Fault Roughness Controls Seismicity Front Migration During Fluid Injection

Abstract The increasing occurrence of injection‐induced earthquakes has raised public concern and highlighted the importance of understanding subsurface processes and mechanisms to assess induced seismic hazards and risks. We develop a simple physics‐based model to investigate how fault roughness controls the migration of seismicity during fluid injection. Simulations reproduce key observations: diffusion‐like seismicity migration and back‐fronts. The apparent diffusivity of seismicity fronts can deviate significantly from the hydraulic diffusivity. Faults, with realistic roughness, generally display slow seismicity migration, producing apparent diffusivities far below the hydraulic values. Thus, seismicity fronts often lag behind the pressure front, especially at low initial stresses and small roughness amplitudes. Only in the rare case of very rough faults stressed very close to failure, apparent diffusivity can exceed the hydraulic diffusivity, leading to seismicity fronts that outpace pressure fronts. In our model, the emergence of a back‐front near the injector well during continuous injection is caused by stress released by early rupture events. These findings demonstrate that fault roughness and initial stress environment control the migration speed of induced seismicity through their influence on the criticality of the fault and stress transfer, and provide valuable insights to interpret seismicity migration patterns in fluid injection scenarios.