Fig. 5: A micromechanical model describing the spatiotemporal evolution of AEs and foreshocks throughout the laboratory seismic cycle.

We propose that AEs in our experiments are generated from slip along localized planes of weakness within the gouge layer which are depicted as brown parallel and sub-parallel structures that span the fault zone. Yellow stars are used to denote individual AE events and groups of spatially clustered AEs represent families. Motivated by the data in Fig. 4 we depict the spatiotemporal evolution of AEs at three locations within the seismic cycle. The inter-seismic period of slow events consists of multiple AE families with high AE similarity and low DTT. In addition, waveform similarity and DTT remain constant throughout the seismic cycle. We depict these characteristics by showing multiple AE families that are tightly clustered/localized in space and invariant to position within the seismic cycle. In contrast, fast stick-slip events in Fig. 4 show three distinct regimes throughout the seismic cycle. The first regime occurs when the shear stress is below 40% of its peak and is characterized by decreasing waveform similarity and increasing DTT. In this regime AEs are spreading out across the fault zone and transitioning from localized to delocalized/randomly distributed. DTT is the highest and waveform similarity is the lowest between 40 and 80% of the peak stress (i.e., second regime), indicating that AEs are located far from one another and spread out across the fault zone. Once the fault surpasses 80% of its peak shear strength, DTT begins to decrease and waveform similarity begins to increase, indicating that AEs are transitioning from being delocalized/randomly distributed to more localized and clustered in space. We depict this localization process with multiple groups of tightly clustered AEs. It is worth noting that the clustering and localization of AEs prior to fast stick-slip (between 80 and 100% of the peaks stress) is similar to the localization/clustering that occurs throughout all stages of the seismic cycle for slow slip events.