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Ishimaru, Tsuneari; Shimada, Koji; Sueoka, Shigeru; Yasue, Kenichi; Niwa, Masakazu; Umeda, Koji
no journal, ,
The Nuclear Regulation Authority (NRA) instructed to develop a further additional research plan regarding the crushed zones on the Monju site against the JAEA on September 25, 2013. The JAEA developed a research plan in response to this instruction, and, the stripping investigation with expansion of the area, the additional detailed geographical and geological surveys in the mountains/terrace boundary, and the marine seismic surveys in the coastal waters, were conducted. And, the JAEA was submitted to the NRA "Compilation Report" on March 28, 2014. From the investigation results so far, no clear evidence was observed to support that the on-site crushed zones are active faults. And, in the sea and land vicinity of the site, other than to the Shiraki-Nyu active fault, structure associated with the active fault is not recognized. From the plastic deformation of the biotite which is observed in the latest shear plane, the on-site crushed zones are considered to be a geological structure of the pre-Quaternary, which is formed in the deep underground environment of the several kilometers.
Shimada, Koji; Ishimaru, Tsuneari; Sueoka, Shigeru; Yasue, Kenichi; Niwa, Masakazu; Umeda, Koji
no journal, ,
Shear sense inversion of small crush zones is observed in the Kojaku granite. Two group of small crush zones are observed in basement granitic rock at the Monju site based on the strike and dip of these zones: NNE group and ENE group. Two types of fault core is also discriminated. Inversions of shear sense are observed in the both groups as well as types of crush zones. A sinistral sense of shear was followed by dextral one at the ENE group, and a dextral sense of shear was followed by sinistral one at the NNE group. We describe occurrences of the two groups, two types of crush zones and microstructures including sense of shear.
Ishimaru, Tsuneari; Shimada, Koji; Sueoka, Shigeru; Yasue, Kenichi; Niwa, Masakazu; Umeda, Koji
no journal, ,
In JAEA, geological investigation of fracture zones has been carried out at the Monju site based on the instruction received from the Nuclear Regulation Authority. Results of the investigation, it has shown that no clear evidence was observed to indicate that on-site fracture zones are active faults. In the activity evaluation of the on-site fracture zones, we examined cross-cutting relationships of fractures in detail, and we estimated that these fracture zones are older small-scale geological structure which was formed under the high-temperature environment of the deep part before exposure of the granitic body from the microscopic observation of the plastic deformation of biotite grains in the fracture zones and the deformation twins in the calcite veins along the fracture zones. This investigation of fracture zones is considered one of good examples shown that it is possible to evaluated activity of fracture zones in granite.