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  • 1
    Electronic Resource
    Electronic Resource
    Conserved quantities and the inverse problem of reflection seismology (1990)
    Springer
    Pure and applied geophysics 132 (1990), S. 583-597 
    Details
    ISSN: 1420-9136
    Keywords: Reflection ; seismology ; conservation ; inversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We show that the time-dependent wave equation in both one and two spatial dimensions possesses quantities which are globally conserved. We show how these conserved quantities can be used to determine the characteristic impedance, the rock density and the elastic constant of the rock. We also demonstrate that the conserved quantities possess the capability of determining and/or bracketing the unknown component of the direct pressure response, which is required to begin downward continuation algorithms. Further, we demonstrate that the conserved quantities are always available irrespective of the source structure in time. Numerical instability, arising if the “filtering” due to the source structure is too harsh, can then be controlled to a degree by demanding that the conserved quantities be indeed conserved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876931
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  • 2
    Electronic Resource
    Electronic Resource
    Reflection of wide-angle acoustic waves from a high velocity interface (1990)
    Springer
    Pure and applied geophysics 134 (1990), S. 109-115 
    Details
    ISSN: 1420-9136
    Keywords: Wide-angle reflections ; planar shift
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract At angles other than normal incidence a pencil of plane acoustic waves, incident on a planar interface separating a low velocity medium from a high velocity medium, gives rise to a reflected pencil of waves which is laterally displaced from the illumination point of the incident pencil. The importance of this planar shift for understanding and interpreting wide-angle acoustic reflections is discussed, as is the variation of the equivalent depth below the interface at which a “point-like” reflection would be considered as an equivalent reflecting horizon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00878083
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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    Quantitative models of very high fluid pressure: the possible role of lateral stresses (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Terra nova 7 (1995), S. 0 
    Details
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Because of the occurrence of very large observed overpressure in a well located in SE Asia, numerical modelling has been undertaken to evaluate evolution of the sediments. The intensity of the excess pressure, close to lithostatic pressure, and the likely relation to induced, open-fracture anomalies, as well as evidence of large fluid transfers, all lead to the suggestion that the tectonic regime is related to the generation of high excess pressure. To verify this hypothesis, a 2D fluid-flow/compaction model (GEOPETTI) was used to test whether high excess pressure could be obtained without considering the effect of lateral stresses. While high excess pressures are possible, even if undercompaction is the only process considered, the distribution of fluid pressure with depth does not correspond to that observed, and the migration of fluids cannot be reproduced because of the extremely low permeability of the sediments. Accordingly, the model has been modified so that the effect of lateral stresses can be investigated through: (1) the value of the fracturing coefficient which controls the maximum overpressure that it is possible to generate; (2) the sensitivity of the system to a possible compressive event, which could squeeze the sediments laterally so that the rate of fluid expulsion would be greater than if the fluids were driven only by the mechanical load of sediments. Finally, the role of faulting or fracturing is discussed as a possible mechanism responsible for the upward transfer of fluid which can lead to an increase of excess pressure at depths shallower than the depth where excess pressure was first generated, a mechanism also leading to high excess pressure. Moreover, this mechanism allows for a good reproduction of observed excess pressure distributions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3121.1995.tb00669.x
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  • 5
    Electronic Resource
    Electronic Resource
    Age interpolation (1986)
    [s.l.] : Nature Publishing Group
    Nature 323 (1986), S. 471-471 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THE equivalence of depth to age in a stratigraphic sequence can normally be established (radiometrically or palaeon-tologically) at only a finite number of discrete points. Age estimation between such points is impossible because sedimentary accumulation is the result of sedimentation minus ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/323471a0
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  • 6
    Electronic Resource
    Electronic Resource
    On the birtrate of galactic supernovae (1981)
    Springer
    Astrophysics and space science 74 (1981), S. 273-286 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The birthrate of galactic supernovae is estimated in three different ways: (i) on the basis of the historical record (eight events) the mean time interval between supernovae, τ, is considered to be in the range τ=60±40 yr; (ii) on the basis of an approximate total of 120 supernovae events in hundreds of other galaxies, considered similar to our own, the interval obtained is in the range τ=70±50 yr; (iii) on the (iii) on the basis of the 130 supernovae remnants in our own Galaxy, the interval is estimated to be in the range τ=80±30 yr. The three ranges overlap, and we suggest that 70±35 yr represents a more realistic estimate of the rate than some that have previously been made. The galactic radio supernovae 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 indicate that the galactic magnetic field's scale-height is about 300 pc. Long standing anomalies associated with (a) the young remnant AD 1006, (b) the galactic loops, and (c) faint remnants, are accounted for by the brightness gradient effect, providing independent, and firm, corroborating evidence for the fundamental validity of the remnant method of deducing the galactic supernova birthrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00656439
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  • 7
    Electronic Resource
    Electronic Resource
    Some notes on entropy measures. II. The relative entropy matrix and the positivity constraint (1989)
    Springer
    Mathematical geology 21 (1989), S. 843-852 
    Details
    ISSN: 1573-8868
    Keywords: Entropy ; positivity ; autocorrelation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Based on the maximum entropy concept with the number of “bins” (class intervals), N, maximized in terms of residual errors in sampling of the system, the residual entropy matrix (REM), which is intrinsically positive definite, is sampled uniformly at N equal intervals in entropy space. The mandatory constraint of positivity shows that the finitely sampled REM then provides estimates on the magnitudes of “missing” components of the autocorrelation sequence describing REM. If the mandatory constraint is relaxed to its limit, the resulting prediction for REM is identical to Burg's (1967) maximum entropy algorithm. The advantages are that assessments can be made: (i) whether the “missing” components are known accurately enough that no further measurements are needed; (ii) the N equal intervals of the entropy measure are sufficient to provide resolution on the REM for each and every sample; or (iii) whether finer interval resolution is needed to extract information for a particular sample.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00894451
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  • 8
    Electronic Resource
    Electronic Resource
    Inverse methods and kinetic models of hydrocarbon generation: III. Case histories for autoclave product analysis (1991)
    Springer
    Mathematical geology 23 (1991), S. 325-347 
    Details
    ISSN: 1573-8868
    Keywords: hydrocarbons ; kinetics ; inverse methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract From a determination of the transformation matrix for three pyrolysis product experimental data sets, an examination is given of both the applicability of the laboratory experimental data to the modeling of oil cracking in a sedimentary basin, and of the appropriateness of an inverse model. The results of the laboratory experimental data sets, which were done under different thermodynamic conditions and using different sources, show that the transformation matrix varies over each data set and also with time. Therefore, it is necessary to check the data sets before applying them to a basin for hydrocarbon modeling. The laboratory experimental data taken at lower temperature and over longer times appear more pertinent for the construction of an oil-cracking kinetic model suitable for geologic conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02065786
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  • 9
    Electronic Resource
    Electronic Resource
    Book reviews (1989)
    Springer
    Mathematical geology 21 (1989), S. 395-400 
    Details
    ISSN: 1573-8868
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00893700
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  • 10
    Electronic Resource
    Electronic Resource
    Book review (1990)
    Springer
    Mathematical geology 22 (1990), S. 871-877 
    Details
    ISSN: 1573-8868
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00890668
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