jgg     2013 33 (增1):  61-63    ISSN: 0412-1961  CN: 21-1139/TG SEASONAL VARIATION CHARACTERISTICS OF SHANDONG  GRAVITY FIELD Earthquake Administration of Shandong Province, Jinan 250014 Received: 2012-11-14  Revised: null  Online: 2013-09-25 Supporting info