable geodetic strain and moderate seismicity. Results are encouraging and a similar approach can help in other regions where surface evidence of active faults are rare or non-existing and field geological investigations are hence difficult.

In the western Mediterranean, following the intervening continent-continent collision, the subduction of the Tethyan ocean has progressively come to an end or almost in large sectors. Compressional deformation connected with the ongoing Africa–Eurasia convergence has therefore progressively resumed mostly along the southern passive margins of the Mediterranean back-arc basins. The aim of this paper is to trace this nascent boundary and constrain its kinematics through geodetic and seismological data recorded between the Ionian Sea and Gulf of Cadiz, and through pre-existing tectonic data. Based on these data, the nascent plate boundary is drawn, kinematically defined, and compared with the previously identified boundaries in the same region. The nascent boundary is weaving and formed by variably oriented inherited structures. It is characterized by a discrepancy between the general motion of Africa with respect to Eurasia and the local contractional/compressive axes deduced from geodetic and seismic data. The oblique convergence along the nascent boundary matches that recorded in other instances of subduction initiation elsewhere; however, the average convergence rate (∼5mm/yr) in the Mediterranean seems currently too small for such a subduction initiation. Based on the assumption of a future northward tectonic vergence (i.e., Eurasian foreland), the Tyrrhenian, Algerian, and Betic salients, the Oran and Fès recesses, and the Ionian, Trans-Alboran, and Gibraltar transfer zones are identified along the nascent boundary. The latter zones connect salients and recesses through strike-slip displacements. The Algerian offshore hosts a long segment of the boundary characterized by locally increased seismic rate and actual northward vergence that would suggest this area being the first nucleus of subduction initiation in the western Mediterranean, as was previously proposed.

Seismic tomography represents a very powerful and effective tool to look at depths beneath volcanic systems thus helping to better understand their behavior. In particular, a key parameter useful to discriminate the presence of gas, fluids and melts is represented by the P-wave and S-wave velocity ratio. In the present study, we collected ~ 4400 crustal earthquakes that occurred in the last thirty years and we used the LOcal TOmography Software LOTOS to estimate the first 3D overall model of Vp, Vs and Vp/Vs for the Lipari–Vulcano complex belonging to the Aeolian islands system (southern Tyrrhenian sea). The investigated area has been characterized both in old and recent times by fumaroles, hydrothermal activity and active degassing. In particular, in the past decades several episodes of anomalous increases of fumarole temperature and strong degassing have interested the Vulcano Island, the latter of which started in September 2021.The results of the tomographic investigation indicate the presence of two main anomalies of low Vp and low Vp/Vs, clearly depicted up to ~ 8 km depths, and related to gas-rich materials beneath the central-northern sector of Vulcano and the western off-shore of Lipari, respectively.The anomaly beneath Vulcano is located in close correspondence with La Fossa caldera area and with the sector where fumaroles, hydrothermal activity and active degassing are widely documented. Moreover, beneath the western Lipari off-shore a new, previously undetected, volume of strong gas-concentration has been identified. Even if these two anomalies show almost the same intensity, no evidence of degassing activity is available for the latter one because of its location at sea depths where the relevant water column pressure may inhibit the observation of possible degassing processes.The obtained results furnished a picture of the spatial distribution of gas-filled volumes feeding the main degassing activity of the Lipari-Vulcano complex and allowed to highlight the main role played by volcanic gas in the whole system, thus furnishing invaluable constraints for improved modelling of the volcanic system and of its possible evolution.

Seismic tomography is a very powerful and effective approach to look at depths beneath volcanic systems thus helping to better understand their behaviour. The P-wave and S-wave velocity ratio, in particular, is a key parameter useful to discriminate the presence of gas, fluids and melts. We computed the first 3-D overall model of Vp, Vs and Vp/Vs for the Lipari–Vulcano complex, central sector of the Aeolian volcanic archipelago (southern Italy). The investigated area has been characterized in recent times by fumaroles, hydrothermal activity and active degassing. In particular, in the Vulcano Island, several episodes of anomalous increases of fumarole temperature and strong degassing have been recorded in the past decades and the last “crisis”, started in September 2021, is still ongoing. For tomographic inversion we collected ~ 4400 crustal earthquakes that occurred in the last thirty years and we used the LOcal TOmography Software LOTOS. The results clearly depicted two low Vp and Vp/Vs anomalies located up to ~ 8 km depths below Vulcano and the western offshore of Lipari, respectively. These anomalies can be associated to the large presence of gas and they furnish a first picture of the gas-filled volumes feeding the main degassing activity of the area.

We reconstruct the 3D fault model of the structures causative of the 2010–2014 Pollino seismic activity by integrating structural–geological and high-resolution seismological data. We constrained the model at the surface with fault-slip data, and at depth, by using the distributions of selected high-quality relocated hypocenters. Relocations were performed through the non-linear Bayloc algorithm, followed by the double-difference relative location method HypoDD applied to a 3D P-wave velocity model. Geological and seismological data highlight an asymmetric active extensional fault system characterized by an E- to NNE-dipping low-angle detachment, with high-angle synthetic splays, and SW- to WSW-dipping, high-angle antithetic faults. Hypocenter clustering and the time–space evolution of the seismicity suggest that two sub-parallel WSW-dipping seismogenic sources, the Rotonda–Campotenese and Morano–Piano di Ruggio faults, are responsible for the 2010–2014 seismicity. The area of the seismogenic patches obtained projecting the hypocenters of the early aftershocks on the 3D fault planes, are consistent with the observed magnitude of the strongest events (Mw=5.2, and Mw=4.3). Since earthquake-scaling relationships provide maximum expected magnitudes of Mw=6.4 for the Rotonda–Campotenese and Mw=6.2 for the Morano–Piano di Ruggio faults, we may suppose that, during the sequence, the two structures did not entirely release their seismic potential. The reconstructed 3D fault model also points out the relationships between the activated fault system and the western segment of the Pollino Fault. The latter was not involved in the recent seismic activity but could have acted as a barrier to the southern propagation of the seismogenic faults, limiting their dimensions and the magnitude of the generated earthquakes.