Chong Zang, University of Science and Technology of China, School of Earth and Space Sciences, Hefei, China, Sidao Ni, Institute of Geodesy and Geophysics, Chinese Academy of Sciences, State Key Laboratory of Geodesy and Earth's Dynamics, Wuhan,Hubei, China and Zhichao Shen, CalTech Seismological Laboratory, Pasadena, CA, United States