Analysis of Earthquake Swarm and the Dynamic Change of Gravity Field in Cixian , Hebei Province in 2022

Based on the mobile gravity observation data in southern Hebei Province, this study investigates the dynamic characteristics of the gravity field in the region before and after the Cixian earthquake swarm from August to September 2022. The results indicate that: （1） The significant dynamic characteristics associated with earthquake preparation and occurrence of the Cixian earthquake swarm are continuous positive changes in gravity and a zone of changing gravity gradients, which are consistent with the recognized patterns of typical preseismic gravity change anomalies. （2） Due to previous seismic activity prior to the 2022 gravity observations in this region, stress within the seismogenic zone has been partially released, resulting in an insignificant high gradient zone on adjacent period difference maps without evident energy accumulation. （3） The maximum cumulative change in observed gravity difference is 60 μgal, occurring over a distance of approximately 70 km. Following these observations, small earthquakes have occurred, with M_L3.4 being the largest recorded on September 16th. （4） The capture of pre-earthquake dynamic changes in gravity and understanding the evolution process of small and medium-sized earthquakes needs further improvement due to limitations by point layout density and re-measurement periods.