Alessandro Galvani, Istituto Nazionale di Geofisica e Vulcanologia, ONT, Rome, Italy, Vincenzo Sepe, National Institute of Geophysics and Volcanology, ONT, Rome, Italy, Roberto Devoti, INGV National Institute of Geophysics and Volcanology, ONT, Rome, Italy, Mario Dolce, National Institute of Geophysics and Volcanology, Osservatorio Vesuviano - Napoli, Rome, Italy and Guido Ventura, National Institute of Geophysics and Volcanology, Rome, Italy