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Nishiyama, Nariaki; Nakajima, Toru; Goto, Akira*; Hakoiwa, Hiroaki; Sueoka, Shigeru; Shimada, Koji; Niwa, Masakazu
no journal, ,
For some earthquakes of magnitude 6 to 7, the surface earthquake fault is unclear, and it is necessary to establish an evaluation method to understand the active faults that cause such earthquakes. In this study, in the source area of the 1984 western Nagano Prefecture earthquake, where no distinct surface earthquake faults appeared, we estimated the stress field that may have affected the activity of small faults by stress tensor inversion method using striation data of small faults collected by surface exploration, and extracted areas with many small faults consistent with the regional stress field. As a result of the surface survey, we collected data on 321 small faults. Considering the location and number of these small fault data, the study area was divided into 13 areas. As a result of stress tensor inversion method in each area, stress with a maximum compressive stress axis in the NW-SE direction, which is harmonic to the regional stress field in this area, was detected in the area near the upper end of the hidden fault. In these regions, there are relatively many small faults that were displaced by the activity of the hidden fault, and their distribution area is expected to correspond to the damage zone of the hidden fault or a deformation zone that extends over a wider area. Therefore, even when no clear fault displacement topography is recognized, we expect to be able to estimate its distribution and extent of influence by surface exploration. This study was funded by the Ministry of Economy, Trade and Industry (METI), Japan as part of its R&D supporting program titled "Establishment of Advanced Technology for Evaluating the Long-term Geosphere Stability on Geological Disposal Project of Radioactive Waste (JPJ007597) (Fiscal Years 2020-2022)".
Hisashi, Kanta*; Kawasaki, Kazuo*; Yasue, Kenichi*; Niwa, Masakazu; Yokoyama, Tatsunori
no journal, ,
no abstracts in English
Tateishi, Ryo*; Shimada, Koji; Iwamori, Akiyuki*; Ogita, Yasuhiro; Wada, Shinya*; Kunimatsu, Wataru*; Otsuka, Yoshiharu*
no journal, ,
It has been demonstrated that active faults (strike-slip faults) and non-active faults developed in granitic rocks in Japan can be discriminated with high probability by linear discriminant analysis using chemical compositions of fault gouge samples. Although, the result included that a reverse fault type active fault was discriminated on the inactive fault side. In this study, to confirm whether this result is due to the difference in fault type or the difference in rock body, chemical composition and linear discriminant analysis of the fault gouge of active reverse faults, active strike-slip faults, and non-active faults in the Kojyaku granite were carried out. As a result, the discrimination rate between active and inactive faults was 100% for 13 (chemical) components and 7 components selected by AIC, and 90% for 3 components. This result suggests the possibility that the difference in the granite bodies affected the discrimination more than the difference of their fault type.