| Abstract |
Effective management of induced seismicity is essential for safe operation of subsurface activities that disturb tectonic stresses in the Earth's crust. Failure in brittle, porous materials initiates when structural damage localises along an emergent failure plane in a transition from stable crack growth to dynamic rupture. The precise micro-mechanisms involved are crucial drivers for earthquakes, including induced seismicity. However, due to the rapid nature of this critical transition, these mechanisms are difficult to capture. Here, we present results from rock deformation experiments that combine acoustic monitoring and feedback control with contemporaneous operando X-ray imaging of the microstructure. Our loading protocol controlled the rate of micro-seismic events to slow down the transition to failure, preventing runaway instability and allowing us to capture an integrated picture of how microscale damage mechanisms and associated micro-seismic events evolve together during sample weakening. We explain the stress evolution in terms of a new, sub-critical fracture mechanics model and directly constrain the micro-scale partition between seismic and aseismic deformation. Compared with loading under a constant strain rate, reactive loading to maintain a constant micro-seismic event rate suppresses the number of events of all sizes, decreases the maximum event magnitude, increases the seismic b-value, and reduces the seismic strain partition coefficient. Qualitative inspection of comparable grey-scale X-ray volumes showed less brittle damage and later microcrack localization in the sample deformed under a constant micro-seismic event rate. Our findings suggest that seismic event rate control may be effective for managing the risk from induced seismicity in field settings. |