1. Consiglio Nazionale delle Ricerche-Istituto dei Sistemi Complessi (CNR-ISC), Via Madonna del Piano 10, Sesto Fiorentino, 50019 Firenze, Italy
2. Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, 00143 Rome, Italy
3. The Abdus Salam International Centre for Theoretical Physics (ICTP), Strada Costiera 11, 34151 Trieste, Italy
4. Boston College, USA (BC), Institute of Scientific Research, Chesnut Hill, MA 02467, USA
5. National Institute of Astrophysics (INAF), Institute for Space Astrophysics and Planetology (IAPS), Tor Vergata, Via del Fosso del Cavaliere 100, 00133 Rome, Italy