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Ishii, Eiichi
no journal, ,
no abstracts in English
Oikawa, Teruki; Umeda, Koji; Matsuzaki, Tatsuji*
no journal, ,
K-Ar and FT analyses were carried out on biotite, zircon and apatite from the granitic rocks in Kashiwazima district, western Shikoku in order to reveal the cooling history. These ages suggest rapid cooling of the granitic rocks in the temperature range to 100
C from 300C in 14-13Ma.
Niwa, Masakazu; Shimada, Koji; Nohara, Tsuyoshi; Miwa, Atsushi*; Kurosawa, Hideki*
no journal, ,
Detailed topographical and geological researches for understanding fracture zone structures in fault steps are necessary to estimate the extent of the mechanical damage to basement rocks due to strike-slip fault activities. Our research of the western part of the Atotsugawa Fault in the Hida City, Gifu Prefecture shows that the faults high-angle oblique to the principal direction of the Atotsugawa Fault characteristically occur in fault steps, which effect that the fracture zone increases in width. The Atotsugawa fault, which is one of the Class A active faults, trends ENE-WSW and shows dextral strike-slip displacement. We firstly checked the occurrence of the fault step in the Miyagawa-cho area of the western part of the Atotsugawa Fault by way of aerial photograph interpretation. Then we researched the distribution and feature of fracture zone in the Kawai-cho area where the fault continues lineally and in the Miyagawa-cho area where the fault steps. In the Kawai-cho area, Fault planes mostly strike ENE-WSW to E-W and dip steeply N or S, subparallel to the principal direction of the Atotsugawa Fault. Width of the fracture zone is several tens meters. In the Miyagawa-cho area, NW-SE and N-S strike faults dominantly occur as well as ENE-WSW to E-W strike faults. Width of the fracture zone is more than a hundred meter. Remarkable existence of NW-SE and N-S strike faults distinguishes the fracture zone in the Miyagawa-cho area as that in the Kawai-cho area.
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.
Umeda, Koji; Asamori, Koichi; Negi, Tateyuki*; Ogawa, Yasuo*
no journal, ,
Mesozoic crystalline mountains (Iide Mountains) in a non-volcanic region of the Northeast Japan arc were imaged by wide-band magnetotelluric soundings. A two-dimensional model showed that an anomalous conductive body (
10 ohm-m) is clearly visible beneath the Iide Mountains. The conductor widens with increasing depth, and extends from the near-surface down to the base of the crust and perhaps into the upper mantle. Considering several signals imaging the presence of crustal magma storage, such as high-temperature regime, hot spring gases with high 
He/
He ratio, thinning of the brittle seismogenic layer and anomalies of low seismic velocity, it is reasonable to suppose that the conductor reflects partial melt and/or high-temperature aqueous fluids in the crust, related to renewed magmatism in the present-day subduction system.
Mizuno, Takashi; Iwatsuki, Teruki
no journal, ,
no abstracts in English
Mizuno, Takashi; Metcalfe, R.*; Mie, Hideki; Iwatsuki, Teruki
no journal, ,
no abstracts in English
Nohara, Tsuyoshi; Nakata, Takashi*; Shimada, Koji; Niwa, Masakazu; Kinoshita, Hirohisa; Sagiya, Takeshi*
no journal, ,
Features of subsurface active faults are studied using data of the damaging earthquake, geological structure and diastrophism. The hypocenter of the damaging earthquakes distribute around the Quaternary volcanoes and the active faults. The direction of strike and displacement of the active faults and the earthquake faults of the damaging earthquakes occurred around the active faults are almost same. The dispersion of the deformation of the mylonite zone related to geological condition may be one of the indicators of generation of subsurface active fault.
gas corresponding to attitudes of incohesive fault rock layersShimada, Koji; Niwa, Masakazu; Nohara, Tsuyoshi; Tanaka, Hidemi*
no journal, ,
no abstracts in English
Asamori, Koichi; Umeda, Koji; Negi, Tateyuki*; Ogawa, Yasuo*
no journal, ,
no abstracts in English
Saegusa, Hiromitsu; Inaba, Kaoru*; Moriya, Toshifumi; Onoe, Hironori
no journal, ,
In the study, groundwater flow modeling has been performed in order to evaluate influence of topographic and climatic perturbations on groundwater flow conditions in the Tono area, Gifu, Japan. It was shown from the results of this study that the topographic and climatic perturbations influence hydraulic gradient, and groundwater flow path, path length and travel time. It is also found that these influences have spatial difference due to hydrogeological heterogeneity caused by faults with hydraulic contrast.
Funaki, Hironori; Ishii, Eiichi
no journal, ,
Through out the surface-based investigations in the Horonobe Underground Research Project, studies were performed in the boreholes to identify and characterize potentially water-conducting features in the Neogene sedimentary Formations (Wakkanai and Koetoi formations). Specifically, core observation and Electrical Micro-Imaging logging were carried out to characterize the spatial distribution and geometry of faults and hydraulic tests were conducted to define the hydraulic significance of the faults. In addition, data monitored during drilling was used to support the hydraulic interpretation.
Ohara, Hidefumi; Tsukui, Rota; Kunitomo, Takahiro; Nakajima, Takahiro; Niizato, Tadafumi; Aoki, Kazuhiro; Shigeta, Naotaka; Kumazawa, Mineo
no journal, ,
Japan Atomic Energy Agency (JAEA) is developing a remote monitoring system using seismic and electromagnetic ACROSS(Accurately Controlled Routinely Operated Signal System), to monitor changes in the geological environment. ACROSS has been researched and developed in Tono Geoscience Center for 9 years, and we introduce it to the Horonobe Underground Research Laboratory (URL) project. The Horonobe URL project is devoted to the technological development over 20-years from March 2001 for a safe geological disposal of high level radioactive wastes in Horonobe-cho in northern Hokkaido, Japan. We install the monitoring system before the shaft excavation, and collect data before, during and after the excavation, in order to permit assessment of the system's reliability. The source and receivers of electromagnetic ACROSS were installed in the winter before last, and we are carrying out the test of the system. In last December, the source and receivers of a seismic ACROSS were installed in Horonobe. Then we are going to examine the practicability of ACROSS.
Seno, Shoji; Niizato, Tadafumi; Kurikami, Hiroshi; Yasue, Kenichi; Yabuuchi, Satoshi; Hara, Minoru; Kunimaru, Takanori; Nakayama, Masashi; Funaki, Hironori; Yamaguchi, Takehiro
no journal, ,
We should estimate ten-thousand-year stability of geological environment to meet the geological disposal of high level radioactive waste. Especially groundwater flow plays an important role because it might cause migration of nuclides. Since long term transitions of geology and topography may influence hydrogeological conditions such as hydraulic gradient and hydraulic conductivities, estimations of vertical displacement rate and erosion rate are also important. This report discusses the method to estimate an amount of erosion in the future based on suspended sediment concentration in rivers as an example in Horonobe area, northern part of Hokkaido.
Hara, Akio
no journal, ,
To investigate mass transport and rock properties of diatomaceous mudstone, pore size distribution, chemical composition and air permeability are analyzed on specimens of Koetoi and Wakkanai formation sampled from boreholes HDB-1, HDB-2 and HDB-5 which drilled by Japan Atomic Energy Agency in Horonobe area Hokkaido, Japan. Permeability of Koetoi and Wakkanai formation is related to diagenetic facis changes of diatom fossils. Diatom fossils included in the Koetoi formation are belonging to Opal-A facies. Permeability and porosity of Koetoi formation is decreases by compaction of stratum due to increasing of burial depth. The diagenetic facies of diatomaceous fossil is changes into Opal-CT facies at Wakkanai formation. Macroscopic crystals of Opal-CT, such as cristobalite, are crystallized in the pore of hardshale at Wakkanai formation. Low permeability of Wakkanai formation should be caused by crystallization of these minerals. The feature of cumulative curves indicate pore throat radius concentration about 20 to 40 angstroms should be formed by phase change of silica minerals. These nallow pore throat may be not contribute to transport of ground water. Core specimens sampled 600 depth below the foemation boundary, pore throat ranged around 100 angstrom in radius are concentrated, but pore throats ranged between 20 to 40 angstrom are not observed. Porosity and permeability of these samples are higher than the sample which have pore throat ranged 20 to 40 angstrom. As the result, The lowest permeability is observed in Wakkani formation at 200 to 300m depth the formation boundary. Abnormal high-pressures have been reported more than 200 to 300m beneath the facies boundary of Opal-A and Opal-CT at the boreholes HDB-2 and Kita-kawaguchi SK-1. Wakkanai formation below 200 to 300m depth from Opal-A and Opal-CT boundary has the possibility of functioning as a seal rock, which can keep the high pressure, disturb ground water flow and delay mass transportation.
Niizato, Tadafumi; Shigeno, Kiyoyuki*; Takashimizu, Yasuhiro*
no journal, ,
Ainu oral traditions and historical records on earthquake events in the Ainu Cultural period were investigated, and the reliability of occurrence of the past earthquake events in Hokkaido was examined. As a result of investigation, 28 oral traditions and historical records were collected from the Ainu-related literatures. Based on the examination, we interpreted 24 traditions and records as results of past earthquakes, and the others were not related to earthquakes. It is inferred that earthquake hit Hokkaido were mainly distributed around the Pacific coastal area during the Ainu Cultural period and the previous period. Those areas are adjacent to the seismically active area at present in and around Hokkaido. On estimating of probability of future seismicity by extrapolation of the past to present seismicity, it may be presumed that future distribution of earthquake will be same as that of present-day earthquake in the same future period of Ainu Cultural period.
Iwatsuki, Teruki; Amano, Yuki; Mie, Hideki
no journal, ,
Hydrochemical changes of groundwater have been observed around the shaft of Mizunami underground research laboratory. Water pressure, pH, and concentrations of calcium, sulphate and bicarbonate ions in groundwater changed in response to shafts sinking. Hydrochemical disturbance seems to reach within the range of surrounding shaft tens of m.
Mashima, Hidehisa
no journal, ,
Basaltic andesites distributed at Saga-Futagoyama, northwest Kyushu, southwest Japan are high magnesium andesites (HMA) originally equilibrated with Fe-rich mantle. The reasonsfor thinking so are twofold. The andesites contain orthopyroxene phenocrysts with Mg/(Mg+Fe)=0.8. The bulk rock Mg-Fe-Ni compositions suggest that the andesite magmas could equilibrate with mantle olivines. Hydrous components derived from the subducting slab played an insignificant role in the genesis of the Saga-Futagoyama HMA magmas. Lines of evidence for this interpretation are following. KD
=1.25 between plagioclase and melt suggests that the HMA magmas originally contain less than 1.8 wt.% HO. Nb/La of the Saga-Futagoyama samples is higher than one and has an insignificant correlation with SiO. All of previously reported mantle xenoliths from NW Kyushu have anhydrous mineral assemblages. The subducted Philippine Sea plate does not extend to NW Kyushu. Normative Jd+CaTs-Ol-Qz compositions of the HMA suggest that they were separated from their source mantle at 0.5 GPa. This abnormally low pressure partial melting would be caused by the weakening of the lithospheric mantle beneath the Karatsu-Sasebo basin during its subsidence and uplift.
Mashima, Hidehisa; Tajima, Toshihiko*
no journal, ,
High magnesium andesites (HMAs) with island arc geochemical signatures are distributed in Nagasaki, Northwest Kyushu, Southwest Japan. The genesis of the Nagasaki HMAs cannot be explained by current flux melting models for HMA magmas since mantle xenoliths from NW Kyushu suggests that the NW Kyushu mantle is anhydrous. Normative Jd+CaTs-Ol-Qz compositions of the HMAs suggest that they were separated from their source mantle at 0.5 GPa. This abnormally low pressure partial melting would have been caused by the large contrast of lithospheric strength between the land area composed of the Nagasaki metamorphic rocks and the sea area where sedimentary basins have been formed. The large contrast of lithospheric strength would have concentrated mantle upwelling at the boundary between the land and the sea areas. In the genesis of the Nagasaki HMA magmas, the subduction of the Philippine Sea plate would habe played not as the source of hydrous components but as the driving force of strike-slip tectonics in NW Kyushu.