Comparative study of cataclastic rocks from a drill core and outcrops of the Nojima Fault zone on Awaji Island, Japan   总被引：3，自引：0，他引：3  

Aiming Lin  Toshihiko Shimamoto  Tadashi Maruyama  Motoko Sigetomi  Takao Miyata  Keiji Takemura  Hidemi Tanaka  Shinichi Uda  Akihiro Murata 《Island Arc》2001,10(3-4):368-380

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Deformation mechanisms and fluid behavior in a shallow, brittle fault zone during coseismic and interseismic periods: Results from drill core penetrating the Nojima Fault, Japan   总被引：1，自引：0，他引：1  

Hidemi Tanaka  Shin-Ichiro Hinoki  Kazuo Kosaka  Aiming Lin  Keiji Takemura  Akihiro Murata  Takao Miyata 《Island Arc》2001,10(3-4):381-391

Abstract This paper describes the results of petrographical and meso- to microstructural observations of brittle fault rocks in cores obtained by drilling through the Nojima Fault at a drilling depth of 389.52 m. The zonation of deformation and alteration in the central zone of the fault is clearly seen in cores of granite from the hanging wall, in the following order: (i) host rock, which is characterized by some intragranular microcracks and in situ alteration of mafic minerals and feldspars; (ii) weakly deformed and altered rocks, which are characterized by transgranular cracks and the dissolution of mafic minerals, and by the precipitation of zeolites and iron hydroxide materials; (iii) random fabric fault breccia, which is characterized by fragmentation, by anastomosing networks of transgranular cracks, and by the precipitation of zeolites and iron hydroxide materials; and (iv) fault gouge, which is characterized by the precipitation of smectite and localized cataclastic flow. This zonation implies that the fault has been weakened gradually by fluid-related fracturing over time. In the footwall, a gouge layer measuring only 15 mm thick is present just below the surface of the Nojima Fault. These observations are the basis for a model of fluid behavior along the Nojima Fault. The model invokes the percolation of meteoric fluids through cracks in the hanging wall fault zone during interseismic periods, resulting in chemical reactions in the fault gouge layer to form smectite. The low permeability clay-rich gouge layer sealed the footwall. The fault gouge was brecciated during coseismic or postseismic periods, breaking the seal and allowing fluids to readily flow into the footwall, thus causing a slight alteration. Chemical reactions between fluids and the fault breccia and gouge generated new fault gouge, which resealed the footwall, resulting in a low fluid condition in the footwall during interseismic periods.  相似文献   

Genetic variation of Chinese and Japanese wild Pacific abalone(Haliotis discus hannai) measured by microsatellite DNA markers     

LI Qi  KIJIMA Akihiro 《海洋学报(英文版)》2006,25(4):146-155

1Introduction ThePacificabaloneHaliotisdiscushannaiisan importantspeciesinthecoastalfisheriesofnorthern China,andisofhighcommercialvalue.Thepro ductionofcultureseedsfortheabalonebeganin Chinaintheearly1980s.Duringthelasttwodec ades,productionofabalonehasi…  相似文献   

Primary productivity in the offshore Oyashio in the spring and summer 1990     

Akihiro Shiomoto  Katsuyuki Sasaki  Toru Shimoda  Satsuki Matsumura 《Journal of Oceanography》1994,50(2):209-222

Primary productivity was measured byin situ method using¹³C in the offshore Oyashio region in the spring (May) and summer (September) of 1990. Most of the values were within the range of 0.1 to 4 gC 1^–1 h^–1 although a very large value, 7.96 gC l^–1 h^–1, was observed in summer. Most daily primary production fell within the range of 372 to 633 mgC m^–2 d^–1 although a very large value, 2,109 mgC m^–2 d^–1, was observed around the frontal area in summer. Chlorophylla (Chl.a) exceeded 1 g l^–1 in many cases, and the maximum was 4.61 g l^–1 in spring and 7.53 g l^–1 in summer. Most primary productivity per unit Chl.a (photosynthetic assimilation ratio) was within the range of 0.1 to 3 gC gChl.a ^–1 h^–1 although higher values, 3–6 gC gChl.a ^–1 h^–1, were observed where small-size phytoplanktons (<2 m) were dominant. These results were compared with results obtained until now in the Oyashio region. The values beyond the range obtained so far in the offshore region were also observed in this study. Furthermore, it was pointed out that the size composition of phytoplankton community has significant influence on the results of Chl.a and photosynthetic assimilation ratio in the Oyashio region.  相似文献   

Effect of Mine Water on the Stability of Underground Coal Mine Roadways     

Takashi?SasaokaEmail author  Tri?Karian  Akihiro?Hamanaka  Hideki?Shimada  Kikuo?Matsui  Masatomo?Ichinose 《Geotechnical and Geological Engineering》2016,34(2):671-678

The basic objectives of mine roadways are to provide sufficient cross sections to accommodate equipment, transport, personnel travel and ventilation. However, many roadways become damaged to the extent of needing maintenance, generally dinting, and in some cases requiring re-ripping. Strata conditions play important effects on stability of roadways and other mining activities. Weak rocks cause excessive roadway closures, and water softens some rocks and worsens the closure problem. Therefore, study on effect of mine water on the stability of underground coal mine roadways is important for underground coal mine development. A scientific discussion on the effect of water on the stability of roadways is given on the basis of results obtained by means of field investigation and laboratory tests. Based on analysis, rock in saturated condition has only between 0.19 to 0.49 of its compressive strength and 0.17 to 0.59 of its tensile strength in dry condition. Among the coal measures rock in research area, water has the most obvious effect on the strength reduction of shale. The slaking behavior of shale has also been the worst among the other. Field investigation of roadway driven in shale shown vertical closure in the wet and dry condition area reached 40–60 and 5–15 cm respectively, in 30 days after the drivage. Among the measures, drainage is considered to be the most economical and simplest method to reduce the water content in the rocks or the rock masses.  相似文献   

Electric currents along earthquake faults and the magnetization of pseudotachylite veins   总被引：2，自引：1，他引：2  

Friedemann Freund  Manuel A. Salgueiro da Silva  Bobby W.S. Lau  Akihiro Takeuchi  Hollis H. Jones 《Tectonophysics》2007,431(1-4):131

Pseudotachylites occur in the form of thin glassy veins quenched from frictional melts along the fault planes of major earthquakes. They contain finely grained magnetite and often exhibit a high natural remanent magnetization (NRM). High NRM values imply strong local electric currents. These currents must persist for some time, while the pseudotachylite veins cool through the Curie temperature of magnetite around 580 °C. There is no generally accepted theory explaining how such powerful, persistent currents may be generated along the fault plane. Data presented here suggest the activation of electronic charge carriers, which are present in igneous rocks in a dormant, inactive form. These charge carriers can be “awakened” by the application of stress. They are electrons and defect electrons, also known as positive holes or p-holes for short. While p-holes are capable of spreading out of the stressed rock volume into adjacent p-type conductive unstressed rocks, electrons require a connection to the hot, n-type conductive lower crust. However, as long as the (downward) electron flow is not connected, the circuit is not closed. Hence, with the outflow of p-holes impeded, no current can be sustained. This situation is comparable to that of a charged battery where one pole remains unconnected. The friction melt that forms coseismically during rupture, provides a conductive path downward, which closes the circuit. This allows a current to flow along the fault plane. Extrapolating from laboratory data, every km³ of stressed igneous rocks adjacent to the fault plane can deliver 10³–10⁵ A. Hence, the current along the fault plane will not be limited by the number of charge carriers but more likely by the (electronic) conductivity of the cooling pseudotachylite vein. The sheet current will produce a magnetic field, whose vectors will lie in the fault plane and perpendicular to the flow direction.  相似文献   

Carbon isotope stratigraphy of Torinosu‐type limestone in the western Paleo‐Pacific and its implication to paleoceanography in the Late Jurassic and earliest Cretaceous     

Yoshihiro Kakizaki  Akihiro Kano 《Island Arc》2014,23(1):16-32

Carbon isotope stratigraphy of the Late Jurassic and earliest Cretaceous was revealed from Torinosu‐type limestone, which was deposited in a shallow‐marine setting in the western Paleo‐Pacific, in Japan. Two sections were examined; the Nakanosawa section of the late Kimmeridgian to early Tithonian age (Fukushima Prefecture, Northeast Japan), and the Furuichi section of the late Kimmeridgian to early Berriasian age (Ehime Prefecture, Southwest Japan). The age‐model was established using Sr isotope ratio and fossil occurrence. The limestone samples have a low Mn/Sr ratio (mostly <0.5) and lack a distinct correlation between δ¹³C and δ¹⁸O, indicating a low degree of diagenetic alteration. Our composite δ¹³C profile from the two limestone sections shows three stratigraphic correlation points that can be correlated with the profiles of relevant ages from the Alpine Tethyan region: a large‐amplitude fluctuation (the lower upper Kimmeridgian, ～152 Ma), a positive anomaly (above the Kimmeridgian/Tithonian boundary, ～150 Ma), and a negative anomaly (the upper lower Tithonian, ～148 Ma). In addition, we found that δ¹³C values of the Torinosu‐type limestone are ～1‰ lower than the Tethyan values in the late Kimmeridgian. This inter‐regional difference in δ¹³C values is likely to have resulted from a higher productivity and/or an organic burial in the Tethyan region. The difference gradually reduces and disappears in the late Tithonian, where the Tethyan and our δ¹³C records show similar stable values of 1.5–2.0‰. This isotopic homogenization is probably due to changes in the continental distribution and the global ocean circulation, which propagated the ¹³C‐depleted signature from the larger Paleo‐Pacific to the smaller Tethys Ocean during this time.  相似文献   

Molecular and isotopic composition of hydrate-bound and dissolved gases in the southern basin of Lake Baikal, based on an improved headspace gas method   总被引：1，自引：1，他引：0  

Hirotoshi Sakagami  Nobuo Takahashi  Akihiro Hachikubo  Hirotsugu Minami  Satoshi Yamashita  Hitoshi Shoji  Oleg Khlystov  Gennadiy Kalmychkov  Mikhail Grachev  Marc De Batist 《Geo-Marine Letters》2012,32(5-6):465-472

Assessments of the molecular and isotopic composition of hydrate-bound and dissolved gases in pore water were conducted during the multi-phase gas hydrate project (MHP-09) cruise VER09-03 to the southern basin of Lake Baikal in September 2009. To avoid changes in gas composition during core sampling and transport, various headspace methods were investigated aimed at preserving the dissolved gases in pore water. When distilled water was added to the sediment samples, the concentrations of carbon dioxide and oxygen decreased because of dissolution into the water and/or microbial consumption. When the headspace was not flushed with inert gases, trace levels of hydrogen and ethylene were detected. The findings suggest that best preparation is achieved by flushing the headspace with helium, and adding a saturated aqueous solution of sodium chloride. This improved headspace method served to examine the molecular and isotopic compositions of gas samples retrieved at several new sites in the southern basin. Methane was the major component, and the proportion of ethane ranged widely from 0.0009 to 1.67?mol% of the total hydrocarbon gases. The proportions of propane and higher hydrocarbons were small or less than their detection limits. The carbon isotope signatures suggest that microbial-sourced methane and ethane were dominant in the Peschanka study area, whereas ethane was of thermogenic origin at all other study sites in the southern basin of Lake Baikal.  相似文献   

A multi‐geochronological study of the Hakusan volcano,central Japan          下载免费PDF全文

Noriko Hasebe  Yasuyuki Nakano  Hikaru Miyamoto  Toshio Higashino  Akihiro Tamura  Shoji Arai  Ju‐Yong Kim 《Island Arc》2016,25(2):111-125

The Hakusan volcano, central Japan, is located in a region where two subducting plates (the Pacific Plate and the Philippine Sea Plate) overlap near the junction of four plates adjacent to the Japanese Islands (the Pacific Plate, the Philippine Sea Plate, the Eurasia Plate, and the North American Plate). The Hakusan volcano consists of products from four major volcanic episodes: Kagamuro, Ko‐hakusan, and Shin‐Hakusan I and II. To date the eruption events of the Hakusan volcano we applied thermoluminescence and fission track methods. ²³⁸U(²³⁴U)–²³⁰Th disequilibrium and ²⁰⁶Pb/²³⁸U methods were applied to date the zircon crystallization ages for estimating the magma residence time before the eruptions. The eruption ages we obtained are ca 250 ka for Kagamuro, ca 100 ka and ca 60 ka for Ko‐Hakusan, ca 50 ka for Shin‐Hakusan I, and <10 ka for Shin‐Hakusan II. They are concordant with previous reports based on K–Ar dating. Some of the pyroclastic rocks, possibly originating from Shin‐Hakusan II activities, are dated to be ca 36 ka or 50 ka, and belong to the Shin‐Hakusan I activity. The zircon crystallization ages show several clusters prior to eruption. The magma residence time was estimated for each volcanic activity by comparing the major crystallization events and eruption ages, and we found a gradual decrease from ca. 500 ky for the Kagamuro activity to ca. 5 ky for the Shin‐Hakusan II activity. This decrease in residence time may be responsible for the decrease in volume of erupted material estimated from the current topography of the region. The scale of volcanic activity, which was deduced from the number of crystallized zircons, is more or less constant throughout the Hakusan volcanic activity. Therefore, the decrease in magma residence time is most likely the result of stress field change.  相似文献   

Redistribution and export of contaminated sediment within eastern Fukushima Prefecture due to typhoon flooding          下载免费PDF全文

Akihiro Kitamura  Hiroshi Kurikami  Kazuyuki Sakuma  Alex Malins  Masahiko Okumura  Masahiko Machida  Koji Mori  Kazuhiro Tada  Yasuhiro Tawara  Takamaru Kobayashi  Takafumi Yoshida  Hiroyuki Tosaka 《地球表面变化过程与地形》2016,41(12):1708-1726

Tropical cyclones expose river basins to heavy rainfall and flooding, and cause substantial soil erosion and sediment transport. There is heightened interest in the effects of typhoon floods on river basins in northeast Japan, as the migration of radiocaesium‐bearing soils contaminated by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident will affect future radiation levels. The five main catchments surrounding FDNPP are the Odaka, Ukedo, Maeda, Kuma and Tomioka basins, but little quantitative modelling has been undertaken to identify the sediment redistribution patterns and controlling processes across these basins. Here we address this issue and report catchment‐scale modelling of the five basins using the GETFLOWS simulation code. The three‐dimensional (3D) models of the basins incorporated details of the geology, soil type, land cover, and used data from meteorological records as inputs. The simulation results were checked against field monitoring data for water flow rates, suspended sediment concentrations and accumulated sediment erosion and deposition. The results show that the majority of annual sediment migration in the basins occurs over storm periods, thus making typhoons the main vectors for redistribution. The Ukedo and Tomioka basins are the most important basins in the region in terms of overall sediment transport, followed by the other three basins each with similar discharge amounts. Erosion is strongly correlated with the underlying geology and the surface topography in the study area. A low permeability Pliocene Dainenji formation in the coastal area causes high surface water flow rates and soil erosion. Conversely, erosion is lower in an area with high permeability granite basement rocks between the Hatagawa and Futaba faults in the centre of the study area. Land cover is also a factor controlling differences in erosion and transport rates between forested areas in the west of the study area and predominantly agricultural areas towards the east. The largest sediment depositions occur in the Ogaki and Takigawa Dams, at the confluence of the Takase and Ukedo Rivers, and at the Ukedo River mouth. Having clarified the sediment redistribution patterns and controlling processes, these results can assist the ongoing task of monitoring radioactive caesium redistribution within Fukushima Prefecture, and contribute to the design and implementation of measures to protect health and the environment. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献