Aseismic strain localization prior to failure and associated seismicity in crystalline rock.

Recent laboratory tests and large-scale observations have revealed the complex interplays between aseismic and seismic deformation, as well as the progressive localization of the rock failure process. To investigate these processes, we conducted triaxial tests that combined distributed strain sensing (DSS) with acoustic emission (AE) sensors. Progressive strain localization was detected by DSS at 80% of the peak stress but did not produce measurable AEs. Closer to the peak stress, regions exhibiting strain localizations began to show clusters of AEs. This reveals that DSS measurements are more informative during the preparatory stage of brittle rock failure. The frequency-magnitude distribution of the AEs showed an inverse correlation with the volumetric deformation rate a few seconds preceding catastrophic failure. Our results are consistent with recent large-scale observations and offer crucial insights into progressive failure assessment.