1. Professor, School of Geomatics, Xi’an Univ. of Science and Technology, Xi’an 710054, PR China; Key Laboratory of Coal Resources Exploration and Comprehensive Utilization, Ministry of Land and Resources, Xi’an 710021, PR China.
2. Assistant Professor, Disaster Prevention Research Institute, Kyoto Univ., Uji, Kyoto 611-0011, Japan (corresponding author).