This research is supported by Supported by State Key Laboratory of Geodesy and Earth's Dynamics (Institute of Geodesy and Geophysics, CAS, Grant No. SKLGED2017-4-3-E) and Sinopec Key Laboratory of Geophysics (Grant No. 33550006-15-FW2099-0017). J. Xie is supported by China Scholarship Council (201606440091). J. Xie also thanks the Shell Ph.D Scholarship to support excellence in geophysical research.