1. Istituto Nazionale di Geofisica e Vulcanologia (INGV), Osservatorio Sismologico di Arezzo, Italy
2. Institute of Information Science and Technologies “A. Faedo” ISTI-CNR, Pisa, Italy
3. National Institute for Astrophysics, INAF-IAPS, Rome, Italy
4. Gravitation and Instrumentation, AGI srl, Rome, Italy