Carbonate reservoirs host faults that can be reactivated in the manner of aseismic creep or large earthquakes. In this study, we experimentally investigate how fault geometry and confining pressure control slip stability and microseismicity in low-porosity (∼1%) carbonates. Displacement-controlled triaxial shear tests were performed at varying confining pressures of 30–90 MPa on carbonate samples cut by smooth (saw-cut) and rough (fractured) faults, while acoustic emission (AE) activity and ultrasonic P-wave transmission were simultaneously monitored. Carbonate samples display pressure-sensitive frictional strength, and strain partitioning is found to be influenced by fault geometry. Rough-fault samples accumulate significant inelastic matrix deformation, characterized by axial strain at the onset of fault reactivation rxn > 0.35% and a relative contribution of fault-zone slip to total shortening R slip 86%, and predominantly aseismic sliding. As the confining pressure increases from 30 MPa to 90 MPa, we observe a mechanical transition from stick-slip events to stable sliding with a shear-enhanced compaction deformation mechanism, as supported by a gradual increase in the compaction source type of associated AEs. The temporal evolution of ultrasonic P-wave velocities and P-wave amplitudes can act as a proxy for tracking evolving damage and fault coupling. These results link laboratory fault mechanics with field observations of earthquakes in carbonate, highlighting the combined role of pressure and fault geometry in governing strain partitioning, fault stability and energy dissipation.
Xie et al. (Sun,) studied this question.