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  • ASTROPHYSICS  (22)
  • Scattering  (3)
  • paleoheat flux  (3)
  • 1
    Electronic Resource
    Electronic Resource
    Stratigraphic filtering of seismic waves: The influence of mode conversion multiples onP-wave andS-wave phase and attenuation (1987)
    Springer
    Pure and applied geophysics 125 (1987), S. 717-751 
    Details
    ISSN: 1420-9136
    Keywords: Scattering ; mode conversion ; seismic waves ; stratigraphy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We demonstrate how multiples, generated at the interfaces of plane parallel beds, modify the propagation characteristics of an originally coherent seismic wave. For waves propagating at an angle to the bedding plane we find that theSV andP-waves couple so that neither is a pure mode. TheSH-wave, while modified in its propagation characteristics by multiples, remains a pure mode. The coupling ofSV-multiples into the quasi-P-mode appears weaker than the coupling ofP-wave multiples into the quasi-SV mode; at least this is so for the two simple cases of (a) density fluctuations only and (b) correlatedV p andV s fluctuations which conserve Poisson's ratio. We also find that the coupling is sensitive to both the angle of propagation and frequency. In addition there is a cut-off angle forP-wave multiples influencing the quasi-SV mode. Propagation angles larger than the cut-off permit theP-multiples to modify the phase of the quasi-SV mode, but not its effective attenuation. No such cut-off effect is found for SV-multiples influencing the quasi-P mode, whose angle-dependent and frequency-dependent phase distortion and effective attenuation are influenced both byP-wave multiples andSV-multiples. In view of the mathematical complexity of the expressions describing the phase, and effective attenuation of modes when allowance is made forP-andS-wave multiples, we strongly advocate numerical coding of the major mathematical formulae. By so doing a systematic study can be undertaken of the frequency and offset dependence of seismic waves as a function of seismic source input and power spectral behavior of the fluctuations in density and elastic constants of beds. It is our opinion that the full mathematical expressions are too involved to permit an analytic, systematic investigation to be given of the phase and attenuation of seismic waves with any degree of sophistication or generality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00878030
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Multiple scattering of seismic waves in fractured media: Velocity and effective attenuation of the coherent components ofP waves andS waves (1986)
    Springer
    Pure and applied geophysics 124 (1986), S. 975-1019 
    Details
    ISSN: 1420-9136
    Keywords: Scattering ; attenuation ; seismic wave-speeds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We show that the multiple scattering by small fractures of seismic waves with wavelengths long compared to the fracture size and fracture spacing is indistinguishable from multiple-scattering effects produced by ‘regular’ porosity, except for an orientation factor due to fracture alignment. The fractures reduce theP-wave andS-wave velocities and produce an effective attenuation of the coherent component of the seismic waves. The attenuation corresponds to 1000/Q of about unity for a Gaussian spectrum of fractures, and it varies with frequencyf asf 3. For a Kolmogorov spectrum of fractures of spectral index ν the attenuation is an order of magnitude or so larger and varies with frequency asf 3-v The precise degree of attenuation depends upon the matrix properties, the fracture porosity, the degree of fracture anisotropy, the type of fluid filling the fractures, and the incidence angle of the wave. For fracture porosities less than about 15% theP-wave andS-wave velocities are decreased by the order of 5–10% with a lesser dependence on the type of fluid filling the fractures (gas, oil, or brine) and with a dependence on both the degree of anisotropy and the incident angle made by the wave. The tendency of fractures to occur perpendicularly to bedding suggests that the best way to measure seismically fractured rock behavior in situ is by using the travel-time delay and reflection amplitude. As both the offset and the azimuth of receivers vary from a shot, the travel-time delay and reflection amplitude should both show an elliptical pattern of behavior—the travel-time delay in response to the varying seismic speed, and the reflection amplitude in response to angular variations in the multiple scattering. Observations of attenuation at several frequencies should permit (a) determination of the spectrum of fractures (Gaussian versus Kolmogorovian) and (b) determination of the contribution of viscous damping to the effective attenuation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879928
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Inversion of multiple thermal indicators: Quantitative methods of determining paleoheat flux and geological parameters. I. Theoretical development for paleoheat flux (1988)
    Springer
    Mathematical geology 20 (1988), S. 1-36 
    Details
    ISSN: 1573-8868
    Keywords: Maturity ; paleoheat flux ; tomography ; thermal indicators ; basin analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract The quantitative inversion of present-day downhole thermal indicator information enables (a) assessment of the effective paleoheat flux recorded by thermal indicators, and (b) determination of geological parameters related to the dynamical burial history of sedimentary strata. The logic of the general inversion scheme underlying seven thermal indicators, viz. vitrinite reflectance, sterane, and/or hopane isomers, sterane aromatization, optical rotation,39Ar/40Ar, pollen translucency, and fission scar tracks in apatite is presented, and their capability for resolving paleoheat flux is noted. In a second paper, determination of chemical and physical parameters, as well as several other quantities of geological interest (such as the sizes and erosion times of multiple unconformities, stratigraphic ages, paleo-overpressure, igneous intrusion timing, overthrust timing and frictional heat generation, fault and slump timing, thermal effects due to radioactive layer emplacement, and salt emplacement and dissolution timing) are discussed. Such events impact on both burial and thermal histories of sedimentary layers. Resolution problems are discussed also in the second paper, as is an attractive scheme called thermal indicator tomography for sorting out degrees of resolution, precision, and uniqueness of the relevant geological parameters for each process in combination with determination of the effective paleoheat flux. Detailed statements on the mechanics of implementing the tomographic approach are provided.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00903186
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  • 4
    Electronic Resource
    Electronic Resource
    Determination of paleoheat-flux using multiple thermal indicator tomography (1992)
    Springer
    Mathematical geology 24 (1992), S. 825-846 
    Details
    ISSN: 1573-8868
    Keywords: heat flux ; thermal models ; thermal tomography ; paleoheat flux
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Multiple thermal indicator tomography is a non-linear inversion procedure which permits simultaneous determination of geological, chemical kinetic, and thermal parameters in the burial and thermal histories of sediments. The procedure is based on inverting measurements with depth in a well of multiple thermal indicators, each of which must have experienced the same thermal history. For two wells from diverse geological settings, tomography is used to assess the paleoheat-flux variations with time most consistent with all the thermal indicator data. Resolution and sensitivity of the results are also addressed. For the case history of well X in the North Sea, with both vitrinite reflectance and sterane isomer thermal indicators, a generally decreasing heat flux from past to present is obtained roughly halving every 50 Ma. The activation energy for the sterane isomer is also determined simultaneously to be 42±20 kJ/mole. For the second case history of the Irma Mclean well in the onshore Gulf of Mexico, data from four thermal indicators are available: vitrinite reflectance, sterane and hopane isomers, and sterane aromaticity. A general decrease in paleoheat-flux from amount 2.8 heat flux units (HFU) at 100 MaBP to 1.25 HFU at the present day is obtained, the activation energy for the sterane isomer is simultaneously determined to be around 50±20 kJ/mole, while the corresponding values are around 80±20 kJ/mole for the hopane isomer, and around 65±20 kJ/mole for sterane aromatization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00890704
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  • 5
    Electronic Resource
    Electronic Resource
    Inversion of multiple thermal indicators: Quantitative methods of determining paleoheat flux and geological parameters IV. Case histories using thermal indicator tomography (1989)
    Springer
    Mathematical geology 21 (1989), S. 523-541 
    Details
    ISSN: 1573-8868
    Keywords: Thermal indicators ; inversion ; tomography ; paleoheat flux
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract A quantitative tomographic method to determine simultaneously several geological, geochemical, and geothermal parameters associated with reconstruction of the geohistory and thermal history of sediments in a well is presented. Using vitrinite reflectance data from the well Inigok-1, National Petroleum Reserve of Alaska, the numerical algorithm was tested and found to be effective in delineating the variation of heat flux with time. In addition, the size and timing of a major unconformity also were bracketed. Application of tomography using apatite fission track distributions with depth as a thermal indicator enabled not only the thermal history of two wells in the NW Canning Basin of Australia to be determined, but also the chemical parameters associated with fission track annealing to be constrained. Results of both the Alaska study and the Australian study were consistent with the qualitative behavior inferred from current geological models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00894667
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  • 6
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    Multiple scattering of seismic waves in fractured media: Crosscorrelation as a probe of fracture intensity (1985)
    In:  Pageoph, Luxembourg, Conseil de l'Europe, vol. 123, no. 1, pp. 503-542, pp. B02405, (ISSN: 1340-4202)
    Details
    Publication Date: 1985
    Keywords: Seismology ; Scattering ; Correlation ; cracks and fractures (.NE. fracturing)
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    BIBLIOGRAPHY SEISMOLOGY
  • 7
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    Binary model of Circinus X-1. I - Eccentricity from combined X-ray and radio observations (1980)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: A binary star model is used to account for the 16.59-d flaring behavior of the X-ray emission from Circinus X-1. The orbital eccentricity of 0.8 + or - 0.1 is derived from the X-ray light curve by assuming that the sharp X-ray cut-off every 16.59-d is a result of bound-free absorption in the primary star's stellar wind. The shape of the light curve has changed over the last eight years, and this is interpreted as due to orbital precession of the binary system. Simultaneous radio and X-ray observations of the flare from Circinus X-1 on February 1-5, 1978 are reported. These are accounted for within the framework of the model. The radio observations at 5 GHz are used independently to derive a high value of the orbital eccentricity (e = 0.7).
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics; 86; 3, Ju; July 198
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Some astrophysical consequences of the existence of a heavy stable neutral lepton (1978)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: It is suggested that a stable, massive, neutral lepton may dominate the present mass density in the universe. To investigate this assumption, attention is given to an analysis of extended gauge theories as they apply to a lepton with a mass of a few GeV/sq cm. A critical factor in the accuracy of the hypothesis is the actual mass of the lepton, and it is noted that the more massive the individual particle, the smaller the particle's aggregate contribution to the universal mass density. High energy accelerators could prove a useful tool in an empirical determination of the lepton's mass. It is further suggested that the lepton considered might provide the material in galactic halos, or supply the mass necessary to bind galactic clusters. A study of intergalactic annihilation radiation is expected to yield more data pertaining to the lepton's existence.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 223
    Format: text
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    NASA TECHNICAL REPORTS
  • 9
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    On equilibrium states of heated self-gravitating gas clouds cooling by conduction in an external gravitational field (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Exact analytic solutions are presented for equilibrium states of a self-gravitating one-dimensional cloud of gas, embedded in an external gravitational field due to a plane of 'stars' being heated at a rate proportional to the local gas density, and cooling by thermal conduction. It is found that the general topology of the solutions is such that the gas density has a minimum on the plane of 'stars', rising to an infinite but integrable peak away from the plane so that the total mass of gas in the cloud is finite. The results may be of interest in investigations of interstellar molecular clouds and of filamentary structures in supernova remnants as well as in the modeling of gas distributions around 'cocoon' protostars.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 242
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    On the birthrate of galactic supernovae (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The birthrate of galactic supernovae is estimated in three different ways. The three ranges overlap, and it is suggested that 70 + or - 35 yr represents a more realistic estimate of the rate than some that have previously been made. The galactic supernova remnants and their observed systematic brightness gradients perpendicular to the galactic plane imply a scale height of about 200 pc for the remnant progenitors and a galactic magnetic field scale height of about 300 pc. Long standing anomalies associated with the young remnant AD 1006, the galactic loops, and faint remnants, are accounted for by the brightness gradient effect. This provides firm, independent evidence for the validity of the remnant method of deducing the birthrate of galactic supernovae.
    Keywords: ASTROPHYSICS
    Format: text
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