Large-magnitude events unlikely in induced earthquake sequences

Injecting fluids into the subsurface frequently triggers earthquakes, yet the maximum size of these events remains difficult to forecast. Earthquake frequencies are typically assumed to decay exponentially with magnitude, a model that fits natural seismicity well. Here, we use a global compilation of injection-induced sequences to show that this model breaks down for about half of the cases, which instead show a downturn in the occurrence of larger events. Numerical simulations and observed spatial patterns of induced seismicity suggest that heterogeneous loading near injection sites and disorganized fault networks may limit the growth of large ruptures. These results provide a possible explanation for why induced earthquakes often remain below magnitude 2-3 and provide a basis for evaluating seismic hazard before and during injection operations.