Integrated Analysis of Seismic Sources and Structures: Understanding Earthquake Clustering During Hydraulic Fracturing

The distribution of hydraulic-fracturing-related seismicity is largely controlled by subsurface structures, yet the physical process that governs the redistribution of injected fluids and stress heterogeneity remains underexplored due to a lack of observational constraints. In this study, we monitored an active hydraulic fracturing (HF) well for two months with a surface nodal array of 60 three-component stations. We built a high-resolution catalog comprised of 1369 events (; Mc = −0.2). Their associated seismogenic structures are resolved by seismic reflection data and a 3D velocity model obtained from ambient noise imaging. Earthquakes concentrate near the transition zone between high and low-velocity structures, with the majority $(\sim 70\%)$ occurring on the high-velocity side, accompanied by abrupt variations in seismic attributes from reflection data. Particularly, relatively large ( 1.0) earthquakes terminate near the edge of the high-velocity zone. This distinct interface may represent a geological boundary or strong material property contrast that acts as a physical barrier to rupture propagation and migration of seismic sequence. Locally, two key nearby clusters exhibit distinct characteristics in spatial concentration, focal mechanisms and statistical features. We suggest that variations of structural dimension (i.e., fractures vs. faults) within a complex fault system can dominate the clustering behaviors. Overall, our integrated analysis provides new constraints on mechanical interactions among seismicity, local geological structure, and fluid migration during HF operations.