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  1. Article ; Online: Estimation of the depth of origin of fluids using noble gases in the surface sediments of submarine mud volcanoes off Tanegashima Island

    Yuki Mitsutome / Tomohiro Toki / Takanori Kagoshima / Yuji Sano / Yama Tomonaga / Akira Ijiri

    Scientific Reports, Vol 13, Iss 1, Pp 1-

    2023  Volume 12

    Abstract: Abstract The helium isotope ratio (3He/4He), concentration ratio of neon-20 to helium-4 (20Ne/4He), argon (Ar), krypton (Kr), and xenon (Xe) concentrations were measured in the porewater of surface sediments of several submarine mud volcanoes. From the ... ...

    Abstract Abstract The helium isotope ratio (3He/4He), concentration ratio of neon-20 to helium-4 (20Ne/4He), argon (Ar), krypton (Kr), and xenon (Xe) concentrations were measured in the porewater of surface sediments of several submarine mud volcanoes. From the 3He/4He values (0.18–0.93RA), the estimated He origin is almost 90% crustal He, with little contribution from mantle-derived He. The determined Ar, Kr, and Xe concentrations lie within the solubility equilibrium range expected for temperatures from 83 °C up to 230 °C and are consistent with the temperature range of the dehydration origin of clay minerals. Considering the geothermal gradient in the investigated region (25 °C/km), these gases are considered to have reached dissolution equilibrium at a depth of about 3.3 km to 9.2 km below the seafloor. As the depth of the plate boundary is 18 km below the seafloor, the noble gas signatures are likely to originate from the crust, not from the plate boundary. This is consistent with the results presented by the He isotope ratios.
    Keywords Medicine ; R ; Science ; Q
    Subject code 550
    Language English
    Publishing date 2023-04-01T00:00:00Z
    Publisher Nature Portfolio
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  2. Article ; Online: Older magma at Aso caldera than at Unzen stratovolcano in south west Japan as recorded through helium isotopes

    Yuji Sano / Takanori Kagoshima / Maoliang Zhang / Naoto Takahata / Tetsuji Onoue / Tomo Shibata / Yoshiro Nishio / Ai-Ti Chen / Hyunwoo Lee / Tobias P. Fischer / Dapeng Zhao

    Communications Earth & Environment, Vol 4, Iss 1, Pp 1-

    2023  Volume 8

    Abstract: Helium isotopes from groundwater and hot springs at the stratovolcano, Unzen, have a stronger mantle signature than for the nearby caldera volcano, Aso, which suggests that magma at Unzen is younger still supplied with primordial mantle helium. ...

    Abstract Helium isotopes from groundwater and hot springs at the stratovolcano, Unzen, have a stronger mantle signature than for the nearby caldera volcano, Aso, which suggests that magma at Unzen is younger still supplied with primordial mantle helium.
    Keywords Geology ; QE1-996.5 ; Environmental sciences ; GE1-350
    Language English
    Publishing date 2023-01-01T00:00:00Z
    Publisher Nature Portfolio
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  3. Article ; Online: Seismic Reflection Images of Possible Mantle-Fluid Conduits and Basal Erosion in the 2011 Tohoku Earthquake Rupture Area

    Jin-Oh Park / Tetsuro Tsuru / Gou Fujie / Ehsan Jamali Hondori / Takanori Kagoshima / Naoto Takahata / Dapeng Zhao / Yuji Sano

    Frontiers in Earth Science, Vol

    2021  Volume 9

    Abstract: Multi-channel seismic reflection and sub-bottom profiling data reveal landward-dipping normal faults as potential conduits for mantle-derived fluids in the coseismic slip area of the 2011 Tohoku earthquake (Mw9.0). Normal faults below the helium isotope ... ...

    Abstract Multi-channel seismic reflection and sub-bottom profiling data reveal landward-dipping normal faults as potential conduits for mantle-derived fluids in the coseismic slip area of the 2011 Tohoku earthquake (Mw9.0). Normal faults below the helium isotope anomaly sites appear to develop through the forearc crust (i.e., the seafloor sedimentary section and Cretaceous basement) and to evolve to lower dip angles as extension progresses deeper, potentially extending down to the mantle wedge, despite their intermittently continuous reflections. The faults are characterized by high-amplitude, reverse-polarity reflections within the Cretaceous basement. Moreover, deep extension of the faults connecting to a low-velocity region spreading from the Cretaceous basement into the mantle wedge across the forearc Moho suggests that the faults are overpressured by local filling with mantle-derived fluids. The locations of the normal faults are roughly consistent with aftershocks of the 2011 Tohoku earthquake, which show normal-faulting focal mechanisms. The 2011 Tohoku mainshock and subsequent aftershocks can lead the pre-existing normal faults to be reactive and more permeable so that locally trapped mantle fluids can migrate up to the seafloor through fault fracture zones. The reactivated normal faults may be an indicator of shallow coseismic slip to the trench. Locally elevated fluid pressures can decrease the effective normal stress for the fault plane, facilitating easier slip along the fault and local tsunami. The landward-dipping normal faults developing from the seafloor down into the Cretaceous basement are predominant in the middle slope region of the forearc. A possible shear zone with high-amplitude, reverse-polarity reflections above the plate interface, which is almost localized to the middle slope region, suggests more intense basal erosion of the overlying plate in that region.
    Keywords fluid migration ; seismic reflection ; normal fault ; shallow coseismic slip ; basal erosion ; Science ; Q
    Subject code 550
    Language English
    Publishing date 2021-07-01T00:00:00Z
    Publisher Frontiers Media S.A.
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  4. Article ; Online: Mantle degassing along strike-slip faults in the Southeastern Korean Peninsula

    Hyunwoo Lee / Heejun Kim / Takanori Kagoshima / Jin-Oh Park / Naoto Takahata / Yuji Sano

    Scientific Reports, Vol 9, Iss 1, Pp 1-

    2019  Volume 9

    Abstract: Abstract On September 12, 2016, a ML 5.8 earthquake hit Gyeongju in the southeastern part of the Korean Peninsula (SeKP), although the area is known to be far from the boundary of the active plate. A number of strike-slip faults are observed in heavily ... ...

    Abstract Abstract On September 12, 2016, a ML 5.8 earthquake hit Gyeongju in the southeastern part of the Korean Peninsula (SeKP), although the area is known to be far from the boundary of the active plate. A number of strike-slip faults are observed in heavily populated city areas (e.g., Busan, Ulsan, Pohang, and Gyeongju). However, dissolved gases related to the active faults have rarely been studied despite many groundwater wells and hot springs in the area. Here we report new results of gas compositions and isotope values of helium and carbon dioxide (CO2) in fault-related fluids in the region. Based on gas geochemistry, the majority of gas samples are abundant in CO2 (up to 99.91 vol.%). Measured 3He/4He ratios range from 0.07 to 5.66 Ra, showing that the mantle contribution is up to 71%. The range of carbon isotope compositions (δ13C) of CO2 is from −8.25 to −24.92‰, showing mantle-derived CO2 is observed coherently where high 3He/4He ratios appear. The weakening of faults seems to be related to enhanced pressures of fluids containing mantle-derived helium and CO2 despite the ductile lower crust underneath the region. Thus, we suggest that the SeKP strike-slip faults penetrate into the mantle through ductile shearing.
    Keywords Medicine ; R ; Science ; Q
    Subject code 550
    Language English
    Publishing date 2019-10-01T00:00:00Z
    Publisher Nature Publishing Group
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  5. Article ; Online: Coseismic changes in groundwater level during the 2018 Hokkaido Eastern Iburi earthquake

    Tomo Shibata / Ryo Takahashi / Hiroaki Takahashi / Takanori Kagoshima / Naoto Takahata / Yuji Sano / Daniele L. Pinti

    Earth, Planets and Space, Vol 72, Iss 1, Pp 1-

    2020  Volume 8

    Abstract: Abstract Six wells were continuously monitored in Hokkaido, northern Japan, to relate groundwater level changes to regional seismic activity. Groundwater level changes following the 2018 Hokkaido Eastern Iburi earthquake were detected in three of the six ...

    Abstract Abstract Six wells were continuously monitored in Hokkaido, northern Japan, to relate groundwater level changes to regional seismic activity. Groundwater level changes following the 2018 Hokkaido Eastern Iburi earthquake were detected in three of the six wells, even though they are located hundreds of kilometers from the epicenter. The groundwater level changes are qualitatively consistent with the volumetric strain induced by the earthquake. We analyzed groundwater level responses to the M2 tidal constituent before and after the earthquake, but related changes in amplitude and phase shifts remained within the usual variation. Observed coseismic change was explained by the response to the M2 tidal constituent component and the calculated volumetric strain for one of the wells, where groundwater level decreased. The observed change in the other two was found to be much greater than the corresponding estimates of the volumetric strain.
    Keywords Groundwater level ; Coseismic change ; 2018 Hokkaido Eastern Iburi earthquake ; Tidal response ; Geography. Anthropology. Recreation ; G ; Geodesy ; QB275-343 ; Geology ; QE1-996.5
    Subject code 550
    Language English
    Publishing date 2020-02-01T00:00:00Z
    Publisher SpringerOpen
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  6. Article ; Online: Mantle-derived helium released through the Japan trench bend-faults

    Jin-Oh Park / Naoto Takahata / Ehsan Jamali Hondori / Asuka Yamaguchi / Takanori Kagoshima / Tetsuro Tsuru / Gou Fujie / Yue Sun / Juichiro Ashi / Makoto Yamano / Yuji Sano

    Scientific Reports, Vol 11, Iss 1, Pp 1-

    2021  Volume 9

    Abstract: Abstract Plate bending-related normal faults (i.e. bend-faults) develop at the outer trench-slope of the oceanic plate incoming into the subduction zone. Numerous geophysical studies and numerical simulations suggest that bend-faults play a key role by ... ...

    Abstract Abstract Plate bending-related normal faults (i.e. bend-faults) develop at the outer trench-slope of the oceanic plate incoming into the subduction zone. Numerous geophysical studies and numerical simulations suggest that bend-faults play a key role by providing pathways for seawater to flow into the oceanic crust and the upper mantle, thereby promoting hydration of the oceanic plate. However, deep penetration of seawater along bend-faults remains controversial because fluids that have percolated down into the mantle are difficult to detect. This report presents anomalously high helium isotope (3He/4He) ratios in sediment pore water and seismic reflection data which suggest fluid infiltration into the upper mantle and subsequent outflow through bend-faults across the outer slope of the Japan trench. The 3He/4He and 4He/20Ne ratios at sites near-trench bend-faults, which are close to the isotopic ratios of bottom seawater, are almost constant with depth, supporting local seawater inflow. Our findings provide the first reported evidence for a potentially large-scale active hydrothermal circulation system through bend-faults across the Moho (crust-mantle boundary) in and out of the oceanic lithospheric mantle.
    Keywords Medicine ; R ; Science ; Q
    Subject code 550
    Language English
    Publishing date 2021-06-01T00:00:00Z
    Publisher Nature Portfolio
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  7. Article ; Online: Influence of normal tide and the Great Tsunami as recorded through hourly-resolution micro-analysis of a mussel shell

    Yuji Sano / Tomoyo Okumura / Naoko Murakami-Sugihara / Kentaro Tanaka / Takanori Kagoshima / Akizumi Ishida / Masako Hori / Glen T. Snyder / Naoto Takahata / Kotaro Shirai

    Scientific Reports, Vol 11, Iss 1, Pp 1-

    2021  Volume 12

    Abstract: Abstract We report here hourly variations of Mg/Ca, Sr/Ca, and Ba/Ca ratios in a Mediterranean mussel shell (Mytilus galloprovincialis) collected at the Otsuchi bay, on the Pacific coast of northeastern Japan. This bivalve was living in the intertidal ... ...

    Abstract Abstract We report here hourly variations of Mg/Ca, Sr/Ca, and Ba/Ca ratios in a Mediterranean mussel shell (Mytilus galloprovincialis) collected at the Otsuchi bay, on the Pacific coast of northeastern Japan. This bivalve was living in the intertidal zone, where such organisms are known to form a daily or bidaily growth line comprised of abundant organic matter. Mg/Ca ratios of the inner surface of the outer shell layer, corresponding to the most recent date, show cyclic changes at 25–90 μm intervals, while no interpretable variations are observed in Sr/Ca and Ba/Ca ratios. High Mg/Ca ratios were probably established by (1) cessation of the external supply of Ca and organic layer forming when the shell is closed at low tide, and (2) the strong binding of Mg to the organic layer, but not of Sr and Ba. Immediately following the great tsunami induced by the 2011 Tohoku earthquake, Mg/Ca enrichment occurred, up to 10 times that of normal low tide, while apparent Ba/Ca enrichment was observed for only a few days following the event, therefore serving a proxy of the past tsunami. Following the tsunami, periodic peaks and troughs in Mg/Ca continued, perhaps due to a biological memory effect as an endogenous clock.
    Keywords Medicine ; R ; Science ; Q
    Subject code 551
    Language English
    Publishing date 2021-10-01T00:00:00Z
    Publisher Nature Portfolio
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  8. Article ; Online: Groundwater Anomaly Related to CCS-CO2 Injection and the 2018 Hokkaido Eastern Iburi Earthquake in Japan

    Yuji Sano / Takanori Kagoshima / Naoto Takahata / Kotaro Shirai / Jin-Oh Park / Glen T. Snyder / Tomo Shibata / Junji Yamamoto / Yoshiro Nishio / Ai-Ti Chen / Sheng Xu / Dapeng Zhao / Daniele L. Pinti

    Frontiers in Earth Science, Vol

    2020  Volume 8

    Abstract: Carbon capture and storage (CCS) is considered a key technology for reducing CO2 emissions into the atmosphere. Nonetheless, there are concerns that if injected CO2 migrates in the crust, it may trigger slip of pre-existing faults. In order to test if ... ...

    Abstract Carbon capture and storage (CCS) is considered a key technology for reducing CO2 emissions into the atmosphere. Nonetheless, there are concerns that if injected CO2 migrates in the crust, it may trigger slip of pre-existing faults. In order to test if this is the case, covariations of carbon, hydrogen, and oxygen isotopes of groundwater measured from Uenae well, southern Hokkaido, Japan are reported. This well is located 13 km away from the injection point of the Tomakomai CCS project and 21 km from the epicenter of September 6th, 2018 Hokkaido Eastern Iburi earthquake (M 6.7). Carbon isotope composition was constant from June 2015 to February 2018, and decreased significantly from April 2018 to November 2019, while total dissolved inorganic carbon (TDIC) content showed a corresponding increase. A decrease in radiocarbon and δ13C values suggests aquifer contamination by anthropogenic carbon, which could possibly be attributable to CCS-injected CO2. If such is the case, the CO2 enriched fluid may have initially migrated through permeable channels, blocking the fluid flow from the source region, increasing pore pressure in the focal region and triggering the natural earthquake where the brittle crust is already critically stressed.
    Keywords Hokkaido earthquake ; carbon capture and storage-CO2 injection ; groundwater ; carbon isotopes ; radiocarbon ; Science ; Q
    Subject code 550
    Language English
    Publishing date 2020-12-01T00:00:00Z
    Publisher Frontiers Media S.A.
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  9. Article ; Online: Groundwater oxygen isotope anomaly before the M6.6 Tottori earthquake in Southwest Japan

    Satoki Onda / Yuji Sano / Naoto Takahata / Takanori Kagoshima / Toshihiro Miyajima / Tomo Shibata / Daniele L. Pinti / Tefang Lan / Nak Kyu Kim / Minoru Kusakabe / Yoshiro Nishio

    Scientific Reports, Vol 8, Iss 1, Pp 1-

    2018  Volume 7

    Abstract: Abstract Geochemical monitoring of groundwater in seismically-active regions has been carried out since 1970s. Precursors were well documented, but often criticized for anecdotal or fragmentary signals, and for lacking a clear physico-chemical ... ...

    Abstract Abstract Geochemical monitoring of groundwater in seismically-active regions has been carried out since 1970s. Precursors were well documented, but often criticized for anecdotal or fragmentary signals, and for lacking a clear physico-chemical explanation for these anomalies. Here we report – as potential seismic precursor – oxygen isotopic ratio anomalies of +0.24‰ relative to the local background measured in groundwater, a few months before the Tottori earthquake (M 6.6) in Southwest Japan. Samples were deep groundwater located 5 km west of the epicenter, packed in bottles and distributed as drinking water between September 2015 and July 2017, a time frame which covers the pre- and post-event. Small but substantial increase of 0.07‰ was observed soon after the earthquake. Laboratory crushing experiments of aquifer rock aimed to simulating rock deformation under strain and tensile stresses were carried out. Measured helium degassing from the rock and 18O-shift suggest that the co-seismic oxygen anomalies are directly related to volumetric strain changes. The findings provide a plausible physico-chemical basis to explain geochemical anomalies in water and may be useful in future earthquake prediction research.
    Keywords Medicine ; R ; Science ; Q
    Subject code 550
    Language English
    Publishing date 2018-03-01T00:00:00Z
    Publisher Nature Publishing Group
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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