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Tang, P.*; Kita, Kazuyuki*; Igarashi, Yasuhito*; Satou, Yukihiko; Hatanaka, Kotaro*; Adachi, Koji*; Kinase, Takeshi*; Ninomiya, Kazuhiko*; Shinohara, Atsushi*
Progress in Earth and Planetary Science (Internet), 9(1), p.17_1 - 17_15, 2022/03
Times Cited Count：5 Percentile：66.48(Geosciences, Multidisciplinary)Sugiyama, Jun*; Umegaki, Izumi*; Nozaki, Hiroshi*; Higemoto, Wataru; Hamada, Koji*; Takeshita, Soshi*; Koda, Akihiro*; Shimomura, Koichiro*; Ninomiya, Kazuhiko*; Kubo, Kenya*
Physical Review Letters, 121(8), p.087202_1 - 087202_5, 2018/08
Times Cited Count：18 Percentile：74.14(Physics, Multidisciplinary)Tampo, Motonobu*; Hamada, Koji*; Kawamura, Naritoshi*; Inagaki, Makoto*; Ito, Takashi; Kojima, Kenji*; Kubo, Kenya*; Ninomiya, Kazuhiko*; Strasser, P.*; Yoshida, Go*; et al.
JPS Conference Proceedings (Internet), 8, p.036016_1 - 036016_6, 2015/09
He/
He ratios along a high strain rate zone, central JapanUmeda, Koji; Kusano, Tomohiro; Ninomiya, Atsushi*; Asamori, Koichi; Nakajima, Junichi*
Journal of Asian Earth Sciences, 73, p.95 - 102, 2013/09
Times Cited Count：4 Percentile：12.21(Geosciences, Multidisciplinary)A linear zone with high strain rates along the Japan Sea coast, the Niigata-Kobe Tectonic Zone (NKTZ), is considered to be associated with rheological heterogeneities in the lower crust and/or upper mantle. Helium isotope variations along the NKTZ reveal a close association with the geophysical evidence for rheological heterogeneities in the crust and mantle. In the northern NKTZ where two large inland earthquakes occurred recently, there appear to be many samples with He/He ratios significantly higher than those observed in the fore-arc side of northeast Japan. A plausible source of mantle helium could be attributed to upward mobilization of aqueous fluids generated by dehydration of the subducting Pacific Plate slab.
Ninomiya, Atsushi; Umeda, Koji; Asamori, Koichi
Gekkan Chikyu, 35(6), p.297 - 304, 2013/06
The seismic tomography study along the Niigata-Kobe Tectonic Zone revealed segmentations of the seismic velocity structure and suggests the variable origin of the high-strain-rate along the NKTZ. We compiled existing helium isotope data to inspect an implication of geographic distribution of helium isotope data to the geophysical structure of the NKTZ.
Asamori, Koichi; Umeda, Koji; Ninomiya, Atsushi*; Negi, Tateyuki
The Earth's Core; Structure, Properties and Dynamics, p.79 - 94, 2011/07
Remarkable uplift of 1400 m during the Quaternary has been recognized in the Mesozoic crystalline mountains (Asahi Mountains) located on the back-arc side of the Northeast Japan Arc. Crustal and mantle structures beneath the mountains were imaged as a 2D resistivity model, using magnetotelluric survey. The resulting resistivity structure clearly indicates that an anomalous conductive body is present in the central part of the mountains. The conductor extends from the middle crust to the upper mantle. Also, helium isotope ratios were determined from free gas and groundwater samples collected in and around the mountains. The highest value is similar to those of MORB-type helium derived from mantle volatiles. These results provide strong evidence for the presence of a latent magma reservoir and related high-temperature aqueous fluids beneath the Asahi Mountains. The presence of a latent magma reservoir could lead to thinning of the brittle upper crust and the aqueous fluids could weaken the crustal rocks. Thus, contractive deformation could arise locally above the reservoir under compressive stress field. Although the uplift is considered to be controlled by active reverse faults on the west side of the mountains, the highest peak of the mountains is not located near the active faults, but rather is above the prominent conductive zone. It is concluded that the notable uplift of the mountains can mainly be attributed to locally anelastic deformation of the entire crust.
Kusano, Tomohiro; Asamori, Koichi; Kurosawa, Hideki; Tanikawa, Shinichi; Ninomiya, Atsushi; Negi, Tateyuki; Hanamuro, Takahiro; Yasue, Kenichi; Yamada, Kunimi; Ishimaru, Tsuneari; et al.
JAEA-Research 2009-072, 72 Pages, 2010/03
JAEA-Research-2009-072.pdf:11.27MB
The Japanese islands are located in the tectonically active Circum-Pacific Mobile Belt. As a result, Japan has a high frequency of earthquakes and eruptions. Special consideration is given to the long-term stability of the geological environment, taking into account volcanism, faulting, uplift, denudation, climatic change and sea-level change in Japan. Development of research/prediction technologies for geotectonic events has been carried out to evaluate the long-term stability of the geological environment in Japan. In fiscal year 2008, we carried out the following researches. For studies on faulting and seismic activity, we developed investigation techniques for evolutional history and activity of fault, and carried out case studies for development of effective assessment model in the fault zones. For volcanological and geothermal studies, we provided an integrated approach for detecting crustal magma and/or geothermal fluid in deep underground using geophysical and geochemical data. For the general evaluation study on uplift/denudation and climatic/sea-level change, we arranged investigation techniques for reconstruction of paleo-topography and paleo-climate, and to establish a simulation model for landform development. For studies on the long-term stability of the geological environments, we developed simulation techniques for groundwater flow related by crustal movement.
Kurosawa, Hideki; Ishimaru, Tsuneari; Shimada, Koji; Niwa, Masakazu; Kosaka, Hideki*; Saito, Satoshi*; Ninomiya, Atsushi
JAEA-Research 2009-043, 144 Pages, 2010/01
JAEA-Research-2009-043-01.pdf:8.09MBJAEA-Research-2009-043-02.pdf:46.22MB
Research on the influence of fault activity on deep geological environments contributes to the reliability of geological disposal systems for HLW. In this study, preliminary test shows that measured value within 1 hour after measurement start is supposed to include hydrogen gas generated by rock fracturing during the drilling of sampling holes and that stored in surrounding disturbed rocks, though the monitoring from a hand-drilled hole is effective for a rapid measurement. We investigated the concentration of hydrogen gas emitted from the Yamasaki fault zone, in southeast Japan. In our survey, the points where high concentrations of hydrogen gas emission was detected were unevenly distributed along the active fault, and in the southeast portion of the study area where small earthquakes frequently occurred.
Umeda, Koji; Ninomiya, Atsushi; Asamori, Koichi
Helium; Characteristics, Compounds, and Applications, 28 Pages, 2010/00
Helium is the lightest noble gas and both stable isotopes, He and He, are produced in the crust in a ratio of 
0.02 R
, with R being the atmospheric He/He ratio of 1.4
10
. Higher values are an indication of helium from the mantle where He captured during planetary accretion has been stored. It has been suspected for some time that degassing of the planet does not occur homogeneously over the Earth's surface, but is rather concentrated along plate boundaries, where the dynamics of the lithosphere are more intense and mantle helium from the Earth's interior can be more easily transported to the surface. We indicate that the spatial distribution of He/He ratios in gas samples from crustal fluids are considered to provide potentially useful information for determining not only latent magmatic activity but also potential pathways for mantle volatiles, such as in tectonically active zones.
Kusano, Tomohiro; Nohara, Tsuyoshi; Umeda, Koji; Ishimaru, Tsuneari; Hanamuro, Takahiro; Saito, Tatsuo; Yasue, Kenichi; Niwa, Masakazu; Shimada, Koji; Yamada, Kunimi; et al.
JAEA-Research 2009-022, 47 Pages, 2009/09
JAEA-Research-2009-022.pdf:48.94MB
The Japanese islands are located in the tectonically active Circum-Pacific Mobile Belt. As a result, Japan has a high frequency of earthquakes and eruptions. Special consideration is given to the long-term stability of the geological environment, taking into account volcanism, faulting, uplift, denudation, climatic change and sea-level change in Japan. Development of research/prediction technologies for geotectonic events has been carried out to evaluate the long-term stability of the geological environment in Japan. In fiscal year 2007, we carried out the following researches, to confirm existence of the phenomena that have influences on geological disposal system (e.g., active faulting, volcanism), and to develop the investigation techniques to reconstruct the history of these phenomena. For studies of faulting and seismic activity, we developed the investigation techniques to research distribution of crush zone, process of faulting, activity, and so on. For volcanological and geothermal studies, we developed a technique for detecting crustal magma and/or geothermal fluid in deep underground. For studies of uplift/denudation and climatic/sea-level changes, we extracted investigation techniques for landform developments and uplift rate with river terraces.
Umeda, Koji; Ninomiya, Atsushi
Geochemistry, Geophysics, Geosystems (Internet), 10(8), p.Q08010_1 - Q08010_10, 2009/08
A magnitude (
) 7.3 crustal earthquake occurred in western Tottori Prefecture, southwest Japan, on 6 October 2000. However, there was no indication of an earthquake surface fault corresponding to the 2000 earthquake. In order to elucidate the geographic distribution of the He/He ratios around the seismic source region, new helium isotope data for groundwater samples from drinking water wells were acquired. The maximum He/He ratio was observed from the well located nearest to the epicenter of the main shock. In addition, there appears to be a clear trend of decreasing He/He ratios with distance away from the main trace of the estimated fault segments. The observations provide significant evidence that the source fault of the 2000 earthquake is associated with leakage of mantle volatiles through the crust to the Earth's surface. We suggest that helium isotopes can be regarded as a tool for investigating concealed active faults with no surface expression.
Umeda, Koji; Ninomiya, Atsushi; Negi, Tateyuki
Journal of Geophysical Research, 114(B1), p.B01202_1 - B01202_10, 2009/01
Although there is no geological evidence of volcanism during the Pliocene and Quaternary in the Noto Peninsula, Central Japan, the peninsula has long been known to be unusual and atypical of non-volcanic regions, as indicated by the presence of high-temperature hot springs and the high geothermal gradient values of more than 50 K/km. In this work, we present new helium isotope data from the Noto Peninsula and examine a possible source of excess heat in this non-volcanic region, including geophysical evidence such as seismic velocity, resistivity structures, and heat flow data.
He emanations from the source regions of recent large earthquakes, Central JapanUmeda, Koji; Ninomiya, Atsushi; McCrank, G. F.*
Geochemistry, Geophysics, Geosystems (Internet), 9(12), p.Q12003_1 - Q12003_7, 2008/12
Times Cited Count：16 Percentile：39.28(Geochemistry & Geophysics)Recently, two shallow MW 6.6 inland earthquakes, the 2004 mid-Niigata Prefecture Earthquake and the 2007 Niigataken Chuetsu-oki Earthquake occurred in the Niigata sedimentary basin, near the boundary between the Eurasian and the North American Plate. In order to elucidate the geographic distribution of He/He ratios in and around the seismic source regions, new helium isotope data from hot spring gases and water samples with a much denser sampling were determined. Higher He/He ratios were observed in a zone along 37.5
N latitude including the source regions than in other regions in the Niigata sedimentary basin. Moreover, the He/He ratios are much higher than the 3.8 RA value, which is the expected He/He ratio at the present time for volcaniclastics of Middle Miocene age. Previous geophysical models of the mechanism for initiation of the 2004 mid-Niigata Prefecture Earthquake proposed that enhanced pore-fluid pressure around the fault system, due to infiltration of aqueous fluids derived from the subducting Pacific Plate slab into the lower crust, reduces frictional strength and triggered the main shock rupture. Geochemical evidence for emergence of hot spring and natural gases with anomalously high He/He ratios also indicates that upward migration of aqueous fluids with mantle volatiles from the subcrustal lithosphere to the Earth's surface could be attributed to the hydraulic gradient along the high permeability of the rupture zone.
Umeda, Koji; Ninomiya, Atsushi; Shimada, Koji; Nakajima, Junichi*
Lithosphere; Geochemistry, Geology and Geophysics, p.141 - 169, 2008/10
A linear zone with high strain rates along the Sea of Japan coast, the Niigata-Kobe Tectonic Zone (NKTZ), is considered to be associated with rheological heterogeneity in the lower crust and/or upper mantle, which may be caused by the upwelling of aqueous fluid and/or melt related to subduction of the Philippine Sea and Pacific Plates. In order to elucidate the geographic distribution of He/He ratios along the NKTZ, new helium isotope data from hot spring gases and water samples were determined. Our study reinforces the clear relationship between helium isotope variations on the surface and the seismicity and resistivity structure of the crust and upper mantle along the Niigata-Kobe Tectonic Zone, Central Japan. In addition, the helium isotopes in hot spring gases may be recognized as a useful geochemical indicator of the presence of concealed active faults with compressional tectonics.
Nohara, Tsuyoshi; Umeda, Koji; Sasao, Eiji; Hanamuro, Takahiro; Saito, Tatsuo; Yasue, Kenichi; Niwa, Masakazu; Mashima, Hidehisa*; Shimada, Koji; Yamada, Kunimi; et al.
JAEA-Research 2008-062, 61 Pages, 2008/07
JAEA-Research-2008-062.pdf:39.02MB
The Japanese islands are located in the tectonically active Circum-Pacific Mobile Belt. As a result, Japan has a high frequency of earthquakes and eruptions. Special consideration is given to the long-term stability of the geological environment in Japan. Development of research/prediction technologies for geotectonic events has been carried out to evaluate the long-term stability of the geological environment in Japan. During fiscal year 2006, we carried out the following researches, to confirm existence of the phenomena that have influences on geological disposal system, and to develop the research techniques to reconstruct the history of these phenomena. For studies of active faulting and seismic activity, we reviewed the existing techniques to research past activities and distribution of active faults (migration, extension, development process of a deformation zone). For volcanological and geothermal studies, we extracted a technique for detecting crustal magma and/or geothermal fluid in deep underground using geophysical and geochemical data, and models assessing the likelihood of future volcanism and its influence on geological environment. For studies of uplift/denudation and climatic/sea-level change, we constructed conceptual models such as landform development model.
Umeda, Koji; McCrank, G. F.*; Ninomiya, Atsushi
Journal of Geophysical Research, 112(B10), p.B10206_1 - B10206_10, 2007/10
Times Cited Count：20 Percentile：45.03(Geochemistry & Geophysics)New helium isotope data from hot springs on the eastern Kyushu Island were obtained from a large number of sampling points in order to elucidate the geographical distribution of He/He ratios in the fore-arc regions of Southwest Japan. Systematic, regional variations in He/He ratios can be identified clearly on between Kyushu Island (0.093-0.79 R), Shikoku Island (0.21-2.5 R) and the Kii Peninsula (0.39-7.4 R). The overall distribution of relative mantle helium reveals a close association with the occurrence of non-volcanic deep low-frequency tremors (LFT), which would be related to the presence of upward aqueous fluids produced by slab dehydration, in Southwest Japan. A flux of He carried by aqueous fluids via the mantle wedge is very low in Kyushu Island where the LFT are not found, resulting in a He/He ratio lower than the atmospheric ratio.
Umeda, Koji; Asamori, Koichi; Ninomiya, Atsushi; Kanazawa, Sunao; Oikawa, Teruki
Journal of Geophysical Research, 112(B5), p.B05207_1 - B05207_9, 2007/05
It has been recognized that the Iide Mountains in Northeast Japan are unique because of their occurrence in a non-volcanic region yet hot springs have anomalously high heat discharge values similar to the heart discharge from hot springs in volcanic regions. In order to attempt to constrain the heat source of hydrothermal activity in the region, new helium isotopic data from hot springs surrounding the Iide Mountains was obtained. The He/He ratios of the hot spring gases sampled range from 0.22 to 7.9 RA, and the highest ratio is similar to MORB-type helium (8 
1 RA), indicating a significant contribution of primordial mantle-derived helium. Estimation of post-intrusive radiogenic ingrowth of He by decay of U and Th suggests that the heat source beneath the Iide Mountains is not likely ancient magma intruded in the Middle Miocene but newly ascending magma derived from mantle material. The geographical distribution of He/He ratios of hot spring gases reveals that crustal magma storage exists beneath the Kitamata-dake, one of the peaks of the Iide Mountains. This can be used to interpret the geophysical anomalies in this region such as crustal seismicity and results of magnetotelluric imaging.
Umeda, Koji; Sakagawa, Yukihiro*; Ninomiya, Atsushi; Asamori, Koichi
Geophysical Research Letters, 34(5), p.L05310_1 - L05310_5, 2007/03
Times Cited Count：21 Percentile：48.56(Geosciences, Multidisciplinary)In order to examine the potential correlation between heat and helium isotope signatures in a non-volcanic region, we estimated the local heat flux using Peclet number analysis of thermal profile from deep boreholes in the Kii Peninsula, Southwest Japan. There is a distinct correlation between the common logarithms of He/He ratio and heat flux. Here heat flux values higher than 90 mW/m
are estimated from the deep boreholes and the upward flow of deep fluids predominates over the groundwater recharge of the local hydrology. These results support the recently proposed source model that shows that the high temperature hot springs with significantly higher He/He ratio in the Kii Peninsula originate due to the effective transfer of mantle helium and heat from the subcrustal lithosphere by aqueous fluids generated by dehydration of the subducting Philippine Sea slab.
Tanase, Atsushi*; Oikawa, Teruki*; Ninomiya, Atsushi; Hayashi, Shintaro*; Umeda, Koji
Kazan, 52(1), p.39 - 61, 2007/02
Temporal and spatial variations on Plio-Pleistocene volcanism in the Ryohaku Mountains, central Japan, have been investigated by newly obtained K-Ar ages on 38 groundmass samples separated from volcanic rocks. The volcanoes in the Ryohaku Mountains form two volcanic rows of the Kuzuryu and hakusan Volcanic Chains which have ESE-WNW and N-S alignments, respectively. Early volcanic activity occurred intermittently from 3.6 Ma to 1.5 Ma, and the volcanoes near the junction of the two volcanic chains were active. The volcanic activity in the ESE-WNW trending Kuzuryu Volcanic Chain was restricted in the age range from 1.2 Ma to 0.7 Ma with migration from Eboshi-Washigatake Volcano (ESE end) to Hoonji Volcano (WNW end). The N-S trending Hakusan Volcanic Chain was active from 0.4 Ma to the present.
Ninomiya, Koji*; Yoshizawa, Hideaki*; Sato, Yasushi*; Onishi, Toshimitsu*
JNC TJ6420 2003-012, 200 Pages, 2004/02
JNC-TJ6420-2003-012.pdf:13.05MB
Layer to be applied for the capping of uranium mill tailings and waste rock yard at Ningyo-toge.In consideration of the business scale, operation efficiency and cost performance, etc, we selected the decomposed granite as a base soil, bentonite as an additive, and a Twister as a mixer for this research. Based on those materials and a mixer, we actually made the cover layer and measured the permeability, N2 ventilation, strength of the layer, using as a parameter different types of bentonite and different bentonite/sand mixture ratios.According to the permeability test results, permeability coefficient proved to be stand at below 1x10-9 m/s, regardless of any combination of bentonite/sand mixture ratios made with the twister. Through a series of laboratory tests, base soil and additive, we found out the optimum phase of combination, which are the 7wt% bentonite/sand mixture in case of Volclay; and 16wt% in case of Redhill. N2 ventilation tests were also carried out, using as a parameter the degree of moisture saturation of cover layer material. Test results showed that the gas ventilation is sensitive to changes of the degree of the saturation, and that under the conditions of moisture saturation of over 90%, the coefficient of N2 ventilation stands at below 1x10-10 m/s, under which conditions the radon barrier will work out in an efficient way.Lastly, we described the directions of future investigations and studies, including the necessity of gathering technical data on the quality variation of cover layer materials, the same caused by continuous mixing process, and the need of further investigations and designing into/of the comprehensive cover layer systems, including the capillary-break layer, etc.
