OSL dating of fault gouges from the Atotsugawa Fault, Japan: Insights into partial resetting conditions by earthquakes

Abstract

Abstract Optically stimulated luminescence (OSL) dating utilises the detection of trapped charge in minerals, and have ultralow closure temperatures. There is the potential for direct dating of fault movement using this method, because frictional heating caused by large earthquakes can reduce the signal intensity. In this study, we conducted quartz OSL dating on four fault gouge and breccia samples from a surface outcrop of the Atotsugawa Fault, one of the most active dextral strike-slip faults in central Japan, where the last large earthquake occurred in AD1858, with an estimated magnitude of 7. The natural OSL signal intensity of fine-grained quartz was clearly below the signal saturation level, with the fraction of saturation (n/N) between 0.34 ± 0.04 and 0.42 ± 0.07. Quartz OSL ages range from 21 ± 2 to 70 ± 3 ka, two orders of magnitude older than the age of the last earthquake, suggesting that the past earthquakes only partially reset the OSL signal. We calculate the mean storage temperature of the samples to be 53 ± 2°C, which reflects past fault activity. Using the known recurrence interval of faulting to be 2.5 ka, the OSL ages, and the thermal stability parameters of the signal, we deduce partial resetting conditions.