1 School of Earth and Space Sciences, Peking University, Beijing 100871, China. Electronic address: zhang-yong@pku.edu.cn.
2 School of Earth and Space Sciences, Peking University, Beijing 100871, China; Institute of Geophysics, China Earthquake Administration, Beijing 100081, China.
3 Guangdong Provincial Key Laboratory of Geodynamics and Geohazards, School of Earth Sciences and Engineering, Sun Yat-sen University, Guangzhou 510275, China.