Stress Evolution Analysis of Induced Seismicity Sequences in Oklahoma and Kansas

Understanding the behavior of induced earthquake sequences can provide insights into the mechanics of fault activation. Induced seismicity studies have suggested an important role for aseismic slip, pore fluid pressure diffusion, stress transfer, poroelastic effects, and earthquake-to-earthquake triggering in the evolution of induced earthquake sequences. To gain further insight into the potential role of these mechanisms in driving induced seismicity, we applied stress evolution modeling to 73 induced sequences of >150 earthquakes in Oklahoma and Kansas for which it appears that a single fault is being activated. Across these sequences, 7499 out of 24,937 earthquakes were identified as occurring on portions of the fault that were destressed by previous earthquakes, whereas 6513 earthquakes occurred at locations where stress transfer from preceding earthquakes increased stress more than 1 MPa. The remaining earthquakes occurred at locations that are ambiguous in the sense that the stress change imparted by previous earthquakes is small. These categories of stressed, destressed, and small stress change earthquakes account for similar total moment fractions: estimated to be 32%, 32%, and 36% of the seismic moment, respectively, though this varies between induvial sequences. Our analysis suggests that multiple processes are driving seismicity, and the observed variability in behavior suggests that the relative role of different driving mechanisms may vary as well.