The Mefite d’Ansanto (Southern Apennines, Italy) is one of the largest non-volcanic CO2 emission areas worldwide, representing a unique natural laboratory for investigating the interactions between geofluid circulation and external forcing mechanisms. In this study, we analyzed continuous seismic noise recorded by three stations deployed around the vent area, with the aim of exploring the influence of external drivers on noise parameters. We applied a combination of multiple linear regression (MLR) and Singular Spectrum Analysis (SSA) to seismic noise attributes, specifically RMS amplitude and polarization (Rlen), in two frequency bands associated with the activity of the emission vents. Our results indicate that environmental variables (mainly wind, solar radiation, air temperature, and soil moisture) and tidal strain contribute to signal modulations (20%–30% of the variance) on semidiurnal to monthly time scales. We propose that meteorological and tidal processes, by inducing variations in the physical properties of the shallow crust (permeability, pore pressure, stress distribution), can affect both near-surface seismic noise sources as well as the dynamics of the deeper degassing system. These findings highlight the potential of seismic noise as monitoring tool for tracking external forcing mechanisms acting on geofluid systems.

Mefite D’Ansanto is a remarkable mantle origin CO2 emissions system, and the understanding of the relative source mechanisms is one of the fundamental aspects for the comprehension of the evolution of the southern Apennines active dynamics. Moreover, due to its lively activity in a nearly quiet place, Mefite also represents a natural laboratory for the investigation of hydrothermal system dynamics. The seismic wavefield sourced by these CO2 emissions is complex, characterized by a background stationary hydrothermal tremor, with intermittent superposition wavetrains of variable duration. Here we focus on the transient signals generated by the emissions, which show a spectral content in 0.7–7.0 Hz and a peculiar waveform, described here for the first time. Due to their similarities with Long Period earthquakes occurring in volcanic/hydrothermal systems, we classify them as LP quakes and investigate their propagation and source processes. The Mefite LPs appear to be a mixture of P- and surface waves, generated at a depth slightly greater than that of the hydrothermal tremor and likely associated with bubbling mechanisms.

On 22–23 April 2025, a seismic noise survey was conducted at the Maccalube di Aragona, a mud volcano field located in Sicily (southern Italy), with the aim of characterizing the background signal associated with vent activity and the shallow subsurface structure. The experiment, named DEMETRA (DEnse MaccalubE TRomino Acquisition), was carried out within the framework of the multidisciplinary INGV-PROMUD research project, which aims to identify key indicators of mud volcano activity and potential precursors of paroxysmal events. Ambient seismic noise was recorded at 21 sites using a three-component, 24-bit digital tromograph. Measurements were conducted with a dense spatial sampling scheme covering both vent areas and peripheral zones. Preliminary data analyses included spectral estimates, computation of horizontal-to-vertical spectral ratio (HVSR) curves and evaluation of the polarization patterns. The HVSR curves do not display clear amplification peaks but rather show deamplification at specific sites. The polarization patterns exhibit spatial consistency across the vent areas. In addition, transient signals were identified in the background noise at some sites; based on their spectral and polarization characteristics, these signals are possibly associated with degassing, mud emissions, or bubbling phenomena. The dense spatial coverage of the DEMETRA experiment provides a valuable dataset for investigating subsurface properties and dynamic processes in an active mud volcano environment.

In the last decades, the scientific community has been focused on searching earthquake signatures in the Earth’s atmosphere, ionosphere, and magnetosphere. This work investigates an offshore Mw 5.5 earthquake that struck off the Marche region’s coast (Italy) on 9 November 2022, with a focus on the potential coupling between the Earth’s lithosphere, atmosphere, and magnetosphere triggered by the seismic event. Analysis of atmospheric temperature data from ERA5 reveals a significant increase in potential energy (Ep) at the earthquake’s epicenter, consistent with the generation of Atmospheric Gravity Waves (AGWs). This finding is further corroborated by the MILC analytical model, which accurately simulates the observed Ep trends (within 5%), supporting the theory of Lithosphere–Atmosphere–Ionosphere–Magnetosphere coupling. The study also examines the vertical Total Electron Content (vTEC) and finds notable fluctuations at the epicenter, exhibiting periodicities (7–12 min) characteristic of AGWs and traveling ionospheric disturbances. The correlation between ERA5 observations and MILC model predictions, particularly in temperature deviations and Ep distributions, strengthens the hypothesis that earthquake-generated AGWs impact atmospheric conditions at high altitudes, leading to observable ionospheric perturbations. This research contributes to a deeper understanding of Lithosphere–Atmosphere–Ionosphere–Magnetosphere coupling mechanisms and the potential for developing reliable earthquake prediction tools.

We discuss some relevant results obtained in recent works on the Neapolitan Volcanoes, i.e., Campi Flegrei, Ischia, and Vesuvius (southern Italy) regarding the coupling between ground deformation detected by tiltmeters and volcano-tectonic seismicity. Great interest is devoted to those volcanoes because of the high level of volcanic risk, to which the inhabitants are exposed. Indeed, continuous and dense monitoring of their activity is provided by the Istituto Nazionale di Geofisica Vulcanologia, which employs different types of instrumentation, among which borehole tiltmeters and seismic networks. The works we consider in the present review focus on the link between seismicity and ground tilt anomalies covering the years 2015–2022. In detail, for the Campi Flegrei caldera, a significant variation in the tiltmeter pattern has been identified. Such anomaly indicates a transition to a different dynamical regime starting since 2020, also supported by some changes in the seismicity, ground temperatures of the fumarolic field, gravimetric and geochemical parameters. Concerning Ischia Island, a variation in the main tilt direction, which switched from NNW to NNE, has been detected in response to the Md 4.0 earthquake that occurred on 21 August 2017. Finally, at Vesuvius the relation among seismicity, ground inclination, and geochemical observables was investigated over the time interval 2012–2020 providing evidence of several simultaneous anomalies as proxies of the dynamical evolution of the volcanic system. Moreover, the comparison of the static displacement induced by seismicity with the measured tilt sheds light on the strict link between these two observables. The joint analyses of the seismic and tiltmeter signals represent a powerful tool for unraveling the volcanic dynamics and separating inner sources from external contributions.

In the Summer 2021 a seismic passive survey was carried out at Mefite d’Ansanto (Italy), well-known for the cold non-volcanic and lethal CO2 emissions. Mefite is located close to that part of Irpinia region hosting the large historical earthquakes’ faults, that generated the destructive magnitude 6.8 earthquake of 1980 and have been related to the CO2 leakage by the scientific community. The survey was conducted by installing a small short-period seismic array with the purpose of determining the wavefield features and detecting the possible signature of the regional stress variations. By analyzing the acquired data, we have determined the properties of the seismic wavefield associated with the emission vents, in the intermediate frequency band, 1–15 Hz, which was found to be composed of a stationary background component and an intermittent higher energy one. Basing on our results, considerations on the medium properties and the deep source available information, we have depicted a schematic model of the shallow seismic source: the background components are linked to the shallower activity of the hydrothermal system, e.g. the bubbling, while the intermittent ones are likely generated by the passage of the overpressured gas, trapped in the first-tens-meters’ layers, after overcoming the internal cohesion charge. The characteristics of the wavefield that we have defined, refer to a condition in which no regional earthquakes occurred and could be considered as a basis to identify possible significant variations linked to CO2 emissions and to the regional stress changes.

We propose and test a procedure in the time domain to directly compare the waveforms of teleseismic events recorded by seismic stations located a few kilometres from each other and equipped with different instrumentations. The method is based on the deconvolution of the signals at each seismic station for its sensor own frequency response and data sampling to equalise the waveforms, making them directly comparable. The horizontal components of the events are rotated versus back-azimuth, considering that P-to-S converted phases along a crustal discontinuity are generally more evident in the radial and transverse components. Finally, we apply the cross-correlation technique to the resulting signals to quantify the similarities among the waveforms. The method has been tested on teleseismic events recorded by the seismic stations located in and close to the Mefite d'Ansanto area (southern Apennines), which represents the largest non volcanic low temperature CO2 emission area on Earth.

The ability to image the underground structures of volcanoes is limited by the precision, resolution and pene-tration depth of each single geophysical method. In order to improve the knowledge of specific volcanic edifices and to better understand the general behavior of structures, the use of a combination of methods is strongly recommended to exploit and maximize their complementary capabilities of resolution and penetration depths. In this work a large dataset of seismic and electromagnetic measurements has been used to provide a more detailed and improved geophysical image of the shallower portion of the northern sector of Ischia Island (Campania region, Italy), severely hit by the August 21, 2017 earthquake (Mw 3.9). We analysed data by using different methodologies: Horizontal-to-Vertical Spectral Ratio (HVSR), seismic array technique (f-k), polarization analysis and Time Domain ElectroMagnetic (TDEM) survey. These methods are sensitive in a different way to tectonic features, lithologies, layer geometry and fluid distribution. Thus, their combination is useful for studying sites with complex crustal structures such as Ischia island, which is characterized by a well-developed geothermal system linked to the presence of a shallow magmatic body. Results of our study provides detailed information of the physical properties of the subsoil through: 1) the spatial distribution of the amplification parameters of ground motion, showing frequency peaks below 1 Hz and/or between 1 Hz and 5 Hz; 2) the definition of the velocity models up to 600 m depth, with shear wave velocities ranging from 150 m/s for the shallower layers to 2500 m/s for the half space; 3) the recognition of the correlation between the principal fault structures and polarization directions of the noise wavefield, mostly oriented along EW and NE-SW directions; 4) the resistivity models of the first 80 m depth with high resistivity values of the shallow layers in the range 50-100 omega.m and low resistivity values of the bottom layers in the range 1-10 omega.m.

We compiled a database for the Campi Flegrei seismic events that occurred from 2011 to 2018 at all stations available (merging permanent and temporary networks). Then we computed the two observables of the crustal anisotropy: time delay between fast and slow S-wave’s arrivals, and polarization direction of the fast S-wave. These results provide useful information about the amount of crustal anisotropy and the main direction, respectively, with this latter representing a proxy for the local stress field. We could thus obtain a picture of their spatial and temporal distributions to be compared with other geophysical and geochemical observations. In particular we could identify common features, such as change points, to several time series. This helps us in building a more complete interpretation of the volcanic system changes that were occurring during the recent ongoing unrest phase, which started in 2005.

A passive seismic experiment is carried out at the non-volcanic highly degassing site of Mefite d’Ansanto located at the northern tip of the Irpinia region (southern Italy), where the 1980 MS 6.9 destructive earthquake occurred. Between 2020 and 2021, background seismic noise was recorded by deploying a broadband seismic station and a seismic array composed of seven 1 Hz three-component sensors. Using two different array configurations, we were allowed to explore in detail the 1–20 Hz frequency band of the seismic noise wavefield as well as Rayleigh wave phase velocities in the 400–800 m/s range. Spectral analyses and array techniques were applied to one year of data showing that the frequency content of the signal is very stable in time. High frequency peaks are likely linked to the emission source, whereas at low frequencies seismic noise is clearly correlated to meteorological parameters. The results of this study show that small aperture seismic arrays probe the subsurface of tectonic CO2-rich emission areas and contribute to the understanding of the link between fluid circulation and seismogenesis in seismically active regions.

<p>Mefite d’Ansanto (Italy) is the largest non-volcanic CO<sub>2</sub> emission field on the Earth. The isotopic signature of the CO<sub>2</sub> testifies a deep origin of the gases emitted at this site, whose source is probably the mantle wedge beneath the Apennines along the Tyrrhenian side (Chiodini et al., 2010). Mefite is located between the Sannio and the Irpinia seismogenic regions, that are considered among the most active areas of the southern Apennines. The emission site falls at the northern tip of the Irpinia fault system that is associated with the destructive M<sub>S</sub> = 6.9, 1980 Irpinia earthquake. The gas leakage from this zone is linked to active faulting that characterized the area and determined large historical earthquakes</p> <p>A temporary acquisition survey close to the Mefite emission field was carried out between 8 June and 28 September 2020 by using a seismic array, named Array MEfite (AME), composed of seven short-period stations. We have analyzed the characteristics of the recorded background seismic noise, e.g., spectral properties, energy temporal pattern (RMS) and polarization (Montalbetti et al., 1970), and estimated site effects (Nakamura, 1989; http://www.geopsy.org/). The seismological temporal patterns have been compared with the meteorological parameters, such as temperature and rainfall, to find possible relationships with exogenous factors. We found a well-defined spatial pattern for the spectral components above 5 Hz, which appear clearly linked to the emission field dynamics. On the other hand, the spectral components below 5 Hz result from the overlapping of multiple sources, of both exogenous, such as anthropogenic and meteorological factors, and endogenous nature. Application of the Independent Component Analysis (ICA) technique (Hyvärinen et al., 2001) contributed to discriminate between natural and anthropogenic sources.</p> <p> </p> <p>References</p> <p>Chiodini, G., D. Granieri, R. Avino, S. Caliro, A. Costa, C. Minopoli, and G. Vilardo (2010). Non‐volcanic CO<sub>2</sub> Earth degassing: Case of Mefite d’Ansanto (southern Apennines), Italy, Geophys. Res. Lett. 37, L11303, doi: 10.1029/2010GL042858.</p> <p>Hyvärinen, A., Karhunen, J. & Oja, E. (2001). Independent Component Analysis. Wiley, New York,</p> <p>Montalbetti, J. R., Kanasevich, E. R. (1970): Enhancement of teleseismic body phase with a polarization filter. Geophys. J. Int. 21 (2), 119–129.</p> <p>Nakamura, Y. (1989). A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface, Railway Technical Research Institute, Quarterly Reports, 30 (1), 25-33.</p>

One of the strategies to detect the precursors of an eruption is to define the background dynamical state of a volcano for a prompt recognition of deviations from the basic condition. Mt. Vesuvius (Italy), currently in a quiescent state, is one of the most monitored volcanoes in the world, inciting multidisciplinary advanced studies. Hence an understanding of the links among the different monitored parameters is mandatory. In recent decades the joint analyses of ground tilt and seismicity have added to the understanding of the volcano’s activity. In this paper, we outline the first steps towards a comprehension of the link between Mt. Vesuvius earthquakes and co-seismic ground tilt, after excluding the contribution of other external forces acting on the ground, such as tides, landslides or exceptional meteorological phenomena. We used the seismicity with a duration magnitude ≥ 2.0 recorded at Mt. Vesuvius in the period 2018–2020 to estimate the source parameters and to calculate the associated static displacement. Then, we compared the ground inclination retrieved from the estimated seismic deformation with the long-term ground motion trend measured by tiltmeters. We found that in most cases the two vectors have a comparable size and direction.

An accurate survey of old and new datasets allowed us to probe the nature and role of fluids in the seismogenic processes of the Apennines mountain range in Italy. New datasets include the 1985–2021 instrumented seismicity catalog, the computed seismogenic thickness, and geodetic velocities and strains, whereas data from the literature comprise focal mechanism solutions, CO2 release, Moho depth, tomographic seismic velocities, heat flow and Bouguer gravity anomalies. Most of the inspected datasets highlight differences between the western and eastern domains of the Apennines, while the transition zone is marked by high geodetic strain, prevailing uplift at the surface and high seismic release, and spatially corresponds with the overlapping Tyrrhenian and Adriatic Mohos. Published tomographic models suggest the presence of a large hot asthenospheric mantle wedge which intrudes beneath the western side of the Apennines and disappears at the southern tip of the southern Apennines. This wedge modulates the thermal structure and rheology of the overlying crust as well as the melting of carbonate-rich sediments of the subducting Adriatic lithosphere. As a result, CO2-rich fluids of mantle-origin have been recognized in association with the occurrence of destructive seismic sequences in the Apennines. The stretched western domain of the Apennines is characterized by a broad pattern of emissions from CO2-rich fluids that vanishes beneath the axial belt of the chain, where fluids are instead trapped within crustal overpressurized reservoirs, favoring their involvement in the evolution of destructive seismic sequences in that region. In the Apennines, areas with high mantle He are associated with different degrees of metasomatism of the mantle wedge from north to south. Beneath the chain, the thickness and permeability of the crust control the formation of overpressurized fluid zones at depth and the seismicity is favored by extensional faults that act as high permeability pathways. This multidisciplinary study aims to contribute to our understanding of the fluid-related mechanisms of earthquake preparation, nucleation and evolution encouraging a multiparametric monitoring system of different geophysical and geochemical observables that could lead the creation of a data-constrained and reliable conceptual model of the role of fluids in the preparatory phase of earthquakes in the Apennines.

Seismic noise recorded during a seismic survey carried out at Solfatara Volcano in the period 2-6 April 2007. Five circular seismic arrays were deployed inside the crater; an other seismic station was installed on the eastern rim for a hardrock reference. Details on the experiment, as well as data description and station coordinates are reported in: Petrosino, S., Damiano, N., Cusano, P., Veneruso, M., Zaccarelli, L., Torello, V., & Del Pezzo, E. (2008). Seismic noise at Solfatara Volcano (Campi Flegrei, Italy): acquisition techniques and first results. Quaderni di Geofisica. Shallow crustal structure of Solfatara volcano, inferred from dataset analysis has been published in: Petrosino, S., Damiano, N., Cusano, P., Di Vito, M. A., de Vita, S., & Del Pezzo, E. (2012). Subsurface structure of the Solfatara volcano (Campi Flegrei caldera, Italy) as deduced from joint seismic‐noise array, volcanological and morphostructural analysis. Geochemistry, Geophysics, Geosystems, 13(7).

FURTHER – “The role of FlUids in the pReparaTory pHase of EaRthquakes in Southern Apennines” is an INGV Departement Strategic Project devoted to define the role of fluids in earthquake genesis. One of the target areas of the multidisciplinary study is Mefite d’Ansanto, which is the largest area of non-volcanic low temperature CO2 emission field on the Earth. In particular, Work Package 1.4 is dedicated to the application of analysis methodologies in time and frequency domains, aimed to intercept eventual variations in fluid behavior before or in correspondence of local and regional earthquakes, using recordings from the INGV National Seismic Network (IV) and local networks. For this purpose, temporary acquisition surveys have been locally deployed. On November 20, 2020, a stand-alone seismic station equipped with a Guralp CMG40T 60s broadband sensor, was installed close to the Mefite emission field. In this study we analyze some characteristics of the local seismicity, e.g., frequency content, energy temporal pattern (RMS) and polarization (Montalbetti et al., 1970), and estimate site effects (Nakamura, 1989; http://www.geopsy.org/). Here we present the first results of the ongoing investigation of the seismic noise wavefield in the Mefite area. The temporal pattern of the retrieved seismological observables is compared with the meteorological parameters, such as temperature and rainfall, to find possible relationships with exogenous factors. Preliminary analysis of the waveforms acquired by the stations of the (IV) have been also performed. We selected the stations inside a radius of 30 km from Mefite area to eventually retrieve the fluid dynamics footprint in the recorded wavefield. The identification of the wavefield and site characteristics will be useful to define the features of the next survey planned in the area. References Montalbetti, J. R., Kanasevich, E. R. (1970): Enhancement of teleseismic body phase with a polarization filter. Geophys. J. Int. 21 (2), 119–129. Nakamura, Y. (1989). A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface, Railway Technical Research Institute, Quarterly Reports, 30 (1), 25-33.

In this paper, we analyse the seismic noise at Ischia Island (Italy) with the objective of detecting the hydrothermal source signals taking advantage of the Covid-19 quiescence due to lockdown (strong reduction of anthropogenic noise). We compare the characteristics of the background noise in pre-, during and post-lockdown in terms of spectral content, energy release (RMS) and statistical moments. The continuous noise is decomposed into two independent signals in the 1−2 Hz and 2−4 Hz frequency bands, becoming sharpened around 1 Hz and 3 Hz respectively in lockdown. We propose a conceptual model according to which a dendritic system of fluid-permeated fractures plays as neighbour closed organ pipes, for which the fundamental mode provides the persistent whisper and the first higher mode is activated in concomitance with energy increases. By assuming reasonable values for the sound speed in low vapor–liquid mass fraction for a two-phase fluid and considering temperatures and pressures of the shallow aquifer fed by sea, meteoric and deep hydrothermal fluids, we estimate pipe lengths in the range 200–300 m. In this scheme, Ischia organ-like system can play both continuous whisper and transients, depending on the energy variations sourced by pressure fluctuations in the hydrothermal fluids.

In the last decades, thermal infrared ground-based cameras have become effective tools to detect significant spatio-temporal anomalies in the hydrothermal/volcanic environment, possibly linked to impending eruptions. In this paper, we analyzed the temperature time-series recorded by the ground-based Thermal Infrared Radiometer permanent network of INGV-OV, installed inside the Solfatara-Pisciarelli area, the most active fluid emission zones of the Campi Flegrei caldera (Italy). We investigated the temperatures’ behavior in the interval 25 June 2016–29 May 2020, with the aim of tracking possible endogenous hydrothermal/volcanic sources. We performed the Independent Component Analysis, the time evolution estimation of the spectral power, the cross-correlation and the Changing Points’ detection. We compared the obtained patterns with the behavior of atmospheric temperature and pressure, of the time-series recorded by the thermal camera of Mt. Vesuvius, of the local seismicity moment rate and of the CO2 emission flux. We found an overall influence of exogenous, large scale atmospheric effect, which dominated in 2016–2017. Starting from 2018, a clear endogenous forcing overcame the atmospheric factor, and dominated strongly soil temperature variations until the end of the observations. This paper highlights the importance of monitoring and investigating the soil temperature in volcanic environments, as well as the atmospheric parameters.

We reconstruct the composite dynamics of Mt. Vesuvius volcano in the period 2012–2019 from the study of ground deformation, seismicity, and geofluid (groundwater and fumarolic fluids) circulation and recognize complex spatio-temporal variations in these observables at medium (years) and short (months) time-scales. We interpret the observed patterns as the combined effect of structural changes affecting the volcanic edifice and variations of the dynamics of the hydrothermal system. In particular, we identify a change in the activity state of Mt. Vesuvius. After the activity reached minimum levels in 2014, the centroid of the surface manifestations migrated towards the SE. Episodic variations of co-seismic and aseismic deformation and fluid release, if analysed separately, would likely have been interpreted as pseudo-random oscillations of the background geophysical and geochemical signals. When organised in a comprehensive, multiparametric fashion, they shed light on the evolution of the volcano in 4D (x,y,z, time) space. These inferences play a crucial role in the formulation of civil protection scenarios for Mt. Vesuvius, a high risk, densely urbanized volcanic area which has never experienced unrest episodes in the modern era of instrumental volcanology.

The purpose of this work is to study the subsoil structure of the Campi Flegrei area using both spectral ratios and array techniques applied to seismic noise. We have estimated the dispersion curves of Rayleigh waves by applying the Frequency–Wavenumber (f–k hereinafter) and Modified Spatial Autocorrelation (MSPAC) techniques to the seismic noise recorded by the underground short period seismic Array “ARF”, by the broadband stations of the UNREST experiment and by the broadband stations of the seismic monitoring network of INGV – Osservatorio Vesuviano. We have performed the inversion of a dispersion curve (obtained averaging the f–k and MSPAC dispersion curves of seismic noise and single phase velocity values of coherent transient signals) jointly with the H∕V spectral ratio of the broadband station CELG, to obtain a shear wave velocity model up to 2000 m depth. The best-fit model obtained is in a good agreement with the stratigraphic information available in the area coming from shallow boreholes and deep wells drilled for geothermal exploration. In active volcanic areas, such as Campi Flegrei, the definition of the velocity model is a crucial issue to characterize the physical parameters of the medium. Generally, a high quality characterization of the medium properties helps to separate the contributions of the volcanic source, path and site in the geophysical observables. Therefore, monitoring possible variations in time of such properties in general can help to recognize anomalies due to the volcano dynamics, i.e. fluid migration connected to the volcanic activity.