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Yuguchi, Takashi*; Sasao, Eiji; Hibara, Ryoko*; Murakami, Hiroaki; Ozaki, Yusuke
no journal, ,
Understanding of matrix diffusion is important for geological disposal of high-level radioactive waste in terms of retardation of mass transport in deep underground. Matrix diffusion has been evaluated by effective diffusion coefficient and porosity for bulk rock, but contribution of each constituent mineral of rock to matrix diffusion was not evaluated. In the Toki granite, central Japan, micropores are found in constituent mineral of granite such as plagioclase, potassium feldspar and biotite. This study examined contribution of micropores in constituent minerals of granite to matrix diffusion and utilized effective diffusion coefficients obtained by through-diffusion experiment, porosity, petrological mode, fracture frequency, extent of hydrothermal alteration in the minerals, and volume of the micropores in the minerals. As a result of study, the following results were obtained; micropores in minerals act as "storage pore" which contributes retardation of nuclide, retardation could be caused by sorption onto minerals around micropores, and retardation could be expected even in fractured rocks, where advection is dominant. These results imply that evaluation of extent of hydrothermal alteration in the minerals is effective as an indicator of matrix diffusion.
Kawamura, Makoto; Jia, H.*; Koizumi, Yukiko*; Nishiyama, Nariaki; Umeda, Koji*
no journal, ,
Using topographical analysis with GIS using 10 m DEM, we created 2 km river crossing lines on each side of the three rivers, Abegawa, Oigawa and Kumanogawa, starting from the estuary and going straight to the course of the river every 3 km. In addition, the geological information of the river transverse line was extracted. When the cross-sectional lines of the three rivers are displayed together, it can be seen that the river bed rises and the undulations increase as it goes upstream. A comparison of the cross-sectional shapes of the three rivers reveals similar trends, with peaks of undulations on both sides of the rivers in the middle to upper reaches located approximately 500-1,500 m from the center of the river. The relative height between bed and peak also tends to be around 200-600 m. The difference in elevation between the peaks on both sides of the river and the river bed increased in the upstream direction, that is, the depth of the valley to the river bed increased in the upstream direction. When the riverbed slope of the river longitudinal created from the riverbed elevation was taken, an inflection points where the slope trend rose from the upstream area was seen in all three rivers regardless of the geology and geological structure. Although the trend of elevation of the riverbed and increase in undulations from the relatively flat landform near the mouth of the river upstream is pseudo, it suggests a temporal process of landform formation due to uplift and denudation from the flat lowland. This will be information that contributes to verification of the validity of future predictions and performance evaluation models that incorporate topographical changes, such as topographical change simulations.
Yoshida, Hidekazu*; Yamamoto, Koshi*; Asahara, Yoshihiro*; Karukaya, Koichi*; Saito, Akane*; Matsui, Hiroya; Mochizuki, Akihito
no journal, ,
The report are the results of the in situ experiment for sealing to underground cavities by a synthetic concretion-forming solvent and observed phenomenon of the sealing function after a earthquake.
Haji, Toshiki*; Abe, Noriaki
no journal, ,
no abstracts in English
Nishiyama, Nariaki; Nakajima, Toru; Goto, Akira*; Hakoiwa, Hiroaki; Nagata, Mitsuhiro; Shimada, Koji; Niwa, Masakazu
no journal, ,
Earthquakes of magnitude 6-7 class may occur in areas where active faults have not been detected. To reduce earthquake damage, it is important to understand the concealed active fault that generates such earthquakes, but there is little evidence to provide clues to this understanding. In this study, we collected data on striations observed in fractures by geological survey around the source area of the 1984 Western Nagano Earthquake, where the existence of a concealed active fault is known and conducted multiple inverse method. As a result, stress fields similar to the present stress field were detected in minor faults around the known concealed active fault. Some of the minor faults were recognized in Quaternary volcanic rocks, confirming that the minor faults were very recently active. This indicates that these minor faults may be part of the damage zone that develops around the concealed active fault and is expected to provide a clue to understanding a concealed active fault.
Nakajima, Toru; Niki, Sota*; Kudo, Shumpei*; Kawakami, Tetsuo*; Higashino, Fumiko*; Hirata, Takafumi*; Sakai, Harutaka*
no journal, ,
no abstracts in English
Shimooka, Kazuya*; Nagata, Mitsuhiro; Ogita, Yasuhiro; Takahashi, Toshiro*; Tani, Kenichiro*; Saito, Satoshi*
no journal, ,
The Kajishima is located in the northeastern part of Ehime Prefecture, where Cretaceous gabbros with dike-like granite are widely distributed. In this study, we clarified the granitic magma formation process during the Cretaceous flare-up event based on data on field occurrences, petrography, whole-rock geochemistry, Sr-Nd isotope composition, and zircon Hf isotopes. We newly found that many of gabbro and granite 
Nd (t) and zircon Hf (t) are negative. This suggests that the Cretaceous flare-ups enriched the mantle, the origin material of the gabbros. Furthermore, the zircon Hf isotopic composition of the plutonic rocks in this study is consistent with the isotopic compositions of previously reported Cretaceous plutonic rocks in the Eurasian margin. The Kajishima plutonic rocks can be considered representative of the Cretaceous plutonic rocks of the inner zone of southwestern Japan, and can be regarded as a geological unit that records the felsic magma formation process in the mafic lower crust.
Fukui, Toko*; Shimooka, Kazuya*; Ogita, Yasuhiro; Nagata, Mitsuhiro; Takahashi, Toshiro*; Saito, Satoshi*
no journal, ,
no abstracts in English
Yamada, Raiki*; Takahashi, Toshiro*; Nagata, Mitsuhiro; Ueda, Hayato*
no journal, ,
Oligocene-Miocene volcanic rocks distributed in the Toyama Sedimentary Basin of the SW Japan Arc are important for clarifying the temporal evolution of subduction zone volcanic activity during back-arc expansion. In this study, we report zircon U-Pb dates, zircon chemical compositions (trace elements and Hf isotopes), and whole rock compositions (major and trace elements, Sr-Nd isotopes). As a result of each analysis, the ca.23 Ma alkali-series rhyolite shows an isotopic composition that supports its high fertility, and is interpreted as magma that has dissolved the continental crust. The 18-17 Ma igneous activity varied from andesite to rhyolite. This magma diversity is thought to involve melting of the mantle saturated with slab fluids and partial melting of the mantle contaminated with slab melt.
Tamura, Tomonori; Ishii, Eiichi
no journal, ,
no abstracts in English