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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 132 (1990), S. 49-65 
    ISSN: 1420-9136
    Keywords: Multiple scattering ; dispersion ; earth filter ; Q ; random scattering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A plane-wave signal traveling at normal incidence through the earth's sedimentary layers attenuates, spreads, and changes waveform as it propagates, partly in response to “stratigraphic filtering” resulting from the buildup in the medium of intrabed multiples caused by the layering, and partly in response to absorption. This paper consists of a review of one-dimensional stratigraphic filtering. The action of stratigraphic filtering resembles that of absorption, and the filter's spectrum can be characterized by an effective quality factor. A comparison between the spectra of field data and synthetic data derived from absorption-free one-dimensional models suggests that in some geologic formations, stratigraphic filtering causes a significant fraction of the total attenuation evident on seismic records. In such studies, however, the simplicity of one-dimensional models leaves some uncertainty regarding the generality of the results. Nonetheless, one-dimensional stratigraphic filtering can serve as a useful metaphor that provides insight into the workings of more complex multi-dimensional scattering models.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 132 (1990), S. 93-121 
    ISSN: 1420-9136
    Keywords: Scattering ; attenuation ; coda ; Q ; heterogeneity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A unified model is proposed for explaining the frequency dependent amplitude attenuation and the coda wave excitation on the basis of the single scattering process in the randomly inhomogeneous lithosphere. Adopting Birch's law and a direct proportion between density and wave velocity, we statistically describe the inhomogeneous medium by one random function characterized by the von Karman autocorrelation function. We calculate the amplitude attenuation from the solid angle integral of scattered wave energy on the basis of the Born approxiimation after subtracting the travel-time fluctuation effect caused by slowly varying velocity inhomogeneities. This subtraction is equivalent to neglect energy loss by scattering within a cone around the forward direction. The random inhomogeneity of the von Karman autocorrelation function of order 0.35 with the mean square fractional fluctuation of 7.2×10−3 ≈1.3×10−2 and the correlation distance of 2.1≈5.1 km well explains observed backward scattering coefficientg π and the ratioQ P −1 /Q S −1 , and observed and partially conjecturedQ S −1 for frequencies between 0.5 Hz and 30 Hz.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Marine geophysical researches 13 (1991), S. 227-237 
    ISSN: 1573-0581
    Keywords: Q ; attenuation ; ophiolite ; oceanic crust ; velocity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Compressional wave attenuations and velocities have been measured as a function of confining pressure in ophiolite samples representing a cross-section of the oceanic crust and uppermost mantle. Data are presented for basalts, diabase dikes, gabbros and a suite of serpentinites and peridotites showing a range of serpentization. An ultrasonic pulse-echo spectral ratio technique was used to determine the attenuations to confining pressures of 500 MPa. From this data a Q profile for the oceanic crust and upper mantle is presented. Q is found to moderately increase with depth through the pillow basalts of the upper oceanic crust. The sheeted dike rocks of Layer 2C show an increase in Q with depth due to progressive metamorphism (from greenschist to amphibolite facies). Q drops abruptly from Layer 2C to Layer 3, though it is not clear why the gabbros have such low Q's. The crust-mantle boundary is a Q discontinuity; however, the Q contrast between Layer 3 and the upper mantle could be altered by upper mantle serpentinization, interlayered gabbros and peridotites at the boundary, or serpentinized peridotite diapirs intruding the gabbroic section. Q varies significantly with the percentage of serpentinization in the ultramafic samples, with the largest changes in Q being at the extremes of zero and full serpentinization. Q is sensitive to the overburden pressure for all of the samples.
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