Structural Constraints of Induced Earthquakes in the Weiyuan Shale Gas Field Revealed by High-Resolution Body-Wave Tomography and Earthquake Relocation

Increasing concerns have been raised about hydraulic fracturing (HF) due to its capability of triggering damaging earthquakes. Although there is a common consensus that local geological settings play significant roles in these earthquakes, to what extent they influence earthquake locations and magnitudes within a shale gas field remains unclear. Here we conduct body-wave travel time tomography, earthquake relocation, and structural analysis in the Weiyuan Shale Gas Field (WSGF), Sichuan Basin, China. We find that structural deformation of the Weiyuan anticline and the newly revealed basement rift constrained the locations and magnitudes of M-L >= 3.0 earthquakes in the WSGF. We also observe that M-L >= 3.0 earthquakes are more prone to occur in low-velocity or velocity transition zones that are geologically susceptible. Based on high-resolution earthquake locations, we use aftershocks to delineate the fault plane of the largest Mw 5.0 in the WSGF. Our analysis shows the Mw 5.0 event nucleated in the basement rift and ruptured a fault plane strikes along northeast. Our results shed light on mitigating destructive earthquakes in shale gas fields by identifying geologically susceptible zones using structural deformation simulation and high-resolution tomography methods.