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  • Articles  (5,321)
  • 1955-1959  (5,321)
  • 1956  (5,321)
  • Geosciences  (3,872)
  • Mathematics  (1,449)
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  • Articles  (5,321)
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  • 1955-1959  (5,321)
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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 4 (1956), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: An experimental arrangement is described using an electric spark as source and barium titanate as a detector. Model experiments were made in water with the source mounted above the surface. The effect on the pulse shape on transmission through the air-water interface and the change of pulse shape with depth were investigated. A number of profiles are presented of reflections from a slate slab immersed in the water with different arrangements of the model and detector.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 4 (1956), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The background of automatic data processing as well as other improvements in prospecting methods is almost certainly economic. Consciously and intentionally or intuitively and even subconsciously, economic forces are the drive for improvements.Automatic processing can contribute to the increasing utility of seismic data. Reduction in the amount of routine work will permit talented people to utilize their time creatively on the more difficult problems. At the same time automatic reduction will provide for a greater volume of work. These two aspects will probably provide the first effective pressure for a high degree of automation.It is to be expected, however, that the ultimate and greatest value will be better interpretation; possibly more detail, possibly clearer more definitive interpretation, possibly both.Time concepts in the processing of seismic data are, of course, vital; either in simple time corrections of either static or dynamic nature or in treatment of signals in the time domain.Much development work is needed before these advantages can be realized. Principal development needed is an increase in dynamic range in the overall system.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 4 (1956), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Book review in this articleHarold M. Mooney and W. W. Wetzel: “The Potentials about a Point Electrode and Apparent Resistivity Curves for a Two-, Three- and Four-Layer Earth”, The University of Minnesota Press, Minneapolis. Price $ 18.–.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 4 (1956), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The term shallow refraction, as used in this paper, refers to investigations confined to the superficial layer of rocks, composed primarily of unconsolidated material. To define the scope of the discussion it will be assumed that the term shallow refraction applies to work of which the lower limit is approximately 300 feet and the upper of the order of a few feet. The consideration of the small magnitude of quantities measured (distances and times) determines the perspective of the problems involved, since difficulties encountered in the interpretation, although equally disturbing whether in deep or shallow work, will cause a greater percentage of error in the latter case. The purpose of this paper is to discuss and illustrate these problems. The factors considered include the location of the geophone spread in relation to the topography of the site, influence of the ground conditions in the vicinity of geophones on recorded times, consideration of the shallow uphole shots and problems arising from the repeated use of the same shothole. The rapid variation in the vertical velocity of the overburden and errors due to it are discussed together with the effects of a non homogeneous unconsolidated material and velocity reversal. The effects of the ill-defined solid rock surface are also considered. It appears that as the depth of investigations becomes shallower, the limits of the practical capabilities of the method are approached, because the differences between the theoretical assumptions and the actual conditions become more pronounced.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 4 (1956), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Experiments carried out using charges of up to 200 lbs. at a distance of about 20,000 ft. from the geophones suggest that the amplitude of the refracted wave ground motion is roughly proportional to the weight of charge. Simple energy considerations lead one to expect a relation of a form in which velocity amplitude is proportional to W.An explanation of the observed relation may be based on a theory according to which the efficiency of the explosion increases with the source size, that is the distance from the source at which the pressure wave of the explosion ceases to cause permanent deformation of the surrounding medium.The above theory was further confirmed by measurements of the radius of the cavity produced by explosions of charges of different size in clay. Also, explosion of charges in artificial water-filled cavities were found to give seismic wave amplitudes three or four times greater than those produced by the same charge in a narrow hole. It is possible that these observations explain in part why the charges required in marine refraction experiments are very much smaller than those needed in refraction work on land, but additional reasons for this difference are also discussed.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 4 (1956), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: In N.W. Germany multiple reflections have been observed in numerous areas. They are not curiosities but represent true problems.In many cases these multiples are recognizable by routine Δt analysis of the records. Sometimes the Δt anomalies are so great that multiples can be recognized without any computational work, merely by looking at the records. This is due to the great contrast between the interval velocities of the Tertiary and of the Upper Cretaceous. One example is discussed fully.Most of the multiples are of the type AB (a multiple caused by reflections at two different reflectors A and B, and at the surface). It is also shown (by a rough estimate) that this type of multiple is theoretically the most probable. Finally, the interference between the two components of AB (one multiple being reflected first at A, then at B, and the other reflected first at B, then at A), and its appearance in constructed examples, are discussed.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 4 (1956), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The paper describes a vertical component magnetometer for field work whose magnet system is provided with a torsion axis and in which torsion serves as a standard of measurement. When a measurement is taken the magnetic axis of the system is brought back into the horizontal position by altering the angle of twist (null-method). The angle of twist is thus a direct measure of the vertical intensity. The instrument is within wide limits independent of the magnetic north-south direction and may therefore be set up in practically any position. The magnet system is temperature compensated, well damped and provided with an automatic clamping device. With a scale value of 25 gammas per scale division the range of the instrument for direct measurements is 65000 gammas. A tripod of special design enables a measurement to be taken in about one minute. The weight of the torsion magnetometer inclusive of tripod is only 2.9 kg (6.4 lb).
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 4 (1956), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Since harmonic analysis of seismograms seems to become more familiar in the interpretation of seismic data, the author presents the results of a thorough check analysis. Following a fixed scheme, one seismogram is analysed by means of a mechanical analyser (system Mader-Ott). Standard deviation of Fourier coefficients is examined, and scattering in phase values is discussed. At the best, in the range of maximum amplitudes of the spectrum, the method yields 6% in phase scattering. At the worst, on either side of the spectrum, 13 % are obtained. Generally 8 % have to be taken in account. (Percentages in periods of partial-waves of the analysis). The results are in accordance with former routine analysis (Korschunow, 1955).
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 4 (1956), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The well known quantities, delay and intercept times, can be made fully useful in the interpretation of multilayer refraction problems dealing with small undulating dips.The identification of the individual refractors is made by the use of reciprocal and intercept times and by applying an additional and useful relationship, namely that the delay time profile between two shot-points should match the half-intercept time profile when calculated using the true velocity of the refractor.With a suitable arrangement of shot-points this relation permits us to obtain the true horizontal velocity of a refractor from one direction of shooting only.Presentation of the refraction results in the form of time sections, similar to those used in reflection surveys, is often desirable. These sections can be converted easily into depth sections, once the overburden velocities are defined.The use of the method is limited not only by the dip, but also by the depth of the refractor. Deep refractors can be, however, worked out by this method, by reducing a multilayer problem to that of two layers, using again the delay times.
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 4 (1956), S. 0 
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The parameters which characterize an explosive are derived from laboratory tests and none is directly usable for seismic purposes. Another one, derived from field experiments is proposed in this paper. It allows the comparison of two different explosives. The test must be conducted with care. Precautions concerning the equipment and the shot point detailed. The first available results suggest that the new parameter does not depend on the size of the charge nor on the shooting conditions, though the experimental data are not numerous enough to allow a general statement. It is shown how a coefficient of seismic efficiency can be used for selecting an explosive; and considerable amounts of money can be saved by the best choice. More studies on the generation of artificial seismic waves would be highly profitable.
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