Relationship between gravity change and Yangbi MS6.4 earthquake

Based on the relative and absolute gravity measurements in the southern South-North Seismic Belt since 2015, we analyzed the dynamic change of the regional gravity field and its relationship with the Yangbi M_S6.4 earthquake that occurred on May 21, 2021. The results show that: 1) The regional gravity field changes are closely related to the Weixi-Qiaohou fault, which reflects the surface gravity field changes caused by the fault activity from 2015 to 2021; 2) The gravity field change related to the preparation of Yangbi earthquake has experienced the evolution process of " steady state - regional gravity anomaly - local gravity anomaly - four-quadrant distribution - large area positive anomaly - earthquake occurring in the reverse change process "; 3) The cumulative and differential change images of the gravity field show that there were significant gravity changes in the two years preceding the Yangbi earthquake, and the earthquake occurred in the high-gradient belt of gravity variation, the center of the four-quadrant, and close to the zero contour turn; 4) The dynamic evolution image of the gravity field can well reflect the precursory phenomena during the preparation for the Yangbi M_S6.4 earthquake. Based on the anomaly change of mobile gravity, a certain degree of medium-term prediction was made before the Yangbi M_S6.4 earthquake, especially the determination of strong earthquake location.