Experimental investigation of the effect of stress cycling on seismicity evolution during fault reactivation process

Over the last few years, several experimental and numerical studies have investigated the mitigation and managing of fluid injection-induced seismicity. A cyclic fluid injection has been suggested to have a different seismic response than a monotonic injection, and a cyclic injection may cause less seismicity. However, most studies have been allocated for intact rock medium (not faulted). In this study, faulted (saw-cut) Red Pfaelzer sandstones were subjected to fault reactivation experiments to investigate the effect of stress cycling on seismicity evolution. During the stress-driven fault reactivation experiments, three different reactivation scenarios were carried out: continuous sliding, cyclic sliding, and under-threshold cycling sliding. The results showed that in comparison to continuous sliding, cyclic sliding triggers less seismicity in terms of b-value and significant AE events due to the uniform reduction in roughness and asperities on the fault plane. In addition, increasing the number of cycles decreases the number of AE events. The under-threshold cycling strategy prevents seismicity and pure shear slip; however, if the stress exceeds the previous maximum stress (critical), seismicity risk increases drastically in terms of b-value, maximum AE energy, and magnitude.