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Kanazawa-shi, Japan

Tanikawa W.,Japan Agency for Marine - Earth Science and Technology | Mukoyoshi H.,Marine Works Japan Ltd. | Tadai O.,Marine Works Japan Ltd.
Journal of Structural Geology | Year: 2012

We used a rotary shear apparatus to investigate changes of fluid transport properties in a fault zone by real-time measurement of gas flow rates during and after shearing of hollow sandstone cylinders at various slip rates. Our apparatus measures permeability parallel to the slip plane in both the slip zone and wall rocks. In all cases, permeability decreased rapidly with increasing friction, but recovered soon after slip, reaching a steady state within several tens of minutes. The rate of reduction of permeability increased with increasing slip velocity. Permeability did not recover to pre-slip levels after low-velocity (ca. 0.0019 m/s) tests but recovered to exceed them after high-velocity (ca. 0.29 m/s) tests. Frictional heating of gases at the slip surface increased gas viscosity, which increased gas flow rate to produce an apparent permeability increase. The irreversible permeability changes of the low-velocity tests were caused by gouge formation due to wearing and smoothing of the slip surface. The increase of permeability after high-velocity tests was caused by mesoscale fracturing in response to rapid temperature rise. Changes of pore fluid viscosity contributed more to changes of flow rate than did permeability changes caused by shear deformation, although test results from different rocks and pore fluids might be different. © 2011 Elsevier Ltd.

Honda G.,Osaka University | Ishikawa T.,Japan Agency for Marine - Earth Science and Technology | Hirono T.,Osaka University | Mukoyoshi H.,Marine Works Japan Ltd.
Geophysical Research Letters | Year: 2011

To investigate the slip behavior of a megasplay fault branching from a subduction boundary megathrust, we investigated the geochemistry of an out-of-sequence thrust that formed at 2.5-5.5 km depth. Rocks from the slip zone show major-element and fluid-immobile trace-element compositions that are consistent with disequilibrium flash melting. Distinct depletions of Li, Rb, and Cs in the slip-zone rocks indicate fluid-rock interactions at high temperatures (>350C). These findings suggest a slip process in which high-temperature pore fluids were generated by frictional slip, but the thermally-enhanced pressure might not have reached a sufficient level to cause thermal pressurization, and the temperature continued to increase to attain melting of mica minerals. Comparison with slip zone that formed at a shallower depth (1-2 km), where only thermal pressurization occurred, suggests a transition from melt lubrication at depth to thermal pressurization at shallower depths along a megasplay faults. Copyright 2011 by the American Geophysical Union.

Ishikawa T.,Japan Agency for Marine - Earth Science and Technology | Nagaishi K.,Marine Works Japan Ltd.
Journal of Analytical Atomic Spectrometry | Year: 2011

We present a methodology for the precise and accurate analysis of boron isotope ratios ( 11B/ 10B) by positive thermal ionization mass spectrometry (P-TIMS) using Cs 2BO 2 + ions. Samples in the form of caesium borate were loaded onto Ta filaments together with graphite and mannitol. The addition of mannitol to the samples is essential to suppress boron volatilization during acid treatment of the samples but is known to lower the performance of P-TIMS. Therefore, the prepared filaments were preheated in an oven at 240 °C to eliminate the mannitol thus stabilizing the chemical species of boron on the filament and increasing the ionization efficiency of Cs 2BO 2 +, which enabled high-precision isotopic analysis of boron with small sample sizes. Analyses of NIST SRM 951 standard showed external reproducibility (2RSD) better than ±0.1‰ for 50-100 ng B and ±0.2‰ for 10 ng B. Ultrafiltration followed by cation- and anion-exchange chromatography was used to chemically separate boron from natural samples. Analyses of coral standard GSJ JCp-1 and seawater standard IRMM BCR-403 gave average δ 11B values of +24.25 ± 0.08‰ and +39.58 ± 0.11‰ (2SD), respectively. The P-TIMS method developed in this study is applicable to a wide field of boron isotopic research that requires high precision and accuracy, including paleo-pH studies using marine carbonate samples. © 2011 The Royal Society of Chemistry.

Kitamura M.,Hiroshima University | Mukoyoshi H.,Marine Works Japan Ltd. | Fulton P.M.,University of Texas at Austin | Hirose T.,Hiroshima University | Hirose T.,Japan Agency for Marine - Earth Science and Technology
Geophysical Research Letters | Year: 2012

The detection of frictional heating effects along faults provides key insight into the dynamics of earthquakes and faulting. Thermal maturity of organic matter has been considered a possible fault-thermometer that records the frictional heat signature of ancient earthquakes. However, whether or not organic matter can mature on the order of seconds, typical earthquake rise time, remains uncertain. Here we present the results of experiments aimed at revealing coal maturation by frictional heat generated at slip velocities representative of natural earthquakes of up to 1.3 m/s. Our results show that coal can mature coseismically in ∼11 seconds at temperatures induced by frictional heat ranging from 26 to 266C. Even with a temperature rise to only 28.7C over 15 m displacement in ∼3.2 hours, coal can slightly mature within a shear localized zone. The commonly used kinetic model of vitrinite maturation cannot predict the experimental results. A kinetic model involving the effect of flash temperature at grain contacts and mechanochemical effects on reaction kinetics is necessary to better estimate heat generation along a fault. © 2012. American Geophysical Union. All Rights Reserved.

Morono Y.,Japan Agency for Marine - Earth Science and Technology | Terada T.,Marine Works Japan Ltd. | Kallmeyer J.,German Research Center for Geosciences | Inagaki F.,Japan Agency for Marine - Earth Science and Technology
Environmental Microbiology | Year: 2013

Development of an improved technique for separating microbial cells from marine sediments and standardization of a high-throughput and discriminative cell enumeration method were conducted. We separated microbial cells from various types of marine sediment and then recovered the cells using multilayer density gradients of sodium polytungstate and/or Nycodenz, resulting in a notably higher percent recovery of cells than previous methods. The efficiency of cell extraction generally depends on the sediment depth; using the new technique we developed, more than 80% of the total cells were recovered from shallow sediment samples (down to 100 meters in depth), whereas ∼50% of cells were recovered from deep samples (100-365m in depth). The separated cells could be rapidly enumerated using flow cytometry (FCM). The data were in good agreement with those obtained from manual microscopic direct counts over the range 104-108cellscm-3. We also demonstrated that sedimentary microbial cells can be efficiently collected using a cell sorter. The combined use of our new cell separation and FCM/cell sorting techniques facilitates high-throughput and precise enumeration of microbial cells in sediments and is amenable to various types of single-cell analyses, thereby enhancing our understanding of microbial life in the largely uncharacterized deep subseafloor biosphere. © 2013 The Authors. Environmental Microbiology published by John Wiley & Sons Ltd and Society for Applied Microbiology.

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