jgg     2015 35 (4):  589-593    ISSN: 0412-1961  CN: 21-1139/TG Effects of Non-Tectonic Deformation on the Vertical Periodic  Motion of GNSS Reference Stations in China 1 First Crust Monitoring and Application Center，CEA，7 Naihuo Road, Tianjin 300180，China Received: 2014-06-30  Revised: null  Online: 2015-07-29 Supporting info