Characteristics of fault structures in the Hefei Basin based on gravity data and their relationship with earthquake distribution

Abstract Since February 2024, Feidong County in Hefei (Anhui, China) has experienced eight earthquakes of M ≥ 3.0, including an M 4.7 event on 18 September 2024. To investigate the characteristics of fault structures of the Hefei Basin (HB) and their relationship with earthquake distribution, gravity data were collected at scales of 1:100 000 and 1:200 000. Using potential field edge detection techniques, we derived the corresponding potential field edge information. Combined with earthquake catalogues and published geological and geophysical studies, we analysed gravity anomalies and potential field edge information to delineate the western boundary of the HB, determine the configuration of internal fault systems, and evaluate how fault-structure characteristics influence the spatial distribution of earthquakes. The results show that fault structures are highly developed in the study area, comprising five basin-bounding faults along the HB margin and seven major intra-basin deep faults, trending approximately W-E, NNE, NW, and N-S. Analysis of the correlation between fault structures and earthquake distribution suggests that the spatial pattern of earthquake distribution in this region is chiefly controlled by: (ⅰ) fault intersections and geometric discontinuities govern earthquake occurrence; (ⅱ) strain accumulation driven by differences among tectonic units; (ⅲ) dominant energy release by major fault activity; and (ⅳ) multiple stress sources and local release.