Differences in spatial localization of acoustic emissions during stick-slip and stable-sliding on laboratory fault gouge

Roshan Koirala, Navin Thapa, & Thomas H. Goebel

Submitted September 7, 2025, SCEC Contribution #14480, 2025 SCEC Annual Meeting Poster #TBD

Acoustic emission (AE) events during frictional sliding on laboratory fault gouge are closely linked to microphysical processes, including grain comminution, force chain collapse, and strain localization. Here, we locate AE events with millimeter accuracy and compare their spatiotemporal evolution during stick-slip in soda-lime glass and stable sliding in quartz sand gouge. The gouges are sandwiched between corrugated PMMA blocks and loaded to failure under constant shear velocity and constant normal displacement boundary conditions. Changes in spatial AE distributions during stick-slip indicate long-term localization followed by short-term delocalization across the soda glass gouge layers. The onset of delocalization coincides with rapidly accelerating slip, starting approximately after 95% of the interseismic periods between stick-slips. Stable sliding on quartz gouge exhibits long-term AE localization but lacks a delocalization phase, and AE events are overall more distributed (i.e., higher fractal dimension) than in soda-lime glass. To assess the influence of fault zone complexity and material properties on AE patterns, we compare the observed AE distributions with previous stick-slip and stable sliding tests conducted on rough faults with different degrees of off-fault damage in granite cores. The width of AE activity zones across stick-slip faults in granite is reduced by a factor of ~2.5 (i.e., 10 mm to 4 mm) before dynamic failure compared to a factor of ~2 in soda lime glass (i.e., from 2 to 1). Collectively, these findings demonstrate that the observed AE localization, and thus underlying strain localization, during fault slip is strongly influenced by fault geometry, gouge composition, and off-fault cracks. The most pronounced spatial localization of microseismic activity occurs over long periods of time and is driven by progressive strain partitioning from the damage zone into the gouge layer. In contrast, the gouge zone itself exhibits only modest strain localization followed by increasingly dispersed AE activity associated with rupture nucleation and rapid slip acceleration. Documenting these factors is crucial for an improved understanding of fault mechanics and earthquake nucleation.

Key Words
Acoustic emission, Localization, Faults, Friction

Citation
Koirala, R., Thapa, N., & Goebel, T. H. (2025, 09). Differences in spatial localization of acoustic emissions during stick-slip and stable-sliding on laboratory fault gouge. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)