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Since the Late Pliocene - Early Pleistocene, the Calabrian Arc (southern Italy) is affected by extensional and transcurrent tectonic superimposed on the previous collisional context. Various seismogenic sources have been proposed over time to explain such a complex structural framework, but the topic is still matter of debate. In this work we apply a multidisciplinary approach, concerning Geology, Geomorphology, Seismology and Geodesy, to develop a reliable 3D model of the Cittanova and Serre faults. These faults are considered the causative faults for the 1783 seismic sequence (M 6.5-7) as proposed by Jacques et alii (2001). We used CROP data to investigate the crustal architecture of the area and to constrain the geometry at depth of the major structures. through two schematic geological sections orthogonal to these two faults. The shallow geometric patterns of the Cittanova and Serre faults, were verified trough geological, geomorphological and structural field data. Earthquakes hypocentres were analysed and relocated in order to recognize possible cluster alignments useful to constrain the faults geometry at depth. The high-density level of crustal seismicity attests that this domain is seismically active, between 0 km and 23 km and it concentrates along the main faults. To compute the strain and velocity field of the area (time span of the last 20 years) we measured the IGM95 (Instituto Geografico Militare) benchmarks and processed several GNSS permanent stations belonging to the RING Network (http://ring.gm.ingv.it) and TopNETlive Italy Network (https://rtk.topnetlive.com/italy/networks/topnet-live-italy) using GipsyX 1.5 Strain inversion (performed through grid_strain 2D software) allowed us to define a predominant WNW-ESE extensional deformation, in agreement with previous studies). Combining all previous data, we built for the first time a reliable 3D model of the Cittanova and Serre fault planes, that are consistent with: i) fault magnitude/size empirical relations (Magnitude vs rupture Area, Magnitude vs fault length; ii) geological and geomorphological field observation (fault attitude and kinematic), iii) seismological and geodetic data. Results show that our model is compatible with the seismogenic sources of the 1783 seismic sequence.

Highlights • A fiber optic strain cable is used to monitor a fault offshore Catania, Sicily. • Brillouin laser reflectometry detects 2.5 cm of cable elongation on the seafloor. • The cable elongation may be caused by fault slip or by seabottom currents. • Submarine telecom cables are likely suitable to detect deformation on the seafloor. Abstract Oceans cover more than 70 percent of the Earth's surface making it difficult and costly to deploy modern seismological instruments here. The rapidly expanding global network of submarine telecom cables offers tremendous possibilities for seismological monitoring using laser light. Recent pioneer studies have demonstrated earthquake detection using lasers in onland and submarine fiber optic cables. However, permanent strain at the seafloor has never before been measured directly as it happens. With this aim, we deployed a dedicated 6-km-long fiber optic strain cable, offshore Catania Sicily, in 2000 m water depth, and connected it to a 29-km long electro-optical cable for science use. We report here that deformation of the cable equivalent to a total elongation of 2.5 cm was observed over a 21-month period (from Oct. 2020 to Jul. 2022). Brillouin laser reflectometry observations over the first 10 months indicate significant strain (+25 to +40 microstrain) at two locations where the cable crosses an active strike-slip fault on the seafloor, with most of the change occurring between 19 and 21 Nov. 2020. The cause of the strain could be fault slip or seabottom currents. During the following 11 months, the strain amplitude increased to +45 to +55 microstrain, affecting a longer portion of the cable up to 500 m to either side of the first fault crossing. A sandbag experiment performed on the distal portion of the cable (3.2–6.0 km) starting Sept. 2021 demonstrates how the fiber optic cable deforms in response to an applied load and how the deformation signal partially dissipates over time due to the elastic properties of the cable. These preliminary results are highly encouraging for the use of BOTDR (Brillouin Optical Time Domain Reflectometry) laser reflectometry as a technique to detect strain at the seafloor in near real time and to monitor the structural health of submarine cables.

The determination of seismic risk in urban settlements has received increasing attention in the scientific community during the last decades since it allows to identify the most vulnerable portions of urban areas and therefore to plan appropriate strategies for seismic risk reduction. In order to accurately evaluate the seismic risk of urban settlements it should be necessary to estimate in detail the seismic vulnerability of all the existing buildings in the considered area. This task could be very cumbersome due to both the great number of information needed to accurately characterize each building and the huge related computational effort. Several simplified methods for the assessment of the seismic vulnerability of existing buildings have been therefore presented in the literature. In order to estimate the occurrence of damage in buildings due to possible seismic phenomena, the published studies usually refer to response spectra evaluated according to seismic events expected in the territory with assumed probabilities. In the present paper seismic events are instead simulated using a modified Olami–Feder–Christensen (OFC) model, within the framework of self-organized criticality. The proposed methodology takes into account some geological parameters in the evaluation of the seismic intensities perceived by each single building, extending the approach presented in a previous study of some of the authors. Here, a large territory in the Sicilian oriental coast, the metropolitan area of Catania, which includes several urbanized zones with different features, has been considered as a new case study. Applications of the procedure are presented first with reference to seismic sequences of variable intensity, whose occurrence is rather frequent in seismic territories, showing that the damage can be progressively accumulated in the buildings and may lead to their collapse even when the intensities of each single event are moderate. Moreover, statistically significant simulations of single major seismic events, equivalent to a given sequence in terms of produced damages on buildings, are also performed. The latter match well with a novel a-priori risk index, introduced with the aim of characterizing the seismic risk of each single municipality in the considered metropolitan area. The proposed procedure can be applied to any large urbanized territory and, allowing to identify the most vulnerable areas, can represent a useful tool to prioritize the allocation of funds. This could be a novelty for risk policies in many countries in which public subsidies are currently assigned on a case-by-case basis, taking into account only hazard and vulnerability. The use of an a-priori risk index in the allocation process will allow to take into due account the relevant role of exposure.

The goal of the ERC (European Research Council) funded project - FOCUS is to apply laser reflectometry on submarine fiber optic cables to detect deformation at the seafloor in real time using BOTDR (Brillouin Optical Time Domain Reflectometry). This technique is commonly used monitoring large-scale engineering infrastructures (e.g. - bridges, dams, pipelines, etc.) and can measure very small strains (<< 1 mm/m) at very large distances (10 - 200 km), but until now has never been used to study tectonic faults and deformation on the seafloor.Here, we report that BOTDR measurements detected movement at the seafloor consistent with ≥1 cm dextral strike-slip on the North Alfeo fault, 25 km offshore Catania, Sicily over the past 10 months. In Oct. 2020 a dedicated 6-km long fiber-optic strain cable was connected to the INFN-LNS (Catania physics institute) cabled seafloor observatory at 2060 m depth and deployed across this submarine fault, thus providing continuous monitoring of seafloor deformation at a spatial resolution of 2 m. The laser observations indicate significant elongation (20 - 40 microstrain) at two fault crossings, with most of the movement occurring between 19 and 21 Nov. 2020. A network of 8 seafloor geodetic stations for direct path measurements was also deployed in Oct. 2020, on both sides of the fault to provide an independent measure of relative seafloor movements. These positioning data are being downloaded during ongoing oceanographic expeditions to the working area (Aug. 2021 R/V Tethys; Jan. 2022 R/V PourquoiPas) using an acoustic modem to communicate with the stations on the seafloor. An additional experiment was performed in Sept. 2021 using an ROV on the Fugro vessel Handin Tide, by weighing down unburied portions of the submarine cable with pellet bags and sandbags (~25kg each) spaced every 5m. The response was observed simultaneously by DAS (Distributed Acoustic Sensing) recordings using two DAS interrogators (a Febus and a Silixa). The strain caused by the bag deployments was observed using BOTDR and typically produced a 50 - 100 microstrain signal across the 120 meter-long segments which were weighed down. In Jan. 2022 during the FocusX2 marine expedition, 21 ocean bottom seismometers were deployed for 12-14 months, which together with 15 temporary land-stations as well as the existing network of permanent stations (both operated by INGV) will allow us to perform a regional land-sea passive seismological monitoring experiment.

Offshore data in the western Ionian Sea indicate that the NW-SE trending dextral shear zone of the Alfeo-Etna fault system turns to N-S direction near the Ionian coastline, where the Timpe fault system occurs. This latter deform the lower eastern slope of Mt. Etna, showing NNW-SSE to NNE-SSW orientation and resulting from E-W trending regional extension. They are seismically active having given rise to shallow and low-moderate magnitude earthquakes in the last 150 years. Morpho-structural data show that NW-SE trending right-lateral strike-slip faults connect the Timpe fault system with the upper slope of the volcano, where the eruptive activity mainly occurs along N-S to SW-NE trending fissures. As a whole, morpho-structural, geodetic and seismological data, seismic profiles and bathymetric maps suggest that similar geometric and kinematic features characterize the shear zone both on the eastern flank of the volcano and in the Ionian offshore. The Alfeo-Etna fault system probably represents a major kinematic boundary in the western Ionian Sea associated with the relative motion of Africa and Eurasia since it accommodates, by dextral transtensional kinematics, diverging motions in adjacent western Ionian compartments. Along this major tectonic alignment, crustal structures such as releasing bends, pull-apart basins and extensional horsetails occur both offshore and on-land, where they probably represent the pathway for magma uprising from depth.

International audience; The Quaternary geodynamics of the Central Mediterranean region is controlled by the migration of narrow orogenic belts within the slow Nubia-Eurasia plate convergence. As testified by the occurrence of major volcanic and seismic events, the Eastern Sicilian Margin is presently one of the most active regions. Using a Permanent-Scatterer approach, we process Sentinel-1 satellite images acquired from 2015 to 2020 to provide an island-wide quantification of surface displacements at a high spatiotemporal resolution. We then convert the calculated mean surface velocities along the ascending and descending satellite line of sight into the ITRF2014 reference frame by using GNSS velocity data derived from regional stations. The resulting pseudo-3D velocity field mainly highlights a general uplift of about 1.5 ± 0.5 mm/yr of the Nebrodi-Peloritani range and its differential motion with respect to mainland Sicily along the Cefalù-Etna seismic zone. Permanent/Persistent-Scatterer (PS) vertical velocities in the Eastern Hyblean region reveal a long wavelength eastward downbending of the margin, including the inferred epicentral area of the 1693 Noto earthquake. Compared to Quaternary coastal uplift rates, these results confirm the relative low activity of Western Sicily, a potential slow uplift of South-Central Sicily and a significant discrepancy along the Eastern Hyblean margin were PS-derived vertical velocities that appear 2-3 mm/yr lower than the Quaternary rates. Over the 2015-2020 timespan, transient processes are also captured, notably on Mount Etna, showing both magmatic pressurization uplift and collapse of the eastern flank, but also all over Sicily where numerous gravitational mass movements and anthropogenic ground subsidence are detected.

International audience; Southeastern Sicily is characterized by a prominent topography known as the Hyblean Plateau. It is commonly considered as a flexural bulge formed by the northwest plunging of the Hyblean‐Malta platform beneath the Sicilian Fold and Thrust Belt. However its noncylindrical shape and multiphase uplift history correlated to the Late Miocene and Plio‐Pleistocene volcanism outline a possible magmatic control on the Hyblean Plateau topographic expression. We argue, using 2‐D flexural models, that the flexural bending alone is unlikely to explain the high anomalous elevation of the Hyblean Plateau. Moreover, topographic analysis show that the Hyblean Plateau has a dome shape composed of radially tilted preserved surfaces defining individual blocks. The block edges seem to be related to deep‐seated inherited faults. Using an analogue modeling approach, we show that magmatic intrusions beneath the thick Meso‐Cenozoic sedimentary cover can reproduce the first‐order morphology of the Hyblean Plateau when a structural inheritance is imposed. Accordingly, we propose a tectono‐magmatic model that favors mafic sill intrusions as the major uplift source for the topographic anomaly. However, to explain the strong positive Bouguer anomaly, a deeper high‐density intracrustal body is needed. Moho uprising related to Mesozoic rifting or mafic lower crust underplating/intraplating since the Late Cretaceous can be evoked. The small wavelength of the topography and the deep intracrustal mass anomaly makes the lithospheric elastic stresses sufficiently high to maintain a nonisostatic state over the geological time scales.

A multidisciplinary work integrating structural, geodetic and seismological data was performed in the Catanzaro Trough (central Calabria, Italy) to define the seismotectonic setting of this area. The Catanzaro Trough is a structural depression transversal to the Calabrian Arc, lying in-between two longitudinal grabens: the Crati Basin to the north and the Mesima Basin to the south. The investigated area experienced some of the strongest historical earthquakes of Italy, whose seismogenic sources are still not well defined. We investigated and mapped the major WSW–ENE to WNW–ESE trending normal-oblique Lamezia-Catanzaro Fault System, bounding to the north the Catanzaro Trough. Morphotectonic data reveal that some fault segments have recently been reactivated since they have displaced upper Pleistocene deposits showing typical geomorphic features associated with active normal fault scarps such as triangular and trapezoidal facets, and displaced alluvial fans. The analysis of instrumental seismicity indicates that some clusters of earthquakes have nucleated on the Lamezia-Catanzaro Fault System. In addition, focal mechanisms indicate the prevalence of left-lateral kinematics on E–W roughly oriented fault plains. GPS data confirm that slow left-lateral motion occurs along this fault system. Minor north-dipping normal faults were also mapped in the southern side of the Catanzaro Trough. They show eroded fault scarps along which weak seismic activity and negligible geodetic motion occur. Our study highlights that the Catanzaro Trough is a poliphased Plio-Quaternary extensional basin developed early as a half-graben in the frame of the tear-faulting occurring at the northern edge of the subducting Ionian slab. In this context, the strike-slip motion contributes to the longitudinal segmentation of the Calabrian Arc. In addition, the high number of seismic events evidenced by the instrumental seismicity, the macroseismic intensity distribution of the historical earthquakes and the scaling laws relating to earthquakes and seismogenic faults support the hypothesis that the Lamezia-Catanzaro Fault System may have been responsible for the historical earthquakes since it is capable of triggering earthquakes with magnitude up to 6.9.

Highlights • Seismic reflection profiles evidence tectonic inversion and active strike-slip faults offshore SW Sicily foreland • Pliocene-Quaternary transpressional inversion of Late Miocene extensional basins • Transpressional fold growth rates were high in Latest Miocene-Pliocene and decreased during Quaternary Joint analysis of high-penetration multi-channel and high-resolution single-channel seismic reflection profiles, calibrated by deep well boreholes, allowed a detailed reconstruction of the Late Miocene to Recent tectonic history of the Capo Granitola and Sciacca fault systems offshore southwestern Sicily. These two fault arrays are part of a regional system of transcurrent faults that dissect the foreland block in front of the Neogene Sicilian fold and thrust belt. The Capo Granitola and Sciacca faults are thought to reactivate inherited Mesozoic to Miocene normal faults developed on the northern continental margin of Africa. During Latest Miocene-Pliocene, the two ~NNE-SSW striking faults were active in left transpression, which inverted Late Miocene extensional half-grabens and created push-up ridges along both systems. Tectonic activity decreased during the Pleistocene, but transpressional folds deform Middle-Late Pleistocene sediments as well, suggesting that the two fault systems are active. The ~40 km long longitudinal amplitude profile of 1st order folds (Capo Granitola and Sciacca anticlines) shows ~15–20 km bell-shaped undulations that represents 2nd order folds. The length of these undulations together with the map pattern of faults allowed to divide the CGFS and SFS into two segments, northern and southern, respectively. Total uplift of the Sciacca Anticline is twice than the uplift of the Capo Granitola Anticline. Incremental fold growth rates decreased during time from 0.22 mm/yr (Capo Granitola Anticline) and 0.44 mm/yr (Sciacca Anticline) in the Pliocene, to 0.07 and 0.22 mm/yr, respectively, during the last ~1.8 Ma.

The south-western edge of the Calabrian Arc in southern Italy has been investigated throughout a joint analysis of field, marine and geophysical data which provided constraints on the fault pattern and on the seismotectonic potential. The study was focused on a poorly known sector of a larger belt of seismically active faults slicing across the NE corner of Sicily, the so-called Tindari Fault System. Our data pointed out that the investigated area, including the mainland and the Ionian offshore, is deformed by oblique faulting with a general NW-SE tectonic trend. Earthquake distribution and seismic profiles pointed out active deformation in the offshore while the mainland is characterized by the occurrence of a NW-SE oriented, >20 km-long, structural belt. However, scarce seismicity has been recorded in the last 30 years alongside this tectonic structure, accounting for a possible silent segment of the larger fault system. Tomographic images revealed that the Moho discontinuity is deformed by a NE-dipping lithospheric tectonic structure which has been here retained the main mode of deformation and responsible for coseismic displacement in the area. As a whole, field and geophysical data agree with a general NW-SE trend segmented pattern of recent/active faults that have the potentiality of generating magnitude 6.5–7 earthquakes.

Deformation bands, usually recognized in association with faults, are here analyzed in relation to a tight synclinal fold developed in the Miocene Numidian turbidites of Sicily. Deposited above a growing thrust-wedge and then buckled during continued deformation, the porous Numidian sandstones form subsurface gas reservoirs elsewhere in the region and are analogues for deepwater systems in general. Structural data have been collected and statistically analyzed to characterize preferred orientations and size parameters (thickness, spacing, length) of deformation bands. Two distinct populations relate to folding: the most recent one is NE-SW oriented, which produced the most prominent structures, whereas an older one is partially obliterated. Microscopic investigation reveals porosity decreases within deformation bands with respect to host rock. The principal deformation mechanisms are grain rotation/sliding and pore-collapse, consistent with folding having occurred under low burial conditions. Within the thrust wedge, near-surface folding is widespread, as indicated by growth strata. Thus we expect early-burial deformation bands of the types (compaction and shear bands) illustrated here to be a component of reservoir damage in subsurface examples.

The Maltese Islands (central Mediterranean Sea) are intersected by two normal fault systems associated with continental rifting to the south. Because of a lack of evidence for offshore displacement and insignificant historical seismicity, the systems have been considered to be inactive. Here we integrate aerial and marine geological, geophysical and geochemical data to demonstrate that: (i) the majority of faults offshore the Maltese Islands underwent extensional to transtensional deformation during the last 20 ka, (ii) active degassing of CH4 and CO2 occurs via these faults. The gases migrate through Miocene carbonate bedrock and the overlying Plio-Pleistocene sedimentary layers to generate pockmarks at the muddy seafloor and rise through the water column into the atmosphere. We infer that the offshore faults systems are permeable and that they were active recently and simultaneously. The latter can be explained by a transtensional system involving two right-stepping, right-lateral NW-SE trending faults, either binding a pull-apart basin between the islands of Malta and Gozo or associated with minor connecting antitethic structures. Such a configuration may be responsible for the generation or reactivation of faults onshore and offshore the Maltese Islands, and fits into the modern divergent strain-stress regime inferred from geodetic data., peer-reviewed

Since the Neogene, the Central Mediterranean geodynamics is controlled by the migration of narrow orogenic belts, driven by fast slabs retreat, and the slowly converging Nubian and Eurasian plates. Nowadays, the Calabrian Arc continues its southeast migration in response to the Ionian oceanic plate rollback but at a much slower rate. The Sicilian kinematics has reached a transient state between the ending subduction-collision phase that formed the island, and the steady-state convergence between Africa and Eurasia. This setting explains why Sicily is among the most seismically active region of the Mediterranean, gathering the most destructive historical events recorded in Italy, such as the Noto (1693, Mw ∼ 7.4) and Messina earthquakes (1908, Mw ∼ 7.1). Such tectonic activity has led to numerous studies aimed at evaluating current surface motions at a regional scale using GPS networks. To improve the spatial coverage, we built the first 3D geodetic velocity field over the whole Sicily Island by processing from the Sentinel-1 InSAR time-series. Averaged velocities along the ascending and descending satellite line-of-sight (LOS) were obtained using the Permanent-Scatterer approach (PS-InSAR) over the 2015-2020 period. We converted PS velocity fields into the Nubia reference frame, with the ITRF2014 vertical reference, by adjusting PS to 3D-GPS mean velocities. Reliable GPS velocities were retrieved from time-series of the MAGNET GPS network, leading to about 40selectedsitescoveringSicily and south-west Calabria. Onalltracks, theagreementbetweenPSandGPSLOSvelocitiesisexcellent (rms < 1mm/yr), and derived orbital corrections are robust, except for the western descending track that is only constrained by five GPS data. Since the projected north-south GPS velocity difference along the LOS is about 0.5 mm/yr, we assumed that thenorth-componentoftheground displacementisnegligible. By reducing the problem to a 2D estimation(East and Up component) and using both ascending and descending LOS velocities, we derived the East-andUp-component of the ground deformation within the Nubia-ITRF2014 reference frame. Uncertainties are estimated in the order of 1mm/yr. The results show that the Up-component is consistent with previous works indicating a significant uplift of the Peloritani range (~ 1±0.5 mm/yr) in north-eastern Sicily. Together with the East-component, the whole Peloritani block appears, however, as a coherent tectonic unit and does not show any dislocation along the Tindari line, as suggested by previous structural field observations. Interestingly, PS-InSAR data evidence an eastward tilting of the Hyblean Plateau, with about 1.5 mm/yr of subsidence of the Augusta bay relative to the Vittoria plain, and a 1 to 2 mm/yr of differential vertical motion along the southern coast, between Agrigento and the Licata and Sciacca locations. Although the reconstructed ground motion only captures a short time-window of the seismic cycle, these data represent a major milestone to evaluate the seismic hazard of Sicily.

For the first time, a 6-km long fiber-optic strain cable was deployed across an active fault on the seafloor with the aim to monitor possible tectonic movement using laser reflectometry, 25 km offshore Catania Sicily (an urban area of 1 million people). Brillouin Optical Time Domain Reflectometry (BOTDR) is commonly used for structural health monitoring (bridges, dams, etc.) and under ideal conditions, can measure small strains (10-6) along a fiber-optic cable, across very large distances (10 - 200 km), with a spatial resolution of 10 - 50 m. The FocusX1 expedition, (6-21 October 2020) onboard the R/V Pourquoi Pas? was the first experiment of the European funded FOCUS project (ERC Advanced Grant). We first performed micro-bathymetric mapping and a video camera survey using the ROV Victor6000 to select the best path for the cable track and for deployment sites for eight seafloor geodetic stations. Next we connected a custom designed 6-km long fiber-optic cable (manufactured by Nexans Norway) to the TSS (Test Site South) seafloor observatory in 2100 m water depth operated by INFN-LNS (Italian National Physics Institute) via a new Y-junction frame and cable-end module. Cable deployment was performed by means of a deep-water cable-laying system with an integrated plow (updated Deep Sea Net design Ifremer, Toulon) to bury the cable 20 cm in the soft sediments in order to increase coupling between the cable and the seafloor. The cable track crosses the North Alfeo Fault at four locations. Laser reflectometry measurements began on 18 October 2020 and are being calibrated by a 3 - 4 year deployment of eight seafloor geodetic instruments (Canopus acoustic beacons manufactured by iXblue) deployed on 15 October 2020. During a future marine expedition, tentatively scheduled for early 2022 (FocusX2) a passive seismological experiment is planned to record regional seismicity. This will involve deployment of a temporary network of Ocean Bottom Seismometers (OBS) on the seafloor and seismic stations on land, supplemented by INGV permanent land stations. The simultaneous use of laser reflectometry, seafloor geodetic stations as well as seismological land and sea stations will provide an integrated system for monitoring a wide range of slipping event types along the North Alfeo Fault (e.g. - creep, slow-slip, rupture). A long-term goal of the project is the development of dual-use telecom cables with industry partners.

The 2018 December 26th earthquake (MW = 4.9) at the south-eastern slope of Mt. Etna provides new insights for improving the knowledge of the kinematics of the eastern flank of the volcano. The earthquake was preceded by a seismic swarm on the upper southern-western sector of the volcano and by a short eruptive event in the summit area. The associated crustal deformation triggered seismic reactivation of tectonic structures in the eastern flank of the volcano. The seismogenic source has been localized along one of the segments cutting the south-eastern slope the volcanic edifice, the NW-SE trending Fiandaca Fault, one of the most active shear zone belonging to the upslope extension of the Timpe fault system. In the last centuries, all these faults have been the source of very shallow, low magnitude, but destructive earthquakes. In order to determine the response of the unstable eastern flank of Mt. Etna to the volcano-tectonic events, we applied a multidisciplinary approach based on: i) analysis of historical and instrumental seismicity; ii) mapping of coseismic fracturing, iii) analysis of GPS and InSAR data. This study allows to better define the seismotectonic framework of the shear zone occurring in the eastern flank of Mt. Etna, framing it in the seismogenic belt extending as far as the Ionian offshore.

International audience; Tectono-stratigraphic interpretation and sequential restoration modelling was performed over two high-resolution seismic profiles crossing the Western Ionian Basin of southern Italy. This analysis was undertaken in order to provide greater insights and a more reliable assessment of the deformation rate affecting the area. Offshore seismic profiling illuminates the sub-seafloor setting where a belt of active normal faults slice across the foot of the Malta Escarpment, a regional-scale structural boundary inherited from the Permo-Triassic palaeotectonic setting. A sequential restoration workflow was established to back-deform the entire investigated sector with the primary aim of analysing the deformation history of the three major normal faults affecting the area. Restoration of the tectono-stratigraphic model reveals how deformation rates evolved through time. In the early stage, the studied area experienced a significant deformation with the horizontal component prevailing over the vertical element. In this context, the three major faults contribute to only one third of the total deformation. The overall throw and extension then notably reduced through time towards the present day and, since the middle Pliocene, ongoing crustal deformation is accommodated almost entirely by the three major normal faults. Unloading and decompaction indicate that when compared to the unrestored seismic sections, a revision and a reduction of roughly one third of the vertical displacement of the faults offset is required. This analysis ultimately allows us to better understand the seismic potential of the region.

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

Pino et al. (2021, hereinafter PIN2021) commented on the paper by Barreca et al. (2021, hereinafter B2021) titled: “The Strait of Messina: Seismotectonics and the source of the 1908 earthquake”, which was published in the journal Earth-Sciences Reviews in May 2021. PIN2021 argued both on the “source model of the 1908 EQ”, as proposed by B2021, and on the existence of the newly discovered causative fault (i.e. the B2021W-Fault). Based on “objective reading of achieved results along with other existing geophysical information…“, PIN2021 conclude: “the source mechanism for the 1908 EQ is based on incorrect assumptions, while their results are internally inconsistent and with other independent observations”. According to PIN2021, the inconsistency of the proposed “source mechanism”, which foresaw the possibility of an aseismic slip on a low-angle discontinuity preceding the 1908 mainshock (see B2021), would be mainly demonstrated by “the lack of significant variations of the relative sea level in the Messina harbor area, in the time period relevant for the levelling data (1907-1908) ……. and at least for the decade preceding the event”. Moreover, to demonstrate that the deformation is mostly coseismic, PIN2021 proposes a sea level diagram based on unreliable data from the Messina tide gauge. In this paper, we demonstrate that the comments by PIN2021 are unfounded. We strongly confirm the scientific validity of the model proposed in B2021.

International audience; The Apennines-Sicilian-Maghrebian fold-and-thrust belt originated from the subduction of the Alpine Tethys and the later collision of drifted continental blocks against the African and Apulian paleomargins. From North to South, the Sicilian Fold-and-Thrust Belt (SFTB) is divided in four main tectono-stratigraphic domains: (1) the Calabro-Peloritani

The amount of Earth observation images available to the public has been the main source of information, helping governments and decision-makers tackling the current world&rsquo, s most pressing global challenge. However, a number of highly skilled and qualified personnel are still needed to fill the gap and help turn these data into intelligence. In addition, the accuracy of this intelligence relies on the quality of these images in times of temporal, spatial, and spectral resolution. For the purpose of contributing to the global effort aiming at monitoring natural and anthropic processes affecting coastal areas, we proposed a framework for image processing to extract the shoreline and the shallow water depth on GeoEye-1 satellite image and orthomosaic image acquired by an unmanned aerial vehicle (UAV) on the coast of San Vito Lo Capo, with image preprocessing steps involving orthorectification, atmospheric correction, pan sharpening, and binary imaging for water and non-water pixels analysis. Binary imaging analysis step was followed by automatic instantaneous shoreline extraction on a digital image and satellite-derived bathymetry (SDB) mapping on GeoEye-1 water pixels. The extraction of instantaneous shoreline was conducted automatically in ENVI software using a raster to vector (R2V) algorithm, whereas the SDB was computed in ArcGIS software using a log-band ratio method applied on the satellite image and available field data for calibration and vertical referencing. The results obtained from these very high spatial resolution images demonstrated the ability of remote sensing techniques in providing information where techniques using traditional methods present some limitations, especially due to their inability to map hard-to-reach areas and very dynamic near shoreline waters. We noticed that for the period of 5 years, the shoreline of San Vito Lo Capo sand beach migrated about 15 m inland, indicating the high dynamism of this coastal area. The bathymetric information obtained on the GeoEye-1 satellite image provided water depth until 10 m deep with R2 = 0.753. In this paper, we presented cost-effective and practical methods for automatic shoreline extraction and bathymetric mapping of shallow water, which can be adopted for the management and the monitoring of coastal areas.

In Central Mediterranean, the Sicilian Fold and Thrust Belt (SFTB) and Calabrian Arc, as well as the whole Apennine-Maghrebian belt, result from the subduction and collision with drifted micro-continental terranes. These terranes detached from the European margin and migrated southeastward in response to Neogene slab roll-back and associated back-arc extension. From N to S, the SFBT is divided in 4 main tectono-stratigraphic domains: (1) the Calabro-Peloritani terrane, drifted from the European margin and detached from the Corso-Sarde block since the back-arc opening of the Tyrrhenian basin, (2) the Neotethyan pelagic cover, constituting the remnants of the Alpine Tethys oceanic accretionary wedge, (3) the folded and thrusted platform (Panormide) and basinal (Imerese-Sicanian) series of the down-going African margin, and (4) the undeformed african margin foreland (Hyblean). The scarce good quality outcrops of key tectono-stratigraphic units and crustal scale seismic lines makes the structural architecture of the SFTB very controversial, as testified by the wide variety of tectonic interpretations (Bianchi et al., 1987; Roure et al., 1990; Bello et al., 2000; Catalano et al., 2013). Major outstanding issues particularly concern: (1) the occurence of Alpine Tethys units far from the region where the remnants of the Tethyan accretionary wedge outcrop (Nebrodi range); in a forearc position above the Peloritani block north of the SFTB and in an active foreland context along the southern front of SFTB; (2) the diverging suggested tectonic styles, from stacked large-scale tectonic nappes to foreland imbricated thrust systems rooted into a main basal décollement; and (3), the deposition environnement of substantial units such as the widespread Numidian Flyschs, from syntectonic foreland basin to wedge-top sedimentation. We used 2D analogue models to investigate the mechanical processes involved in the formation of the SFTB starting from the Oligocene Tethys subduction to the Middle Miocene - Late Pliocene continental collision with the African paleo-margin. Based on a detailed tectono-stratigraphic synthesis, complemented by field observations, we reproduce the first-order mechanical stratigraphy of the sedimentary and basement units involved in the SFTB as well as the structural inheritance of the African margin. Our models also include: syntectonic erosion and sedimentation, syn-orogenic flexure and adjustable material output via a “subduction channel“. The analog models succeed in reproducing the general structure of the SFTB and main tectono-stratigraphic correlations. For instance, the Panormide platform is underthrusted beneath the Alpine Tethys accretionary wedge, then stacked above the Imerese basinal units and belatedly exhumed in response to basement anticlinal stack. Our results also suggest that the Alpine Tethys units couldn’t overthrust the whole African foreland in the Middle Miocene, nor be back-thrusted over the forearc basin during the Burdigalian. We rather favor a gravity-induced sedimentation process inducing reworking of the tethysian sediments at specific building stages of the accretionary wedge. The structural architecture of the modeled orogenic wedge is also consistent with a SFTB growing by frontal accretion and basal underplating of mechanically resistant stratigraphic units rather than by large-scale nappe overthrusting.

Laser reflectometry (BOTDR), commonly used for structural health monitoring (bridges, dams, etc.), for the first time is being tested to study movements of an active fault on the seafloor, 25 km offshore Catania Sicily (an urban area of 1 million people). Under ideal conditions, this technique can measure small strains (10E-6), across very large distances (10 - 200 km) and locate these strains with a spatial resolution of 10 - 50 m. As the first experiment of the European funded FOCUS project (ERC Advanced Grant), in late April 2020 we aimed to connect and deploy a dedicated 6-km long strain cable to the TSS (Test Site South) seafloor observatory in 2100 m water depth operated by INFN-LNS (Italian National Physics Institute). The work plan for the marine expedition FocusX1 onboard the research vessel PourquoiPas? is described here. First, microbathymetric mapping and a video camera survey are performed by the ROV Victor6000. Then, several intermediate junction frames and short connector cables (umbilicals) are connected. A cable-end module and 6-km long fiber-optic strain cable (manufactured by Nexans Norway) is then connected to the new junction box. Next, we use a deep-water cable-laying system with an integrated plow (updated Deep Sea Net design Ifremer, Toulon) to bury the cable 20 cm in the soft sediments in order to increase coupling between the cable and the seafloor. The targeted track for the cable crosses the North Alfeo Fault at three locations. Laser reflectometry measurements began April 2020 and will be calibrated by a three-year deployment of seafloor geodetic instruments (Canopus acoustic beacons manufactured by iXblue) also started April 2020, to quantify relative displacement across the fault. During a future marine expedition, tentatively scheduled for 2021 (FocusX2) a passive seismological experiment is planned to record regional seismicity. This will involve deployment of a temporary network of OBS (Ocean Bottom Seismometers) on the seafloor and seismic stations on land, supplemented by INGV permanent land stations. The simultaneous use of laser reflectometry, seafloor geodetic stations as well as seismological land and sea stations will provide an integrated system for monitoring a wide range of types of slipping events along the North Alfeo Fault (e.g. - creep, slow-slip, rupture). A long-term goal is the development of dual-use telecom cables with industry partners.

In the last few decades, the use of GNSS Continuously Operating Reference Station (CORS) networks allowed improving the accuracy of real-time positioning and post-processing positioning. In this way, several applications have been performed including remote sensing, agriculture, cultural heritage and geodynamics studies. The latter have been developed analysing CORS time-series and consistent data over long periods were needed to validate the results. In Italy, specifically in Sicily, two CORS networks were be used to monitor the geodynamics motions: the Istituto Nazionale di Geofisica e Vulcanologia (INGV) GNSS CORS network in the eastern part and the University of Palermo (UNIPA) GNSS CORS network in the western part. In this research, preliminary results of time series about geodynamics motions of the western part of Sicily have been presented. In particular, the time series of the UNIPA GNSS CORS network have been analyzed over time by using the static positioning, over a period of approximately 5 years. Results showed a linear trend for all CORS time series, according to literature. An innovative methodology, the static Precise Point Positioning (PPP) has been also tested, to determine the time series of one CORS and compare the results with the static solution. The comparison between the two methodologies (static and PPP) demonstrated the capabilities of PPP technique with benefits in terms of costs and time.

We present the results of the analysis of GNSS (Global Navigation Satellite System) and InSAR (Interferometric synthetic-aperture radar) data collected in the frame of a project financed by the “Struttura Terremoti” of INGV (Istituto Nazionale di Geofisica e Vulcanologia). Combined investigations pointed out for potential seismogenic sources for destructive earthquakes recorded in southwestern Sicily, including the 1968 Belice earthquake sequence and that supposed to have destroyed the Greek city of Selinunte which, according to geoarcheological data experienced two earthquakes in historical times. Our approach is aimed to evaluate the current deformation rate in SW Sicily and to improve the knowledge about the seismic potential of this area. The geodetic data proposed in this paper show that the Campobello di Mazara–Castelvetrano alignment (CCA) is currently deforming with a vertical and horizontal displacements of 2 mm/yr and 0.5 mm/yr respectively, according to the tectonic setting of the area.

The results of absolute satellite-derived bathymetry (SDB) are presented in the current study. A comparative analysis was conducted on empirical methods in order to explore the potential of SDB in shallow water on the coast of Misano, Italy. Operations were carried out by relying on limited in situ water depth data to extract and calibrate bathymetry from a QuickBird satellite image acquired on a highly dynamic coastal environment. The image was processed using the log-band ratio and optimal band ratio analysis (OBRA) methods. Preprocessing steps included the conversion of the raw satellite image into top of atmosphere reflectance, spatial filtering, land and water classification, the determination of the optimal OBRA spectral band pairs, and the estimation of relative SDB. Furthermore, calibration and vertical referencing were performed via in situ bathymetry acquired in November 2007. The relative bathymetry obtained from different band ratios were vertically referenced to the local datum using in situ water depth in order to obtain absolute SDB. The coefficient of determination (R2) and vertical root mean square error (RMSE) were computed for each method. A strong correlation with in situ field bathymetry was observed for both methods, with R2 = 0.8682 and RMSE = 0.518 m for the log-band ratio method and R2 = 0.8927&ndash, 0.9108 and RMSE = 0.35 m for the OBRA method. This indicated a high degree of confidence of the SDB results obtained for the study area, with a high performance of the OBRA method for SDB mapping in turbid water.

Quaternary uplift is well documented in SE Sicily, a region prone to damaging seismic events, such as the 1693 “Val di Noto” Earthquake (Mw 7.4), the largest seismic event reported within the Italian Earthquake Catalogue, whose seismogenic source is still debated and, consequently, the long-term seismic hazard is poorly-understood. However, the spatial variation in the timing and rates of uplift are still debated, so it is difficult to link the dominant tectonic process(es) responsible for the uplift and the location of seismogenic sources. To better constrain the uplift rate, we have refined the dating of Late Quaternary marine terraces, using a synchronous correlation approach, driven by both published and newly obtained numerical age controls (234U/230Th dating on corals). This has allowed re-calculation of uplift rates along a N-S oriented transect within the Hyblean Plateau (HP) foreland region. Consequently, we have mapped the geometry of palaeoshorelines along a coastline-parallel transect, and hence the rates of uplift. The results suggest increasing uplift rate from south to north across the HP, and that uplift rates have remained constant through the late Quaternary. This spatially-changing but temporally constant uplift places constraints on the proportion of uplift produced by regional geodynamic processes versus produced by local faults, such as an offshore E-dipping active normal fault. We discuss these new findings in terms of the long-term seismic hazard for one of the most seismically-active regions in the Mediterranean Basin.

The Calabrian subduction zone is one of the narrowest arcs on Earth and a key area to understand the geodynamic evolution of the Mediterranean and other marginal seas. Here in the Ionian Sea, the African plate subducts beneath Eurasia. Imaging the boundary between the downgoing slab and the upper plate along the Calabrian subduction zone is important for assessing the potential of the subduction zone to generate mega‐thrust earthquakes and was the main objective of this study. Here we present and analyze the results from a 380 km long, wide‐angle seismic profile spanning the complete subduction zone, from the deep Ionian Basin and the accretionary wedge to NE Sicily, with additional constraints offered by 3‐D Gravity modeling and the analysis of earthquake hypocenters. The velocity model for the wide‐angle seismic profile images thin oceanic crust throughout the basin. The Calabrian backstop extends underneath the accretionary wedge to about 100 km SE of the coast. The seismic model was extended in depth using earthquake hypocenters. The combined results indicate that the slab dip increases abruptly from 2‐3° to 60‐70° over a distance of ≤50 km underneath the Calabrian backstop. This abrupt steepening is likely related to the roll‐back geodynamic evolution of the narrow Calabrian slab which shows great similarity to the shallow and deep geometry of the Gibraltar slab. Plain language abstract We investigate the deep crustal structure of southern Italy and the Central Mediterranean where some of the oldest oceanic crust on Earth is actively descending (subducting) into the earth's interior (Speranza et al., 2012). This process causes much of the moderate seismicity observed in this region and may be responsible for strong historical earthquakes as well (Gutscher et al., 2006). Deep seismic data recorded during a marine geophysical expedition performed in 2014, allow us to reconstruct the 3‐D geometry of this subduction zone. Our data reveal a 1‐4 km thick evaporitic (salt bearing) layer in the 13 km thick accretionary wedge. The thin underlying crust has characteristics of oceanic crust. The adjacent onshore domains (E Sicily and SW Calabria) are composed of 25‐30 km thick crust with velocities typical of continental crust. Together with earthquake travel‐time tomography (providing images of the subducting slab down to 300 km) and gravity modeling we can for the first time image the abrupt steepening of the subducting slab, the “slab hinge”, where slab dip increases from ≤5° to >60° over a downdip distance of 50 km. This slab dip is steep compared to other subduction zones, for example in Northern Honshu Japan or Sumatra, where the slab dip remains roughly 10° down to 40 km depth and therefore may have consequences on the seismicity of the region.

A detailed 3D image of the Calabro-Ionian subduction system in the central Mediterranean was obtained by means of a seismic tomography, exploiting a large dataset of local earthquakes and computing algorithms able to build a dense grid of measure nodes. Results show that the slab is continuous below the southern sector of the Calabro-Peloritan Arc, but the deformation processes developing at its edges are leading to its progressive narrowing, influencing tectonics and magmatism at the surface, and with possible stress concentration in the tip zones. In the southwest, the deformation occurring at a free slab edge lead to propagation of a vertical lithospheric tear in the overriding plate, which extends along a NW-SE fault system (Aeolian-Tindari-Letojanni) up to about 30 km into the Ionian Sea; further southeast, the lithosphere appears only flexed and not broken yet. In the northeast, the slab seems to break progressively, parallel to the trench. Finally, northwest of Mt. Etna, the tomography highlights low VP that can be related to an upwelling of deep mantle material likely flowing laterally through a window opened by the complete slab detachment.

More than 100 years after the devasting Messina-Reggio Calabria earthquake (M = 7.1), the largest seismic event ever recorded in southern Europe in the instrumental epoch, its causative seismic source is still unknown, and the several rupture models proposed in the last decades are far from any shared solution. Data interpretation on a new dataset of sub-seafloor geophysical soundings with unprecedented resolution, relocated seismicity, and Vp model, together with morphotectonic investigations and inverse modelling of available levelling data, provide additional constraints on the deformation mechanisms and seismotectonics of the Strait of Messina area. High-resolution seismic lines in the offshore, along with displaced Quaternary marine terraces on land, point to active deformation along a previously unmapped ~34.5 km-long extensional fault. Spatial distribution of relocated earthquakes highlighted that a cut-off of the seismicity occurs within the crustal depth. The seismic discontinuity roughly delineates a foreland-dipping and low-angle discontinuity apparently confirming previous studies predicting low-angle seismogenic sources for the 1908 seismic event. However, according to the overburden stress and the attitude of the discontinuity, stress analysis suggests that a seismic slip is unlikely along it. This therefore weakens the hypothesis that a large earthquake may have nucleated along a low-angle discontinuity. Rather, aseismic creeping is instead expected since movement is allowed only by assuming a mechanical weakness of the plane. This mechanical behaviour is currently also supported by the large interseismic strain-rate recorded in the area. Both seismic tomography and crustal-to-subcrustal scale 3D-modelling strongly suggest a cause-and-effect relationship between slab retreat, mantle wedging, uplift in the upper plate block, and active extension in the Strait of Messina area. Lithospheric doming of the upper plate is here interpreted to be the main process controlling uplift in the Peloritani Mts. of Sicily and subsidence in the Strait of Messina region where deformation is mainly accommodated by the weak low-angle discontinuity. In this frame, an almost aseismical slip towards the foreland of the low-angle discontinuity is here accounted to produce stress perturbation in the area. Coulomb stress change modelling revealed that simulated normal slip on the foreland-dipping discontinuity can induce additional stress and promote failure in the overlying brittle faults. An excellent fit between calculated and observed subsidence is achieved by geodetic data inversion that resolved a normal slip on the low-angle discontinuity and a transtensional (slightly left-lateral) motion on the 34.5 km-long and previously unknown extensional fault. The fault-length along with the observed seafloor displacement make this tectonic structure as the most likely to have produced large earthquakes in the Strait of Messina area.

Joint analysis of multichannel seismic reflection profiles calibrated with well-logs across the northern part of the Lampedusa Plateau (central sector of the Pelagian Block, Sicily Channel), of structural data collected on Lampedusa island, and of GNSS geodetic velocities of sites on the islands and on the northern shore of the Channel, suggests that this part of the plateau forms an anticlinorium (Lampedusa Plateau Anticlinorium, LPA). The LPA developed during Paleogene to Early Miocene intraplate contraction followed by Miocene to current strike-slip deformation. It is formed by WNW-ESE striking highs and lows, which have an ~20 km average wavelength and culminate at the Lampione-Lampedusa High. These broad folds are bounded by high-angle faults with a reverse component of displacement, which cut Eocene to Lower Pliocene strata offshore, and Late Miocene strata on Lampedusa. Extensional faults, that have a bathymetric expression and are responsible for marked stratal tilting due to their listric geometry, are only found to the NE of the island and are associated to the rifting that affected the central part of the Sicily Channel in the Pliocene-Quaternary. Seismic reflection profiles show that normal fault activity peaked during the middle part of the Pliocene and strongly diminished afterward. Appraisal of recent plate motion reconstructions and of published and new structural data offshore and on-land suggest that the main growth phase of the LPA occurred during (Late Cretaceous?) Paleocene-Early Miocene ~N-S convergence between Nubia and Eurasia and associated intraplate shortening. Starting from Early Miocene, likely in response to a CCW rotation of the plate convergence direction, strike-slip deformation occurred with a ~NW-SE shortening axis and ~NE-SW extension axis. During this time span the previous contractional structures were locally reactivated in transpression. The two different strain regimes, extensional and transpressional that established since Miocene NE and W to NW of Lampedusa, respectively, still persist today as documented by geodetic velocities.