1. Researcher, National Research Council, Research Institute for Geo-Hydrological Protection, Via Madonna Alta 126, 06128 Perugia, Italy (corresponding author).
2. Researcher, National Research Council, Research Institute for Geo-Hydrological Protection, Via Madonna Alta 126, 06128 Perugia, Italy.
3. Engineer, Umbria Region Functional Centre, Via Romana Vecchia, 06034 Foligno (Perugia), Italy.
4. Professor, Dept. of Civil and Environmental Engineering, Univ. of Perugia, Via Duranti 93, 06125 Perugia, Italy.