Second experiment RICEN FIRST ACT (Solfatara, Campi Flegrea caldera) - May, from 19th to 23rd, 2014.
RICENis a series of experiments, whose goal is to study the changes in the properties of the medium at small scales through repeated observations over time. The acronym RICEN stays for Repeated InduCed Earthquakes and Noise and is mostly oriented to the use of seismic waves (both in passive and active mode) as a diagnostic tool, but also magneto-electric analysis was performed at the same time of the seismic survey.
RICEN experiment is organized in the framework of the European FP7 MEDSUV - MEDiterranean Supersite Volcanoes project.
The Research Groups involved in it are AMRA s.c.ar.l., Italy - Università di Napoli Federico II, Italy - GFZ Potsdam, Germany - Université Joseph Fourier - Grenoble, France - Université de la Savoie, France - Istituto Nazionale di Geofisica e Vulcanologia, Italy - Università del Sannio, Italy - Consiglio Nazionale Ricerche, Italy.
Specifically RICEN aims at studying the structural changes of a volcanic structure, analyzing the changes in the seismic records acquired at a large number of sensors. Records are either ambient noise or the signals produced by the MiniVib shots (see photo).
The investigation area is the Solfatara, one the forty volcanoes of the Campi Flegrei area, characterized by an intense hydrothermal shallow activity, which results in fumarolic emission and a gas release of approximately 1,500 tons per day. The hydrothermal activity is mostly due to the interaction between the atmospheric agents and the deep convection which produces an seasonal change in the structural properties of the area.
The structural properties of the subsoil can change for different reasons, such as for a perturbation of the stress field in the preparatory phase of earthquakes, for the migration of fluids, mainly in volcanic areas, or for the fracturing induced by injection in geothermal exploration. If there was no change in the properties of the subsoil, the same source of seismic waves, activated at different times, would reproduce the same signal to an observation site. Changes in the structure, instead, generate differences in the signal, in the arrival times of seismic phases or in the coda, where the effect of the variation of scatterers is more evident due to diffracted waves. If this change is consistently recognized at several receivers it becomes possible to locate the anomaly. The critical aspect of this analysis is the need to reproduce the same seismic source with time, or to use the cross- correlation of the ambient noise, which is less sensitive to the position of the sources.
The Second Experiment RICEN FIRST ACT was realized from May 19 to 23, 2014, at the Solfatara.
For the seismic part, ambient noise was acquired all along the experiment by 50 GFZ –wise station, equipped with 4.5Hz, three components geophones, sparsely distributed inside the area and 7 intermediate period-velocimeters from INGV. Such recording is aimed to characterize the dispersion curve of the surface waves and to obtain the Green’s functions through cross-correlation analysis. (in the photo the experiment acquisition geometry)