Abstract: In order to explore the abnormal gravity variations before and after the Wen'an M5.1 earthquake occurred on July 4 2006, the data observed by Wenba gravity observation network before and after the earthquake are analyzed. The relations between gravity change with vertical displacement and shallow groundwater level were discussed, and elevation effects are corrected. The results show that there were abnormal gravity changes before the M5.1 earthquake, which appeared as gravity rising in the whole observation network especially in the south part of it. High gradient of gravity variation appeared around the epicenter before the M5.1 earthquake, especially during the short period from October 2005 to April 2006. The boundary between the positive and negative gravity variations was gradually deflected and began recovering from October 2007.

Key words: Wen'an earthquake, Wenba gravity observation network, Dynamic gravity change