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  • Articles  (46)
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  • 1
    Publication Date: 1994-09-09
    Description: The addition of hydrothermal fluids to heated, intact granite leads to permeability reductions in the temperature range of 300 degrees to 500 degrees C, with the rate of change generally increasing with increasing temperature. The addition of gouge enhances the rate of permeability reduction because of the greater reactivity of the fine material. Flow rate is initially high in a throughgoing fracture but eventually drops to the level of intact granite. These results support the fault-valve model for the development of mesothermal ore deposits, in which seals are formed at the base of the seismogenic zone of high-angle thrust faults. The lower temperature results yield varying estimates of mineral-sealing rates at shallower depths in fault zones, although they generally support the hypothesis that such seals develop in less time than the recurrence interval for moderate to large earthquakes on the San Andreas fault.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Moore, D E -- Lockner, D A -- Byerlee, J D -- New York, N.Y. -- Science. 1994 Sep 9;265(5178):1558-61.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17801532" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 2
    Publication Date: 1975-01-01
    Print ISSN: 0149-1423
    Electronic ISSN: 1943-2674
    Topics: Geosciences
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 114 (1976), S. 425-433 
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary We propose a method that may be used to determine the spatial orientation of the fracture plane developed during hydraulic fracture. In the method, magnetic particles are injected into the crack with the fracturing fluid so as to generate a sheet of magnetized material. Since the magnetization of a body with extreme dimension ratios, such as a crack, exceeds that of an equidimensional body and since this magnetization is sensitive both to orientation and geometry, this could be used to obtain information about the crack. By measuring the vertical and horizontal components of the magnetic field and field gradients at the earth's surface surrounding the injection well with superconducting magnetometers having 10−4 gamma sensitivity and also by measuring field direction within the well itself, it should be possible to calculate the orientation and perhaps infer the approximate geometry of the fracture surface. Experiments on electric field potential operated in conjunction with this experiment could further constrain estimates of shape and orientation.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 116 (1978), S. 765-772 
    ISSN: 1420-9136
    Keywords: Velocity anomalies ; Microfractures ; Stick-slip
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Locations and velocities were calculated for microseisms occurring in samples of rock subjected to triaxial loading and injection of pore fluid. This was accomplished by analyzing arrival times of acoustic emission using an automatic first arrival picker. Apparent velocity anomalies were observed prior to both failure of intact samples and violent slip in samples containing saw cuts. Further analysis revealed that these fluctuations in calculated velocity were not due to changes in the true seismie velocity. Instead, variations in calculated velocity are shown to be related to sampling errors in picking first arrivals. The systematic picking of late first arrivals for small magnitude events was found to be a persistent bias resulting in low calculated velocities. This has encouraged the reexamination of earthquake records to determine how important sampling biases are in contributing to reported velocity anomalies.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 124 (1986), S. 31-52 
    ISSN: 1420-9136
    Keywords: Fault gouge ; friction ; deformation textures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The frictional properties of a crushed granite gouge and of gouges rich in montmorillonite, illite, and serpentine minerals have been investigated at temperatures as high as 600°C, confining pressures as high as 2.5 kbar, a pore pressure of 30 bar, and sliding velocities of 4.8 and 4.8×10−2 μm/sec. The gouges showed nearly identical strength behaviors at the two sliding velocities; all four gouges, however, showed a greater tendency to stick-slip movement and somewhat higher stress drops in the experiments at 4.8×10−2 μm/sec. Varying the sliding velocity also had an effect on the mineral assemblages and deformation textures developed in the heated gouges. The principal mineralogical difference was that at 400°C and 1 kbar confining pressure a serpentine breakdown reaction occurred in the experiments at 4.8×10−2 μm/sec but not in those at 4.8 μm/sec. The textures developed in the gouge layers were in part functions of the gouge type and the temperature, but changes in the sliding velocity affected, among other features, the degree of mineral deformation and the orientation of some fractures.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 113 (1975), S. 63-68 
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary The distance of stable sliding before sudden slip on fault surfaces in granite decreases rapidly as the confining pressure is increased. At a pressure of 6 kb the amount of stable creep is very small or absent. Two orders of magnitude change in strain rate has no effect on the distance of stable sliding. Our results suggest that in the earth, fault creep should predominate in the shallow crust but in the deep crustal layer most of the stresses are probably relieved by sudden earthquake type of motion. Below the crust high temperature would promote stable-slip so in this region creep would once more predominate.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 124 (1986), S. 445-469 
    ISSN: 1420-9136
    Keywords: Shear strength ; temperature ; deformation rate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Layers of artificial granite gouge have been deformed on saw-cut granite surfaces inclined 30° to the sample axes. Samples were deformed at a constant confining pressure of 250 MPa and temperatures of 22 to 845°C. The velocity dependence of the steady-state coefficient of friction (μss) was determined by comparing sliding strengths at different sliding rates. The results of these measurements are consistent with those reported bySolberg andByerlee (1984) at room temperature andStesky (1975) between 300 and 400°C. Stesky found that the slip-rate dependence of (μss) increased above 400°C. In the present study, however, the velocity dependence of (μss) was nearly independent of temperature.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 116 (1978), S. 583-585 
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 124 (1986), S. 601-608 
    ISSN: 1420-9136
    Keywords: Induced polarization ; earthquake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Measurements of charge separation in rock during stable and unstable deformation give unexpectedly large decay times of 50 sec. Time-domain induced polarization experiments on wet and dry rocks give similar decay times and suggest that the same decay mechanisms operate in the induced polarization response as in the relaxation of charge generated by mechanical deformation. These large decay times are attributed to electrochemical processes in the rocks, and they require low-frequency relative permittivity to be very large, in excess of 105. One consequence of large permittivity, and therefore long decay times, is that a significant portion of any electrical charge generated during an earthquake can persist for tens or hundreds of seconds. As a result, electrical disturbances associated with earthquakes should be observable for these lengths of time rather than for the milliseconds previously suggested.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 350 (1991), S. 39-42 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The failure process in a brittle granite sample can be stabilized by controlling axial stress to maintain a constant rate of acoustic emission. As a result, the post-failure stress curve can be followed quasi-statically, extending to hours the fault growth process which normally would occur ...
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