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RICEN : Repeated Induced Earthquakes and Noise. Seismic campaigns at Solfatara

RICEN is 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 as a diagnostic tool. Records are either ambient noise or the signals produced by the MiniVib shots. The investigation area is the Solfatara, 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.

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Figure 1 : Experimental layout, with position of stations during the active campaign in RICEN.

The structural properties of the subsoil can change for different reasons, such as a perturbation of the stress field in the preparatory phase of earthquakes, the migration of fluids or hydraulic fracturing. No changes in the properties of the subsoil indicate that the same source of seismic waves, activated at different times, reproduces the same signal to an observation site. Differences in the signal recorded over time may be ascribed to specific changes in the structure. If this variation is consistently recognized at several receivers it becomes possible to locate the source of the anomaly in the data.
During the first year of MEDSUV, we performed two campaigns at Solfatara (RICEN PILOT and RICEN FIRST). We acquired ambient noise for a week by about 25 to 50 GFZ and 7 INGV stations sparsely distributed inside the area. Such recording is aimed to characterize the dispersion curve of the surface waves and to obtain the Green’s functions through cross-correlation analysis. The active experiment was performed in the central area of the Solfatara, with a 2D distribution of 108 shots were acquired by about 300 stations. In the last experiment, a 400 m long 2D profile was also performed with 240 sensors located at 2m distance along the profile and 100 shots about every 4m.

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Figure 2 : A seismic section, with data collected in common shot gather.

A first velocity model, obtained from the PILOT experiment indicates a decrease of velocity toward the Fangaia and a high velocity body below the central part of the Solfatara. This anomaly was also detected by resistivity measurements and was ascribed to a gas-rich shallow reservoir at a depth of 30-50 m.

RICEN involves people from AMRA, University of Naples, University of Grenoble, INGV, CNR and GFZ.

Work presented in EGU2014 Supersites session, EGU2014-9454 abstract

Authors : G. Festa (1,2), A. Zollo (1), M. Serra (1), G.De Landro (1), F. Bianco (3), P.P. Bruno (3), V. Di Fiore (4), S. Maraio (5), I. Nazzaro (6), M. Pilz (7), P. Roux (8), J. Vandemeulebrouck (9), H. Woith (7).
(1) Università di Napoli Federico II, Italy ; (2) AMRA : Analisi e Monitoraggio del Rischio Ambientale, Italy ; (3) Istituto nazionale di Geofisica e Vulcanologia, Italy ; (4) Consiglio Nazionale delle Ricerche, Italy ; (5) Dipartimento di Scienze Biologiche, Geologiche e Ambientali di Bologna, Italy ; (6) Dipartimento di Scienze e Tecnologie del Sannio, Italy ; (7) Helmotz-Zentrum Potsdam DeutschesGeoForschungsZentrum (GFZ), Germany ; (8) Université de Grenoble Joseph Fourier, France ; (9) Universitè de Savoie, France .

Contact : Gaetano Festa (festa[at]na.infn.it)

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Last update : 11-07-2016