Exploring the Effects of Hydraulic Fracturing on the 2019 Mw 5.0 Weiyuan Earthquake in Sichuan, China

The seismicity inside the Sichuan Basin in southwest China has been dramatically intensified with the increase of shale gas exploitation recently. On 8 September 2019, an M_W 5.0 earthquake struck Weiyuan County in the Sichuan Basin, representing the largest earthquake in the Weiyuan shale gas field. It caused substantial damage and raised local awareness of the potential seismic risks induced by hydraulic fracturing (HF). Occurring 110 days after the shut-in of a HF site ∼1.25 km away, the seismogenic mechanisms of this event remain unclear. In this study, we use a 3D poroelastic coupled model to investigate how the HF potentially affected the M_W 5.0 mainshock. We find that events before the M_W 5.0 earthquake were mostly in the area where HF at platform Wei204H37 induced positive Coulomb failure stress change ($\Delta$CFS). The mainshock hypocenter was at the transition between the positive and negative $\Delta$CFS. Considering the uncertainty of the hypocentral depth, the hypocenter could be in the positive $\Delta$CFS zone when the hypocenter was shallow. Additionally, the main slip area of the M_W 5.0 earthquake constrained by InSAR observation lay within the positive $\Delta$CFS region, suggesting that the rupture process may have been intensified by HF. Moreover, we find a foreshock sequence that could encourage the initiation of the mainshock, intensified by HF-induced positive $\Delta$CFS and migrating toward the mainshock. This demonstrates that the region affected by static Coulomb stress transfer due to earthquake interactions exceeds the region affected by HF-induced positive $\Delta$CFS.