jgg     2008 28 (2):  16-21    ISSN: 0412-1961  CN: 21-1139/TG GRAVITY VARIATION BEFORE WENAN Ms5.1 EARTHQUAKE Sun Mingxin, Liu Shanhua and Yang Huaining National Earthquake Response Suppor Service, Beijing 100049 Received: 1900-01-01  Revised: 1900-01-01  Online: null Supporting info null