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  • 1
    Electronic Resource
    Electronic Resource
    Seismic velocity changes during fracture and frictional sliding (1978)
    Springer
    Pure and applied geophysics 116 (1978), S. 732-742 
    Details
    ISSN: 1420-9136
    Keywords: Velocity changes ; Fracture ; Friction ; Holography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Fracture and frictional sliding are considered as phenomena involving brittle failure. Brittle failure is preceded by the formation of small (subcritical) cracks. In non-water-saturated rock, the distribution, shape and size of these suberitical cracks determine the change in the physical properties prior to failure. A model is proposed which suggests that the spatial and temporal distribution, shape and size of subcritical cracks within a stressed rock depend upon the rate of deformation and the volatile content. As a rock is stressed beyond about 50 percent of its ultimate failure stress, dilatancy is initiated. With increasing stress a broad zone of cracks develops within the dilatant region. The seismic velocities through this zone decrease markedly and the cracks grow more numerous., changing in size and shape. Before brittle failure of the rock occurs, the subcritical cracks interact, leading to a concentration of the zone. During the stage when the zone narrows, the seismic velocities in crease in the surrounding volume due to local rotation of stresses and consequent closure of some cracks. In most laboratory experiments the stage during which the velocity increases and the now intense deformation zone becomes narrow is very short and difficult to observe experimentally. At very low strain rates and with volatiles present, the crack growth and subsequent interaction lead to the narrowing of the intense deformation zone and therefore to an observable increase in velocity. The above is based upon an interpretation of a number of experiments. Using optical holography we have observed the development and subsequent intensification of a deformation zone. Ultrasonic velocity measurements showed a distinct anomaly (decrease followed by an increase) before failure. The anomaly was only detectable at our lowest experimental strain rates (3×10−8/sec).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876535
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  • 2
    Electronic Resource
    Electronic Resource
    Velocity changes associated with generalized triaxial deformation of pyrophyllite (1980)
    Springer
    Pure and applied geophysics 118 (1980), S. 975-989 
    Details
    ISSN: 1420-9136
    Keywords: Rock mechanics ; Dilatancy-diffusion, Velocity changes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Compressional and shear-wave velocities (V p andV s ) were measured during the generalized triaxial deformation (i.e.σ 1≠σ 2=2σ 3) of pyrophyllite. Observed velocity changes could be ascribed to crack development during dilatancy. Velocity changes were very localized with respect to the ultimate failure plane. The orientation and development of the failure plane was continuously observed with laser holography. Velocity reverals, i.e. changes from a decreasing trend to an increasing trend, were documented in a wet sample in bothV p andV s . These changes in bothV p andV p are inconsistent with dialatancy-diffusion models. The reversals were interpreted as a reflection of local stress reorientation caused by a slowly propagating fault.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01593044
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  • 3
    Electronic Resource
    Electronic Resource
    Experimental investigation of the elastic modulus of a fractal system—A model of fractured rocks (1990)
    Springer
    Pure and applied geophysics 134 (1990), S. 31-43 
    Details
    ISSN: 1420-9136
    Keywords: Rock failure ; fractal ; percolation ; rock modulus ; damage parameter ; rock mechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The elastic properties of a physical model representing a damaged rock matrix were studied using a square lattice deformed under tensile stress. The elastic modulusM of such a system varies in agreement with percolation theory as|x−x c | f , wherex is the damage parameter andx c the threshold value of the damage parameter,f≃3.6. Atx≃x c the scale dependence ofM can be expressed asM∼L −f/v , whereL is the size of the sample andv the correlation exponent in percolation theory. The experimental results are of interest in assessing elastic properties in earthquake focal zones and fault zones in general.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00878078
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  • 4
    Electronic Resource
    Electronic Resource
    An experimental study of triggered stick-slip (1993)
    Springer
    Pure and applied geophysics 140 (1993), S. 79-94 
    Details
    ISSN: 1420-9136
    Keywords: Stick-slip ; rock friction ; instability ; precursor ; earthquake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Stick-slips have been studied in the laboratory on granite, labrodorite and sandstone samples of two different sizes. Different roughness was achieved on the sawcut surfaces by finishing them with different grinding compounds ranging from grit 40 to grit 1000. Stick-slips occurred as a result of 1) slowly increasing the shear and normal stresses, 2) superimposing a sinusoidal stress modulation (0.1 and 10 Hz) on the slowly increasing stresses, 3) triggering by a stress impulse when the shear stress was well below the levels where stick-slips occurred without the impulse, and 4) foreshocks. Stick-slips triggered by impulses or foreshocks occurred “long” after the beginning of the triggering events, i.e., long in comparison with elastic wave travel times through the sample. All triggered events were very rich in high frequencies (corner frequency of ∼100 kHz). The untriggered stick-slips did not contain much energy at the high frequencies (corner frequency of ∼10 kHz). The dynamic friction coefficients for the triggered stick-slips were smaller than for the untriggered events. The “long” delay between the onset of the trigger and the stick-slip, and the high frequencies may be a consequence of corrosion of asperities. The ultimate triggering and the rate of corrosion are likely related to the interplay of the normal and shear stresses as they load and unload the fault surface. The consistent shape of the high frequency spectra is probably due to sample resonances which are excited rather than being characteristic of the details of the stick-slips. If these laboratory observations are directly applicable to earthquake seismology, the spectra of earthquakes which were triggered by other earthquakes should be anomalously rich in high frequencies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876872
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  • 5
    Electronic Resource
    Electronic Resource
    Absorption of strain waves in porous media at seismic frequencies (1996)
    Springer
    Pure and applied geophysics 147 (1996), S. 25-55 
    Details
    ISSN: 1420-9136
    Keywords: Dissipation ; strain waves ; poroelasticity ; surface energy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract An understanding of strain wave propagation in fluid containing porous rocks is important in reservoir geophysics and in the monitoring in underground water in the vicinity of nuclear and toxic waste sites, earthquake prediction, etc. Both experimental and theoretical research are far from providing a complete explanation of dissipation mechanisms, especially the observation of an unexpectedly strong dependence of attenuationQ −1 on the chemistry of the solid and liquid phase involved. Traditional theories of proelasticity do not take these effects into account. In this paper the bulk of existing experimental data and theoretical models is reviewed briefly in order to elecidate the effect of environmental factors on the attenuation of seismic waves. Low fluid concentrations are emphasized. Thermodynamical analysis shows that changes in surface energy caused by weak mechanical disturbances can explain observed values of attenuation in real rocks. Experimental dissipation isotherms are interpreted in terms of monolayered surface adsorption of liquid films as described by Langmuir's equation. In order to describe surface dissipation in consolidated rocks, a surface tension term is added to the pore pressure term in the O'Connell-Budiansky proelastic equation for effective moduli of porous and fractured rocks. Theoretical calculations by this modified model, using reasonable values for elastic parameters, surface energy, crack density and their geometry, lead to results which qualitatively agree with experimental data obtained at low fluid contents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876435
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  • 6
    Electronic Resource
    Electronic Resource
    Seismic Attenuation in Partially Saturated Dime-shaped Cracks (2000)
    Springer
    Pure and applied geophysics 157 (2000), S. 435-448 
    Details
    ISSN: 1420-9136
    Keywords: Key Words: Attenuation, surface contamination, partially saturated cracks, dime-shaped.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —We have examined the effect of surface contamination on the attenuation and stiffness of compressional seismic waves in artificial cylindrical glass cracks that are partially saturated with water. The compression of the gap perpendicularly to its plane reduces the gap volume and forces the water to redistribute within the gap (conservation of volume of an incompressible liquid). On clean surfaces, the water can flow without significant resistance across the glass. This leads to a very low and almost constant attenuation over a wide frequency range (approx. 3 mHz to 10 Hz), while the sample stiffness is constant. In the case of propanol contaminated surfaces, both the attenuation and the stiffness are considerably higher than in the clean case, and display a considerable frequency dependence. Both effects can be explained with the Restricted Meniscus Motion Model. In this model, the redistribution of the liquid in the gap first leads to a change (increase) of the contact angle. The change of the meniscus curvature results in an increase of the pressure in the liquid and thus to a stiffening of the sample. When the resistive force, that prevents the contact line from sliding along the surface, is finally overcome, the contact line starts moving across the contaminated surface. The motion against the resistive force dissipates energy and increases the attenuation. The calculated data are in good agreement for both the clean and the contaminated case; the model parameters fall in the range that was established by independent experiments (e.g. ).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050007
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  • 7
    Electronic Resource
    Electronic Resource
    Temperature fluctuation and thermodynamic properties in Earth's lower mantle: An application of the complete travel time equation of state
    Amsterdam : Elsevier
    Earth and Planetary Science Letters 126 (1994), S. 369-377 
    Details
    ISSN: 0012-821X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0012-821X(94)90118-X
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  • 8
    Electronic Resource
    Electronic Resource
    Partial melting and the low-velocity zone
    Amsterdam : Elsevier
    Physics of the Earth and Planetary Interiors 4 (1970), S. 62-64 
    Details
    ISSN: 0031-9201
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0031-9201(70)90030-0
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  • 9
    Electronic Resource
    Electronic Resource
    Improved acoustic emission locations (1986)
    Springer
    Journal of nondestructive evaluation 5 (1986), S. 133-143 
    Details
    ISSN: 1573-4862
    Keywords: Acoustic emission location ; anisotropic velocity ; transducer size effects ; rock deformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Acoustic emission locations have been determined in a modest-size specimen of Westerly granite (∼ 50×50×200 mm) under uniaxial compressive loading to failure. Periodically during the experiment acoustic pulses were transmitted from a set of source transducers to an acoustic emission receiver array. Axial and transverse velocities were determined from these transmission data. The piezoelectric transducers used in this study were too large to be treated as points. A separate experiment was performed to determine the effect of finite transducer size and incident angle on observed arrival times. Velocity pulse arrival times were inverted for the known source transducer positions using (1) an isotropic, fixed velocity model, (2) the observed anisotropic, stress dependent velocity field, and (3) transducer size corrections. Incorporation of the observed velocity field and transducer size effects dramatically improved location accuracy. Acoustic emissions were located using this technique. Synthetic data, exact and with realistic “errors,” were inverted to determine location uncertainties at various locations throughout the sample. Suggestions are made for further improvements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00570622
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  • 10
    Electronic Resource
    Electronic Resource
    Correlation of strain and velocity during dilatancy (1974)
    [s.l.] : Nature Publishing Group
    Nature 252 (1974), S. 30-31 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Here we correlate spatial variations in compressional velocity with spatial variations in strain over the extended time interval required for the rock to fail under constant stress. A right circular cylinder of Westerly granite was statically loaded in uniaxial compression and velocity observed ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/252030a0
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