The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
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Volume 120, Issue 12
Displaying 1-5 of 5 articles from this issue
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SP ISSUE;Deep geological disposal of radioactive waste and geological sciences:Long-term behavior of geological environment and site characterization
Review
  • Uncertainty of faulting for long-term safety assessment in geological disposal
    Makoto Otsubo, Ayumu Miyakawa, Hitoshi Tsukamoto, Takahiro Yamamoto, Y ...
    2014 Volume 120 Issue 12 Pages 423-433
    Published: December 15, 2014
    Released on J-STAGE: May 19, 2015
    DOIhttps://doi.org/10.5575/geosoc.2014.0042
    JOURNAL FREE ACCESS
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    We classified the uncertainties in the mechanism and timescale of faulting for long-term safety assessment of the geological disposal of radioactive waste. We categorized faulting into three phenomena: (1) rupture of main active faults; (2) formation of splay faults; and (3) reactivation of existing faults. The reactivation of existing faults is classified into three types: (1) faults induced by earthquakes around the ones; (2) faults reactivated by the change of stress regimes from the large trench type earthquakes; and (3) faults reactivated by the change of regional stresses. The uncertainty in the frequency of faulting in the Kyushu-Ryukyu arc was classified into five different timescales: (a) <100 years; (b) a few hundred to a few thousand years; (c) a few thousand years to 1 Myr; (d) 1-2 Myr; and (e) >2 Myr. Identifying the temporal and spatial heterogeneities and factors in faulting are the keys to evaluating the uncertainty of faulting for safe, long-term disposal of radioactive waste.
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Articles
  • Study on index of erosion rate in inland mountains: Case study using old river valley around detached meander core
    Ken-ichi Yasue, Ryoichi Takatori, Shin-ichi Tanikawa, Atusi Ninomiya, ...
    2014 Volume 120 Issue 12 Pages 435-445
    Published: December 15, 2014
    Released on J-STAGE: May 19, 2015
    DOIhttps://doi.org/10.5575/geosoc.2014.0045
    JOURNAL FREE ACCESS
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    Estimating the rate of change in landforms and geological environments due to erosion is important when assessing the safety of the geological disposal of high-level radioactive waste in Japan. The aim of this study is to develop an index of erosion rates in inland mountains in Japan. We focused on “circular abandoned channels”, which are old river valleys around detached meander cores formed by the cut-off of incised meandering rivers. Circular abandoned channels can be useful for estimating incision rates because they occur at a range of elevations throughout the Japanese Islands. We undertook a case study to determine the incision rate using a circular abandoned channel in the middle reaches of the Kumanogawa (Totsukawa) River in the Kii Peninsula, where many circular abandoned channels have been identified. We obtained undisturbed core samples of old river channel deposits and angular gravel deposits that overlie the circular abandoned channel. The old river channel deposits have been emergent since at least MIS5 (i.e., 125 ka), based on an analysis of the soil color in angular gravel deposits. This interpretation is also supported by the composition of volcanic ash grains in the deposits. The incision rate, as calculated from this age and the difference in elevation between the abandoned and present channels, is less than about 0.9 m/ky. This study shows that analyses of circular abandoned channels can yield estimates of incision rates and potentially also uplift rates. More accurate estimates of incision rates require further studies of the dating and evolution of sediments that overlie circular abandoned channels.
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  • Verification study on technology for site investigation for geological disposal: Confirmation of the applicability of survey methods through establishing site descriptive models in accordance with stepwise investigation approach
    Hirofumi Kondo, Koichi Suzuki, Takuma Hasegawa, Takaomi Hamada, Kimita ...
    2014 Volume 120 Issue 12 Pages 447-471
    Published: December 15, 2014
    Released on J-STAGE: May 19, 2015
    DOIhttps://doi.org/10.5575/geosoc.2014.0044
    JOURNAL FREE ACCESS
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    The Yokosuka Demonstration and Validation Project, which uses the Yokosuka Central Research Institute of Electric Power Industry (CRIEPI) site, a Neogene sedimentary and coastal environment, has been conducted since the 2006 fiscal year as a cooperative research project between NUMO (Nuclear Waste Management Organization of Japan) and CRIEPI. The objectives of this project were to examine and refine the basic methodology of the investigation and assessment in accordance with the conditions of geological environment at each stage of investigations from the surface (Preliminary Investigation and the first half of Detailed Investigation conducted by NUMO) for high level radioactive waste geological disposal. Within investigation technologies at these early stages, a borehole survey is an important means of directly obtaining various properties of the deep geological environment. On the other hand, surface geophysical prospecting data provide information about the geological and resistivity structures at depth for planning borehole surveys. During the 2006-2009 fiscal years, a series of on-site surveys and tests, including borehole surveys of YDP-1 (depth: 350 m) and YDP-2 (depth: 500 m), were conducted in this test site. Furthermore, seismic surveys (including seismic reflection method) and electromagnetic surveys (including magnetotelluric method) were conducted within the expanded CRIEPI site in the 2010 fiscal year to obtain information about the geological structure, and the resistivity structure reflecting the distribution of the salt water/fresh water boundary, respectively, to a depth of over several hundred meters. The validity of existing survey and testing methods for stepwise investigations (from surface to borehole surveys) for obtaining properties of the geological environment (in various conditions relating to differences in the properties of the Miura and the Hayama Groups at this site) was confirmed through establishing site descriptive models based on the results of the above surveys.
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