[SSS15-P10] Characteristics of the fault zone with only the recent slips in the Atera Fault
Keywords:fault zone, recent slips, Atera Fault
The detailed observation of the fault structure, thin section observation, the powder X-ray diffraction (XRD) and the X-ray fluorescence analysis (XRF) were performed using the samples collected along the upper fault. The detailed observation of the fault structure revealed that the upper fault consists of A1 and A2 fault zone and their branch point is consistent with that of the upper and lower faults. The brown fault gouges distributes in the recent slip zone from the branch point of A1 and A2 to 4 m away from the branch point, and the light gray fault gouge far from 4 m. The latest slip occurred in the A1 fault zone based on the radiocarbon dating (Toda et al., 1994), and the cumulative amount of A1 displacement is 2.5 m from the upper plane of the granite. These fault zones involve the fragments of the surrounding weathered granite. The XRD results show that smectite appears within 1 m from the branch point. The XRF results show that Mn-rich zones are within 4 m and 3 m, respectively.
The lower fault zone had been displaced before the upper fault zone was formed, and the brown fault gouge, smectite and Mn-rich zone are included in the lower fault zone. This indicates that some of them in the upper fault zone should be displaced from the lower zone. The distribution of brown fault gouge and Mn-rich zone in the upper zone, however, cannot be explained only the fault displacement. This suggests that the recent Mn concentration would be occurred in the upper fault zone within recent several thousand years.