Interdependent effects of injection volume and rate on fault slip behavior: A large-scale numerical study

Various injection parameters have been shown to pose significant effects on human-induced seismicity due to a variety of activities such as wastewater injection, carbon storage and geothermal energy production. In this study, we used numerical modeling to investigate how different injection parameters, namely injected volume and injection rate, affect the behavior of faults in the context of fluid-induced seismicity. We tested a large model space (4500 simulations) and modeled injection cases with both spatially homogenous and heterogenous pore-pressure perturbations. Simulation results showed that the two parameters can have various impacts on fault behavior, and that in some cases their effects are interconnected. We discovered that aseismic slip plays a significant role in altering the timing of triggered earthquakes and has lasting impacts on future seismic activity. Moreover, we found that increasing the injection rate tends to increase the size of the triggered cluster of earthquakes, while increasing the injection volume increase the overall rate of earthquakes. We find that spatial heterogeneity has qualitatively similar effects as compared to spatially homogenous cases, with a few quantitative differences. Lastly, we also performed a case study of an injection scenario based on realistic values of pore-pressure diffusion and injection operations in Oklahoma, and we found that for an injection duration of one year, the pore pressure on the faults in the region does not go back to zero even after 70 years and can cause earthquakes years after the end of injection, perturbing the seismic cycles for ~200 years. Our work has potential important implications for safe operation of injection processes which can reduce the risk of seismic hazards.