Identification of fault displacement and stratigraphic correlation of black soils based on radiocarbon ages

Yasue, Kenichi; Hirouchi, Daisuke*; Kokubu, Yoko   ; Matsubara, Akihiro; Furusawa, Akira*

In order to clarify the stratigraphic correlation around the fault and the timing of faulting event, we carried out radiocarbon dating of the black soil sampled from the trench wall of the Atera Fault. The dating results show that the soil ages varies from 4,000 to 2,000 years with depth. Black soil was deposited at approximately constant rate each at both sides of the fault in 4,000-2,000 years ago. This indicates that the fault wasn't displaced during this period. In the upper part, there is no variation in ages of black soils with depth. This suggests that sedimentation rate was faster. One of the causes that the sedimentation rate around the fault suddenly changes is fault displacement. It is thought that the faulting was about 2,000 years ago. About this timing, it is necessary to consider in behavioral segments of Atera fault zone in detail.