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SUMMARYThe south-eastern sector of the Mount Etna, Italy, is characterized by numerous active faults, in particular the Belpasso–Ognina lineament, the Tremestieri–San Gregorio–Acitrezza fault, the Trecastagni fault and the Fiandaca–Nizzeti fault including the Timpe Fault System. Their activity is the result of both volcanism and tectonics. Here, we analyse the ground deformation occurred from 2016 to 2019 across those active faults by using the GNSS data acquired at 22 permanent stations and 35 campaign points observed by the Etna Observatory (INGV) and by the University of Catania. We also use the time-series of line of sight displacement of permanent scatterers SENTINEL-1 A-DInSAR obtained by using the P-SBAS tool of the ESA GEP-TEP (Geohazards Thematic Exploitation Platform) service. We discriminate the contributions of the regional tectonic strain, the inflations, the deflations of the volcano and the gravitational sliding in order to analyse the deformation along the faults of the south-eastern flank of Etna. The shallow and destructive Mw = 4.9 earthquake of 2018 December 26 occurred within the studied area two days after a dyke intrusion, that propagated beneath the centre of the volcano accompanied by a short eruption. Both GNSS and InSAR time-series document well those events and allow to investigate the post-seismic sliding across the faults of south-eastern flank. We analyse the slow slip events (SSE) that are observed in the GNSS and InSAR time-series in the vicinity of the Acitrezza fault. We quantify and discuss the tectonic origin of the Belpasso–Ognina lineament that we interpreted as a tear fault.

The ionosphere is a region of the upper atmosphere (50-1000 km a.s.l.) characterized by free electrons and ions produced mainly by solar radiations (UV, X) and subordinately by cosmic radiations (RAVANELLI, 2021). It’s a very sensitive plasma to energy variations, mostly the F2 layer (240-400 km a.s.l.) that is a region of maximum ionization with an electron density of 10 6 e - /cm 3 . For this reason, the ionosphere (in particular the F region) can be seen as a field of remote sensing monitoring from which to extrapolate various informations by the natural systems that make up our planet.About this, solid Earth (e.g. litoshpere, internal structure) and fluid Earth (e.g. idrosphere, atmosphere) are two open systems that exchange energy continuously. It means that big dynamic processes (e.g. plate tectonics, genesis of magmas) can release amounts of energy, in the form of earthquakes, volcanic eruptions and correlate phenomena (e.g. tsunami), capable to perturb the earth’s matter at every aggregation state and up to planetay scale with propagation of gravity-acoustic waves. In this field, the ionospheric volcanology is a targered discipline for the study of the effects that great volcanic eruptions (VEI > 3-4) cause to Total Electron Content (TEC) in the ionosphere (F2 level) through propagation of internal gravity waves (0.1 – 2 mHz) and acoustic waves (2 – 10 mHz). The study of the TEC’s variations caused by strong geodynamic events represents a new approach with which to contribute to implementation of the monitoring and research systems in order to mitigate the volcanic and seismic risks.The method consists to extrapolate the temporal variations of TEC during the volcanic activity period by RINEX and navigational data GNSS registered by RING (Rete Integrata Nazionale GNSS) and local GPS networks. By the way, others outputs can be derived from TEC series such as spectrograms and hodocrones in order to better understand the evolution of the electron activity in ionosphere excited by the volcanic eruption. This study method is applied for some paroxysmal eruptive activities of Mt.Etna analyzing and comparing the volcanological data with TEC outputs. The latter have been processed with VARION (Variometric Approach for Real-time Ionosphere Observation) algorithm, designed within the Geodesy and Geomatics Division of Sapienza University of Rome in 2015. VARION is based on single time differences of geometry-free combination of GNSS carrier-phase measurements, using a standalone GNSS receiver and standard GNSS broadcast products (orbits and clocks correction) that are available in real time. One of the goals to be pursued in the Research is to comprehend the differences between eruptive mechanisms capable to generate gravity waves rather acoustic waves, and how such mechanisms may depend by physical-geometric features of the plumbing system of the volcano and by chemical-physical features of the magma and its amount of gas.

The geodynamic framework of Mount Etna volcano (Italy) is characterised by two superimposed tectonic domains: a compressional one, oriented N-S, and an extensional one, oriented approximately WNW-ESE. The combination of these two domains and the volcano activity, has generated a complex system of faults prevalently on the eastern flank of the volcano. The eastern flank is the most active area of the volcano in terms of deformation and seismicity. The velocities there are at least one order of magnitude greater than in the rest of the volcano flanks due to the eastward sliding of the eastern flank.The monitoring and analysis of the acceleration occurring on the eastern flank of Mount Etna is the keystone to understand the volcano-tectonic dynamics that, apart from the tectonic and magmatic processes, involves the instability of this flank in a densely inhabited area.In order to monitor the deformation, Istituto Nazionale Geofisica e Vulcanologia – Osservatorio Etneo (INGV-OE) and the GeoDynamic & GeoMatic Laboratory of the University of Catania integrate GNSS and InSAR products with twofold objective: to characterize the dynamics of the area and to analyse the deformation transients, this last in view of a possible use in the framework of an alert system.Here, we analyse the ground deformation that occurred between 2016 and 2019 across the faults of the south-eastern flank of Mount Etna. On the south-eastern flank the deformation is accommodated by several faults which have different kinematics and behaviours. We discriminate the deformation transient and the activity of the Belpasso-Ognina lineament, Tremestieri, Trecastagni, San Gregorio-Acitrezza, Linera, Nizzeti and Fiandaca faults. The latter generated the 26 December 2018 earthquake, two days after the eruption of 24 December, which induced a clear post seismic deformation, detected by GNSS and InSAR data. In particular, we discriminate the deformation occurred along the San Gregorio-Acitrezza fault, which is accommodated by the Nizzeti fault, and we analyse the post seismic deformation along the Linera fault. We analyse the Slow Slip Events (SSE) that are observed in the GNSS and InSAR time series in the vicinity of the Acitrezza fault and we quantify and discuss the tectonic origin of the Belpasso-Ognina lineament that we interpreted as a tear fault.

The Hunga Tonga-Hunga Ha’apai volcano (Pacific Ocean) generated a cataclysmic explosion on 15 January 2022, triggering several atmospheric disturbances at a global scale, as a huge increase in the total electron content (TEC) in the ionosphere, and a pressure wave travelling in the troposphere. We collected and analysed data over the Mediterranean to study these disturbances, and in particular, (i) data from the barometric and infrasonic stations installed on Italian active volcanoes by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) for investigating the tropospheric pressure waves; (ii) barometric data from the INGV-TROPOMAG and SIAS (Sicilian Agro-meteorological Information System) networks, for investigating the interaction between the orography and pressure waves; (iii) ionograms from the Advanced Ionospheric Sounder-INGV ionosonde at Gibilmanna (Sicily, Italy); (iv) data from the RING (Rete Italiana Integrata GNSS) network, to retrieve the ionospheric TEC; (v) soil CO2 flux data from the INGV surveillance network of Vulcano Island. The analysis of the ground-level barometric data highlights that pressure waves were reflected and diffracted by the topographic surface, creating a complex space–time dynamic of the atmospheric disturbances travelling over Sicily, driven by the interference among the different wavefronts. The ionograms show that a medium-scale travelling ionospheric disturbance (MSTID), with a horizontal wavelength of about 220 km and a period of about 35 min, propagated through the ionospheric plasma in the correspondence of the first barometric variations. Moreover, comparing detrended TEC and barometric data, we further confirmed the presence of the aforementioned MSTID together with its close relation to the tropospheric disturbance.

Ground deformation monitoring of active volcanoes is used routinely to determine phases of vol‐ cano unrest and can provide insights in the evolving plumbing system of a volcano and the influence local tectonics structures have on the volcano tectonic evolution of the volcanic edifice. Volcanic deformation analysis can be performed using velocity and direction measurements of the ground surface using Global Navigation Satellite System (GNSS). In this study, we perform two‐dimen‐ sional deformation analyses of pre‐ and post‐eruptive phases with the scope of determining the strain before and after an eruptive phase at Mt. Etna Volcano (southern Italy) during 2004‐2006. In order to do so, we analyse the GNSS displacement data from Mt. Etna between 2004‐2005 and 2005‐2006 using the dedicated SSPX software. The extention, dilation and rotation maps of the study area were determined. The contraction and volumetric decrease concomitant the 2004‐2005 effusive eruptive period and extension and volumetric increase for the 2005‐2006 data series were observed. The deformation on the northeast part of Mt. Etna Volcano, which showed different characteristics with respect to its surroundings, was thought to be conditioned by the dynamic of the Pernicana fault system. Additionally, Complete Spherical Bouguer (CSB) gravity anomaly and the gravity gradient tensors were calculated giving insight on the subsurface structures of Mt. Etna Volcano and its surroundings.

Lunar Gravitational-wave Antenna (LGWA) proposes to deploy an array of high-end seismometers on the surface of the Moon. The LGWA network will measure the lunar surface displacement excited by Gravitational waves (GWs) with a targeted observation band of 1mHz – few Hz. Seismic noise in that frequency band is very low due to the absence of atmosphere and oceans, representing the main inherent advantage that makes the Moon an ideal target for a GW detection experiment. The scientific and technical challenges of LGWA are diverse. Since its initiation, LGWA has relied on experts from fundamental physics, astrophysics, geophysics, engineering, and planetary science. The collaboration is currently organized in working groups (WGs) to cover five key themes: GW science, lunar science, payload, deployment, and operations. At the beginning of 2022, we started the activities of WG2 to assess the current knowledge of the lunar environment. We aim to characterize and develop models of deployment scenarios suitable for LGWA sensors, via a multi-pronged approach of data analysis and on-field experiments probing terrestrial analogs of lunar terrains. Besides characterizing the lunar seismic background noise, other goals of the group are related to modeling the lunar interior structure as well as Moon’s normal modes. These will be further used to develop a model of the interaction between the Moon and GWs. The knowledge about the displacement level of this excitation and the background noise will be used to define novel techniques for background noise reduction.For this purpose, WG2 is composed of physicists, engineers, geophysicists, and geologists. For our activities, we chose an interdisciplinary approach that requires initial communication efforts to create a common ground that will evolve into a crucial baseline activity for the whole LGWA project.Here we will report our progress in the first months of the activity of our collaboration.

Mt Etna, Europe’s largest active volcano, is located directly on the Sicilian coastline of the Ionian Sea. In addition to frequent Strombolian eruptions, Etna’s south-eastern flank is currently sliding seawards at a rate of several centimetres per year. Over the past decade, scientists from multiple countries have intensely studied the submerged sector of the volcano and its continental margin, with their results showing that the well-known onshore flank instability proceeds far into the sea and can be measured by marine geodetic networks. Nevertheless, the relationship between volcanic activity and deformation of the continental margin is still unclear, and various scenarios – from small-scale disintegration over geological time periods to abrupt catastrophic failure – have been suggested.During RV Meteor’s expedition M178 (Nov – Dec 2021), we revisited the continental margin offshore Mt Etna and conducted dedicated repeated shallow- and deep-water multibeam surveys. In addition, several gravity cores were recovered from the prominent amphitheatre structure, intra-slope basins, and the proposed southern boundary of Mt Etna’s moving flank. We use the baseline bathymetric data, acquired during RV Meteor’s cruise M86/2 in 2011/2012, to investigate and image changes within the geomorphological and geological setting offshore Etna by comparing them with the new multibeam data. The repeated bathymetry shows minor changes compared to the baseline study, but favours the suggestion of sediment re-deposition in the proximal to distal sectors of the continental margin. Our preliminary results from the sediment record provide evidence for syn- and post sedimentary deformation, with clear indications of compressional and extensional periods at the crest of the prominent amphitheatre structure. Furthermore, sediment cores show that the southern boundary ridge, north of the Catania Canyon, hosts several heavily reworked and disintegrated sediment patches, which indicates active deformation within the intra-slope micro-basins at the crest of the ridge.The results of this project will increase our understanding of how landslides nucleate in extremely active settings such as offshore Mt Etna. Furthermore, the findings will be used to better assess the hazard potential of the sliding flank of the giant volcano and will feed into numerical modelling of the various scenarios that have been postulated for Mt Etna.

Mount Etna is located on eastern Sicily on the border of the collision zone between the Eurasia and Nubia plate. The regional geodynamic framework is characterized by two superimposed regional tectonic domains: a compressional one oriented N-S and an extensional one oriented approximately WNW-ESE. These two domains, together with the volcano-tectonic one, generated a tectonic system which is unique in the world. It exhibits a complex system of faults prevalently on the eastern flank of the volcano, which is the most complicated in terms of interaction between the tectonic, volcano and gravitational processes. The eastern flank of Mount Etna is the most active area of the volcano in terms of deformation and seismicity, because the deformation rates are at least one order of magnitude greater than the surrounding area, due to the eastwards sliding of this flank.The monitoring and analysis of the high deformation occurring on the eastern flank of Mount Etna is the keystone for understanding the volcano-tectonic dynamics that, apart from the tectonic and volcanic processes, it is paramount relevant because involves the instability of this flank in a densely inhabited area. In this context the Istituto Nazionale di Geofisica e Vulcanologia – Osservatorio Etneo (INGV-OE) created one of the most sophisticated and complete monitoring networks in the world in terms of number of multi-disciplinary station (seismic, geodetic, geochemistry). Since 2014, the GeoDynamic & GeoMatic Laboratory (GD&GM-LAB) of the University of Catania started to create many GNSS sub networks, belonging to the UNICT-Net, in order to determine the offsets occurring on the blocks of each fault of the eastern flank.In order to have a complete analysis of deformation, INGV-OE and the GD&GM-LAB started to consider this area as an “open-air laboratory” where integrate GNSS and InSAR data with the twofold objective: to characterize the dynamic of this area for contributing to the volcanic hazard assessment and to identify precursor phenomena on shear structures analysing the relationship between kinematics, dynamics and volcano processes in the frame of the ATTEMPT INGV project.

The Earth’s ocean floor deforms continuously under the influence of tectonic and non-tectonic processes. In the recent decade, the installation of seafloor geodetic instruments to accurately monitor fault displacement and strain accumulation has greatly improved our understanding of seafloor deformation and our knowledge of associated offshore hazards. In particular, the application of acoustic direct-path ranging networks allows the detection of displacement and strain accumulation of faults in millimeter-level precision.On-land geodetic networks revealed that the Southeast flank of Mount Etna slides seawards at a rate of ~3 cm/yrs. The highest rates are observed near the coast and the volcano flank extends far into the Ionian Sea. The long-term deformation is superimposed by frequent slow-slip events with up to ~3 cm displacement. Our first acoustic ranging measurements between 2016 and 2018 confirmed offshore active deformation and seafloor displacement by detecting a slow-event of up to ~4 cm with a right-lateral offset. Thus, the application of direct-path ranging transponders has proven to be a promising tool to monitor horizontal and vertical displacement of such strike-slip fault zones. However, the observation of long-term deformation, as observed on onshore faults, is lacking. Therefore, we conducted a second acoustic geodetic deployment at the same site offshore Mount Etna between September 2020 and November 2021 and used a different network design. The new data set shows an indication for slow long-term seafloor deformation, which had not been resolved in the first deployment. By comparing the different configurations of the acoustic direct-path networks we were able to improve data processing to achieve millimeter-level precision. We have learned that longer-distance measurements over a sharp fault favor the detection of slow-slip events, but impede the observation of slow long-term deformation. In order to resolve the latter movement, very short baselines close to the fault trace are ideal. Therefore, a trade-off between long and short-distance measurements might be the key for compressive deformation monitoring. Our results prove that the direct-path acoustic ranging technique is well-suited to detect different styles of fault slip at faults with sharp surface traces.

Coastal and ocean island volcanoes are renowned for having unstable flanks, which expresses as slow seawards flank sliding observable by geodetic techniques and/or catastrophic sector collapses. A large section of these unstable flanks is often below sea level, where information on the volcanotectonic structure and, in particular, ground deformation are limited. Consequently, kinematic models that attempt to explain measured onshore ground deformation associated to flank instability are poorly constrained in the offshore area. This is also the case for Mount Etna’s unstable south-eastern flank that slides seawards at rates of 2-3 cm/yr. Displacements associated to flank movement, observed onshore by geodetic and remote sensing techniques, show maximum values at the coast and kinematic models consistently predict even larger movements seawards of the coast. Our seafloor geodetic measurements between 2016 and 2018 confirmed that offshore flank slip is equal or slightly larger compared to onshore slip. The main displacement was released during one slow slip event. Here, we present new data from a second deployment of the seafloor geodetic network in the same location with the same direct-path acoustic ranging technique and a modified network design. The measurements allow reconstructing relative seafloor displacement within the network at sub-centimetre precision, from September 2020 until November 2021. The preliminary results indicate a possible eastward sliding of the flank, although the overall slip of

Slope dynamics in volcanic environments comprise a wide spectrum of phenomena, from large lateral collapse to shallow debris remobilization, which may represent a major threat for human communities and infrastructures. Many volcanos built up from the ocean floor and large portions of the volcano edifice are submerged. In these settings, only the edifice's summit can be investigated by terrestrial remote sensing and in-situ approaches. Growth and destruction, including tectonics and gravitational phenomena, affect entire volcano flanks and are not limited to the physical boundary of the sea level but could comprise their subaqueous parts

Vulcano Island is a composite volcanic edifice located in the south-central sector of the Aeolian Archipelago (Tyrrhenian Sea, Italy). Historic activity has been characterized by frequent transitions from phreatomagmatic to minor magmatic activity. The last eruption in 1888–90 saw powerful explosive pulses and this eruption defines what we call ‘vulcanian’ also for other volcanoes. Since then, volcanic activity has been in the form of fumarolic emanations of variable intensity and temperature, mainly concentrated at “La Fossa” crater. We investigated Vulcano dynamics through ca. 40 years of ground deformation and seismicity data collected by the discrete and continuous INGV monitoring networks. We considered levelling, GPS, EDM, seismic and tilt data. EDM and levelling measurements began in the middle of the 1970s; since the late 1990s, the EDM benchmarks have been measured using GPS. We performed a data inversion identifying, for the 1999–2013 period, the action of a deflating magmatic source, located under Vulcanello at 4–5 km a.s.l, just at the top of a wide regional tectonic tabular source. We analyzed data on different time-space scales, distinguishing the dynamics of different sectors of Vulcano (Piano, Vulcanello, La Fossa cone and Caldera) and three periods (1974–1984, 1984–1999, 1999–2013) and the time evolution of the dynamics of the island. We also show how the regional tectonic stress plays an important role in the transition of the volcanic system from a phase of stability to one of unrest, inducing the heating and expansion of shallow hydrothermal fluids.

We propose a multi-temporal-scale analysis of ground deformation data using both high-rate tilt and GNSS measurements and the DInSAR and daily GNSS solutions in order to investigate a sequence of four paroxysmal episodes of the Voragine crater occurring in December 2015 at Mt. Etna (Italy). The analysis aimed at inferring the magma sources feeding a sequence of very violent eruptions, in order to understand the dynamics and to image the shallow feeding system of the volcano that enabled such a rapid magma accumulation and discharge. The high-rate data allowed us to constrain the sources responsible for the fast and violent dynamics of each paroxysm, while the cumulated deformation measured by DInSAR and daily GNSS solutions, over a period of 12 days encompassing the entire eruptive sequence, also showed the deeper part of the source involved in the considered period, where magma was stored. We defined the dynamics and rates of the magma transfer, with a middle-depth storage of gas-rich magma that charges, more or less continuously, a shallower level where magma stops temporarily, accumulating pressure due to the gas exsolution. This machine-gun-like mechanism could represent a general conceptual model for similar events at Etna and at all volcanoes.

Collapses of coastal and ocean island volcanoes can cause damaging tsunamis and thus pose ocean-wide hazards. To assess the collapse hazard of an unstable flank, a profound understanding of its structural setting and active deformation is essential. This knowledge is, however, often missing, especially for the remote and submerged offshore part of the edifice. Long before satellite-based techniques were available, observations of extensional structures in the summit region and transpressive to compressional structures farther downslope helped to constrain flank instability onshore at many volcanoes globally. Similar deformation structures are also expected offshore where they might be even better preserved due to the absence of anthropogenic influence, limited weathering and erosion. However, in the offshore realm structures related to flank instability are masked by and interact with other processes that act on underwater slopes, such as bottom currents, downslope sediment transport, and regional tectonics. Furthermore, the remote location of offshore flanks complicates geophysical, geomorphological, and geological investigations. Using (micro-) bathymetric and high-resolution seismic data we analyse the seascape forming processes at the Eastern Sicily continental slope at the foot of Mount Etna's unstable south-eastern flank. We untangle seafloor structures related to volcanotectonic, sedimentary, and regional tectonic processes. This allows singling out patterns and structures related to volcano flank instability, such as the lateral and outward boundaries of the unstable flank. We identify a strike-slip fault that changes its morphological appearance from a sharp linear feature atop a pressure ridge north of Catania Canyon to an almost smooth seafloor further downslope, where gravitational sediment transport outbeats volcanotectonic activity. Sediment transport from the continent to the abyss occurs along several canyons and channels that partly align with fault systems. Furthermore, uplift at the distant toe of Etna‘s south-eastern flank may indicate compression from the downwards moving flank, while at the same time provoking erosional responses, e.g. landslides. This new information provides important constraints for kinematic models that seek to explain the drivers of flank instability. It also forms the base for future studies that will infer the styles and rates of offshore flank deformation from the geological record.

Structure and dynamics of fault systems can be investigated using repeating earthquakes as repeatable seismic sources, alongside ground deformation measurements. Here we utilise a dataset of repeating earthquakes which occurred between 2000 and 2019 along the transtensive Pernicana fault system on the northeast flank of Mount Etna, Italy, to investigate the fault structure, as well as the triggering mechanisms of the seismicity. By grouping the repeating earthquakes into families and integrating the seismic data with GPS measurements of ground deformation, we identify four distinct portions of the fault. Each portion shows a different behaviour in terms of seismicity, repeating earthquakes and ground deformation, which we attribute to structural differences including a segmentation of the fault plane at depth. The recurrence intervals of repeating earthquake families display a low degree of regularity which suggests an episodic triggering mechanism, such as magma intrusion, rather than displacement under a constant stress. Repeating earthquakes display variable behaviour across distinct portions of the Pernicana fault system, Mt. Etna, indicating structural differences and episodic triggering, according to a 20 year earthquake dataset, and GPS ground deformation measurements.

The complex interaction between regional stress, gravity forces and dike-induced rifting of Mount Etna, seems to have a role in the eastward movement of the Mt. Etna eastern flank. In this context, the Trecastagni-Tremestieri Fault system identifies the southern boundary of the unstable sector.The Trecastagni fault is a NNW-SSE tectonic structure developing on the lower southern flank, characterized by evident morphological scarps and normal and right-lateral movements that directly affect roads and buildings. Continuous creep affects this fault, with episodic accelerations accompanied with shallow seismicity.The dynamics of these faults has been analysed by a multi-disciplinary approach with terrestrial and satellite deformation data. Terrestrial data consist in levelling across both faults and extensometers record on the Trecastagni fault. Satellite data consist in InSAR data and GPS surveys on wide and local networks.The levelling route on Mt Etna is 150 km long and consists of 200 benchmarks. The portion of the levelling network, crossing the Trecastagni fault, has been installed on 2009; the surveys show a long-term mean vertical slip rate of about 10 mm/y and episodic acceleration on short segments of the fault, with displacements of almost 30 mm.The in-situ monitoring of the Trecastagni fault is also performed by two continuous wire extensometers. Each extensometer is equipped with a data-logger programmed for 48 data/day sampling, storing displacement and ground temperature. The two stations measure the relative displacements perpendicular to the fracture. Data recorded by extensometers highlight an opening trend of about 2-3 mm/year with some acceleration leading up to more than 2 mm in 15 days at the end of 2009.The fault shows clear traces on SAR interferograms and Persistent Scatterers (PS) time series. InSAR data allows tracking the path of fault down to the coastline. The Trecastagni fault shows a main vertical kinematics, with an evident downthrow of the eastern side at a rate of about 4 mm/y. Subsidence increase eastwards away from the structure, reaching a maximum rate of almost 10 mm/y. The fault produces a minor increase in the eastwards velocity on its eastern side evidencing also a minor extension of the structure. Episodic accelerations affect the fault and are visible on some interferograms from different sensors.The dense GPS network is measured periodically and has more than seventy benchmarks. The time series of this network began in 1988 and from then on its configuration has been continuously improved. Integration of this wide spectrum of geodetic data allows strongly constrained ground deformation pattern to be defined and modeled. Furthermore, the very long time series available for the different datasets on the fault, allows its behavior to be investigated in time and its role and relationships in the framework of flank instability and eruptive activity to better understood.

Here we present the results of repeated Absolute Gravity and GNSS measurements, collected at Mt. Etna (Italy) between 2009 and 2018. We aim at investigating the capabilities of this integrated approach for understanding the dynamics of magmatic sources over time-scales of months to years. The absolute gravity and GNSS campaign measurements were repeated roughly once a year; in order to improve the time resolution of gravity data, in some stations we performed, besides absolute gravity measurements, also relative measurements at intervals shorter than 1 year.After being corrected for the effect of elevation changes, gravity data reveal an increase/decrease cycle, well spatio-temporal correlated with a general pattern of uplift/subsidence, during a period of intense lava fountains from the summit craters.Our results provide insight into the processes that controlled the transfer of the magma from deeper to shallower levels of the plumbing system of Mt. Etna volcano, in periods preceding/accompanying the eruptive activity during 2009–2018.Specifically, we propose that coupled changes in height-corrected gravity and elevation might be induced either by the magma storage/withdrawal below the volcanic pile, or by fluids pressurization/depressurization, or by a combination of both processes.The application of the proposed approach could led to an improved capability to identify processes heralding eruptions.

On September 11, 1989, after four months of Strombolian activity at the summit craters, effusive activity began on Mt. Etna and lasted about a month.The 1989 eruption of Mt. Etna was characterized by the formation of two fracture systems, striking NE-SW and NNW-SSE, and both starting from the SE Crater on September, 24.The NE-SW system was followed by effusive activity while the NNW-SSE fractures opened for a length of 7 km without eruptive phenomena. Between September, 27 and October, 3 the fracture system propagated until it reached and cut the SP 92 provincial road (Zafferana - Rifugio Sapienza), near the 1792 effusive mouth, and continued southward for another 700 m.We investigated the fracture southern branch dynamics through 30 years of ground deformation data collected by the discrete and continuous INGV monitoring networks. We considered levelling, GPS, EDM, and extensometers data. EDM and levelling measurements began in the 80s; on 2003 EDM measurements have been replaced by GPS.During the 1989 eruption, EDM measurements showed variations of tens of centimeters on the lines close to the fracture.Precise levelling discrete measurements revealed, in the period 4-16 October 1989 and during the 1991-1993 eruption a subsidence of some centimeters on benchmarks close to fracture.A network of rod extensometers evidenced the fracture activation during the 2001 intrusion phases (12-17 July) measuring several centimeters of left lateral slip. Distance measurements and InSAR show signs of the fracture reactivation during the 2002 and 2018 eruptions.Several authors show as the 1989 fracture zone connects the summit region of the volcano with the tectonic structures of the lower SE flank considering it as well part of the NNW-SSE oriented structure.The dynamics of these last 30 years suggests that the 1989 fracture play an important role on the flank dynamics and strain distribution. It also represents a potential hazard to population because it represents a possible way of ascending magma also testified by cones aligned along the structure.

In this paper, an integrated analysis of microgravity and ground deformation measurements at Mt. Etna is performed over a 21-years time span (1994–2014), a period encompassing several flank and summit eruptions. Data were collected along a common gravity and ground deformation network located on the volcano's southern flank to monitor the dynamics of the main volcanic and tectonic processes. Gravity variations have first been corrected for the free-air effect using the vertical deformation and the experimental vertical gravity gradients measured at each station. The free-air corrected gravity changes were then reduced for seasonal fluctuations, mainly imputable to water-table fluctuations, and for high frequency variations (noise). This long-term dataset constitutes a unique opportunity to examine the behavior of Mt. Etna in a period in which the volcano exhibited different styles of activity characterized by recharging, flank eruptions and fountaining episodes at summit craters. The joint analysis highlights common periods in which gravity and deformation underwent contemporaneous changes occurring mainly in the central and eastern stations of the profile. Specifically, it was possible to distinguish three different sectors, showing significant deformation and gravity patterns: a western sector, lying west of the South Rift, a central one between the South Rift and the 1989 fracture zone, and an eastern one lying east of the 1989 fracture system. The data shows that the deflation dynamics accompanying the eruptive phases mainly affect the western portion of the profile, gradually disappearing toward East, where the more constant sliding dynamics dominates. This pattern defines a transition zone corresponding to the sector comprised between the South Rift and the 1989 fracture. Furthermore, it was also possible to detect at least three main magma charging phases in 1996, 2000 and 2011 which preceded and accompanied the onset of intense flank eruptions and lava fountaining activity at the summit craters.

Persistent motion of the south flank of Kīlauea Volcano, Hawai'i, has been known for several decades, but has only recently been identified at other large basaltic volcanoes—namely Piton de la Fournaise (La Reunion) and Etna (Sicily)—thanks to the advent of space geodetic techniques. Nevertheless, understanding of long-term flank instability is based largely on the example of Kīlauea, despite the large differences in the manifestations and mechanisms of the process when viewed through a comparative lens. For example, the rate of flank motion at Kīlauea is several times that of Etna and Piton de la Fournaise and is accommodated on a slip plane several km deeper than is probably present at the other two volcanoes. Gravitational spreading also appears to be the dominant driving force at Kīlauea, given the long-term steady motion of the volcano's south flank regardless of eruptive/intrusive activity, whereas magmatic activity plays a larger role in flank deformation at Etna and Piton de la Fournaise. Kīlauea and Etna, however, are both characterized by heavily faulted flanks, while Piton de la Fournaise shows little evidence for flank faulting. A helpful means of understanding the spectrum of persistent flank motion at large basaltic edifices may be through a framework defined on one hand by magmatic activity (which encompasses both magma supply and edifice size), and on the other hand by the structural setting of the volcano (especially the characteristics of the subvolcanic basement or subhorizontal intravolcanic weak zones). A volcano's size and magmatic activity will dictate the extent to which gravitational and magmatic forces can drive motion of an unstable flank (and possibly the level of faulting of that flank), while the volcano's structural setting governs whether or not a plane of weakness exists beneath or within the edifice and can facilitate flank slip. Considering persistent flank instability using this conceptual model is an alternative to using a single volcano as a “type example”—especially given that the example is usually Kīlauea, which defines an extreme end of the spectrum—and can provide a basis for understanding why flank motion may or may not exist on other large basaltic volcanoes worldwide.

High-resolution digital topography is essential for land management and planning in any type of territory as well as the reproduction of the Earth surface in a geocoded digital format that allows several Digital Earth applications. In a volcanic environment, Digital Elevation Models are a valid reference for multi-temporal analyses aimed to observe frequent changes of a volcano edifice and for the relative detailed morphological and structural analyses. For the first time, a DTM (Digital Terrain Model) and a DSM (Digital Surface Model) covering the entire Mt. Etna volcano (Italy) derived from the same airborne Light Detection and Ranging (LiDAR) are here presented. More than 250 million 3D LiDAR points have been processed to distinguish ground elements from natural and anthropic features. The end product is the highly accurate representation of Mt. Etna landscape (DSM) and ground topography (DTM) dated 2005. Both models have a high spatial resolution of 2 m and cover an area of 620 km2. The DTM ha...

In active volcanic zones, fault dynamics is considerably fast but it is often difficult to separate the pattern of nearly continuous large-scale volcanic processes (inflation/deflation processes, flank instability) from impulsive episodes such as dyke intrusions or coseismic fault displacements. At Etna, multidisciplinary studies on active faults whose activity does not strictly depend on volcanic processes, are relatively few. Here we present the case-study of the San Leonardello fault, an active structure located in the eastern flank of Mt. Etna characterised by a well-known seismic history. This fault saw renewed activity in May 2009, when pre-seismic creeping along the southern segment preceded an MW 4.0 earthquake in the northern segment, followed by some twenty-five aftershocks. Later, in March–April 2016, creep events reactivated the southern section of the same fault. Both the seismic and aseismic phenomena were recorded by the seismic and GNSS networks of INGV-Osservatorio Etneo, and produced surface faulting that left a footprint in the pattern of ground deformation detected by the InSAR measurements. We demonstrate that the integration of multidisciplinary data collected for volcano surveillance may shed light on different aspects of fault dynamics, and allow understanding how coseismic slip and creep alternate in space and time along the strike. Moreover, we use findings from our independent datasets to propose a conceptual model of the San Leonardello fault, taking into account behaviour and previous constraints from fault-based seismic hazard analyses. Although the faulting mechanisms described here occur at a very small scale compared with those of a purely tectonic setting, this case-study may represent a perfect natural lab for improving knowledge of seismogenic processes, also in other fault zones characterised by stick slip vs. stable-sliding fault behaviour.

On 29 December 2013, the Chaparrastique volcano in El Salvador, close to the town of San Miguel, erupted suddenly with explosive force, forming a column more than 9 km high and projecting ballistic projectiles as far as 3 km away. Pyroclastic density currents flowed to the north-northwest side of the volcano, while tephras were dispersed northwest and north-northeast. This sudden eruption prompted the local Ministry of Environment to request cooperation with Italian scientists in order to improve the monitoring of the volcano during this unrest. A joint force, made up of an Italian team from the Istituto Nazionale di Geofisica e Vulcanologia and a local team from the Ministerio de Medio Ambiente y Recursos Naturales, was organized to enhance the volcanological, geophysical and geochemical monitoring system to study the evolution of the phenomenon during the crisis. The joint team quickly installed a multiparametric mobile network comprising seismic, geodetic and geochemical sensors (designed to cover all the volcano flanks from the lowest to the highest possible altitudes) and a thermal camera. To simplify the logistics for a rapid installation and for security reasons, some sensors were colocated into multiparametric stations. Here, we describe the prompt design and installation of the geodetic monitoring network, the processing and results. The installation of a new ground deformation network can be considered an important result by itself, while the detection of some crucial deforming areas is very significant information, useful for dealing with future threats and for further studies on this poorly monitored volcano.

On 28 December 2014, eruptive activity resumed at Mount Etna with fire fountain activity feeding two lava flows on the eastern and southwestern upper flanks of the volcano. Unlike all previous summit activity, this eruption produced clear deformation at the summit of the volcano. GPS displacements and Sentinel-1A ascending interferograms were calculated in order to image the ground deformation pattern accompanying the eruption. The displacements observed by GPS depict a local ground deformation pattern, affecting only the upper part of the volcano. Despite snow cover on the summit, differential interferometry synthetic aperture radar (DInSAR) data allowed obtaining more detail on the ground deformation pattern on the upper eastern side of the volcano. Three-dimensional GPS displacements inversion located a very shallow NE-SW intrusion just beneath the New Southeast Crater. However, this model cannot justify all the deformation observed by DInSAR thus revealing a gravitational failure of the lava flow field.

A geologic and geodetic integrated analysis of the northern margin of the Hyblean Plateau (SE Sicily) has been carried out in order to test the relationship between the active deformation, recorded by GPS data, and the long-term tectonic evolution, reconstructed by the interpretation of structural and morphological data. Our study revealed the active growth of a large antiform, as a consequence of the positive tectonic inversion of the previous flexure, bordering the Hyblean Foreland. The deformation of Middle–Late Pleistocene marine terraces and the evolution of the drainage system are consistent with a progressive regional tilting of the entire eastern sector of the Hyblean Plateau (Siracusa Domain), representing the southern limb of the active antiform. The geometry of the Late Quaternary marine strandlines, compared with the results of analogue models, is compatible with the effects of the NW-ward propagation of a detachment fault at depth. The active deformation of the Hyblean region, coherent with the Nubia–Eurasia plate convergence, suggests to candidate the inverted tectonics at the northern border of the Hyblean Plateau as potential seismogenic sources of the area.

Along the similar to 500 km long Sicily-Calabria segment of the Nubia-Eurasia plate boundary GPS data highlight a complex, and debated, kinematic pattern. We focus on eastern Sicily, where the style of crustal deformation rapidly changes in the space of few tens of kilometers. In southeastern Sicily, struck by the 1693 M-W similar to 7.4 earthquake, GPS measurements highlight a steep velocity gradient, with similar to 2.4 mm/yr of similar to N-S shortening in similar to 10 km, changing to broader extension (similar to 3 mm/yr in similar to 60 km) in northern Sicily and shortening in the southern Tyrrhenian Sea. GPS data and kinematic elastic block models highlight a complex fragmentation of the Sicilian domain into three tectonic blocks, which move independently from Nubia, describing an overall clockwise rotation of this crustal domain with respect to Eurasia. Shortening in southeastern Sicily is associated with a system of high-angle reverse faults resulting from tectonic inversion of extensional faults at the northern tip of the Hyblean plateau. Extension in northern Sicily occurs on a broader deformation belt, developed on the former Kumeta-Alcantara line, extending west of Mount Etna toward the southwestern Tyrrhenian Sea, accommodating the faster rotation of the northeastern Sicily block with respect to central Sicily. Although the seismic potential of inland faults is not negligible, our results strengthen the hypothesis that the Malta escarpment is the likely source of the large 1693 earthquake and tsunami. The observed kinematics appears only subordinately driven by the Nubia-Eurasia convergence and the dynamics of the Mediterranean subduction system is likely playing a major role in governing block motions and active tectonics in Sicily. (C) 2014 Elsevier B.V. All rights reserved.

Mount Etna volcano is subject to transient magmatic intrusions and flank movement. The east flank of the edifice, in particular, is moving eastward and is dissected by the Timpe Fault System. The relationship of this eastward motion with intrusions and tectonic fault motion, however, remains poorly constrained. Here we explore this relationship by using analogue experiments that are designed to simulate magmatic rift intrusion, flank movement, and fault activity before, during, and after a magmatic intrusion episode. Using particle image velocimetry allows for a precise temporal and spatial analysis of the development and activity of fault systems. The results show that the occurrence of rift intrusion episodes has a direct effect on fault activity. In such a situation, fault activity may occur or may be hindered, depending on the interplay of fault displacement and flank acceleration in response to dike intrusion. Our results demonstrate that a complex interplay may exist between an active tectonic fault system and magmatically induced flank instability. Episodes of magmatic intrusion change the intensity pattern of horizontal flank displacements and may hinder or activate associated faults. We further compare our results with the GPS data of the Mount Etna 2001 eruption and intrusion. We find that syneruptive displacement rates at the Timpe Fault System have differed from the preeruptive or posteruptive periods, which shows a good agreement of both the experimental and the GPS data. Therefore, understanding the flank instability and flank stability at Mount Etna requires consideration of both tectonic and magmatic forcing.

Seismological and geodetic data provide key information about the kinematics and active tectonics of plate margins. Focal solutions enable the determining of the directions in which the current tectonic stress acts when fault rupturing occurs; GPS measurements provide information on the crustal velocity field and on current interseismic strain rates. The comparison of the strain rates resulting from the two datasets provides further insight into how large an area is affected by aseismic deformation, which is a valuable indicator for seismic hazard mitigation and estimation of the seismic potential. In this work, we investigate both seismic and geodetic strain rates and the combined field resulting from the joint inversion of the geodetic and seismic datasets, providing a picture of the overall deformation field and its variation during the last decades. In this way, we try to give an overview of the seismic potential distribution across the Apennines and southern Italy, as a qualitative analysis of space-time variations in the released seismic strain rate, compared to the space-time distribution of the cumulated geodetic strain rate. The results show a variable distribution of the seismic efficiency over Italy. The Southern Apennines shows the greatest seismic potential, highlighting a significantly lower seismicity in the last two decades over an area affected by the highest total strain rates. The Messina Straits and eastern Sicily have a significant seismic potential, together with the Calabrian arc (from the Tindari–Letojanni and central Aeolian islands to the Mt. Pollino area), as a result of seismic gaps with respect to the combined strain rates in the investigated period. This long gap highlights the longer recurrence periods for the strongest earthquakes on this area. The central–northern Apennines and off-shore northern Sicily, show a lower seismic potential than central–southern Apennines, probably due to the more recent seismicity affecting these areas.

Analysis of 1549 DInSAR interferograms, covering the period from 2003 to 2010, has highlighted significant motion along the entire set of the active faults identified by advanced DInSAR analyses (i.e. Permanent Scatterers Features, PSF), affecting the Mount Etna volcano, in eastern Sicily. In the analysed period, the absence of significant seismicity producing co-seismic ground deformation suggests that the overall deformation that has been recognized on the interferograms is to be associated with interseismic, almost continuous creep which is, well documented along most of the active faults. According to field evidence, the structures should accumulate displacements resulting in their permanent visibility on the interferograms, progressively increases through time. This expected behaviour has been recognised only for part of the entire set of structures. Other tectonic features, in fact, show episodic appearances, alternating with periods of absence of ground displacement on the interferograms, simulating a stick-slip mechanism of deformation, conflicting with field evidence. This apparently incongruous behaviour can be interpreted as the result of topographic changes due to the combination of the tectonic displacements with related amounts of the differential erosion and deposition across the fault line. The comparison between the history of the appearances and the monthly rainfall in the region seems to demonstrate that these structures appear when one of the two interacting processes governing the topographic changes around the fault, i.e. tectonic vs. erosional, prevails over the other. Otherwise, the same structures are not evident on the interferograms when the two components are in balance.