Temporal gravity changes before the 2008 Yutian Ms7.3 earthquake

Based on the data of the repeated gravity observation network in Chinese mainland since 1998,we analyzed the temporal changes of regional gravity field before the 2008 Yutian Ms7.3 earthquake.The result shows some mid-to-long term(two to ten years)changes during the earthquake's preparation.Notable features are a gravity increase lasting several years and a relatively large-scaled gradient zone of gravity change,the former indicating a continuous energy accumulation and the latter a possible location of seismic rupture.These gravity changes showed a trend of increase-accelerated increase-decelerated increase,similar to that of the Tangshan Ms7.8 earthquake in 1976.The maximum accumulated gravity change related to the earthquake reached 200×10-8 ms-2.