1. School of Geosciences and Info-Physics, Central South University, Changsha, 410083 Hunan, China
2. School of Mathematics and Statistics, Central South University, Changsha, 410083 Hunan, China
3. Department of Earth Sciences, Uppsala University, 75236 Uppsala, Sweden
4. Department of Earth Sciences, Institute of Geophysics, ETH Zurich, 8092 Zurich, Switzerland
5. Institute of Geology and Geophysics, Chinese Academy of Sciences, 100029 Beijing, China