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- Volume 12, Issue 2, 1964
Geophysical Prospecting - Volume 12, Issue 2, 1964
Volume 12, Issue 2, 1964
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GRATICULES FOR THE COMPLETE DETERMINATION OF THE MAGNETIC FIELD OF HOMOGENEOUSLY MAGNETIZED CYLINDRICAL BODIES WITH ARBITRARY CROSS SECTION AND FINITE LATERAL EXTENSION*
By KLAUS HELBIGABSTRACTGraticules are known for the calculation of the magnetic field of homogeneously magnetized “two‐dimensional” structures. For bodies whose lateral dimensions are comparable with the dimensions of the cross section and/or the distance between the point of observation and the structure, these graticules allow an approximative computation of the field in the plane of symmetry only. The degree of approximation can be improved by means of end corrections, but the amount of work involved increases rapidly. Moreover, even with end corrections the applicability of the graticules is still restricted to cases of rather simple geometry.
In this paper, a set of graticules is proposed which already incorporates all end corrections. The set consists of three graticules, and it can be shown that at any point of observation lying outside the body each graticule needs be applied once only in order to calculate any component of the magnetic field produced by a homogeneously magnetized cylinder of arbitrary cross section, finite lateral extension and arbitrary spatial orientation.
Curves and tables have been prepared, which allow the construction of the graticules under consideration. The application is illustrated by a hypothetical example. Possibilities for further improvements of the method are discussed.
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DESIGN OF SUB‐OPTIMUM FILTER SYSTEMS FOR MULTI‐TRACE SEISMIC DATA PROCESSING*
Authors M. R. FOSTER, R. L. SENGBUSH and R. J. WATSONABSTRACTUsing optimum filter theory as a starting point, we describe a method for the design of practical multi‐trace seismic data processing systems. We assume the inputs to be the superposition of signal, coherent noise, and incoherent noise. The signal and coherent noise moveouts are described statistically by their probability densities. Our approach is to split the system into two stages. The first stage achieves optimum noise suppression but distorts the signal. The signal distortion is reduced in the second stage by an optimum finite memory inverse filter.
The system that is obtained using our method of design depends upon the form of the probability density functions. We show two examples, ghost suppression and velocity filtering. In ghost suppression we choose a model with moveouts known exactly, which corresponds to delta functions for the probability densities. In velocity filtering the signal and coherent noise moveouts are equally probable within non‐overlapping ranges.
The resulting system in each case is both simple and effective. In ghost suppression a simple shift and subtract cancels the coherent noise. The signal distortion is reduced by an inverse filter. The velocity filter system consists of differentiated moving averages applied to each trace, followed by a 90° phase shift and a low pass filter.
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SOME PHYSICAL ASPECTS OF SEISMIC SCALING LAWS FOR UNDERWATER EXPLOSIONS*
By H. BURKHARDTAbstractThe paper deals with quantitative seismic measurements near underwater explosions. The blastings were carried out in an artificial small pond, the records were taken in adits, situated vertically below the charge. The range of charges extended from one detonator to 200 g of Ammon‐Gelit explosive.
Conventional seismic scaling by comparing amplitude and size of charge does not yield a simple power law, the exponent being larger for smaller charges and vice versa. This result is due to the different frequency‐spectra of the seismic pulses, as shown by harmonic analysis. In contrast to this, the seismic energy as calculated from the records is directly proportional to the size of charge over the whole range.
During the Lago Lagorai experiments in 1962 some quantitative seismic measurements near the shot point were also carried out. The relevant results are compared with the preceding ones and some differences are discussed.
Some conclusions can be drawn:
- 1 The normal methodes, investigating the amplitude only, gives in many cases no clear description; this is especially true for nearby measurements with widely varying frequencies. Therefore it is suggested to extend conventional seismic scaling by including information on the frequency‐spectrum and the kinetic energy of the seismic signal.
- 2 In order to get clear experimental data for theoretical investigations, it is necessary to extend the recording over a half‐space, i.e. in adits or boreholes.
- 3 Influences of shape and size of the lake, in which the shots are fired, should be taken into account, too.
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THE USE OF ISOCHRON CHARTS IN SEISMIC REFRACTION INTERPRETATION*
By R. N. NEALEABSTRACTA graphical method of interpreting refraction data is presented based upon wave front construction in which different overburden velocity distributions can be used. The wave fronts are constructed with the aid of an Isochron Chart. By using two or more Isochron Charts, the effect of velocity variations above the refractor of interest can be allowed for.
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EIN NÄHERUNGSVERFAHREN ZUR BERECHNUNG VON GRAVITATIONS‐ANOMALIEN FÜR BELIEBIG GEFORMTE INHOMOGENE MASSEN MIT DEM DIGITAL‐RECHNER*
By GY. SZELÉNYIABSTRACTBy this method an approximation of gravity‐anomaly of an inhomogeneous mass with any form is calculated. The mass is inbedded in a homogeneous medium. The density of the medium differs from the density‐distribution of the mass.
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BOOK REVIEWS
Book Review in this Article:
H. Israel and A. Krebs, Nuclear Radiation in Geophysics
B. A. Tkhostov, Initial Rock Pressures in Oil and Gas Deposits
John S. Steinhart and Robert P. Meyer, Explosion Studies of Continental Structure
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Volumes & issues
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Volume 72 (2023 - 2024)
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Volume 71 (2022 - 2023)
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Volume 70 (2021 - 2022)
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Volume 69 (2021)
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Volume 68 (2020)
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Volume 67 (2019)
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Volume 66 (2018)
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Volume 65 (2017)
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Volume 64 (2015 - 2016)
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Volume 63 (2015)
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Volume 62 (2014)
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Volume 61 (2013)
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Volume 60 (2012)
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Volume 59 (2011)
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Volume 58 (2010)
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Volume 57 (2009)
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Volume 56 (2008)
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Volume 55 (2007)
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Volume 54 (2006)
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Volume 53 (2005)
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Volume 52 (2004)
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Volume 51 (2003)
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Volume 50 (2002)
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Volume 49 (2001)
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Volume 48 (2000)
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Volume 47 (1999)
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Volume 46 (1998)
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Volume 45 (1997)
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Volume 44 (1996)
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Volume 43 (1995)
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Volume 42 (1994)
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Volume 41 (1993)
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Volume 40 (1992)
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Volume 39 (1991)
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Volume 38 (1990)
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Volume 37 (1989)
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Volume 36 (1988)
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Volume 35 (1987)
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Volume 34 (1986)
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Volume 33 (1985)
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Volume 32 (1984)
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Volume 31 (1983)
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Volume 30 (1982)
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Volume 29 (1981)
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Volume 28 (1980)
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Volume 27 (1979)
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Volume 26 (1978)
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Volume 25 (1977)
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Volume 24 (1976)
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Volume 23 (1975)
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Volume 22 (1974)
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Volume 21 (1973)
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Volume 20 (1972)
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Volume 19 (1971)
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Volume 18 (1970)
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Volume 17 (1969)
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Volume 16 (1968)
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Volume 15 (1967)
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Volume 14 (1966)
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Volume 13 (1965)
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Volume 12 (1964)
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Volume 11 (1963)
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Volume 10 (1962)
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Volume 9 (1961)
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Volume 8 (1960)
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Volume 7 (1959)
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Volume 6 (1958)
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Volume 5 (1957)
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Volume 4 (1956)
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Volume 3 (1955)
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Volume 2 (1954)
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Volume 1 (1953)