The role of ongoing industrial operations in the triggering of the Stanton, Texas earthquakes

Seismic activity in the Midland Basin, west Texas increased significantly beginning in mid-2020, creating concern among the residents of the area. On December 31, 2020 and December 28, 2021, two earthquakes with Mwr 4.0 and Mwr 4.3, respectively, occurred near the city of Stanton. In response, Texas Railroad Commission in cooperation with industry established Seismic Response Areas (SRA) near Stanton with the goal of mitigating induced seismicity. Here, we examine how hydraulic fracturing, oil production and wastewater injection affected fault stability in the runup to the Stanton earthquakes. In this study, we develop a detailed catalog of the Stanton earthquakes to examine their spatio-temporal proximity to fluid injection/production at nearby hydraulic fracking and wastewater disposal wells. The earthquake catalog for Stanton was created using a deep learning phase picker, PhaseNet, and a back-projection based associator. After location using the double difference method, the seismicity reveals an optimally oriented near-vertical fault was activated in a shallow crystalline basement between 8 km to 4.5 km. Seismic activity on this fault began on December 20, 2020, 11 days before the first Mwr 4.0 event. The 2021 Mwr 4.3 event ruptured the same fault, suggesting reactivation in response to continuing industrial activity. We examined seismicity before the 2020 Mwr 4.0 event using a matched filter and found no additional events in the 35 months preceding the Stanton sequence. To compare competing causal factors contributing to the initiation of the Stanton earthquakes, we applied simplified elastic modeling to quantify elastic stress changes due to pressure changes for fracking, production and disposal operations. Our modeling indicates the disposal of wastewater is the dominant effect and promotes fault instability at the hypocenter. Stress changes due to hydraulic fracking were counterbalanced by continuing hydrocarbon production with the net effect of fault stabilization. These results suggest that accumulated elastic changes from deep injection can destabilize a fault at remote distances without the need to invoke pore pressure transmission. They also emphasize the importance of microseismic monitoring for detecting sudden fault activation during operations.