Drilling Into the Active Fault Damage Zone: the Use of Luminescence Dating Techniques on the Assessment of Previous Activations of the Nojima Fault-Japan

There is a very limited number of absolute dating studies of neotectonic events, with previous attempts to date faulting events mainly focusing on ESR and being limited by the use of grain size plateau for D_E values.

In this study, absolute dating of fault gouges and intercalated breccia and cataclasite samples using the Optically Stimulated Luminescence (OSL) and the Isothermal-Thermoluminescence (ITL) technique on fine quartz and medium quartz and feldspar grains from the Nojima and Asano faults has been attempted for the first time.

Luminescence dating demonstrated the potential of fault gouge to be successfully dated using the two techniques. Qualitative observations of the OSL and ITL signals of the natural and subsequent regenerated beta doses from both Nojima and Asano gouge samples revealed that they follow a typical decay, signifying that quartz and feldspar grains respond well to radiation they receive. However, quartz OSL signals of the breccia and cataclasite samples from both Nojima and Asano faults, appear unusual, not following the typical signal decay behaviour.

Luminescence ages obtained from the gouge samples represent the time of formation of the fault gouges layers (during fault raptures). The luminescence analyses suggest the occurrence of neotectonic activity with repeated raptures at the Nojima and Asano faults during the Middle-Upper Pleistocene, with OSL and ITL ages being in fair agreement. In this regard, this is the first successful absolute dating attempt on the Nojima and Asano faults using fine quartz and medium quartz and feldspar grains and the only luminescence study, as yet known, producing a series of ages representing previous activations of the two faults.