1. Department of Engineering, University of Messina, I-98166 Messina, Italy
2. Politecnino di Torino, Torino, Italy
3. Istituto Nazionale di Geofisica e Vulcanologia (INGV), Via Vigna Murata 605, 00143 Roma, Italy
4. Department of Mathematical and Computer Sciences, Physical Sciences and Earth Sciences, University of Messina, I-98166 Messina, Italy