The 11-month precursory fault activation of the 2019 Mw 5.0 earthquake in the Weiyuan shale gas field, China

Anthropogenic activities such as hydraulic fracturing (HF) can trigger destructive earthquakes, the triggering mechanisms of which are still largely in debate. We utilize near-fault seismic recordings to study the preparatory phase of the 2019 Mw 5.0 earthquake in the Weiyuan shale gas field, Sichuan Basin, China, which struck 3 months after stimulation completion. This is one of the largest HF-triggered earthquakes worldwide. We observe an 11-month long precursory fault activation, during which continuous seismicity illuminated the fault plane and provided warnings for a potential destructive earthquake. The fault activation is a consequence of injections in multiple HF well pads, with a variety of mechanisms at play. Numerical simulation reveals that the occurrence of the mainshock involves stress perturbation from post-injection aseismic slip. This work promotes our understanding of HF-induced earthquakes and suggests incorporating long-term near-fault observations and taking post-injection aseismic slip into account for effective hazard management.