1. School of Earth Sciences and Engineering, Nanjing Univ., 22 Hankou Rd., Nanjing 210093, China (corresponding author).
2. School of Earth Sciences and Engineering, Nanjing Univ., 22 Hankou Rd., Nanjing 210093, China.
3. Dept. of Civil Engineering, Univ. of North Carolina, Charlotte, NC 28223.