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Journal Articles

Changes in chemical composition caused by water-rock interactions across a strike-slip fault zone; Case study of the Atera Fault, Central Japan

Niwa, Masakazu; Mizuochi, Yukihiro*; Tanase, Atsushi*

Geofluids, 15(3), p.387 - 409, 2015/08

 Times Cited Count:8 Percentile:47.55(Geochemistry & Geophysics)

It is expected that in some cases water-rock interaction in fault zones can strongly affect nuclide migration. In this study, we analyzed the chemical composition of well-exposed fault rocks from the Atera Fault, Central Japan, to understand the variability and behavior of major and some selected trace elements. Hydrogen and oxygen isotope ratios in fault gouges, and carbon and oxygen isotope ratios in carbonates indicate that the two major clay-rich zones formed in bedrock at near surficial depth, consistent with observed deformation structures. Based on the analyses of chemical compositions, we identified depletion of SiO$$_{2}$$, Na$$_{2}$$O, K$$_{2}$$O, and light rare earth elements associated with the formation of smectite and kaolinite, and increase of CaO, MnO, and heavy rare earth elements associated with carbonate precipitation caused by the mixing of allochthonous basalt fragments during fault activities.

Journal Articles

Reconstructing the evolution of fault zone architecture; Field-based study of the core region of the Atera Fault, Central Japan

Niwa, Masakazu; Mizuochi, Yukihiro*; Tanase, Atsushi*

Island Arc, 18(4), p.577 - 598, 2009/12

 Times Cited Count:12 Percentile:10.48(Geosciences, Multidisciplinary)

Architecture of fault/crush zones and their development histories are closely linked to the long-term stability of the underground environment. Herein, we studied part of the Atera Fault System, one of several large, active faults in Central Japan, and described the detailed mesoscopic and microscopic features of a crush zone to reveal its development at higher structural levels of the fault (i.e. several hundred meters to kilometers in depth). The zone is characterized by brittle fracturing and rock mass pulverization, lacks both ultracataclasite bands and any deformation structures showing pressure solution. The characteristics of the deformation structures suggest that the exposed crush zone was formed at a depth of less than several kilometers. Features of clay mineral and carbonate precipitations in the zone indicate the repetition of intense fragmentation and shear localization through periodic activities on the Atera Fault after the Pleistocene.

JAEA Reports

Perform Test of a Directional Borehole Rader

Nagata, Kazuhiro*; Kajikawa, Kazahiro*; Mizuochi, Yukihiro*

JNC TJ7420 2003-001, 51 Pages, 2003/02

JNC-TJ7420-2003-001.pdf:4.8MB

Directional borehole rader (DBRD) measurements and core description were carried out and the reliability of fracture orientations determined by DBRD was discussed. DBRD ran into the borehole (01MS-06, depth 400m) drilled at the Syobasama site and 17 fractures were detected. 10 fracture orientations were determined from those fractures. Reflection waves from amother borehole (MIU-2) located about 14m away from 01MS-06 borehole were not detected, so the reliability of orientation could not be evaluated quantitatively. Judging from the result of a laboratory experiment, wa conclude that the error of fracture orientations determined by DBRD, in case of clearly observed reflector planes, would be within the range of plusmn 10 deg. in this work. Comparing DBRD reflector plane with fractures obtained by the core logging, it is found that the reflection occurs from fractured zone of rock mass. DBRD measurements with directional antennas having sufficient resolution are applicable to ...

Oral presentation

Fracture zone structure of the Atera Fault in Kawaue, Nakatsugawa city, Gifu prefecture

Niwa, Masakazu; Nohara, Tsuyoshi; Mizuochi, Yukihiro*; Tanase, Atsushi*; Kobayashi, Hirohisa*

no journal, , 

The Atera Fault in the eastern part of Gifu Prefecture is a NW-trend active fault and shows sinistral strike-slip displacement. A fracture zone of the Atera Fault, in which granite (Naegi-Agematsu Granite) is in fault contact with welded tuff of the Nohi Rhyolite, is exposed several tens meters in width in Kawaue, Nakatsugawa City. Detailed occurrence of the fracture zone is described in this study to examine the research method to reveal histories of active faults. In the studied fracture zone, fault rocks of the welded tuff origin consist of fault breccia and clay, while those of the granite consist of cataclasite. The fault rocks of the welded tuff origin are more clay-rich than those of the granite origin. Textures of host rocks are more well-preserved in the fault rocks of the granite origin than in those of the the welded tuff origin.

Oral presentation

Development of fault fracture zones of several hundred meters to 1 km in depth; An Example of the Atera Fault, eastern Gifu Prefecture

Niwa, Masakazu; Mizuochi, Yukihiro*; Tanase, Atsushi*

no journal, , 

no abstracts in English

Oral presentation

Spatial distribution, age, chemical composition and tectonic implication of Miocene dikes in central Japan

Niwa, Masakazu; Tanase, Atsushi*; Mizuochi, Yukihiro*; Kurosawa, Hideki

no journal, , 

no abstracts in English

Oral presentation

Mass transport in a fault zone; Effects of fracturing and host rock lithology

Niwa, Masakazu; Kurosawa, Hideki; Mizuochi, Yukihiro*; Tanase, Atsushi*

no journal, , 

Fault zone development has the potential to impact regional groundwater flow. Groundwater flow plays an important role in mass transport and nuclide migration. Thus understanding mass transport along fault zones is one of the major subjects for topical issues such as geological disposal of radioactive waste. In this study, we analyzed whole-rock chemical composition of fault rocks from well-studied outcrops of the Atera Fault in central Japan. We particularly focused on REE, U, Th, as an analogue of radionuclides included in high-level radioactive waste. As a result, it is suggested that heterogeneity of host rock lithology presented as mixing of fragments of mafic volcanic rocks in the fault core has a great influence on the material transport in the fault zone, as well as water-rock interaction and clay mineral formation caused by fracturing.

Oral presentation

Fault zone characteristics between two faults (Gero and Yugamine Faults of the Atera Fault System) arranged in parallel

Niwa, Masakazu; Mizuochi, Yukihiro*; Tanase, Atsushi*

no journal, , 

We described features of fault zones where active faults are arranged in parallel for understanding the interaction of the two faults. We selected the Atera Fault System in central Japan as a case study. In the studied area, two sets of fault zones, subparallel (NW-SE to E-W trend) and high-angle oblique (NE-SE to N-S trend) to the active fault planes, are developed. The fault zones of NW-SE to E-W trend cut those of NE-SE to N-S trend and trace more recent fault activities.

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