1. Shandong Earthquake Agency, Jinan, Shandong, China
2. GFZ German Research Centre for Geosciences Department 1, Potsdam, Germany
3. Institute of Space Science and Physics, Navigation and Remote Sensing Group, Shandong University, Weihai, P.R. China
4. School of Space Science and Physics, Shandong University, Ji'nan, Shandong, China
5. CRRC SHANGDONG WIND POWER CO., LTD, Jinan, Shandong, China