Dating deep? Luminescence studies of fault gouge from the San Andreas Fault zone 2.6Â km beneath Earth's surface

► We have studied IRSL and TL from fault gouge from SAFOD drill core. ► Trap resetting is evident in both TL and IRSL data. ► Charge-trapping window exists between 112 °C geotherm and higher energy ruptures. ► SAR IRSL De data indicate ages ranging from decades to centuries may be measured.