1. Senior Researcher, High Speed Railroad Systems Research Center, Korea Railroad Research Institute, 176, Cheoldo bangmulgwan-ro, Uiwang-si, Gyeonggi-do 437-757, Republic of Korea (corresponding author).
2. Professor, Earth Science and Engineering, King Abdullah Univ. of Science and Technology, Bldg. 5, Thuwal, Saudi Arabia 23955-6900.