04. Solid Earth

Earthquakes are, by far, the most relevant source of hazard for the densely urbanised areas of Mt. Etna volcano. Local communities continuously suffer social and economic losses due to the high occurrence of damaging earthquakes, which produce intensities up to degree X EMS despite of low magnitude (M < 5.0). In the framework of the PANACEA project, seismic hazard was performed following the probabilistic approach (PSHA) based on historical macroseismic data. The probability distribution of the expected earthquake damage to residential buildings and the resulting risk effects on population are calculated for exposure times of 30 and 10 years.

L'Istituto Nazionale di Geofisica e Vulcanologia (INGV) è componente del Servizio Nazionale di Protezione Civile, ex articolo 6 della legge 24 febbraio 1992 n. 225 ed è Centro di Competenza per i fenomeni sismici, vulcanici e i maremoti per il Dipartimento della Protezione Civile Nazionale (DPC). L’Osservatorio Vesuviano, Sezione di Napoli dell’INGV, ha nei suoi compiti il monitoraggio e la sorveglianza H24/7 delle aree vulcaniche attive campane (Vesuvio, Campi Flegrei e Ischia). Tali attività sono disciplinate dall’Accordo-Quadro (AQ) sottoscritto tra il DPC e l’INGV per il periodo 2022-2025 e sono dettagliate nell’Allegato Tecnico del suddetto AQ. Il presente Rapporto sul Monitoraggio dei Vulcani Campani rappresenta l’attività svolta dall’Osservatorio Vesuviano e dalle altre Sezioni INGV impegnate nel monitoraggio dell’area vulcanica campana nel 2023.

Seismic data are influenced by various types of noise, which are typically categorized into two primary classes: anthropogenic and environmental. However, the detection of instrumental noise or malfunctioning stations also plays a crucial role in ensuring the data quality and the efficiency of a seismic network. The visual inspection of seismic spectral diagrams (e.g. power spectral density) enables us to identify issues that could potentially compromise data quality, thereby affecting subsequent calculations such as Magnitude or Peak Ground Acceleration (PGA). However, this process is time-consuming and demands significant human expertise due to the complexity of the diagrams, compounded by the sheer number of stations requiring examination. Therefore, in this paper, we explore the feasibility of transferring human expertise into an artificial intelligence system to create an automated system capable of rapidly performing such detection. More specifically, in the first part of this paper, we use Probability Density Function (PDF) diagrams, enabling an initial assessment of station performance via visual inspection. We describe this plot type and provide examples that reveal whether a station is functioning correctly or if technical issues exist. A table containing the main evaluation criteria is provided. In the second part of this paper, we demonstrate that these plots can serve as input for a neural network, allowing the development of the aforementioned automated system. Through extensive testing under various conditions, we have observed that the trained network consistently achieves an accuracy rate exceeding 85% across all four conducted tests. In the latest and most significant test, the achieved accuracy is approximately 87%.

Volcanic activity is intrinsically a multi-hazard problem. Different phenomena accompanying volcanic activity, such as seismicity, static deformation, lava flows, gas emission and tephra fallout, can be dangerous to the society and economy with a wide range of impacts. Moreover, the physical parameters representing the intensity measure of such hazards are of different nature and therefore their integration in a single analysis is not straightforward. The most frequent approaches for multi-hazard assessment usually start from considering each hazard as the primary subject of the analysis; afterwards, the multi-hazard analysis is generally based on the integration of multiple volcanic hazards independently assessed, often without any effort of harmonization of the results. Afterwards, the final multi-hazard integration is done using different approaches as e.g., the definition of subjective indexes (for example "Low", "Medium" and "High" hazard zones) or by the spatial overlap of hazard maps representing a specific (sometimes termed "reference") scenario. From a decision-maker point of view, these multi-hazard analyses may not be sufficiently informative, and may be biased by the subjective choices taken by the hazard analysts. In this work, we introduce a target-based approach for multi-hazard assessment in which the target (objective) of the analysis is the starting point of the process. The method is implemented using a fully probabilistic approach that allows also propagating epistemic uncertainties (often quantified while evaluating single hazards separately). The approach is based on a system for the solution of "fault trees" and "event trees" called MERGER [1], and involves: (i) the definition of a clear objective for the analysis (i.e., the "target"), which is probably a more clear task for a decision maker; (ii) the identification of hazardous events that can potentially contribute to the achievement of the "target" objective; and (iii) the definition of possible logical relationships between the events that identify the way in which they can contribute to achieving the target objective. As a demonstrator of our approach, we present some 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 volcano. In particular, we identify a few target objectives related to mobility disruption due to Mt Etna activity, and we show how the MERGER model can integrate the probabilistic hazard for seismic events, lava flow inundation and tephra fallout.

In fossil subduction zones associated with massive exhumation of (ultra)high-pressure ((U)HP) rocks such as the Western Alps, the geometry and behavior of subduction-channel and mantle-wedge rocks during exhumation are still poorly constrained by independent geophysical observations. Here we use a new local earthquake tomography model of the entire fossil subduction zone of the Western Alps based on data collected during the CIFALPS and CIFALPS2 passive seismic experiments, and the first receiver- function profile across the Ligurian Alps, to investigate the styles of subduction-channel and mantle- wedge exhumation as a function of increasing upper-plate divergence motion. In the northern Western Alps (low divergence), a thickened subduction channel can be detected, but no exhumed mantle wedge is found beneath the Gran Paradiso (U)HP dome. In the southern Western Alps (intermediate divergence), an exhumed mantle wedge is detected beneath the Dora-Maira (U)HP dome above a serpen- tinized subduction channel. In the Ligurian Alps (high divergence), an exhumed mantle wedge and a for- mer subduction channel are detected at much shallower levels beneath the Voltri-Valosio (U)HP dome, and above a shallow-dipping lower-plate Moho. In this latter case, the lower boundary of the exhumed subduction channel is the most evident seismic-velocity interface, which may be easily misinterpreted as a true Moho. Similar Moho-like interfaces are found beneath the exhumed (U)HP domes of eastern Papua New Guinea and the Dabie Shan, which suggests that the results of the CIFALPS experiments may be used as a reference case for the interpretation of other (U)HP terranes worldwide.

Currently many studies are carried out in the Neapolitan Volcanic District (Vesuvius, Campi Flegrei and the Island of Ischia), thus demonstrating the interest by the Supersite science teams and the scientific community as a whole in this active volcanic area. The aims of these studies by the science teams, though not limited to, are:  research, by taking part into international research projects/activities and  monitoring, focused on the near real time surveillance of the volcanoes belonging to the Neapolitan Volcanic District, for benefit of the local and national Civil Protection agencies. Such monitoring activities are now mainly focused on Campi Flegrei, currently at the attention (yellow) level according to the Campi Flegrei Emergency Plan issued by the Italian Civil Protection Department, where an anomalous seismic activity has been recorded starting from September 2023, with shallow events with magnitude up to 4.4, clearly felt by people, also in the city of Naples. Since the beginning of the current unrest phase in November, 2005, Campi Flegrei area underwent an uplift > 130 cm to date in the maximum deformation area, close to the coastline (see the INGV-"Osservatorio Vesuviano" monthly surveillance reports https://www.ov.ingv.it/index.php/monitoraggio-e-infrastrutture/bollettini-tutti/bollett-mensilicf/anno-2024-3/). No significant events have been recorded in the time span covered by this report (2022-2024) neither in the Vesuvius area, nor in the Island of Ischia where, conversely, a Md=3.9 earthquake occurred on August 21 st , 2017. Moreover, during the 2022-2024 biennium of the Supersite initiative, there was an improvement and fine-tuning of the EPOS Data Portal infrastructure (https://www.ics-c.eposeu.org/), conceived for data and products dissemination within the scientific community and accessible through the Volcano Observations Thematic Core Service (VO-TCS) gateway (https://vo-tcs.ct.ingv.it/gateway/). In this biennium, besides the provision of InSAR data from X-and C-bands (TSX/TDX/CSK/S-1) already exploited since many years, more activities supporting scientists involved in this Supersite took place, i.e. the provision of PLEIADES tri-stereo optical data over Vesuvius, jointly

The Maule 2010 and Tohoku-Oki 2011 earthquakes demonstrated how dormant upper plate faults can be reactivated as normal faults by plate margin relaxation following megathrust slip. However, the reactivation mechanisms of these types of faults are yet unexplored. To provide a better understanding of these mechanisms, we collected fault core samples from fault segments of the Atacama Fault System in northern Chile. The sampled fault segments have clear morphological evidence of Quaternary reactivation as normal fault. We performed laboratory experiments to measure the fault strength, stability and dynamic weakening. We consider low-velocity tests for exploring the frictional strength and velocity dependence of friction via a double-direct shear apparatus and ii) high-velocity tests for investigating the frictional properties at seismic velocities via a rotary shear apparatus. The experiments revealed that fault cores have low frictional strength, velocity-strengthening behaviour and strong dynamic weakening. Additionally, a novel experimental procedure that simulates stress relaxation by stepwise reducing of the normal stress on the sample assembly showed: 1. Accelerating creep towards dynamic weakening in chlorite-rich gouges and 2. oscillatory sliding in fault gouges enriched in illite. By extrapolating our experimental observations to natural conditions, we conclude that stable sliding is favoured during the interseismic phase of the subduction earthquake cycle, whereas unstable sliding is favoured during the coseismic and postseismic phases. The latter occurs via normal stress reduction during the shift from interseismic compression to co- and postseismic tension at the plate margin.

Earthquakes are frictional instabilities caused by the shear stress decrease, that is, dynamic weakening, of faults with slip and slip rate. During dynamic weakening, shear stress depends on slip, slip rate, and temperature, according to constitutive laws governing the earthquake rupture process. In the laboratory, technical limitations in measuring temperature during frictional instabilities inhibit the investigation and interpretation of shear stress evolution. Here we conduct high velocity friction experiments on calcite-bearing simulated faults, both on bare-rock and on gouge samples, at 20-30 MPa normal stress, 1-6 m/s slip rate and 1-20 m total slip. Seismic slip pulses are reproduced by imposing boxcar and regularized Yoffe slip rate functions. We measured, together with shear stress, slip, and slip rate, the temperature evolution on the fault by employing an innovative two-color fiber optic pyrometer. The comparison between modeled and measured temperature reveals that for calcite-bearing faults the heat sink caused by decarbonation reaction controls the temperature evolution. In bare-rocks, energy is dissipated as frictional heat, and temperature increase is buffered by the heat sink of the calcite decarbonation reaction. In gouges, energy is dissipated as frictional heat and for plastic deformation processes, balanced by the heat sink caused by the decarbonation reaction enhanced by the mechanochemical effect. Our results suggest that in calcite-bearing rocks, a common fault zone material for earthquake sources in the continental crust at shallow depth, the type of fault materials (bare-rocks vs. gouges) controls the energy dissipation during seismic slip. Plain Language Summary During earthquakes, faults rocks lose strength, and therefore the ability to sustain shear stress as a consequence of slip, slip rate, and temperature resulting in dynamic weakening. The mathematical relationships between the decreasing strength and slip, slip rate, and temperature and the energy balance describing the partition of energy are of fundamental importance to model the propagation of an earthquake rupture. These relationships can be defined thanks to laboratory experiments that simulate seismic slip. Here, we tested calcite-bearing fault rocks simulated as bare-rock and gouges. During the experiments, temperature was monitored thanks to an innovative measuring system. Numerical models were done assuming all mechanical energy was converted into heat. By comparing all results above, we discovered that the mechanical energy in both bare-rocks and gouges is converted to heat but limited by the occurrence of endothermic decarbonation reaction. In gouges, also an energy contribution for plastic deformation processes is required. Our work implies significant changes in the commonly accepted energy budget for earthquake propagation and show the importance of slip rate and temperature in driving together the dynamic weakening during seismic slip.

The region between central Europe and the centre of the Mediterranean is characterised by complex tectonics and kinematics. Here, the interaction between thickened crust, subducting lithosphere and surrounding asthenosphere produces strong and pervasive anisotropy in the upper mantle. Shear wave splitting measurements, the most adopted method to image seismic anisotropy so far, when interpreted in a ray-based framework result in little or no depth resolution, hampering a correct image of the anisotropy distribution with depth. In this study, we aim to better constrain the depth-dependent seismic anisotropy beneath Italy and surrounding regions, by isolating for the first time the source region of anisotropy at different depths. To do that, we perform an anisotropy tomography, adopting the splitting intensity inversion method. It is entirely based on the finitefrequency effect in the splitting of SKS waves. We first computed the splitting intensity using SKS waves recorded at all available permanent and temporary stations over the region, obtaining a huge dataset of measurements used as an input for the tomographic inversion. The large-scale 3D model of seismic anisotropy obtained with the inversion shows a clear change of anisotropy properties in terms of fast polarisation direction and intensity for different depths, thus improving the characterization of the main sources of anisotropy in the mantle as a function of depth. Shallower layers (70-100 km depth) are characterised by a complex and variable oriented pattern of anisotropy fast direction and intensity, which becomes progressively more organised with depth (100-300 km). This pattern suggests a strong control exerted by the geometry and motion of the different slab segments and the large-scale asthenospheric flow generated by subduction and roll-back processes. The strength of anisotropy increases with depth, with high values affecting the bulge of the Alps and Apennines chains and the southern Tyrrhenian subduction system. On the contrary, weaker anisotropy characterises the transition zone from the Apennines to Alpine domains beneath the Po plain, and both the Adriatic and European domains.

Hai Sentito Il Terremoto (HSIT: Did You Feel the Earthquake?) is one of the longest-running citizen science projects on the web. Launched experimentally in 1996 and fully operational since 2007, HSIT has collected data on over 16,800 earthquakes felt in Italy through more than 1,500,000 questionnaires submitted by citizens. Of these, nearly 30,000 participants are registered with HSIT, ensuring continuous engagement across the national territory. The results of this collaboration are bidirectional: citizens contribute their experience of earthquake perception, forming a core dataset that provides localized information. In return, they receive real-time feedback on the earthquake's effects on their region, represented in macroseismic intensity using the Mercalli (MCS) and European (EMS) scales. This partnership enables seismologists to access high-resolution data for analyzing territorial responses to seismic events, including attenuation laws, identifying amplification and/or attenuation zones, and perception patterns based on urban characteristics and behavioral factors. Citizen involvement has expanded the scope of the investigation to include moderate-to-low magnitude earthquakes and distant areas affected by stronger quakes. Registered participants, in particular, gain awareness of earthquakes as ongoing, active phenomena, shifting from a perception of rare catastrophic events to a continuous focus on regional seismic risks. The HSIT project bridges the gap between scientific knowledge and common understanding, fostering a shared experience of living in earthquake-prone regions with awareness and respect for associated risks and preventive measures.