On 21 August 2017, a Mw 3.9 earthquake struck the island of Ischia, causing two casualties and significant damage in the village of Casamicciola Terme and its surroundings. The earthquake was recorded by the local INGV-OV seismic network, and represents the first relevant instrumentally recorded earthquake on the island. However, it is not possible to perform a statistical analysis based on past recordings, which forms the basis of the Ground Motion Model at a local scale. The numerical simulations can help overcome this problem. Here, we first analysed the low magnitude seismicity of the island and focused on estimating the seismic attenuation and average static stress drop through spectral inversion analysis. We then used a stochastic finite-fault approach considering two source models to simulate the Casamicciola earthquake’s strong ground motion by also taking into account the site effect at the IOCA station. The numerical simulations were also extended to the localities for which observed macroseismic intensity values are available. The simulated peak ground motions, converted into intensities through empirical relationships, are somewhat higher than the observed values for both source configurations, suggesting that the regional dependence between intensity and peak ground motion cannot be overlooked. Future investigations should be undertaken to improve seismic hazard assessment at a local scale. Conversely, synthetic PGAs and PGVs show a satisfactory match with the values predicted by the generic GMM calibrated for volcanic areas in Italy. The results underscore the importance of region-specific GMMs for reliable seismic scenarios.

Field surveys focused on detailed mapping and measurements of coseismic surface ruptures along the causative fault of the 6 February 2023, Mw 7.8 Kahramanmaraş earthquake. The aim was filling gaps in the previously available surface-faulting trace, validating the accuracy of data obtained from remote sensing, refining fault offset estimates, and gaining a deeper understanding of both the local and overall patterns of the main rupture strands. Measurements and observations confirm dominating sinistral strike-slip movement. An integrated and comprehensive slip distribution curve shows peaks reaching over 700 cm, highlighting the near-fault expressing up to 70% of the deep net offset. In general, the slip distribution curve shows a strong correlation with the larger north-eastern deformation of the geodetic far field dislocation field and major deep slip patches. The overall rupture trace is generally straight and narrow with significant geometric complexities at a local scale. This results in transtensional and transpressional secondary structures, as multi-strand positive and negative tectonic flowers, hosting different patterns of the mole-tracks at the outcrop scale. The comprehensive and detailed field survey allowed characterizing the structural framework and geometric complexity of the surface faulting, ensuring accurate offset measurements and the reliable interpretation of both morphological and geometric features.

In this study, seismic hazard, a component of the multi‑hazard assessment studied in the framework of the PANACEA project, was performed following the probabilistic approach (PSHA) based on historical macroseismic data. This approach uses intensity site observations to compute the seismic history for each investigated locality. Site seismic histories completeness are improved the integrating observed intensities with “virtual” values calculated according to attenuation laws, starting from the earthquake parameters (epicentre and epicentral intensity). The probability distribution of the expected intensities at a given site is calculated for exposure times of 10, 30 and 50 years. Results are given as reference intensity and peak ground acceleration for a chosen exceeding probability. In order to obtain hazard also in terms of expected peak ground acceleration (PGA) a relation between macroseismic intensity and ground acceleration calibrated for Mt. Etna was also developed. A PGA value was predicted for each intensity site observation using a specific ground motion model for Mt. Etna shallow events, assuming a soil class A. We tested the performance of the obtained relationship through synthetic and observed PGAs associated with the most energetic seismic event instrumentally recorded at Etna. Finally, the probability distribution for PGA at the site for a given exposure time results from the combination of the corresponding seismic hazard curve for the macroseismic intensity and the specific local intensity‑PGA relationship.

Etna-Creep monitors fault displacement at localized site along active faults on the instable SE flank of Mt. Etna. Currently two instruments are installed across the Macchia Fault in the S. Leonardello - Macchia Graben System close to the coastline. Creepmeters can capture fault creep, slow slip events as well as triggered slip events from near field or far field sources, and allow us to detect signals of volcano-tectonic interactions. Our instruments monitor continuous slip with a resolution of 1 micrometer and a sampling rate of 2/min. These installations complement the GEOSEA array (https://www.geomar.de/en/news/article/geosea-array-records-sliding-of-mount-etnas-southeastern-flank) offshore Catania and strongly link research on flank instability processes onshore with the offshore GEOMAR activities. Installed in 2022, these instruments already recorded several triggered slip events, characterised also by sudden acceleration episodes of slip. This dataset enables us to study how extensional faulting at the SE flank of Mt. Etna contributes to the slow sliding of the flank into the Ionian Sea. With the high temporal resolution of this network, we also retrieve information about potential triggering sources reflected in the stress regime change allowing the unclamping of the monitored fault. Dynamic triggering caused a slip event on the Macchia fault during the passage of surface waves during the February 6th 2023, M7.8 Kahramanmaras earthquake in Turkey. Additional slip events were triggered after an earthquake offshore Catania (M4.5) and by other earthquakes in the Mediterranean. Shallow micro-seismicity along the Acicatena fault, located close to the monitored fault, is synchronous with events at the monitored Macchia fault showing elastic unclamping with no permanent slip. These events demonstrate the susceptibility of the extensional fault system to external perturbation (i.e. triggering). With Etna-Creep we hope to be able to better understand the contribution of these faults to the SE-ward motion of the Etna’s eastern flank as well as its driving processes, but also insights into the basic process of tectonic loading on earthquake faults.

This work presents the first results of the PANACEA project regarding the assessment of different volcano-related hazards at Mt. Etna (lava and pyroclastic flows, tephra fallout and earthquakes) by exploiting data deriving from the volcano's history with accurate physical–mathematical models. Volcano-related hazards are distributed differently on Etna—from the deserted summit area down to the densely populated flanks—but must be considered together for long-term territorial planning.

Managing multiple hazards simultaneously affecting a territory is a challenge for effective risk mitigation. This is particularly true on active volcanoes like Mt. Etna, characterized by effusive and explosive eruptions, often coupled with intense seismic activity. This work presents the PANACEA project’s approach to treating multi-hazards in terms of risk, which requires a common definition of the exposed elements and their vulnerability. Another aspect emerging from the recent and historical volcanic crises at Etna is the cascading effects and the problem of assessing their short-term interactions. A risk model is presented considering a set of sequences of hazardous events that may result from volcano unrest to possible impacts on some infrastructural elements. The project’s outcomes are intended to be a significant step toward a more comprehensive resilience to volcanic disasters, leading to a safer society.

In this paper, we tackle the problem of the intensity attenuation at Ischia, a critical parameter in a high seismic risk area such as this volcanic island. Starting from the new revised catalogue of local earthquakes, we select a dataset of 118 macroseismic observations related to the four main historical events and analyse the characteristics of the intensity attenuation according to both the deterministic and probabilistic approaches, under the assumption of a point seismic source and isotropic decay (circular spreading). In the deterministic analysis, we derive the attenuation law through an empirical model fitting the average values of ΔI (the difference between epicentral intensity I 0 and intensities observed at a site I S ) versus the epicentral distances by the least-square method. In the probabilistic approach, the distribution of I S conditioned on the epicentre-site distance is given through a binomial-beta model for each class of I 0 . In the Bayesian framework, the model parameter p is considered as a random variable to which we assign a Beta probability distribution on the basis of our prior belief derived from investigations on the attenuation in Italy. The mode of the binomial distribution is taken as the intensity expected at that site ( I exp ). The entire calculation procedure has been implemented in a python plugin for QGIS ® software that, given location and I 0 (or magnitude) of the earthquake to be simulated, generates a probabilistic seismic scenario according to the deterministic or probabilistic models of attenuation. This tool may be applied in seismic risk analyses at a local scale or in the seismic surveillance to produce real-time intensity shake-maps for this volcanic area.

At Mt. Etna volcano, flank eruptions are often accompanied by seismic swarms with damaging earthquakes; the most recent case‐history is the 2018 flank eruption, associated with a destructive earthquake ( M w 5.0). In this paper, we analyze the earthquake and eruptive catalogs from 1800 to 2018, to produce quantitative estimates of the earthquake rate under the influence of flank eruptions. We quantify that 30% of the flank eruption onsets precede a major (i.e., damaging, I x ≥ V–VI EMS) earthquake by 30 days or less; 18% of the major earthquakes follow a flank eruption onset in 30 days or less. Thus, we show that the probability of major earthquakes increases 5–10 times after the onset of flank eruptions and this effect lasts for 30–45 days. This is also observed after the end of the eruptions. Results indicate different relationships depending on the location of the volcano‐tectonic systems considered individually (eruptive fissures, seismogenic faults). For instance, we describe a 10–20 times increased probability of earthquakes for 65–70 days after eruptions on the northeastern flank, and of new flank eruptions for 45–70 days after earthquakes of the Pernicana fault.

The effects of volcanic hazards can be quantified by applying new methods to provide support for rational decision-making. Mt Etna is one the most active volcanoes in the world, producing both effusive and explosive eruptions together with a very intense seismic activity, which significantly affect the territory and human society. We present the preliminary results obtained in the framework of the PANACEA project (INGV’s project “Pianeta Dinamico”, funded by the Italian Ministero dell’Università e la Ricerca, MUR) regarding the multi-hazard assessment around Mt Etna. These include: (i) the production of an updated spatio-temporal probability map of vent opening at Etna, using a procedure exploiting different Kernel functions (e.g. the exponential, Cauchy, and Gaussian functions), and testing volcanic deformation patterns to explore possible dynamic, structural conditioning on the vent opening process; (ii) the identification of a set of cascading effects scenarios that account for volcanic phenomena (i.e., volcanic unrest, seismicity, volcanic explosions, volcanic effusive events, lava flows, tephra/ballistic fall, and PDC), as well as other external hazards potentially linked in such chains (e.g., flooding, forest fires, etc.); and (iii) the identification of scenarios involving systemic impacts (e.g., impacts on the functionality or connectivity of networks).

At Mt. Etna (Italy), volcano‐tectonic earthquakes produce impressive surface faulting despite their moderate magnitude ( M < 5.5), with historically well‐documented ruptures featuring end‐to‐end lengths up to 6–7 km. The 26 December 2018, M w 5.0 earthquake represents the strongest event of the last 70 years, with ground ruptures extending for 7.5 km along the Fiandaca fault, a partially hidden structure in the volcano's eastern flank. Field data collected by the EMERGEO Working Group (INGV) are here integrated with high‐resolution photogrammetric surveys and geological‐morphological observations to enable a detailed structural analysis and to reconstruct the morphotectonic process of fault growth. The deformation zone develops in a transtensional regime and shows a complex pattern, consisting of brittle structures arranged in en‐échelon scale‐invariant overlapping systems. Offsets and kinematics vary along the strike due to a major bend in the fault trace. We reconstructed a prevailing right‐lateral displacement in the northern section of the fault and a dextral oblique slip in the southern one (max 35 cm); the dip‐slip component increases southward (max 50 cm) and overall resembles the along‐strike pattern of the long‐term morphological throw. The kinematic analysis indicates a quasi‐rigid behavior of the two fault blocks and suggests a geological model of rupture propagation that explains both the location of the seismic asperity in the northern section of the Fiandaca fault and the unclamping in the southern one. These findings are used to propose a conceptual model of the fault, representing insights for local fault‐based seismic hazard assessment.

Misterbianco is located on the southern flank of Mt. Etna (Unesco site), in eastern Sicily (Italy). This site, also known as Monasterium Album, has a long and tormented history linked with volcanic activity of Mt. Etna and regional seismicity. This site received much attention in the 2000s when excavation works brought to light a 14th century church remains below the thick layer of the 1669 lava. This study documents the first diagnostic multidisciplinary survey performed at this site 350 years after the eruption: the investigations were performed by using techniques such as ground-penetrating radar, infrared thermography, a terrestrial laser scanner and a drone survey to analyze the site’s topography, to adequately map the hidden structures inside the building and to identify fractures and deformations in the church. Starting from the site history, we present the results of the multidisciplinary approach aimed at reconstructing the historical events that led to the damage in the church.

An application for a quick earthquake damage scenario assessment is here presented as a potential tool for planning prevention actions or managing seismic emergencies in the volcanic region of Mt. Etna (Italy). As case-study, we considered the December 26, 2018 earthquake that, with a magnitude MW 4.9, represents the largest event occurring in the area during the last 70 years. The QUEST working group (the INGV macroseismic team) carried out a detailed survey in the damage area, collecting data on the number of buildings in the different vulnerability classes and related damage, with the aim to assign intensity. The maximum intensity reached degree VIII EMS along a narrow strip extending for 5 km astride the Fiandaca fault. In this paper, we simulated the damage scenario in the most struck municipalities of the epicentral area by testing different methodological approaches proposed in the literature using the information of the ISTAT census data collected by the Italian Institute of Statistics. We evaluated the damage level of the residential buildings and we validated the results comparing with the real damage data recognized in the field. Our analysis highlighted the difficulty of applying methods calibrated for larger earthquakes in tectonic domains, to small magnitude events in volcanic zones, where some operating assumptions must be introduced. Despite this, the results confirm the potential of the simulations based on statistical damage assessment methods also in these peculiar conditions, opening the way to finalized plans of pre- and post-earthquake interventions.

Understanding damage to non-structural elements, identifying sources of critical issues, and how damage affects the functionality of facilities are all critical aspects for developing general recommendations concerning disaster risk management. In the present paper a review of non-structural damage caused by recent earthquakes was performed in several localities exposed to seismic hazard such as Mt. Etna in Italy, Lisbon and Azores islands in Portugal and southern Lowland in Iceland. This was needed in order to derive the most common non-structural damage framed into the local situation, which in turn is a basic requirement for a well tailored communication campaign. The observed damage to non-structural elements as derived in this study led to the conclusion that the most commonly damaged elements are partition walls, ceiling systems, non-structural vaults, chimneys, building contents and storage racks. Analyses proved that substantive efforts are needed worldwide to improve techniques for reducing damage to non-structural elements. Non-structural mitigation represents a major opportunity for immediate low-cost action to reduce the impacts of earthquakes at home, school and workplaces. Research results within the KnowRISK EU project was the reference ground upon which a wide range of tools for multi-stakeholders (students, business and citizens) to improve seismic performance of non-structural elements and reducing the associated economic losses, loss of functionality, and potential threats to life safety was designed.

Ischia is a densely inhabited and touristic volcanic island located in the northern sector of the Gulf of Naples (Italy). In 2017, the Mw 3.9 Casamicciola earthquake occurred after more than one century of seismic quiescence characterized only by minor seismicity, which followed a century with three destructive earthquakes (in 1828, 1881, and 1883). These events, despite their moderate magnitude (Mw < 5.5), lead to dreadful effects on buildings and population. However, an integrated catalogue systematically covering historical and instrumental seismicity of Ischia has been still lacking since many years. Here, we review and systematically re-analyse all the available data on the historical and instrumental seismicity, to build an integrated earthquake catalogue for Ischia with a robust characterization of existing uncertainties. Supported by new or updated macroseismic datasets, we significantly enriched existing catalogues, as the Italian Parametric Earthquake Catalogue (CPTI15) that, with this analysis, passed from 12 to 57 earthquakes with macroseismic parametrization. We also extended back by 6 years the coverage of the instrumental catalogue, homogenizing the estimated seismic parameters. The obtained catalogue will not only represent a solid base for future local hazard quantifications, but also it provides the unique opportunity of characterizing the evolution of the Ischia seismicity over centuries. To this end, we analyse the spatial, temporal, and magnitude distributions of Ischia seismicity, revealing for example that, also in the present long-lasting period of volcanic quiescence, is significantly non-stationary and characterized by a b-value larger than 1.

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.

ABSTRACTWe present a set of revised ground-motion models (GMMs) for shallow events at Mt. Etna Volcano. The recent occurrence of damaging events, in particular two of the strongest earthquakes ever instrumentally recorded in the area, has required revising previous GMMs, as these failed to match the observations made for events with local magnitude ML>4.3, above all for sites situated close to the epicenter. The dataset now includes 49 seismic events, with a total of 1600 time histories recorded at distances of up to 100 km, and ML ranging from 3.0 to 4.8. The model gives estimates of peak ground acceleration (both horizontal and vertical), peak ground velocity (both horizontal and vertical), and 5% damped horizontal pseudoacceleration response spectral ordinates up to a period of 4 s. GMMs were developed using the functional form proposed by Boore and Atkinson (2008). Furthermore, with a slightly modified approach, we also considered a regression model using a pseudodepth (h) depending on magnitude according to the scaling law by Azzaro et al. (2017). Both models were applied to hypocentral distance ranges of up to 60 km and up to 100 km, respectively. From the statistical analysis, we found that reducing the maximum distance from the event up to 60 km and introducing a magnitude-dependent pseudodepth improved the model in terms of total error. We compared our results with those derived using the GMMs for shallow events at Mt. Etna found by Tusa and Langer (2016) and for volcanic areas by Lanzano and Luzi (2019). The main differences are observed at short epicentral distances and for higher magnitude events. The use of variable pseudodepth avoids sharp peaks of predicted ground-motion parameters around the epicenter, preventing instabilities when using a GMM in probabilistic seismic hazard analysis.

We provide a database of the surface ruptures produced by the 26 December 2018 Mw 4.9 earthquake that struck the eastern flank of Mt. Etna volcano in Sicily (southern Italy). Despite its relatively small magnitude, this shallow earthquake caused about 8 km of surface faulting, along the trace of the NNW-trending active Fiandaca Fault. Detailed field surveys have been performed in the epicentral area to map the ruptures and to characterize their kinematics. The surface ruptures show a dominant right-oblique sense of displacement with an average slip of about 0.09 m and a maximum value of 0.35 m. We have parsed and organized all observations in a concise database, with 932 homogeneous georeferenced records. The Fiandaca Fault is part of the complex active Timpe faults system affecting the eastern flank of Etna, and its seismic history indicates a prominent surface-faulting potential. Therefore, this database is essential for unravelling the seismotectonics of shallow earthquakes in volcanic areas, and contributes updating empirical scaling regressions that relate magnitude and extent of surface faulting.

The macroseismic surveys of earthquakes occurred in Sicily during the time­span 2014­2018, are hereinafter presented. Analysed data mainly concern significant or damaging events located in the volcanic region of Mt. Etna, together with other regional shocks in southern Sicily and Aeolian islands. Data have been collected and processed following the guidelines of the QUEST working group (QUick Earthquake Survey Team) of INGV and then parametrised according to the procedures used for compiling the CPTI catalogue and DBMI macroseismic database.

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.

The macroseismic surveys of earthquakes occurred in Sicily during the time-span 2014-2018, are hereinafter presented. Analysed data mainly concern significant or damaging events located in the volcanic region of Mt. Etna, together with other regional shocks in southern Sicily and Aeolian islands. Data have been collected and processed following the guidelines of the QUEST working group (QUick Earthquake Survey Team) of INGV and then parametrised according to the procedures used for compiling the CPTI catalogue and DBMI macroseismic database.