The Nirano Salse , known since the Roman Times, are one of the most beautiful and scenic mud volcanoes areas of Italy with thousands of visitors every year. In this work, we apply novel (for the context) hydrogeological techniques to characterize mud levels in the Salse by means of GPS-RTK positioning and continuous level logging within mud conduits. This is important to quantify the gas–liquid ratio in the conduits and evaluate the potential for dangerous abrupt mud eruptions. The results presented suggest that different mud levels in mud volcanoes clusters are due to the different gas–liquid ratio in the conduits and not necessarily exclude interconnection at depth, a hypothesis, on the other hand, that seems strengthened by mud level time series correlations. The presence of shallow aquifers at a depth of 5 to 30 m is also supported by our field data and allows us to delineate the boundaries of the shallow mud reservoir—pipes system and its overall shape. The shallow aquifers may provide a temporary storage for the ascending gas and when fluid pressure in these aquifers exceeds the tensional strength of the sedimentary rock, leakage of fluids to the surface would occur. In this case, if the gas–liquid ratio is high, mud volcanoes develop into tall gryphons and tend to have a discontinuous activity with sudden eruptions of mud after long periods of quiescence. This, together with the knowledge of shallow conduits localization has an important implication for site safety in proximity to the mud volcanoes. Our inferences based on mud level relationships to mud extrusion dynamics can be applied to lower risk in other mud volcanoes areas of the world with high geo-tourist visits, such as those of Trinidad, Azerbaijan, and Colombia.

In this study the geochemical composition of the fluids belonging to the geothermic reservoir of Casaglia is presented. The site is located few kilometers northward of Ferrara, probably the only city in Italy whose heating system is fed by the geothermal heat near the top of the Dorsale Ferrarese, a structural anticline raising the Mesozoic limestones up to few hundred meters below the surface. Measurements of the chemical and isotopic composition of the gas phase (e.g., CO2 and noble gas) were carried out, together with a full characterization of the physico-chemical parameters and the chemistry of the water phase. Fluids derive from a well at a depth of about 322+15meters and the temperature of the emerging water is of 78,6 °C, pH of 6.29 and Eh of -470 mV. Salinity is up to 115.6 mS/cm with a TDS varying between 71024 mg/L and 73718 mg/L. The hydrochemical facies is identified as clorurato-alkaline and the Cl/Br ratio suggest mixing with fossil brines. dD and d18O vary from 4.70 to 5.02 and from -12.0 to -12.2 respectively. The volatile phase is mainly composed of N2 (24.9-40.5 %),CH4 (21.1-29.5 %) and CO2 (37.1-18.6 %), with d13C(CO2), d13C(CH4) and dD(CH4) varying from -4.4 to -3.7 ‰, from -41.7 to 41.2 ‰ and from -152 to -171 ‰, respectively. The He amounts are extraordinary high (up to 3956 ppm) with a 3He/4He of 0.02Ra unequivocally pointing to a crustal origin (e.g., Caracausi & Sulli, 2019). The 40Ar/36Ar ratios span the range 300-374, being very close to the same ratio in atmosphere. Such high He concentration cannot be explained by a simple steady-state crustal degassing, taking into account the Th and U contents of the sedimentary cover and the metamorphic basement (Coltorti et al. 2011) which lead also to consider that the thermal state of the Casaglia reservoir involve the entire crustal thickness and not only the Mesozoic carbonate succession that hosts the reservoir itself. It is inferred that under an active tectonic regime, as it is that where Casaglia is located, the formation of micro-fracturation, due to the field of stress generated by the local seismicity, increases the He release from the rocks and can contribute to the observed He excess in the geothermal reservoirs (e.g., Buttitta et al., 2020). In this respect, the fault system of Dorsale Ferrarese contributes to generate a preferential pathway for rising fluids with consequent mixing phenomena and provides a reasonable explanation about the presence of this high He content in the reservoir. References: Buttitta D. et al. (2020). Continental degassing of helium in an active tectonic setting (northern Italy): the role of seismicity. Scientific Reports, 10(1), 1–13. Caracausi A. & Sulli A. (2019). Outgassing of Mantle Volatiles in Compressional Tectonic Regime Away From Volcanism: The Role of Continental Delamination. Geochemistry, Geophysics, Geosystems, 20(4), 2007–2020. Coltorti M. et al. 2011. U and Th content in the Central Apennines continental crust: a contribution to the determination of the geo-neutrinos flux at LNGS. Geoch. Cosmoch. Acta 75, 2271-2294.

Hydrogeologic and geochemical analyses are carried out in groundwaters and in gaseous emissions on order to contribute to earthquake prediction research. At presently the main test sites are in Japan, China, and Taiwan. Catalogs of presumed precursory episodes have been compiled over the years and provided preliminary conclusions about site-selection techniques. Controlled experimental sites have recently given the opportunity to better investigate the physical mechanisms originating the recorded preseismic anomalies. The main characteristics and limitations of hydrogeologic and geochemical parameters are discussed. An in depth review of results obtained from the most relevant test site areas identifies future research trends and projectections of future instrumental networks, including geophysical parameters and remote sensing techniques oriented to hazard reduction policies.

Earthquake precursors are elusive, and this elusiveness has hampered earthquake prediction. In this paper, the available catalogues of historical and contemporary geochemical and fluid-related precursors of earthquakes are considered.The locations of recording sites are mapped and compared with data concerning volcanic locations, heat flows, crustal velocities and the depth of seismic events. Possible relations among the considered geophysical parameters and the occurrence of fluid-related earthquake precursors are discussed. Only some geological and geophysical conditions may allow for the occurrence of fluid-related earthquake precursory phenomena. As a consequence, the geophysical models utilized to explain the occurrence of earthquake precursors should be updated. Furthermore, only some areas of the world are deemed suitable for earthquake fluid-related precursor monitoring.

A seismic swarm characterized by a Ml = 5.9 mainshock occurred in the Po Valley, northern Italy, in 2012. The area has been studied for active compressional tectonics since the beginning of the twentieth century. A variety of geophysical and geochemical parameters have been utilized with the purpose of identifying possible precursory signals. This paper considers groundwater level data and geochemical data both in groundwaters and in gases. All considered parameters have led to the conclusion that possible long and medium precursory trends have been identified in geofluids. No short-term precursors have been clearly identified. Hydrogeological and geochemical monitoring could be more effectively utilized in a different geological context, and seismic hazard reduction procedures could benefit from geofluid monitoring.

Fifty-two unusual geological phenomena (up to November 2015) were reported during a three-year observation period after the seismic swarm that occurred in Emilia in May-June 2012. Here we show and discuss for the first time the data collected directly from wells with apparently abnormal temperatures. Most of the abnormal temperatures occurred in the areas struck by earthquakes, but others were located in the urban area of Bologna and in the eastern sector of the Ferrara province. No relationship between the temperature data and the earthquakes was observed. The Italian oil company AGIP (now ENI) has recorded a large number of hydrocarbon surface phenomena in Emilia-Romagna since the early decades of the 20th century. The phenomena were located both in the Po Plain and in the Apennines. This database was recently provided by ENI and, for the first time, utilized for research purposes following the 2012 Emilia seismic sequence. The emissions observed are due to the presence of methane gas mixed with groundwater, resulting from the decomposition of organic matter present in proximity to tapped aquifers, or gas rising from greater depths along tectonic discontinuities. Similar to the findings involving the well temperatures, no significant relationship was found between the geographic distribution of the hydrocarbon emissions and the earthquakes. Ground-shaking phenomena, however, have sometimes induced temporary increases in the gas flow rate.

A network of Extremely Low Frequency (ELF) electromagnetic detectors consisting of identical instruments that continuously record the electrical component of the electromagnetic field, ranging from a few Hz to tens of kHz has been operating in central Italy for several years. These signals are analysed in real time, their power spectrum contents and time/frequency data are saved for further analysis. The spectral contents have evidenced very distinct power spectrum signatures that increase in intensity when strong seismic activity occurs near the stations. During the Emilia seismic sequence in 2012, the network consisted of nine stations, seven in central Italy and two in northern Italy, at Zocca (Modena province) and at Torre Pellice (Turin province). Data recorded by the Zocca station, near Modena, at about 60 km from the Emilia epicentres were analysed. Data analysis shows the existence of several ELF oscillations of the horizontal electric field started on April 2012 and lasted up to the end of June 2012. Recorded ELF oscillations were similar to those recorded before and after the L'Aquila earthquake in 2009. However, since May 2012 was interested by significant rainfall close to the station, it is possible that the selected signals were linked to it. A theoretical model which could explain recorded ELF oscillations in concomitance with seismic and rain events is proposed.

Groundwaters and gaseous emissions have been analyzed in the past with the purpose to contribute to earthquake prediction researches. Main test sites were Japan, U.S.A., former U.S.S.R., China and Turkey. Catalogues of presumed precursory episodes have been compiled over the years and allowed to reach preliminary conclusions about site selection techniques. Controlled experimental sites have recently given the opportunity to better investigate the physical mechanisms originating recorded pre-seismic anomalies. Main characteristics and limitations of hydrogeologic and geochemical parameters are discussed. An in-depth review of results obtained in most relevant test site areas allow to project future instrumental networks oriented to hazard reduction policies.

A ML=5.8 earthquake rocked the L'Aquila area on April 6, 2009. Several aftershocks characterized by 5<ML<4 followed the main seismic event. The depth of mainshock was about 9km and the same region has been hit by strong earthquakes during the past centuries. Possible phenomena related to underground fluid dynamics due to the seismic sequence were reported. Sensors capable of monitoring water level variations and temperatures in selected spring sources of Central Italy were placed in the studied area and their data processed. Fluid sensors located at different distances from the epicentral area were differently affected by the seismic sequence. Collected data during the seismic swarm are discussed and compared to contemporary data recorded by satellite-based techniques.

The occurrence of intense CO2 degassing processes generating hundreds of cold CO2-rich gas emissions is typical of the central Apennines. In 2009, significant anomalies were detected coinciding with the L'Aquila seismic sequence as a consequence of a wide degassing process. Over the same time-span, space-time anomalies in Thermal InfraRed (TIR) satellite imagery possibly related to the increase of green-house gas (such as CO2, CH4, etc.) emission rates were detected in central Italy during the seismic swarm by a Robust Satellite Technique (RST) data analysis. A gas geochemical survey carried out in the L'Aquila area confirms the deep crustal origin of the anomalous gas emission detected by ground measurements. Anomalous fluid related signals were recorded some days before the mainshock coinciding with the most marked TIR anomalies independently detected by the RST analysis over 3 different types of satellite data. Anomalous gas emissions detected by ground measurements lasted some weeks, putting in evidence relationships with crustal deformative processes associated with the seismic sequence. Together with previous ground observations in the Umbria-Marche area, present ground and satellite TIR observations, are compatible with the hypothesis that a central Apennines area, much wider than the L'Aquila (March-April 2009) epicentral one, was actually affected by anomalous increases in CO2 release thus providing new tools to better understand the processes occurring behind a seismic shock.

The Miano borehole, 1047m deep, is located close to the river Parma in the Northern Apennines, Italy. A measuring station has been installed to observe the discharge of fluids continuously since November 2004. The upwelling fluid of this artesian well is a mixture of thermal water and CH4 as main components. In non-seismogenic areas, a relatively constant fluid emission would be expected, perhaps overlaid with long term variations from that kind of deep reservoir over time. However, the continuous record of the fluid emission, in particular the water discharge, the gas flow rate and the water temperature, show periods of stable values interrupted by anomalous periods of fluctuations in the recorded parameters. The anomalous variations of these parameters are of low amplitude in comparison to the total values but significant in their long-term trend. Meteorological effects due to rain and barometric pressure were not detected in recorded data probably due to reservoir depth and relatively high reservoir overpressure. Influences due to the ambient temperature after the discharge were evaluated by statistical analysis. Our results suggest that recorded changes in fluid emission parameters can be interpreted as a mixing process of different fluid components at depth by variations in pore pressure as a result of seismogenic stress variation. Local seismicity was analyzed in comparison to the fluid physico-chemical data. The analysis supports the idea that an influence on fluid transport conditions due to geodynamic processes exists. Water temperature data show frequent anomalies probably connected with possible precursory phenomena of local seismic events.

We analyse geoelectrical and geochemical time series jointly measured by means of a multiparametric automatic station close to an anomalous fluid emission in Val d'Agri (Basilicata, Southern Italy). In the investigated are some destructive seismic events occurred in past and recent years. We analysed the temporal fluctuations of the signals by spectral tools. We detected scaling behaviours in the power spectra of the time series recorded, that are typical fingerprints of fractional Brownian motions. The estimated values of the spectral indices reveal the presence of antipersistent behaviour in the time dynamics of all geoelectrical and geochemical data recorded. This work intends to improve our knowledge of the inner time dynamics of geophysical non-seismometric parameters.

A hydrogeochemical prospection has been carried out in the Milano province with the purpose to better identify and characterize Nitrogen pollution sources. A network of 90 wells has been considered for geochemical prospection and 37 wells were also considered for isotopic survey. A geochemical stratification both in chemical characters and in isotopic ones has been identified and related to local pollution phenomena. The organic character of Nitrogen pollution phenomena has been identified and related to vulnerability characters of surveyed area. The obtained results allow to improve previous vulnerability mapping methods.

Field observations coupled with experimental results show that CO2 can be produced by mechanical energy applied to carbonate rocks becoming an unexpected additional gas source besides that degassed from the mantle or produced by thermometamorphism. The evidence that a large amount of carbon dioxide associated with radiogenic-type helium (R/Ra as low as 0.01–0.08) is released through continental areas, denotes the absence of a contribution from the mantle or from mantle-derived fluids. Data collected during the seismic crisis which struck the Central Apennines in 1997–98 have shown an enhanced CO2 flux not associated with the presence of mantle or thermometamorphic-derived fluids. On the other hand, new experimental results highlight the possibility of producing CO2 by mechanical energy that acts on the calcite crystalline lattice. While the CO2 released over the geothermal areas (e.g., Larderello Geothermal Field) is obviously derived by mantle-derived activities, this is not the case of the huge amount of CO2 released over the seismically active areas where the presence mantle-derived products is ruled out. We propose that mechanical energy, e.g., released during seismic events, microseismicity or creeping processes is a possible additional energy source able to produce CO2 and thus could explain the presence of CO2 degassing over tectonic areas where the influence of the mantle is low.

The 8th International Conference on Gas Geochemistry provided the opportunity for scientists from different countries to meet each other, exchange ideas on the state of the art in gas geochemistry, and discuss advance in fluid geochemistry. The 8th ICGG meeting focused on three main geologic environments currently interacting with the human life: volcanoes, earthquakes and hydrocarbons. Ninety-four presentations gave participants chance to cover a variety of important research topics on gas geochemistry in geosciences including: gas migration in terrestrial and marine environments, Earth degassing and its relation to seismicity, volcanic eruptions, rare gases and application of isotope techniques, measurement and analytical techniques.

Cold CO2 gas emission sites in rainwater-filled pools, so called mofettes, are widely distributed all over Italy. Their gas reservoirs, mostly having a high CO2 content, have a magmatic and/or metamorphic origin. Temporal variations in fluid expulsions were observed at the mofettes of Caprese Michelangelo during the period from 2002 to 2005. These observations were made possible by using a new approach: photographic time-series. A first interpretation of these fluid expulsions was based on meteorological/hydrogeological explanations. However, our long-term observations show that these processes may merely be a side effect. The probable main reason for the anomalous emissions is the long-term variation in the long-distance fluid transport process from the reservoir induced by the local tectonic settings. In the northern part of the Alto Tiberina Fault, a fault intersection was reactivated by a seismic sequence which started on 2001 November 26, and continued for approximately four months. The magnitude of the main shock was M-W = 4.6. As revealed by the drilling of a deep borehole, dug in the direct vicinity, overpressurized fluids trapped at a depth of 3700 m could be activated as a consequence of the improved transport conditions, that is, the fracture apertures that materialized as a result of the rupture process. A migration of the hypocentres towards the surface provides hints of a possible pore pressure diffusion process. The consequence is an increased fluid transport to the mofettes. The first indications of anomalous fluid expulsions at the mofettes of Caprese Michelangelo were detected 18 months after the seismic events.

The Val d Agri area is well-known for oil exploration. An old 500 m deep exploration well in the northern part of this area has been used for long-term hydrogeochemical investigations. The well is characterized by a discharge of about 500 L/min of thermal water (27.8°C) and a simultaneous methane gas emission of about 200 L/min. Gas analyses gave evidence that the methane come from a multiple deep reservoir. Continuous records of gas emission showed some anomalous variations occurred during the past three years. The gas flux anomalies were in a distinctive coincidence with self-potential anomalies of one station close to the hydrogeochemical station. The present paper describes the interpretation of these anomalies in relation to the geodynamic activity in the area.

Geochemical data from mud volcanic fluids obtained from various geological environments have been reviewed and reprocessed. The chemical and isotopic components of the liquid and gas phases have been studied. Notwithstanding the geographical distance between the mud volcanic areas and the differences between the geological environments, a common originating fluid derived from seawater has been recognized. Diagenetic processes due to sediment compaction can be considered to be responsible for the evolutionary patterns observed in the liquid phase and in the associated gas-emissions. Geochemical data fit the currently available physical models.

The geochemical monitoring carried out on fluids released in the Central Apennines (Umbria region) evidenced seismically-induced modifications of the physic-chemical parameters in all the released fluids, including some cold waters circulating in certain carbonate rocks that are exploited for drinking purposes. The results allowed us to recognize the presence of components of diverse origin that changed the chemical composition of the water. These components, potentially dangerous for human consumption, can be considered as being "secondary effects" on local aquifers, induced by crustal deformation.We would also stress the relationship between the circulating fluids and active tectonic structures, as we detected modifications in some springs that were apparently not located anywhere near the local faults. The temporal variations in the geochemical features of the investigated cold waters are related to the local faulting activity that occurs during seismogenesis. The geochemical monitoring that provided information on fault movements during the seismic crisis, is also able to give us information regarding faulting activity in its earlier stages.

It is generally agreed that the occurrence of seismic sequences implies a kind of interaction between different fault segments.The coseismic stress transfer produced by each dislocation is the most obvious component of such an interaction.However, the time intervals elapsing between subsequent events in a sequence indicate that the coseismic stress is not sufficient to trigger other seismic events by itself.We investigate the possibility that the coseismic stress field may induce flow of pore fluids, altering the pore pressure distribution in the region.Since the crust is a fluid-saturated medium at many locations, we consider the crust as a poroelastic solid.Because poroelastic materials exhibit time-dependent stress fields, we examine if this behaviour can explain the triggering of aftershocks.We consider some available analytical solutions for a semi-infinite plane fault.Permeable and impermeable dislocation planes are considered.We compare the solutions for a poroelastic medium with those for a porous medium, and evaluate the effect of the coupling between deformation and fluid diffusion.We find that the Coulomb stress changes due to the main shock may be initially negative at some locations, but become positive as pore fluids are redistributed.These changes are significantly large.If the crust were to behave as an isotropic, fluid-filled, poro-elastic medium, as we assume here, Coulomb stress triggering by means of pore fluid diffusion is likely an important mechanism for aftershock generation over distances and widths of about 2.5 and 0.5 fault lengths, respectively.These distance ranges are smaller than those predicted by previous models which disregarded the mechanical interactions between elastic deformation and pore fluid diffusion.For typical porosities, the stress changes due to fluid flow are diminished greatly after about 1 yr after the main shock.