Experimental investigations on dating the last earthquake event using OSL signals of quartz from fault gouges

Obtaining a reliable age of the latest seismic slip event along an active fault is important for seismic hazard assessment. Here, we observe changes in the optically stimulated luminescence (OSL) signal of quartz crystals due to frictional heating in artificial fault gouges (comprising a mixture of quartz grains and Ca-bentonite powder). The fault gouge was deformed using a high-velocity rotary-shear apparatus at room temperature and room humidity. At a seismic slip rate of 1.31 m·s⁻¹, intense slip localization occurred along a very thin layer (~300 μm thick) within the simulated fault zones (1 mm thick). The estimated temperature of the slip-localized layer (SLL) increased by ~475 °C from frictional heating. The quartz OSL signals of the gouges were fully reset, most noticeably for the SLL. In contrast, there was rare slip-localization at subseismic slip rates (0.06–0.001 m·s⁻¹), for which the estimated temperature rise in the SLL was ~120 °C; hence, the quartz OSL signal was not reset under this condition. The results suggest that quartz OSL dating can be used to constrain the age of the latest seismic event in natural quartz-bearing fault zones where a SLL occurs.