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  • 1
    Electronic Resource
    Electronic Resource
    IN-SEAM SEISMIC LOVE WAVE SCATTERING MODELED BY THE FINITE ELEMENT METHOD (1984)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 32 (1984), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The dynamic finite-element method allows frequency-dependent reflection and transmission coefficients to be computed for Love waves scattered by two-dimensional inhomogeneities in coal seams.Clean faults of zero hade angle show a throw-dependent cross-over frequency in reflection spectra, and throw-dependent conversion from fundamental to first higher mode energy in transmission spectra. Oblique faults show mode conversion in reflection spectra which is relatable to the fault hade angle by simple Huygens-theory models. Thin fracture zones or dykes normal to the seam show a reflection maximum when thickness of the zone is of order one quarter of the seam wave wavelength.Published field data from two known faults and a dyke are compared with the modeling results and support the belief that broad-band seam-wave data are capable of characterizing a seam discontinuity (throw, hade angle, dyke thickness) as well as locating it. Development of such procedures will require extensions to existing field practice and processing.This research was funded in part by the National Energy Research Development and Demonstration Council of Australia. The authors thank The Broken Hill Proprietary Company Limited for permission to quote from company case histories.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2478.1984.tb01711.x
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    THE INFLUENCE OF ELECTRICAL ANISOTROPY ON MISE À LA MASSE SURVEYS (1974)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 22 (1974), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: In a transversely electrically anisotropic rock mass of arbitrary dip, the potential distribution about an electrode at arbitrary depth is the sum of the whole-space potential about that electrode, plus the whole-space potential about a postulated image electrode displaced up-dip from the source position. Equipotential lines on the rock-air surface are ellipses, elongated parallel to strike, and with centers displaced up-dip from the surface projection of the electrode position. In metamorphosed rocks frequently encountered in mining geophysics, anisotropy is such that elongation is most marked in steeply dipping rocks, with displacement most evident in low to moderate dip.Graphs relating the anisotropy coefficient to displacement and elongation assist in separation of the anisotropy-related effects from those of a significant subsurface conductive body, particularly if surface resistivity sounding establishes the coefficient of anisotropy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2478.1974.tb00082.x
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    Paper (German National Licenses)
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  • 3
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    Using the SPAC Microtremor Method to Identify 2D Effects and Evaluate 1D Shear-Wave Velocity Profile in Valleys (2011)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2011-04-01
    Description: The requirement of a layered-earth geology is a restrictive assumption when using the spatially averaged coherency spectra (SPAC) method. Numerical simulations of microtremors and SPAC observations recorded in the Tamar paleovalley, Launceston (Tasmania, Australia), are used to assess the potential of the SPAC method to identify two-dimensional (2D) effects and evaluate one-dimensional (1D) shear-wave velocity (SWV) profile in a valley environment. The Tamar Valley is approximately 250 m deep by 700-1000 m wide. It is filled with soft sediments from the Tertiary and Quaternary periods above hard dolerite bedrock of Jurassic age. Observed coherency spectra of the vertical component are analyzed at two sites in the Tamar Valley; using two 50-m-radius centered triangular arrays above the deepest point of the valley at site DBL, and above the east flank of the valley at site RGB. Simulated and observed coherency spectra suggest the propagation of Rayleigh waves of first higher mode at the SV frequency of resonance of the Tamar Valley affects the coherency spectra recorded with pairs of sensors perpendicular to the valley (transverse-COH). Simulated and observed coherency spectra recorded above the deepest point of the valley (site DBL) with pairs of sensors parallel to the valley axis (axial-COH) are not affected by these edge-generated Rayleigh waves and agree well with the theoretical coherency spectrum computed from the preferred 1D SWV profile. The simulated and observed results from this paper suggest that differences between the observed axial-COH and transverse-COH give an indication of the existence of the 2D buried valley. Results also suggest that the observed coherency spectra recorded on pairs of sensors oriented parallel to the valley axis can provide a reliable evaluation of a 1D SWV profile above the deepest point of a deep and narrow valley, such as the Tamar Valley.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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