1. College of Geoscience and Surveying Engineering, China University of Mining & Technology–Beijing, Beijing 100083, China
2. State Key Laboratory of Fine Exploration and Intelligent Development of Coal Resources, China University of Mining & Technology–Beijing, Beijing 100083, China
3. Civil and Environmental Engineering, University of Connecticut, 159 Discovery Dr., Storrs, CT 06269, USA
4. Department of Geography, University of Tennessee, Knoxville, TN 37996, USA