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  • 1
    Electronic Resource
    Electronic Resource
    Seismic regime of a single fault model (1986)
    Springer
    Pure and applied geophysics 124 (1986), S. 793-810 
    Details
    ISSN: 1420-9136
    Keywords: Plate models ; shear and tensile source mechanisms ; seismotectonic interpretation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A special experimental technique enabled us to study in detail seismic events on a fault model in a uniaxial stress field. The recording system used made it possible to investigate the radiation pattern for all the events observed including the precise determination of the dislocation origin. The aim of the present paper is (1) to find the relation between shear and tensile displacements, (2) to check a possible influence of the process of tensile crack generation on the seismic energy release and (3) to compare the seismic regime of a single fault before and after the tensile crack generation, respectively. Results prove the dominating importance of shear mechanism for the seismic energy release. The tensile displacement can be seismoactive only under special contact conditions on the fault plane. The existence of tensile cracks at the fault tips changed the pattern of seismic energy radiation. This feature is probably caused by subsequent changes in contact conditions on the fault plane and in the stress field around the fault. A comparison of some results of the present model experiments with the already published results of geological and seismological measurements and investigations shows the analogous character in laboratory and in nature of the process of tectonic earthquake preparation, the displacement course on the fault during the earthquake and the manner of seismic energy release on faults.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879611
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  • 2
    Electronic Resource
    Electronic Resource
    Fault interaction and seismicity: Laboratory investigation and its seismotectonic interpretation (1986)
    Springer
    Pure and applied geophysics 124 (1986), S. 857-874 
    Details
    ISSN: 1420-9136
    Keywords: Fault interaction ; seismotectonic interpretation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Systems of two parallel linear faults of the same length with the angle of inclination α=45° were investigated under uniaxial linearly increasing load. Perspex plates were used as models. For each treated fault configuration the morphology of tensile cracks and the sequence of seismoacoustic events of shear and tensile origin were studied. It is shown that the seismic regime of a fault system is strongly influenced by the contact conditions on a fault plane; it is different in the faults with the aseismic contact, represented by open slits, and in the faults with the seismoactive contact, represented by filled slits, respectively. The experiments proved the dominating role of a fast shear displacement of the stick-slip type in the regime of seismic energy release of a fault system. The tensile crack generation seems to be only of little—if not negligible—importance. On the other hand, the existence of tensile cracks in a fault system can play an important role in the course of subsequent loading cycles because the stick-slip displacements can take place not only along the primary faults but also along the planes of tensile cracks. A comparison of some results of model experiments and the already published results of geological and seismological investigations indicated that the way of seismic energy relase on faults in nature and in the laboratory could be of the same character. Several analogies between the seismic regime of a fault model and of real seismic regions were found concerning the morphology of faults, off-fault fore- and aftershocks, and earthquake doublets, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879615
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  • 3
    Electronic Resource
    Electronic Resource
    Influence of Nonlinear Processes in Seismic Foci on Released Energy (1997)
    Springer
    Pure and applied geophysics 149 (1997), S. 337-355 
    Details
    ISSN: 1420-9136
    Keywords: Key words: Self-synchronisation, nonlinear effects, seismic energy release, rock bursts, amplitude- phase analysis, relative width of frequency spectra.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —The results of the frequency analysis of seismoacoustic elastic waves radiated from the loaded rock sample source models and of rock bursts records are presented. For both categories of study the fundamental symptoms of nonlinear processes in seismic foci were found and demonstrated. Namely, the wave-field modulation (satellites in the spectra), forced synchronisation (spectra simplification and their transformation into a narrow spectral band), frequency shift to lower values and, finally, coherency of radiation. A new method of amplitude-phase distribution is worked out. All this indicates that nonlinear processes can participate in a seismic source during the energy release. Also, the disagreement between the source sizes observed in the nature and computed by means of linear physics, can be explained by self-organising processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050029
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  • 4
    Electronic Resource
    Electronic Resource
    Laboratory Approach to the Study of Elastic Anisotropy on Rock Samples (1998)
    Springer
    Pure and applied geophysics 151 (1998), S. 619-629 
    Details
    ISSN: 1420-9136
    Keywords: Key words: Laboratory measurements, elastic anisotropy, kinematic and dynamic parameters of elastic waves, hydrostatic pressure.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —The experimental approach (hardware and software) to the study of the elastic an isotropy of rocks on spherical samples under hydrostatic pressure up to 400 MPa is discussed. A substantial innovation of the existing measuring system and processing methods enabled us to make a detailed investigation and evaluation of the kinematic as well as dynamic parameters of elastic waves propagating through anisotropic media. The innovation is based on digital recording of the wave pattern with a high sampling density of both time and amplitude. Several options and results obtained with the innovated laboratory equipment are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050133
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  • 5
    Electronic Resource
    Electronic Resource
    Nonlinear processes in earthquake foci (1993)
    Springer
    Pure and applied geophysics 140 (1993), S. 29-47 
    Details
    ISSN: 1420-9136
    Keywords: Rock samples ; biaxial compression ; seismogenic structures ; nonlinear processes ; wave coherency ; selforganizing ; underload
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The results of laboratory experiments on biaxially compressed physical models of a seismic source are presented, discussed and interpreted in terms of nonlinear dynamics; the relation is shown between the degree of seismic pulse coherency (expressed through the amplitude frequency spectra development) and energy (or magnitude) in a series of model experiments. It has been ascertained that the degree of radiated waves coherency plays a more important role concerning the seismic energy release than the size (radius) of the seismic source. The relations among individual source parameters obtained in the laboratory were tested by the analysis of three series of seismograms of aftershocks which followed the 1988 Spitak earthquake (two series) and the 1975 Oroville earthquake (one series). The fundamental effect observed in the laboratory, i.e., the growth of pulse coherency with increasing stress concentration in the focal region (reflected in growing earthquake magnitude), was clearly manifested in all three earthquake aftershock series. Due to derivation by a comparison of the above results, obtained on the basis of nonlinear dynamics with the classical source models by Brune, Madariaga and others, it seems to be namely the self-organizing of the structure itself caused by the increasing stress field in the seismic source, which can answer the question concerning the degree of energy cumulation in the earthquake focus at a given moment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876869
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  • 6
    Electronic Resource
    Electronic Resource
    Elastic Parameters of West Bohemian Granites under Hydrostatic Pressure (1998)
    Springer
    Pure and applied geophysics 151 (1998), S. 631-646 
    Details
    ISSN: 1420-9136
    Keywords: Key words: Granite, Bohemian Massif, P-wave velocity, velocity anisotropy, fabric elements, hydrostatic pressure.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —The West Bohemian seismoactive region is situated near the contact of the Moldanu bian, Bohemian and Saxothuringian units in which a large volume is occupied by granitoid massifs. The spatial distribution of P-wave velocities and the rock fabric of five representative samples from these massifs were studied. The P-wave velocities were measured on spherical samples in 132 independent directions under hydrostatic pressure up to 400 MPa, using the pulse-transmission method. The pressure of 400 MPa corresponds to a depth of about 15 km in the area under study. The changes of P-wave velocity were correlated with the preferred orientations of the main rock fabric elements, i.e., rock forming minerals and microcracks. The values of the P-wave velocity from laboratory measurements on granite samples fit the velocity model used by seismologists in the West Bohemian seismoactive region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050134
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  • 7
    Electronic Resource
    Electronic Resource
    Energy - Frequency Distribution of Acoustic Emission from Loaded Rock Samples (1996)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 210-213 (May 1996), p. 541-548 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/01/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.210-213.541.pdf
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  • 8
    Electronic Resource
    Electronic Resource
    Stick-slip unstable shear failure as a source of high frequency elastic radiation (1989)
    Springer
    Studia geophysica et geodaetica 33 (1989), S. 322-337 
    Details
    ISSN: 1573-1626
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Summary The results of laboratory measurements on square perspex models with a stress concentrator under uniaxial compression are presented. An attempt was made to interpret these results in order to determine the mutual relations between the mechanical parameters characterizing the treated models, including their focal zones, parameters of model loading, parameters of seismogenic displacement and parameters of radiated elastic pulses. Particular attention was given to the study of slip displacement, slip velocity, rupture velocity, nucleation points of rupture propagation, nucleation points of elastic radiation and to the frequency analysis of radiated pulses. Measurements of the displacement in the focal zone enabled us to determine the source function, to construct theoretical seismograms in a far field and to compare them with the real pulses from ultrasonic transducers located there. This allowed testing theoretical and experimental approaches to the study of how slip displacement, slip velocity and rupture velocity are related to the parameters of radiated pulses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01637688
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  • 9
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    Non-linearity in multidirectional P-wave velocity: confining pressure behaviour based on real 3D laboratory measurements, and its mathematical approximation (2007)
    In:  Geological Society Special Publication 240: 323-334.
    Details
    Publication Date: 2007-10-08
    Description: Experimental laboratory measurements of P-wave velocity confirm the superposition of linearity over non-linearity by a progressive increase in confining pressure. The increase in confining pressure diminishes the influence of microcracks that are partly or totally closed. At a certain stress level, the trend of P-wave velocity with applied confining pressure approaches that of a solid without cracks, and a linear increase in elastic wave velocity occurs under high confinement. Several studies have focused on the problem of mathematical approximation of this phenomenon (Carlson & Gangi 1985; Wepfer & Christensen 1991; Greenfield & Graham 1996; Meglis et al. 1996). Although successful within a certain degree of error, they provide neither a multidirectional solution nor the comparison of results with rock fabric. In this study, an analytical relation was applied to describe the P-wave velocity-confining pressure behaviour of quasi-isotropic rocks (granites) and their anisotropic equivalents (orthogneisses). Two parameters of this relationship reflect the elastic properties of the rock matrix, and two others are related to the presence of microcracks, their density and genesis. The results of a mathematical approximation of the P-wave velocity-confining pressure behaviour show a favourable correlation to the measured data-sets. Comparison of individual fitted parameters with the rock fabric provides an improved understanding of the material's mechanical behaviour.
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  • 10
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    Acoustic Emission in a Laboratory: Mechanism of Microearthquakes Using Alternative Source Models (2018)
    American Geophysical Union
    Details
    Publication Date: 2018-06-14
    Description: Here a shear-tensile crack (STC) model is presented as suitable for acoustic emission (AE) events. Experimental data were obtained from a uniaxial compression test performed on a Westerly Granite specimen using a 14-channel AE monitoring system. The advantages of the STC versus a traditional MT (moment tensor) approach are as follows: (i) it is a physical source, contrary to the MT, since the STC describes the straight and simple fracture modes anticipated inside a loaded sample, namely, the shear slip and both the opening and closing tensile cracks; and (ii) it is simpler because it is described by fewer parameters (five instead of the six required for an unconstrained MT), which is essential for solving the inverse problem. The presented STC procedure was tested on 38 AE events selected over a range of 50–98% for the uniaxial compressive strength. As compared to the MT model, the STC model displayed a similar fit for input data while providing far smaller confidence regions. The results indicate a more certain determination for the mechanism of orientation and improved reliability for the decomposition components. In addition, use of STC model allowed better distinction between tension and shear type for AE events, which may be crucial for recognizing an approaching failure. For our experiment, application of the STC model proved to be useful for recognizing the threshold of unstable microcracking and indicative for determining the failure plain orientation. ©2018. American Geophysical Union. All Rights Reserved.
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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