Cascade processes of induced and triggered earthquakes-Case study in the Weiyuan shale gas development area in Sichuan Basin, China

Identifying accurate seismogenic faults is critical for studying the mechanisms of induced earthquakes. On February 24th and 25th, 2019, three moderate earthquakes with magnitudes of M_S 4.7, M_S 4.3, and M_S 4.9 occurred successively in the shale gas development area of Weiyuan, China. We utilized high-resolution three-dimensional (3D) seismic data to identify two pre-existing faults (F1 and F2) that were responsible for the three moderate earthquakes. InSAR data were used to validate the rationality of the two seismogenic faults. Furthermore, we analyzed the impact of fluid diffusion on fault F1 near the fracturing well and calculated the Coulomb failure stress (CFS) generated on fault F2 by the M_S 4.7 and M_S 4.3 earthquakes to analyze the interactions between these events. The results indicated that fluid diffusion caused by hydrofracturing induced the M_S 4.3 and M_S 4.7 earthquakes on F1. The static Coulomb stress changes from these two earthquakes subsequently triggered the larger M_S 4.9 earthquake on F2. This study provides a case of a cascading process in which induced earthquake events triggered a more distant and higher-magnitude earthquake. This triggering scenario reminds us that earthquake-to-earthquake interactions may be more hazardous than a “typical” inducing mechanism and challenges current risk management practices.