An automatic monitoring network installed in Tuscany (Italy) for studying possibile geochemical precursory phenomena.

Since late 2002, a continuous automatic monitoring network (CAMN) was designed, built and installed in Tuscany (Italy), in order to investigate and define the geochemical response of the aquifers to the local seismic activity. The purpose of the investigation was to identify eventual earthquake precursors. The CAMN is constituted by two groups of five measurement stations each. A first group has been installed in the Serchio and Magra graben (Garfagnana and Lunigiana Valleys, Northern Tuscany), while the second one, in the area of Mt. Amiata (Southern Tuscany), an extinct volcano. The measured parameters are: T, pH, Eh, EC, dissolved CO2 and CH4. The results of three years of continuous monitoring can be summarised as follows: i) the monitoring stations made it possible to detect even small variations of the measured parameters, with respect to equivalent commercial devices; ii) acquired data made it possible to identify the groundwater circulation patterns; iii) in most locations, the observed trend of the acquired parameters is consistent with the periodic manual sampling results, and confirms the mixture of different water types that the hydrogeochemical model has determined. The absence of seismic events with a sufficient energy precluded the possibility to locate anomalies, with the only exception of the Equi Terme site, where an increase in the dissolved CO2 content was observed twelve days before a M=3.7 earthquake occurred at a distance of 3 km north of the monitoring station. The CAMN resulted as being a suitable tool in order to investigate the anomalous variations of the physical, physicochemical and chemical parameters of aquifer systems as earthquake precursors.