1. Dept. of Earth Science, Univ. of Perugia, Piazza dell’Università, 06123 Perugia, Italy (corresponding author).
2. Dept. of Earth Science, Univ. of Perugia, Piazza dell’Università, 06123 Perugia, Italy.
3. Geologist, Istituto Sperimentale per l’Edilizia “ISTEDIL,” Loc. S. Andrea delle Fratte, 06132 Perugia, Italy.