(1) Istituto Nazionale di Oceanografia e Geofisica Sperimentale – OGS, Trieste, Italy , (2) School of Engineering, University of Basilicata, Potenza, Italy , (3) Institute of Methodologies for Environmental Analysis of the National Research Council, Tito Scalo (PZ), Italy, (4) Graduate School of Science, Chiba University, Chiba, Japan, (5) International Space Science Institute, Bejiing, China, (6) Università degli studi di Udine, Trieste, (7) Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Milano

Hydrological and hydrogeochemical observations (piezometry, chemistry, electric properties, etc.) carried out in groundwaters in Italy in the past 40 years have been recovered and processed. Available data time series recorded by government agencies, scientific institutions and independent researchers in the field of groundwater and geochemical monitoring in 5480 different sites have been recovered, systematized and processed. Meteorological data useful for data evaluation have been recovered too. Some possible precursors have been identified but the relatively high amount of earthquakes not preceded by hydrologic or geochemical anomalies suggest the need to consider all together geophysical and geochemical parameters for future researches. Highest amount of data collected by manual sampling were found in the Lombardy, Veneto, and Emilia-Romagna regions, while most of automatically recorded data were found in the Tuscany region.

The first measurements of radon as a seismic precursor are dated back to 1927, but the first recording, that is reported in many publications, and that encouraged research on seismic precursors, was detected before the Tashkent earthquake of 1966. This paper is a review of the radon measurements performed all over the world, trying to distinguish between discrete and continuous measurements, and between measurements in soil, water or air. The role that the "precursor radon" had in the forecast of strong earthquakes in the past has been examined. The currently monitored sites in Italy are listed, and some of the results obtained are reported.

Anomalous geochemical signals inferred from elemental and isotopic analyses on spring waters and soil degassing are often detected in response to tectonic loading along faults. Recent results highlighted how the geochemical anomalies are closely related to episodes of crustal deformation. In the present study, the carbon dioxide and radon from soil degassing and the geochemical features of springs spatially related to fault zones in the Friuli-Venezia Giulia region (north-eastern Italy), a seismic-prone area, have been coupled with crustal deformation analyses to better define the possible correlations between fluctuations of geochemical parameters and seismicity, with the aim of gaining new information about local geodynamic processes. The natural CO2 and Rn degassing was evaluated by a soil gas survey carried out by a grid of about 100 measuring sites located over the area that had been hit by strong earthquakes, in the past (Gemona - Idrija 1511, Raveo 1700, Tolmezzo 1788 and 1928, Gemona 1976). The results obtained show a significant amount of crustal-originated gases, especially CO2, possibly related to decarbonation reactions and stress accumulation occurring in deep-seated structures. The spring waters show, in some cases, anomalous geochemical transients, in particular concerning the chloride and Rn concentration, that are not related to seasonal changes and interpreted to reflect distinct fluid pressure regimes within the fault zone, yielding the leakage of pore fluids into the country-rock aquifers. In particular, the changes in the chloride content have been tentatively modeled in terms of pore-fluid expulsion from compacting clays during pressure gradients at shallow crustal levels. The flow regimes and chemical evolution have been related to the strain computed at the outlet sites through the Gutenberg-Richter relation parameters and the regional value of the strain rate. The information provided here may be used to start up a long-term geochemical monitoring of this seismically active area able to detect the modifications occurring in the circulating fluids to gain a better insight on the relationships between the geochemistry of the fluids and the activity of the local seismogenic faults.

A periodic sampling of the groundwaters and dissolved and free gases in selected deep wells located in the area affected by the May-June 2012 southern Po Valley seismic sequence has provided insight into seismogenic-induced changes of the local aquifer systems. The results obtained show progressive changes in the fluid geochemistry, allowing it to be established that deep-seated fluids were mobilized during the seismic sequence and reached surface layers along faults and fractures, which generated significant geochemical anomalies. The May-June 2012 seismic swarm (mainshock on May 29, 2012, M 5.8; 7 shocks M >5, about 200 events 3 > M > 5) induced several modifications in the circulating fluids. This study reports the preliminary results obtained for the geochemical features of the waters and gases collected over the epicentral area from boreholes drilled at different depths, thus intercepting water and gases with different origins and circulation. The aim of the investigations was to improve our knowledge of the fluids circulating over the seismic area (e.g. origin, provenance, interactions, mixing of different components, temporal changes). This was achieved by collecting samples from both shallow and deep-drilled boreholes, and then, after the selection of the relevant sites, we looked for temporal changes with mid-to-long-term monitoring activity following a constant sampling rate. This allowed us to gain better insight into the relationships between the fluid circulation and the faulting activity. The sampling sites are listed in Table 1, along with the analytical results of the gas phase. […]

At Cazzaso (Friuli) in northeast Italy, radon (Rn-222) activity concentration in soil gas in a borehole at a depth of 80 cm has been monitored continuously (at a frequency of once an hour) since May 2004, using a Barasol probe (Algade, France). In addition, environmental parameters (air and soil temperature, barometric pressure) have been recorded. The results have been evaluated and the relationship between radon levels and seismic activity is discussed. Correlation between radon concentration and barometric pressure has been observed. Preliminary results have shown a distinct radon anomaly prior to some earthquakes.

In 1995, a radon survey station was set up in the Friuli area (north-eastern Italy). Radon concentration is monitored with a sampling interval of 3 hours. In this work the data recorded from 1996 to 1999 are analysed in a search for a possible correlation between radon anomalies and local earthquakes. The minimum earthquake magnitude required to obtain a radon anomaly at a given distance from the radon recording device is determined. In this way, the selected earthquakes, especially if large, can have their epicentres up to many kilometres away from the radon site. Every datum exceeding the 2-sigma threshold has been considered as an anomalous value. Significant variations in radon concentration have been observed in relation to local events. The most interesting seismic events are characterized by epicentres that are less than 40 km from the radon station and with a magnitude greater than 3.0, followed by seismic series.

During a ten months period a series of 10 Schlumberger V.E.S. have been executed in a spot of the Palermo coastal plane upon a layered structure with unconfined aquifer in order to study the time variations of the shapes of the curves and their interpretations obtained by means of a computerized indirect method. Meanwhile the stratigraphy and the different hydrological conditions have been examined by means of a water well, and also the rainfall has been measured in the same period. The interpretation of the V.E.S., carried out with the help of many geological and hydrological data, has shown a six-layer electrostratigraphy, while the time behaviour of the interpreted resistivities presents large variation coefficients for some layers. These variations have been connected with the different conditions of the water contents of the rocks, showing a good correlation, except for the water-bearing layer, the resistivity variations of which have been ascribed both to small errors due to different locations of the electrodes and to instrumental ones. Finally, the reliability of the V.E.S. for a systematic control of the hydrological behaviour of the water-bearing aquifer is discussed.