Figure 1. In panel a the geo-electrical section is shown with the source zones and the measurement points of the different parameters indicated: FCO2 (flow of CO2 at the Solfatara); RSAM (tremor of the Pisciarelli fumarole recorded by a seismometer); air CO2 (concentration of CO2 in the air near Pisciarelli); P and T, pressure and temperature estimated from the compositions of the BG and BN fumaroles. The figure also roughly indicates the area with the highest microseismic density.
In the panel b the location of the earthquakes (circles proportional to the magnitude) recorded in the area in recent years is reported.
Fig. 2 Time evolution of the parameters considered. The different variables were normalized in order to be able to compare them.
Through the use of a statistical technique, including the common factor of the recent changes in the Solfatara area
The variations in seismic and geochemical parameters in the Solfatara and Pisciarelli area of the Phlegraean Fields (Pozzuoli - Naples) are thought to be caused by the pressure exerted on the subsurface structure of the Solfatara. These are the results of a multidisciplinary study conducted by theIstituto Nazionale di Geofisica e Vulcanologia (INGV) Hydrothermal pressure-temperature control on CO2 emissions and seismicity at Campi Flegrei (Italy) just published in the 'Journal of Volcanology and Geothermal Research'.
“In recent years, more frequent seismic activity and an increase in temperature and pressure estimates based on the composition of the gases emitted by the sampled fumaroles have been observed in the Campi Flegrei, particularly in the Solfatara and Pisciarelli areas. The variation of these parameters”, says Giovanni Chiodini, INGV researcher and first author of the study, “led us to analyze all the data available in the area together, to give an overall interpretation of the phenomenon”.
“By analyzing the data”, continues the researcher, “we observed that completely independent parameters, such as geochemical and seismic ones, have varied together over time. Among the parameters analyzed is the diffuse flux of carbon dioxide (CO2) from the soils of the area. The processing results in an increase in the amount of CO2 emitted which from about 1500 tons per day in the period before 2017 went to about 3500 tons per day in the following period. This change in carbon dioxide emissions is contemporary with the increase in seismicity”.
Furthermore, most of the hypocenters of small earthquakes occurred in the superficial part of a vertical structure that was identified using magnetotelluric techniques. This structure has been interpreted as a plume of gas: the same that feeds the flow of CO2 measured in the soils of the Solfatara and which was the object of the increase in the pressure and temperature estimates. This coincidence, both temporal and spatial, suggested to the researchers that the variations observed are caused by the pressurization of the structure present in the subsoil of the Solfatara.
"The novelties of the study", continues Chiodini, "are the collection of an enormous amount of multidisciplinary data, most of which are already public, and the use of a statistical technique, the Principal Component Analysis, which has made it possible to understand the common elements of the different variables analyzed. The study showed that the variations observed find their common cause in the increase in fluid pressure”.
The next step of the research”, concludes the researcher, “could be the execution of specific studies to define more accurately the geometry of the structure under the Solfatara where the gas, accumulating, triggers seismicity and feeds the emission on the surface. In other words, the study, at the moment, refers to a 2D section while the objective would be to have a 3D model, or a real tomography of the first kilometers of the Solfatara subsoil".
The published research has an essentially scientific value, without immediate implications regarding the aspects of civil protection at the moment.
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