Temporal variation of gravity-field in North China before and after the 2011 Japan Mw9.0 earthquake

:By using absolute and relative-gravity data recorded by the gravity network in North China, we obtained some large-scale and high-spatial-resolution images of gravity variation in this area for the first time. By analyzing these images, we found that the gravity in Liaodong peninsula area showed an obvious increase of 80 × l0− 8ms− 2 during about one- and-half year before the 2011 Japan Mw9.0 earthquake, and a rapid decrease after the earthquake. This gravity variation is similar to that observed previously for the 1976 Tangshan M7.8 earthquake.