The evolution and state of geological structure at Earth’s surface is best understood with an accurate characterization of the subsurface, where fluid distribution plays a key role. We present high-resolution seismic tomographic images of tectonic and geological features of the Italian lithosphere based on ground motion recordings and obtained through an iterative procedure. Enhanced accuracy is enabled by state-of-the-art three-dimensional wavefield simulations in combination with an adjoint-state method. The resulting tomographic model characterizes the subsurface structure in terms of compressional and shear wavespeed values at remarkable resolution, corresponding to a minimum period of ~10 s. As primary findings of our work, images of the lithospheric structure in Central Italy are consistent with recent studies on the distribution of fluids and gas (CO₂) within the Italian subsurface, allowing us to infer the presence of deep melted material that induces shallow gas fluxes, or traps and deep storage of gas that can be correlated with seismicity. We illuminate Mt. Etna volcano and support the hypothesis of a deep reservoir (~30 km) feeding an intermediate-depth magma-filled intrusive body, which in turn is connected to a shallow chamber. We also investigate the intriguing features of the Adriatic plate offshore of the eastern Italian coast. Tomographic evidence reveals a structure of the plate made of two distinct microplates with different fabric and behavior, and separated by the Gargano deformation zone, indicating a complex lithosphere and tectonic evolution.

How to cite: Magnoni, F., Casarotti, E., Komatitsch, D., Di Stefano, R., Ciaccio, M. G., Tape, C., Melini, D., Michelini, A., Piersanti, A., and Tromp, J.: Adjoint Tomography of the Italian Lithosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12491, https://doi.org/10.5194/egusphere-egu23-12491, 2023.

The harnessed Nesjavellir geothermal area is one of several geothermal fields on the flanks of the Hengill volcano, SW-Iceland. In this study, we present a detailed seismic imaging of the area through the mapping of the V_P, V_S and V_P/V_S ratio using seismic data recorded from 2016 to 2020 and compare them to a resistivity model from the same area and rock temperature measured in boreholes. To obtain reliable initial hypocenter locations and a reference seismic velocity, we solve the coupled hypocenter-velocity problem and obtain a reliable minimum 1D P-wave velocity model for the study area. First, we performed the relocation of all the events in the catalogue using the new 1D velocity model and the estimated  V_P/V_S value of 1.77. We chose the highest quality events based on the quality of the relocations and used them to perform the 3D tomographic inversion. We used an iterative linearized delay-time inversion to estimate both the 3D P- and S-wave velocity models and earthquake locations.

The results highlight that at depths less than 1 km the crust has a high V_P/V_S ratio (around 1.9) and low V_P and V_S values. Low resistivity at comparable depths in the same region has been explained as being due to the smectite clay cap. The observed low V_P/V_S ratio of 1.64 to 1.70 for depths between 1 and 3 km coincides with high resistivity values. The seismicity in this region, where temperatures often exceed 240°C, seems to be sparse and concentrated near the production wells. This seismicity has been explained as being caused by both production and tectonic activity.  At depths larger than 3 km significant high V_P/V_S ratio anomaly (>1.9) is observed and coincides spatially with a deep-seated conductive body that domes up at about 4.500 m b.sl. Elevated temperatures are observed above this structure in borehole temperature data. We propose that these signals reflect hot 600-900°C cooling intrusives, close to the brittle ductile transition - possibly the heat source(s) of the geothermal field above. These anomalies are at the same location as the last fissure eruption in Hengill almost 2,000 years ago. A deeper NNE-SSW trending seismic cluster at 3-6 km depth, likely outlining an active fault, is observed at the edge of this high V_P/V_S anomaly. The heat source of the Nesjavellir geothermal field is most likely connected to this most recent volcanism as reflected by the deep-seated low resistivity body and high V_P/V_S ratio, located beneath the deep fault that connects the flow path of the high temperature geothermal fluid, resulting in an actively producing reservoir.

The availability of a 3D model represents a starting point for 4D tomography study which will allow us to track changes in crustal properties over time and the estimation of fault mechanisms and kinematic source parameters.

This work has been partially supported by PRIN-2017 MATISSE project, No 20177EPPN2, funded by the Italian Ministry of Education and Research.

How to cite: Amoroso, O., Napolitano, F., Hersir, G. P., Ágústsdóttir, Þ., Convertito, V., De Matteis, R., Gunnarsdóttir, S. H., Hjörleifsdóttir, V., and Capuano, P.: Seismic Imaging of the Nesjavellir geothermal field, SW-Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7667, https://doi.org/10.5194/egusphere-egu23-7667, 2023.

The Amatrice (Mw 6.0) - Visso (Mw 5.9) - Norcia (Mw 6.5) seismic sequence (hereafter AVN) struck the Central Apennines (Italy) in 6-7 months during 2016-2017, and it has been widely associated with fluid migration in the normal faults network. The analysis of attenuation parameters (e.g., scattering and absorption) gives information about material properties and the presence of fluids and fracturing. In this study, we investigate in a 3D mapping the scattering contribution to the total attenuation of the AVN seismic sequence (August 2016-January 2017), together with a pre-sequence dataset (March 2013-August 2016). We applied peak delay as a proxy of seismic scattering, to obtain further information on the fracturing processes in time and space. Previous 2D mapping of peak-delay time and coda attenuation tomography in the same study area indicated a substantial control on the scattering of seismic waves by structural (e.g., Monti Sibillini thrust) and lithological (e.g., Umbria- Marche and Lazio-Abruzzi geological domains) features.
Our 3D results show clear differences between the pre-sequence and the sequence, where we can identify an increase of scattering with time after the mainshocks. The substantial alterations in scattering are observed between 4 - 6 km depth, in the hanging wall of the Monti Sibillini thrust, which acts as a rheological barrier between high and low scattering zones. Peak delay variations detected a significant anomaly in the Triassic deposits layer, at the roots of the Acquasanta thrust, east of Monti Sibillini. Here, low scattering during the pre-sequence epoch is replaced by high scattering during the mainshocks. The low scattering along the Acquasanta thrust suggests an increment of pore pressure, associated with the presence of fluids in this geological formation. The subsequent release of those fluids may have caused the mainshocks of the seismic sequence, and a subsequent increase in fracturing, as observed by the high scattering anomaly. These results bring a new light on the importance to consider the thrusts systems in the tectonic framework of the Central Italy.

How to cite: Gabrielli, S., Akinci, A., De Siena, L., Del Pezzo, E., Buttinelli, M., Maesano, F., and Maffucci, R.: The impact of tectonic structures on the 3D scattering imaging of the Central Italy Seismic Sequence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5861, https://doi.org/10.5194/egusphere-egu23-5861, 2023.

Non-linear response of the elastic properties of the crust has been studied using the analysis of seismic velocity variations induced by various natural forcing agents (earthquakes, tides, volcanic processes, and others). Here we study 1) the variations of seismic velocities in response non-tectonic deformations associated to phases of groundwater recharge/discharge in large karstic aquifers in the Southern Apennines of Italy and discuss 2) the implications in terms of non-elastic behavior of the crust. Karst systems are complex aquifers common within the carbonate rocks of the Apennines. They store large amount of groundwater producing significant horizontal dilatational strains that modulate the secular, tectonic deformation (~3 mm/yr extension across the Apennines) and background seismicity (Silverii et al., 2019; D’Agostino et al., 2018) with seasonal and multi-seasonal signatures. The availability of accurate and temporally-long hydrological measurements (rainfall and karst spring discharge) in addition to dense seismic and geodetic networks provide the opportunity to assess the elastic response of the crust to strain forcing at various periods and the sensitivity of relative velocity variations to non-tectonic, hydrological strain variations. We performed velocity variation measurements on seismic noise autocorrelation signals recorded at seismic stations for different coda waves time lapse and compared them with strain measured by the GPS network. We observe that seismic velocities decrease during dilatation episodes (high hydraulic head) and increase during contraction (low hydraulic head). We find that the retrieved strain sensitivity of seismic velocity changes is of the order of ~10³ and discuss such sensitivity with previous natural and laboratory results.

How to cite: Tarantino, S., Poli, P., D'Agostino, N., Festa, G., Vassallo, M., Ventraffrida, G., and Zollo, A.: Strain sensitivity of seismic velocity variation induced by hydrological forcing of karst aquifers in the Apennines, Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6668, https://doi.org/10.5194/egusphere-egu23-6668, 2023.

Historic levels of drought, globally, call for sustainable freshwater management. Under pressing demand is a refined understanding of the structures and dynamics of groundwater systems. Here we present an unconventional, cost-effective approach to aquifer monitoring using seismograph arrays. Employing advanced seismic interferometry techniques, we calculate the space-time evolution of relative changes in seismic velocity, as a measure of hydrological properties. During 2000–2020 in basins near Los Angeles, seismic velocity variations match groundwater tables measured in wells and surface deformations inferred from satellite sensing, but the seismological approach adds temporal and depth resolutions for deep structures and processes. Maps of long-term seismic velocity changes reveal distinct patterns (decline or recovery) of groundwater storage in basins that are adjacent but adjudicated to water districts conducting different pumping practices. This pilot application bridges the gap between seismology and hydrology, and shows the promise of leveraging seismometers worldwide to provide 4D characterizations of groundwater and other near-surface systems.

How to cite: Mao, S., Lecointre, A., van der Hilst, R. D., and Campillo, M.: Space-time monitoring of groundwaterfluctuations with passive seismicinterferometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1774, https://doi.org/10.5194/egusphere-egu23-1774, 2023.

The Matese massif is an extensive outcrop of Apenninic Platform carbonate rocks located at the boundary between Central and Southern Apennines (Italy), extending ~74 km from NW to SE over an area of ~1600 km² and reaching a maximum height of 2050 m. Its geological history documents different phases of compressional and extensional tectonics which modeled the shape and size of faults within the massif. The present seismotectonic background belongs to the extensional style of the Central-Southern Apennine chain, with a series of NW-SE active extensional faults and occurrence of seismic activity, which reached intensities up to IX MCS.
The karst features of the Matese significantly affect the hydrology of the massif, where rainfall trends lead to large variations in the water reservoirs.
Recent papers report the presence of deformations induced by the elastic response of the loaded surface and the poroelastic properties of the ground. These two mechanisms are different: in the first the water load causes subsidence, in the second uplift. However, under anisotropic conditions, water pressure changes in poroelastic rocks can induce large horizontal deformations especially where highly fractured rocks may provide permeability for fluid flow. When the porosity is determined by systematic fractures, the medium is anisotropic and the surface deformation is mainly perpendicular to the fracture system. To study such processes, we analyzed the time series of 7 GNSS permanent stations located in the Matese area, and the seismicity, covering the 2005-2022 time interval. The GNSS time series of each station were detrended from a best-fitted linear model plus eventual steps due to instrumental changes, without modeling periodicities, obtaining three time series of residual displacements (N, E, Up) for each site. 
We also analyzed spring discharge and pluviometric data. The latter are used to compute the rainfall excess as the difference between the cumulated daily rainfall and the best-fitting straight line of the cumulated rainfall. Then, we applied an Independent Component Analysis to the GNSS data. This allowed us to extract from the time series, in a blind way, a signal very well correlated with hydrological data. This geodetic signal has a large horizontal amplitude and occurs perpendicular to the fracture orientations. This is also shown by the horizontal strain tensor estimated from the displacements associated with this signal, whose maximum extension axis reaches up 1µstrain perpendicular to the fault direction.
During wet periods, characterized by high rainfall excess and increasing values of spring discharge, we observe extensional deformation with stations moving “away” from the massif center; during dry periods a compressional deformation occurs, with stations coming back “toward” the massif. This suggests that the water stored within the massif is the driver of such geodetic signal: the larger the water pressure is, the larger the extensional deformation becomes; when the water level decreases, the water pressure is reduced and then compressional deformation occurs. 
Further studies should be done to understand if water circulation also indirectly affects the background seismicity. 

How to cite: Pintori, F., Sparacino, F., and Riguzzi, F.: Hydrogeologic processes drive deformations in the Matese massif (Southern Italian Apennines), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2254, https://doi.org/10.5194/egusphere-egu23-2254, 2023.

Natural groundwater level fluctuation in karstic networks resulting from significant recharge (precipitation and/or seasonal snowmelt) can potentially induce seismicity. Triggering is often considered to be the result of pore pressure diffusion front migrating from the surface to focal depth, assuming a homogeneous crust. Although this assumption can be acceptable in some cases (e.g. homogeneously fractured basement) it is hardly justified in known karstic area. Considering the specific features of karst and data of three case studies, we elaborate a conceptual model of rain-triggered seismicity in karstic regions by identifying potential triggering mechanisms and, using simplified analytical solutions, quantifying their impact on fault stability. Results of this analysis indicate that a direct hydrogeological connection between karstic conduits and the hypocenter can lead to pore pressure variation of the order of MPa, potentially initiating a rupture. To test the conceptual model, field investigations are carried out in the Jura Mountains, a well-known karstic area with low to moderate seismicity. Data acquisition consists in monitoring the natural microseismicity and the flowrate at karstic springs, used as a direct proxy for groundwater level fluctuations.Combining both data sets allows to identify events that are potentially rain-triggered and to acquire a quantitative knowledge on what pressure change, inferred from the hydraulic head increase, is affecting the fault’s stability, a valuable information when planning underground projects.

How to cite: Perrochet, L., Preisig, G., and Valley, B.: Hydrogeologic and microseismic monitoring as a tool to evaluate fault criticality in karstic regions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11775, https://doi.org/10.5194/egusphere-egu23-11775, 2023.

Earthquakes are typically followed by a series of aftershocks. Deeply trapped and internally generated high-pressure fluid diffuses along permeable paths and subsequently reactivates faults that drive thousands of seismic events. The thermal decomposition of CO₂ in the carbonate regime in the central Apennines contributes significantly to seismogenesis and provides substantial quantities of internally derived high-pressure fluids. We develop a 3-dimensional model of non-linear diffusion with a source term that diffuses along faults and to the surroundings, triggering seismicity along the flow paths, and compare model results with the spatial and temporal observations from the 2009 L'Aquila (Mw 6.3) and the 2016 Amatrice-Visso-Norcia (Mw 6.5) earthquake sequences. The model mimics the generation of additional fluid by thermal decomposition and shows solid correlations in space by comparing the calculated fluid pressure field and the locations of over 50,000 well-constrained hypocenters.

In contrast, other earthquakes result in only a small number or even no aftershocks. These include the Peru earthquake (Sep. 25, 2013 -Mw 7.1), the Mexiko earthquake (Sep. 19, 2017 - Mw 7.1), and the Crete earthquake (Oct. 12, 2021). Additionally, great earthquakes in Pakistan (Jan. 18, 2011 - Mw 7.2) and Iran ( Apr. 16, 2013 -Mw 7.7) also spawned no aftershocks despite the high magnitudes. These phenomena can be linked to the dynamics of volcanic arcs.

How to cite: Gunatilake, T. and Miller, S. A.: Linking Aftershock-free significant earthquakes to the dynamics of volcanic arcs; and linking aftershock-rich significant earthquakes to devolitization., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15583, https://doi.org/10.5194/egusphere-egu23-15583, 2023.

Over the last decades, many studies highlighted the close relationship between thermal structure, surface processes, and tectonic forces in controlling the deformation of the lithosphere. The contribution of these key factors, however, is not constant in time and may result in a complex deformation history, as already observed in many regions around the globe. In this view, the rheology of the crust is pivotal to leading regional tectonic evolution.

Among the factors that may cause remarkable strength and rheological variations in the crust, the presence of fluid phases is undoubtedly one of the most prominent. The mechanisms of rock-fluid interaction are still a debated field of research. However, it has been suggested in many studies that a major effect of fluids is enhanced seismicity of regions where they are present.

In this framework, the Val d’Agri represents a perfect example of how crustal evolution can be influenced by several factors interacting with one another. In this region, we analyze the relationships between different mechanisms in the final structural setting of the region, with implications on the natural and induced seismicity. To this aim, we built up a numerical model that integrates the combined effects of rheological stratification of the crust, inherited zones of weakness, variations in the tectonic regime, surface erosion, and fluid presence. Our results show that variation in the strength of the evaporite layer between the carbonate platform and the basement has a profound impact on the tectonic style of the Val d’Agri. The uplifting and subsidence pattern in the region follows stages of slow vertical movements to stages of very fast uplifting and denudation, due to the activation of new tectonic structures where movement is enhanced. This reflects on pressure and temperature variations in time, that follow typical yo-yo patterns observed in several tectonically active regions. The present-day configuration of the VA is also influenced by the erosion rate. More in detail, a comparison between the observed structures in the area and our model’s results with varying erosion rates suggests that the VA has been subjected to medium to fast erosion during its evolutionary history. In addition, our model predicts the presence and orientation of faults where fluid percolation or injection at high pressure can generate clusters of microseismicity.

How to cite: Lavecchia, A., Tallarico, A., Serlenga, V., Stabile, T. A., Prosser, G., Filippucci, M., and Clark, S.: Effects of rheological variations, erosion, and geotherm characteristics on tectonic setting and seismic activity in the Val d’Agri (Southern Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1017, https://doi.org/10.5194/egusphere-egu23-1017, 2023.

In volcanic environment, the fluids migration in the crust can affect the evolution of magmatic processes. Meteoric water can for instance infiltrate volcanic rocks developing shallow hydrothermal systems and descending meteoric water may encounter fluids rising up from deep magma feeding system. The accurate tracking of fluid storages and movements turn out to be crucial for the evaluation of the seismic and volcanic activity. Specifically, Campi Flegrei caldera is an example of fluids interaction of different nature, especially at Solfatara crater, where the complexity of this volcanic system is highlighted by diffuse degassing, high temperatures and bradyseism phenomenon.

The Solfatara crater was formed at about 4.2 ka and it consists of a sub-rectangular depression, whose geometry is controlled by N40-50W and N50E trending fault systems. Nowadays, degassing and fumarolic emissions occur at the Solfatara crater, together with a series of small uplift episodes and seismic swarms, particularly from 1984 to 2006 when the whole caldera subsided. Specifically, these earthquakes are likely to be associated with a buried cavity filled with a water-vapour mixture at poor gas-volume fractions.

In this scenario, we propose a 2D multi-physics study of Solfatara volcanic system via the integration of thermodynamic and poroelastic model results.

We start with the first model, for which we collect the available geological and geophysical information, such as the main faults, crustal parameters and the temperature distribution in the conductive regime. This information is merged into a multiphysics Finite Element Model by using COMSOL Multiphysics software: we simulate the crustal thermal regime beneath the Solfatara crater by performing a time-dependent convective thermal model in porous media. We also simulate the fluids circulation in accordance with the Darcy’s Law by considering the bi-phasic water properties (i.e., liquid and vapor states) as approximation to characterize the modelled fluid. Furthermore, the seepage of meteoric water through the high permeable volcanic rocks is also considered. At the end of the simulation, we observe the activation of a convective cell below the Solfatara crater, where the 250°C isotherm reaches ~500 m b.s.l.. The retrieved results is compared with the available data, as the resistivity model proposed by Siniscalchi et al. (2019) and the measured temperature at the CF23 well.

Within the same discretized numerical domain, we perform the second model by considering the previous fluid pore pressure modelled field; we detect the pressure source parameters better explaining the observed ground deformations of Campi Flegrei caldera. The analysed dataset consists of processed SAR images acquired by Sentinel-1A/B satellites constellation during the 2020 – 2022 time interval. We here compare the retrieved stress field within the caldera with the hypocenters distribution.

In conclusion, this study contributes to improve the knowledge about the role of fluids migration in the framework of the magmatic processes.

How to cite: Barone, A., Gola, G., Pepe, A., Tizzani, P., and Castaldo, R.: Fluid migration in volcanic environment: thermo-poroelastic modelling of Solfatara crater., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13270, https://doi.org/10.5194/egusphere-egu23-13270, 2023.

In seismic regions, fluids play active roles during the preparatory phases of large earthquakes and, through their chemical and isotopic signature, transport to the surface information about deep processes within the fault zones.

In this scenario, noble gases are useful to investigate earth degassing, and their isotopic ratios help to decipher the dynamics of natural processes such as volcanic eruptions and earthquakes. The lightest of noble gases is helium (He), and in natural fluids, it is present with two isotopes, ³He and ⁴He. The former being mainly primordial and stored in the mantle, the latter continuously produced by U and Th decay in the earth interior. In stable continental region the He flux is dominated by the radiogenic ⁴He that is produced into the crust (mantle He <1%).  In contrast, primordial ³He escape to the atmosphere in regions of active tectonic (from extensive to compressive).

Experimental studies highlighted that during rocks deformation micro-fracturation increases as an effect of dilation, and consequently, He is liberated from rocks and it escapes towards the pore fluids and successively to the atmosphere. Hence, it indicates a direct link between seismicity and the crustal ⁴He degassing. However, it is mandatory to know the volume of the rocks involved in earthquakes-induced rock-fracturation to quantify the amount of He released in seismic processes.

Fault zones are complex systems whose mechanical properties evolve over time. Field observations and experimental works allow to schematically simplify these zones into two main structural regions: (1) the fault core and (2) the damage zone. However, the lack of direct observations limits the knowledge of their architecture at depth. Thus, in order to understand the multi-scale, physical/chemical processes responsible for the faulting that earthquakes occur on, it is fundamental to consider phenomena that intersect different scientific research fields. Near Fault Observatories (NFOs) are grounded on multidisciplinary infrastructures, collecting near fault high resolution scientific data that allows generation of innovative observations (Chiaraluce et al., 2022).

Here, we analysed a 12-year earthquake catalogue (M<4) in the IRPINIA NFO (Italy), a region affected by high-magnitude disastrous earthquakes (i.e. M= 7.0 in 1857 and M= 6.9 in 1980).

The analysis of this earthquakes catalogue allows reconstructing year by year the volumes of both the fault core and the damage zone. We computed the ⁴He output from the two faults zone observing that the low-magnitude earthquakes (M < 4) efficiently contribute to variations of the crustal helium output into the atmosphere. Our results support the impulsive nature of He degassing in tectonically active continental regions (Caracausi et al., 2022). We recognized a quantitative relationship between crustal helium outputs and the volume of fault zones, and  we suggest that variations in helium flux may represent a gauge of changes in the stress field that are related to the nucleation of earthquakes.

References

Caracausi et al. (2022). doi:10.1038/s43247-022-00549-9.

Chiaraluce et al. (2022). doi:10.4401/ag-8778.

How to cite: Caracausi, A.: Earthquakes and helium: evidences of the impulsive nature of earth degassing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4376, https://doi.org/10.5194/egusphere-egu23-4376, 2023.

The Province of Pesaro-Urbino (northern Marche, central Italy) represents one of most seismically active areas in Italy, since it is interested by the presence of two major composite seismogenic sources: i) the first one is located in the Umbria-Marche Apennines; ii) the second one is along the Adriatic coast from Cattolica to Ancona cities. This area has recently experienced an intense seismic activity, e.g., the 1781 “Cagli Earthquake” with a magnitude of 6.4 M_w, and the 1930 “Senigallia Earthquake” of 5.8 M_w. The last earthquake (5.5 M_w) occurred on November 9, 2022, with its epicenter located in the Adriatic Sea, 35 km away from the city of Pesaro. Since the geochemical knowledge of this area is limited, a large-scale sampling survey was carried out during spring and autumn 2022. A total of 87 samples were collected from different types of emergencies (i.e., cold springs, wells, mineral springs, sulfur springs and ditches) and various geological and tectonic-structural contexts. The study area is dominated by a complex sedimentary structure (e.g., limestones, clays and alluvial deposits) and by climatic and topographic conditions that may influence the chemical and isotopic composition of the investigated fluids. A detailed geochemical characterization is thus of paramount importance in order to define a geochemical background. The aim of this study was to (1) understand the possible interaction of deep-originated fluids and shallow aquifers and (2) evaluate the use of selected geochemical parameters as possible seismic tracers. The results showed the presence of five different geochemical facies: (i) calcium-bicarbonate waters with low TDS (<500 mg/L); (ii) calcium-bicarbonate waters with a strong enrichment in sulfate (up to 200 mg/L); (iii) waters with extreme sodium-carbonate composition and an alkaline pH (>8.8); (iv) calcium-sulfate waters; and (v) sodium-chloride waters. The water isotopic composition showed a clear meteoric origin for all the investigated samples. The composition of major dissolved gases showed two different compositional clusters: (a) N₂-dominated gases with N₂/Ar ratios similar to those of air and ASW (Air Saturated Water); (b) CO₂- and CH₄-rich gases pertaining to mineral and sulfur springs. The origin of Ca-HCO₃ waters is almost exclusively related to the dissolution of carbonate minerals. On the contrary, Ca-HCO₃(SO₄) waters are probably originated by deep circulation pathways and interactions with the Upper Triassic Burano Formation, composed by anhydrite layers. The Ca-SO₄ waters should be considered as the product of ongoing flows within Miocene gypsum formations, whilst Na-HCO₃ waters as the consequence of long-lasting interactions between meteoric waters and silicate rocks (containing albite) in saturation/oversaturation conditions for carbonate-bearing minerals. Finally, the Na-Cl waters probably derive from mixing processes between meteoric and highly saline connate waters trapped into the foredeep clayey deposits. Therefore, the Ca-HCO₃(SO₄) and Ca-SO₄ waters can be regarded as the most interesting fluids to be monitored for a geochemical network aimed at recognizing chemical and isotopic variations related to seismic activity. They are indeed showing a deeper hydrogeological pathway and appear to be less influenced by surface processes.

How to cite: Chemeri, L., Taussi, M., Cabassi, J., Capecchiacci, F., Tassi, F., Renzulli, A., and Vaselli, O.: Hydrogeochemical characterization of the waters circulating in the seismically active area of the Pesaro-Urbino province (northern Marche, central Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2043, https://doi.org/10.5194/egusphere-egu23-2043, 2023.

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. Geodynamics, geophysical and geochemical observations highlight differences between the western and eastern domains of the Apennines, and the main characteristics of the transition zone, which spatially corresponds with the overlapping Tyrrhenian and Adriatic Mohos. Tomographic images exhibit a large hot asthenospheric mantle wedge that 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 study strongly relies on the multidisciplinary analysis of different datasets (both existing and newly acquired) with the most advanced methodologies to stimulate the knowledge of the fluid-related mechanisms of earthquake preparation, nucleation and space-time evolution. Ongoing and future investigations will include the continuous and simultaneous geochemical and geophysical monitoring at the scale of the outcropping seismogenic faults to properly decipher the link between earthquake occurrence, surface rupture and fluid release.

How to cite: Di Luccio, F. and the The FURTHER Team: The role of CO2 degassing in the seismogenic process of the Apennines, Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8292, https://doi.org/10.5194/egusphere-egu23-8292, 2023.

The Apennines mountain range develops all along Italy, presenting important variations in terms of both structural and tectonic environments, and seismogenic patterns as well. This is observed not only along the main NW-SE chain axis, but also by comparing multidisciplinary observations between the western Tyrrhenian and the eastern Adriatic domains (Di Luccio et al., 2022).

We focus on the southern Apennines, where the Adriatic plate subducts westward under the thinner Tyrrhenian plate and the highest seismic release is documented.

Recent studies showed that fluids play an important role in the seismic behavior of the area. The western domain is associated with heterogeneous and distributed patterns of CO₂ gas emission at the surface; the latter ceasing in the east, where high-pressure fluids are trapped in crustal pockets and affect the seismogenic cycle (Chiodini et al., 2004; Improta et al., 2014; Di Luccio et al., 2022 and references therein).

We perform regional-scale P- and S-body waveform analysis and forward numerical modeling, for a selected catalog of crustal events recorded by the broadband seismic stations of the italian network, as well as of temporary passive seismic experiments. We focus on a SW-NE transect, which cross-cuts the southern portion of the Apennines chain, and along which the recorded waveforms exhibit important differences in terms of frequency content and pulse shape. Along the same transect, the waveforms from two events (2013 Mw5 Sannio-Matese and 2014 Mw4.5 Gargano earthquakes) show significant differences in the propagation towards the east and west, respectively.

Starting from two velocity models such as EPcrust (Molinari et al. 2011) and the adjoint tomographic model of Magnoni et al. (2022), we use the finite difference numerical modeling code nbpsv2d (Li et al. 2014) to produce synthetic waveforms to fit and explain the observations. By including information on the earthquake source mechanism and by improving the waveform fit in terms of both arrival time and body-wave coda, we provide new, preliminary information on the crustal structure of the southern Apennines, aimed at improving our understanding of the fluid-seismicity interaction in the area.

Research performed in the framework of FURTHER project (https://progetti.ingv.it/en/further).

References:

• Chiodini G., Cardellini, C., Amato, A., Boschi, E., Caliro, S., Frondini, F., and Ventura, G. (2004). Carbon dioxide Earth degassing and seismogenesis in central and southern Italy. Geophys. Res. Lett., 31, L07615, doi:10.1029/2004GL019480.
• Di Luccio et al., (2022). Geodynamics, geophysical and geochemical observations, and the role of CO₂ degassing in the Apennines. Earth-Sci. Rev., https://doi.org/10.1016/j.earscirev.2022.104236
• Improta L., P. De Gori, and C. Chiarabba (2014). New insights into crustal structure, Cenozoic magmatism, CO2 degassing, and seismogenesis in the southern Apennines and Irpinia region from local earthquake tomography, J. Geophys. Res. Solid Earth, 119, 8283–8311, doi:10.1002/ 2013JB010890.
• Li, D., Helmberger, D., Clayton, R. W., & Sun, D. (2014). Global synthetic seismograms using a 2-D finite-difference method. Geophysical Journal International, 197(2),1166-1183.
• Magnoni, F., Casarotti, E., Komatitsch, D., Di Stefano, R., Ciaccio, M. G., Tape, C., ... & Tromp, J. (2022). Adjoint tomography of the Italian lithosphere. Communications Earth & Environment, 3(1),1-12.
• Molinari, I., & Morelli, A. (2011). EPcrust: a reference crustal model for the European Plate. Geophysical Journal International, 185(1), 352-364.

How to cite: Scarponi, M., Di Luccio, F., and Piromallo, C.: Waveform modeling of moderate earthquakes for the comprehension of the seismic structure and the fluid-seismicity interaction beneath the southern Apennines (Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8375, https://doi.org/10.5194/egusphere-egu23-8375, 2023.

The role of fluids in the preparatory phase of major earthquakes and in the evolution of aftershocks and swarms in space and time is well-documented. In particular, numerous studies evidence the primary role that mantle-derived fluids play in the generation of large upper crustal earthquakes in extensional domains, where crustal-scale faults act as preferential hydraulic pathways.  

We focus on the Mefite D'Ansanto degassing site, the largest low-temperature non-volcanic CO₂ emission in the world, located at the northern tip of the Mw6.9 1980 Irpinia faults. The study area experienced strong historical earthquakes (1702, 1732 and 1930 M6+ earthquakes) but it is characterized by a relatively low background seismicity rate with respect to the nearby Sannio and Irpinia regions.    

To collect high-quality microseismicity data in this key sector of the southern Apennine extensional belt and investigate the relationship among seismicity, crustal fluids, and physical-hydraulic properties of the crust, we installed in July 2021 (up to May 2023) a temporary network composed of 10 stations equipped with short-period velocimeters (5 sec). The temporary network covers an area of approximately 30x30 km² surrounding the Mefite d’Ansanto site and integrates with the numerous permanent stations of the INGV and ISNet networks located at the boundary of the survey area. 

Within the Mefite area, we also deployed a temporary seismo-acoustic dense array to study two CO₂ vents. The seismo-acoustic array is composed of 5 infrasonic stations equipped with IST-2018 broadband microphones developed by The ISTerre (Université Savoie Mont Blanc, France), in addition to one seismo-acoustic station equipped with a co-located digital broadband seismometers (120s). The array is positioned approximately at the vertices of a star, with an aperture of about 50 meters. The deployment lasted for 1 week at the end of May 2022, allowing us to sample the emission site during “dry” weather conditions. 

We show first results of the analysis of seismicity recorded by the temporary network applying both standard (STA/LTA) detection algorithms or innovative enhanced techniques such as cross-correlation based template-matching algorithms and/or Deep-Learning-Phase-Recognition methods.

The activities are developed in the framework of the multidisciplinary project FURTHER (https://progetti.ingv.it/en/further).

How to cite: Valoroso, L., Cianetti, S., De Gori, P., Diaferia, G., Giunchi, C., Improta, L., Piccinini, D., Zuccarello, L., Cogliano, R., Fodarella, A., Minichiello, F., Pucillo, S., and Di Luccio, F.: Passive seismic and infrasonic monitoring at the Mefite d’Ansanto deep-CO2 degassing site (Southern Apennines, Italy)., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9565, https://doi.org/10.5194/egusphere-egu23-9565, 2023.

Structures created by hydraulic fracturing can be identified using the location of induced microseismic events. Estimating the effectiveness of stimulation depends on fracture mapping. Event location errors make precise imaging of fractures in a scattered seismic cloud challenging. In order to increase the reliability of the determined structures on the basis of events with location error, we proposed a several-stage procedure. This procedure was demonstrated on microseismic events located during the fracturing of the Wysin-2H/2Hbis horizontal well, an exploration well for shale gas in northern Poland from June 9, 2016 to June 18, 2016. All located events were subjected to a collapsing that allows obtaining new locations of events that are equivalent to original locations in a statistical sense. The creation of such an equivalent point cloud allows us to see certain structures that may reflect, for example, fractures. To validate the results before and after collapsing method, all events were set against the probability of a given brittleness index map.  It is demonstrated that the collapsed events occurred in regions that were more rigid, while the locations of events prior to this procedure showed no relationship with the occurrence of areas with higher susceptibility to fracking. The unsupervised machine learning algorithm HDBSCAN was used on a collapsed cloud to automatically detect clusters of events. The directions of identified clusters agree with the direction of regional maximum horizontal stress.

How to cite: Weglinska, E., Lesniak, A., Pasternacki, A., and Wandycz, P.: Mapping of structures formed by hydraulic fracturing based on microseismic events location., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14488, https://doi.org/10.5194/egusphere-egu23-14488, 2023.

This study investigates the perturbations of the surrounding stress field caused by the cascade effect of Xiluodu and Xiangjiaba reservoirs after impoundment and a three-dimensional pore-elastic coupling model of the impoundment of cascade reservoirs are established. The finite element method calculates the pore pressure field, elastic stress field, and variation of Coulomb stress on local faults. The results show that: 1) the spatial distribution of the earthquake cluster is obviously consistent with the area where the pore pressure increases; 2) The ΔCFS at the epicenters of the April 2014 Yongshan M_L5.1 earthquake and the August 2014 Yongshan M_L5.2 earthquake imparted by the reservoirs are: 0.67kPa and 10.87kPa, respectively, indicating that impoundment promotes these two earthquakes at different levels, and the latter is more significant; 3) The elastic stress field change imparted by the impoundment of Xiluodu reservoir has an impact on the Xiangjiaba Reservoir in the early stage. However, the earthquakes between two reservoirs are possibly triggered by the latter. The Xiangjiaba reservoir increases the pore pressure in its upstream part by 1.0 kPa; 4) the impoundment of the reservoirs increases the seismic risk of the southern section of the Yanfeng fault and the middle section of the Lianfeng fault, while the Manao fault is less affected.

How to cite: Yin, G., Zhang, H., and Shi, Y.: Cascade effects of triggered earthquakes of cascade dams: Taking Xiluodu and Xiangjiaba reservoirs as examples, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7137, https://doi.org/10.5194/egusphere-egu23-7137, 2023.

Water injection in geothermal areas is the preferential strategy to sustain the natural production of geothermal resources. In this context, monitoring microearthquakes is a fundamental tool to track changes in the reservoirs in terms of soil composition, response to injections, and resource exploitation in space and time. Therefore, the refined source characterization is crucial to better estimate the size, source mechanism, and rupture process of microearthquakes, as possibly related to industrial activities and to identify any potential variation of the background seismicity. Standard approaches for source parameters estimation are ordinarily based on the modelling of Fourier displacement spectra and its characteristic parameters, the low-frequency spectral level and corner frequency. Here we apply a time-domain innovative technique that uses the curves of P-wave amplitude vs time along the seismogram. The methodology allows estimating seismic moment, source radius, and static stress drop from the plateau level and the corner-time and of the average logarithm of P-wave displacement versus time with the assumption of a triangular moment rate function, uniform rupture speed, and constant/frequency-independent Q-factor. In the current paper, this time-domain methodology is implemented to a selected catalog of micro-earthquakes consists of 83 events with moment magnitude ranging between 1.0 and 1.5, occurred during 7 years (2007-2014) of fluid extraction/injection around Prati-9 and Prati-29 wells at The Geysers Geothermal field.

How to cite: Longobardi, V., Nazeri, S., Colombelli, S., Rea, R., De Landro, G., and Zollo, A.: Time-Domain Source Parameter Estimation of natural and man-induced micro earthquakes at The Geysers geothermal field, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7351, https://doi.org/10.5194/egusphere-egu23-7351, 2023.

The rupture process of the recent moderate-to-large earthquakes in the longest seismic sector in Iran's plateau, the Zagros area, has been modeled using the strong motion data provided by the Iranian Building and Housing Research Center (BHRC). The selected dataset includes the largest and deadliest seismic event, the 2017 Mw 7.3, Sarpol-e Zahab earthquake. The earthquake source parameters (moment magnitude, source duration, rupture dimension, and average stress drop) are determined by implementing a parametric modeling technique in the time domain based on the time evolution of the P-wave displacement signals. The seismic source parameters are calculated from simulated trapezoidal and triangular moment-rate functions assuming the unilateral rectangle and circular crack models, respectively, where the rupture propagates at a constant velocity as a fraction (90%) of the average shear-wave velocity in the medium. The anelastic attenuation effect assuming the independent frequency-Q parameter ranging from 50 to 200 is accounted for by a post-processing procedure that retrieved the observed moment-rate triangular shape. Hence, the average stress drop with different varies between <Δ𝜎>=1.50 (1.14−1.95) and <Δ𝜎>=0.90 (0.71−1.14) MPa. Assuming a circular rupture model for Sarpol-e-Zahab, we estimate a moment magnitude of 7, rupture duration of 7 seconds, source radius of 16 km, and statistical stress drop of about 3.5 MPa. Alternatively, a unilateral rupture model calculates the fault length and width at 45 and 16 km, with a lower stress drop of 2 MPa.

How to cite: Nazeri, S., Abdi, F., Ismail, A., Rahimi, H., and Zollo, A.: Earthquake source parameters in the Zagros region (Iran) from the time of evolutionary P-wave Displacement, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7724, https://doi.org/10.5194/egusphere-egu23-7724, 2023.

Seismo-electromagnetic signals are electromagnetic signals generated by the propagation of a seismic wave in a porous media containing fluids (Gao & Hu, 2010).These signals can potentially provide useful information on the poro-elastic media and the hosted fluids (Garambois & Dietrich, 2002).Thus, there has been a growing interest in the study of SES in recent years, due to their potential.

Researchers are focusing both on modelling and analysis of both passive and active experiments to investigate the characteristics of these signals (e.g. Honkura et al., 2000; Matsushima et al., 2002; Warden et al., 2013; Gao et al., 2016; Balasco et al., 2014; Dzieran et al., 2019).Passive experiments involve the observation and analysis of naturally occurring SES triggered by earthquakes, while active experiments involve the controlled generation of these signals using seismic source.

The aim of our work is to present the results deriving from the analysis of SES recorded with both approaches. As for the passive one, the data set consists of the time series recorded by two magnetotelluric stations in continuous monitoring, co-located with two seismic stations, in seismically active areas of Southern Italy (the Gargano promontory and the Agri valley).

As for the active one, the data set derives by an active seismic experiment carried out in the caldera of the Phlegrean Fields, the Italian super-volcano.

How to cite: Ventola, I., Romano, G., Balasco, M., de Girolamo, M., de Lorenzo, S., Filippucci, M., Morga, R., Patella, D., Serlenga, V., Stabile, T. A., Tallarico, A., Tripaldi, S., and Siniscalchi, A.: Exploring the characteristics of seismo-electromagnetic signals (SES) in both passive and active experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16074, https://doi.org/10.5194/egusphere-egu23-16074, 2023.