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  • 1
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    Thermal conductivities under high pressure in core samples from IODP NanTroSEIZE drilling site C0001 (2011)
    Wiley
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    Publication Date: 2011-06-24
    Description: We examined the effects of high pressure on thermal conductivity in core samples from the slope–apron facies and the upper part of the accretionary prism at site C0001 of the NanTroSEIZE drilling program and in other samples of five terrestrial rock types. Thermal conductivity clearly increased with increasing pressure for both wet (water saturated) and dry samples. We determined the rate of thermal conductivity change of the NanTroSEIZE sediments to be 0.014 Wm−1K−1/MPa when pressure was increased, and 0.01 Wm−1K−1/MPa when pressure was decreased. Using the rate determined for decreasing pressure, we estimated that thermal conductivities measured at atmospheric pressure rather than at in situ pressure may be underestimated by 7% for a core sample from around 1 km depth and by 20% for a core sample from around 3 km depth. In general, the rate of thermal conductivity change with pressure showed a positive correlation with porosity. However, the relationship of the rate of thermal conductivity change to porosity is also dependent on the fabric, mineral composition, and pore structure of the sediments and rocks. Furthermore, for two sandstones we tested, the effect of pressure on thermal conductivity for dry samples was greater than that for wet samples.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Correction to “Low- to high-velocity frictional properties of the clay-rich gouges from the slipping zone of the 1963 Vaiont slide, northern Italy” (2011)
    Wiley
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    Publication Date: 2011-11-09
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Correction to “Mechanoradical H2 generation during simulated faulting: Implications for an earthquake-driven subsurface biosphere” (2012)
    Wiley
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    Publication Date: 2012-12-11
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Velocity dependence of shear-induced permeability associated with frictional behavior in fault zones of the Nankai subduction zone (2012)
    Wiley
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    Publication Date: 2012-05-08
    Description: We measured frictional properties and permeability of core materials from the megasplay fault zone (site C0004) and the frontal thrust (site C0007) in the shallow part of the Nankai subduction zone. Permeability was measured before and after 7.9 m slip displacement at high (1.05 m/s) and low velocities (0.013 m/s) under normal stresses of 1.5 MPa using the rotary-shear apparatus, from which we estimated the shear-induced permeability change in an experimental fault gouge prepared from core material. Gouge permeability (10−18 m2) decreased after sliding for wet gouge and increased for dry gouge. The high-velocity friction test under wet conditions yielded a smaller reduction in permeability than the low-velocity test, whereas the opposite trend was observed in dry conditions. We attribute the differences in permeability to the effects of thermal/mechanical pore pressurization upon shear-induced compaction. Symmetric boudin structures may represent evidence of hydrofracturing induced by pore fluid pressurization. The large friction coefficient of the megasplay fault material in the slow and wet friction tests is explained by homogeneous shear deformation and higher permeability that promotes faster shear-induced compaction. The similarity in post-shear permeability for the gouges from the both faults may account for the similar friction coefficients in high-velocity friction, assuming that the pore fluid pressurization process controls high-velocity frictional behavior. This velocity dependence on friction suggests that a large dynamic stress drop is expected for the megasplay fault, implying that large slip displacement followed by a giant tsunami is plausible when a rupture from depth propagates to the megasplay fault.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Low- to high-velocity frictional properties of the clay-rich gouges from the slipping zone of the 1963 Vaiont slide, northern Italy (2011)
    Wiley
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    Publication Date: 2011-09-28
    Description: The final slip of about 450 m at about 30 m/s of the 1963 Vaiont landslide (Italy) was preceded by 〉3 year long creeping phase which was localized in centimeter-thick clay-rich layers (60–70% smectites, 20–30% calcite and quartz). Here we investigate the frictional properties of the clay-rich layers under similar deformation conditions as during the landslide: 1–5 MPa normal stress, 2 × 10−7 to 1.31 m/s slip rate and displacements up to 34 m. Experiments were performed at room humidity and wet conditions with biaxial, torsion and rotary shear apparatus. The clay-rich gouge was velocity-independent to velocity-weakening in both room humidity and wet conditions. In room humidity experiments, the coefficient of friction decreased from 0.47 at v 〈 5.0 × 10−5 m/s to 0.12 at 1.31 m/s. Microstructural and mineralogical analyses of the gouge after experiments indicate that the dramatic weakening results from thermo-chemical pressurization of pore fluids (smectite decomposition to illite-type clays) and powder lubrication. In wet experiments, the coefficient of friction decreased from 0.17 at v 〈 1.0 × 10−4 m/s to 0.0 at v 〉 0.70 m/s: full lubrication results from the formation of a continuous water film in the gouge. The Vaiont landslide occurred under wet to saturated conditions. The unstable behavior of the landslide is explained by the velocity-weakening behavior of the Vaiont clay-rich gouges. The formation of a continuous film of liquid water in the slipping zone reduced the coefficient of friction to almost zero, even without invoking the activation of thermal pressurization. This explains the extraordinary high velocity achieved by the slide during the final collapse.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 6
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    Frictional experiments of dolerite at intermediate slip rates with controlled temperature: Rate weakening or temperature weakening? (2011)
    Wiley
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    Publication Date: 2011-07-26
    Description: A rotary shear apparatus has been newly set up in Chiba University which can control the temperature near a sliding surface, Tmeas, up to 1000°C independently from slip rate, V. Frictional experiments at 0.010 m/s, 1 MPa normal stress, and variable Tmeas for dolerite have revealed a remarkable effect of temperature on the friction coefficient, f. With increasing Tmeas, f starts from 0.7 to 0.8 at room temperature (RT), decreases down to 0.5–0.6 at 400°C, increases until 800°C, and then decreases again. We have also conducted XRD analyses of the wear materials (mainly submicron particles) and investigated microstructures of the sliding surfaces developed at different temperatures Tmeas, and we found that there is a negative correlation between f and the amount of amorphous material except at RT and 1000°C. The generation of the amorphous phase probably causes the weakening. There is no amorphous phase recognized for a sample at 1000°C which is an aggregate of rounded crystals. EBSD analyses show that the material on the sliding surface at 1000°C contains randomly oriented hematite grains, which together with the observed microstructural features suggests that granular flow was taking place. We have also demonstrated that f depends not only on the instantaneous value of temperature, but also on its history. By comparing with conventional rotary shear friction experiment for the same dolerite without temperature control, we conclude that strong “rate weakening” as recently observed in high-velocity frictional experiments without an active control of the temperature has a significant amount of contribution from the temperature effect.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 7
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    Mechanoradical H2 generation during simulated faulting: Implications for an earthquake-driven subsurface biosphere (2011)
    Wiley
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    Publication Date: 2011-09-03
    Description: Molecular hydrogen, H2, is the key component to link the inorganic lithosphere with the subsurface biosphere. Geochemical and microbiological characterizations of natural hydrothermal fields strongly suggested that H2 is an important energy source in subsurface microbial ecosystems because of its metabolic versatility. One of the possible sources of H2 has been considered as earthquakes: mechanoradical reactions on fault surfaces generate H2 during earthquake faulting. However it is unclear whether faulting can generate abundant H2 to sustain subsurface chemolithoautotrophic microorganisms, such as methanogens. Here we present the result of high velocity friction experiments aimed to estimate the amount of H2 generated during earthquakes. Our results show that H2 generation increases with frictional work (i.e., earthquake magnitude) and that a H2 concentration of more than 1.1 mol/kg of fluid can be achieved in a fault zone after earthquakes of even small magnitudes. The estimated earthquake-derived H2 concentration is sufficiently high to sustain a H2-based subsurface lithoautotrophic microbial ecosystem. Furthermore, earthquakes have initiated on the Earth at least since tectonic plate movement began ∼3.8 Ga, implying the possible existence of ancient earthquake-driven ecosystems. Seismic H2 based subsurface ecosystems might exist not only over the Earth but also other planets.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Pressure dependence of fluid transport properties of shallow fault systems in the Nankai subduction zone (2014)
    SpringerOpen
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    Publication Date: 2014-08-14
    Description: We measured fluid transport properties at an effective pressure of 40 MPa in core samples of sediments and fault rocks collected by the Integrated Ocean Drilling Program (IODP) NanTroSEIZE drilling project Expedition 316 from the megasplay fault system (site C0004) and the frontal thrust (site C0007) in the Nankai subduction zone. Permeability decreased with effective pressure as a power law function. Permeability values in the fault zones were 8 x 10-18 m2 at site C0004 and 9 x 10-18 m2 at site C0007. Stratigraphic variation in transport properties suggests that the megasplay fault zone may act as a barrier to fluid flow, but the frontal thrust fault zone might not. Depth variation in permeability at site C0007 is probably controlled by the mechanical compaction of sediment. Hydraulic diffusivity at shallow depths was approximately 1 x 10-6 m2 s-1 in both fault zones, which is small enough to lead to pore pressure generation that can cause dynamic fault weakening. However, absence of a very low permeable zone, which may have formed in the Japan Trench subduction zone, might prevent facilitation of huge shallow slips during Nankai subduction zone earthquakes. Porosity tests under dry conditions might have overestimated the porosity.
    Print ISSN: 1343-8832
    Electronic ISSN: 1880-5981
    Topics: Geosciences
    Published by SpringerOpen
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  • 9
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    Graphite as a lubricating agent in fault zones: an insight from low- to high-velocity friction experiments on a mixed graphite–quartz gouge (2013)
    Wiley
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    Publication Date: 2013-04-04
    Description: [1]  Graphite is a very low-friction material, often enriched within fault zones due to mechanical or chemical processes. The effects of weak minerals on the strength of faults have been examined by friction experiments on bimineralic mixtures. However, previous experiments were conducted with limited shear strains, even though applied shear strains and textural developments had already been signaled as significant factors in the weakening of faults. We therefore conducted large-displacement, low- to high-velocity friction experiments with graphite–quartz gouges, to determine how much graphite is needed to reduce frictional strength, and to examine how textures contribute to the strength reduction of a mature fault at various slip rates. We found that the coefficients of friction of the gouges decrease non-linearly with increasing graphite fraction for any given shear strain and slip rate, decreasing first with 5–20 vol% graphite, then reaching similar frictional levels to pure graphite with 30–50 vol% graphite. The non-linear weakening trends can be fitted by sigmoidal curves. The weakening with 10–30 vol% graphite is associated with zones of slip-localization and the development of a graphite-lubricated penetrative slip surface(s). With increasing shear strain, the relationship between strength and graphite fraction evolves abruptly from an early gentle curve to a sigmoidal curve, and the frictional strength drops significantly even with small amounts of graphite (ca. 10 vol%). Our results highlight the importance of shear strain and textural developments on weak faults, not only with respect to graphite, but also other fault lubricants such as the phyllosilicates.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 10
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    Frictional melting of clayey gouge during seismic fault slip: Experimental observation and implications (2014)
    Wiley
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    Publication Date: 2014-07-31
    Description: Clayey gouges are common in fault slip zones at shallow depths. Thus, the fault zone processes and frictional behaviors of the gouges are critical to understanding seismic slip at these depths. We conducted rotary shear tests on clayey gouge (~41 wt.% clay minerals) at a seismic slip rate of 1.3 m/s. Here, we report that the gouge was melted at 5 MPa of normal stress and room-humidity conditions. The initial local melting was followed by melt layer formation. Clay minerals (e.g., smectite and illite) and plagioclase were melted and quenched to glass with numerous vesicles. Both flash heating and bulk temperature increases appear to be responsible for the melting. This observation of clayey gouge melting is comparable to that of natural faults (e.g., Chelungpu fault, Taiwan). Due to heterogeneous fault zone properties (e.g., permeability), frictional melting may be one of the important processes in clayey slip zones at shallow depths.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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