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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 8 (1960), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Reflected refractions are considered as the limiting case for ordinary steeply dipping reflections. Particularly, reflected refractions may be constructed (migrated) according to the same principles as ordinary reflections. In view of the inherent inaccuracy of the velocity data, there is no discrimination between reflected refractions and other steep events by methods of construction. Velocity determinations from reflection data also show a continuous transition from steep reflections to reflected refractions. I.e., it is impossible to discriminate by seismic ray methods between reflected refractions and other steep events.If disturbing, steep events may be attenuated to a great extent by special shot and geophone set-ups. Also in this connection it is unnecessary to distinguish between reflected refractions proper and steep reflections.It seems to be more rational to consider steep events as ordinary steep reflections in the beginning of a survey, because otherwise real structural indications might possibly be thrown away.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 24 (1976), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 21 (1973), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 15 (1967), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The problem of elastic waves–from point sources–in layered media is solved in a general and elementary way. Only the simplest principles of the Theory of Functions are necessary. The solutions can immediately be used for numerical applications.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 12 (1964), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The exact responses of plane interfaces to incident spherical compressional waves are calculated by an electronic computer. The reflected part of the response is shown for various positions of the ‘shot’ and of the ‘receiver’ as well as for various velocity contrasts. This makes it possible to study some features of the reflection process, especially the behaviour beyond the critical angle.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 9 (1961), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The reflection and transmission coefficients for vertical incidence can be very closely approximated by computing the direct-reflected and the direct-transmitted portion for transition layers, and letting the thickness approach zero. The same procedure can then be applied to the general case of oblique incidence, which yields approximate values of the respective coefficients, including those of the converted waves. The approximate values compare well with the exact values calculated by Muskat and Meres (1940).These approximations might be adequate for all cases occurring in reflection seismic prospecting. They can also be used, possibly even more profitably, for the derivation of some rules governing the reflection process. The influence of Poisson's ratio can be read more or less directly from the approximate formulas. All converted waves depend primarily on the ratio of the shear velocities.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 8 (1960), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: By direction shooting is understood a method of continuous seismic profiling with shots distributed along the total length of the geophone spread, the shots being fired either with time delays in the field, or, recorded singly on magnetizable material and composited with time-delays. Therewith, the subsurface can be probed in any desired direction, enhancing reflections from these directions and attenuating or eliminating events from all other directions. For each reflection, the correct delay can be found by a simple procedure from a single trial record.A complete description of the method is given, inclusive of all procedures and proofs pertaining to it. Synthetic examples and field examples illustrate the efficiency of the method and its resolving power.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 40 (1992), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The effect of wave-equation migration on amplitudes is determined. This effect is derived for zero-offset traces and for second-order approximations of the traveltimes. Three steps are followed: firstly, the amplitudes of zero-offset traces are established; secondly minus half the traveltimes are used as input for downward continuation in migration (forward in space and time); thirdly, the amplitudes of the migrated events are determined by downward continuation (at zero-traveltimes).Layered models (piles of homogeneous layers) with smooth interfaces are used. The determinants of the 2 × 2 matrices B0 obtained for these models are responsible for the main effect on migration. The migration result primarily depends on the overburden as the inverse of det (B0). Drastic effects can occur over small distances. For weakly reflecting media, it is confirmed that wave-equation migration gives “correct” results (but the input data must be multiplied by V0T0), i.e. amplitudes proportional to the reflection coefficient. For any velocity changes, the inverse of det (B0) will, in general, give inaccurate migration amplitudes and inaccurate lithological interpretations. In a simple step, true amplitude migration, or exact migration, is derived from our results.It is assumed that no focus phenomena are present. The effect of buried foci is discussed briefly.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 10 (1962), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The exact expressions for the reflection and refraction of homogeneous spherical compressional waves at the plane contact between two semi-infinite media are obtained by a new simple method. Whilst its general ideas were outlined in a previous paper (Bortfeld 1962) dealing with some special interfaces, this method is now applied to all kinds of contact (solid-solid, solid-fluid, fluid-solid, solid-free, fluid-fluid, fluid-free). By some improvements, the treatment of the general case is even more simple than the previous one of the special cases.Integrating the potentials for sinusoidal excitation over the circular frequency and adding the static potentials yields expressions for the step-response which consist of (infinite) single integrals of elementary functions. By a single application of Cauchy's theorem, the complete set of wavefronts is obtained and the step-response is put into forms suitable as a basis for numerical calculations. The responses for arbitrary source excitations are given in the usual way by superposition integrals.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: A new method of treating three-dimensional elastic wave problems is described by applying it to the most simple case of the reflection and transmission of arbitrary homogeneous spherical compressional waves at plane liquid-liquid interfaces. The case of plane solid-solid interfaces with equal shear velocities and equal densities can be treated under the same heading.The step-response is obtained from the expressions for sinusoidal source excitation by a simple direct integration. The solutions for arbitrary source excitations are given in the usual way by the superposition integral. The solutions are proved by inserting them into the differential equations, followed by an application of the uniqueness theorem. The method is simple; all stages of establishing the solution (with the exception of the proof) are carried through in detail.
    Type of Medium: Electronic Resource
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