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- Volume 6, Issue 3, 1958
Geophysical Prospecting - Volume 6, Issue 3, 1958
Volume 6, Issue 3, 1958
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REFLECTION SHOOTING TECHNIQUES IN THE NETHERLANDS*
More LessABSTRACTReflection quality in the Netherlands is extremely variable, ranging from very good to very poor. It is believed that the variation is caused mainly by the changing surface conditions. This suggestion is discussed in the light of available geological data.
Several examples are given showing the usefulness of making broad band recordings on normal reflection spreads.
The combination of data obtained from the study of the surface conditions and from broad band seismograms is used to select the best shooting method.
Some suggestions are made regarding seismometer and shot‐hole patterns, shot medium and the choice of filters.
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THEORETISCHE UNTERSUCHUNG ÜBER DIE MEHRFACHAUFSTELLUNG VON GEOPHONEN*
More LessABSTRACTThe receiving of seismic waves by multiple geophones (geophone‐group) is described by a system of coupled differential equations considering only effective resistances. For so‐called symmetrical connections of the geophone‐group which are used in practice nearly in all cases, a method can be given for solving this system of differential equations. The solutions so derived are valid for seismic waves of any shape. The calculation takes into account the coupling of the geophones as well as the building‐up transient oscillations.
A suitable measure of superposition is defined, based on the energy transferred during the receiving of the seismic waves. By this means effects similar to interference are investigated which occur at the geophone‐group. As a numerical example calculation is carried out for a geophone‐group consisting of three geophones which is excited by impulse‐shaped waves of the form of a damped sinusoidal oscillation. The occurring effect of superposition and its dependence on direction are discussed. In the appendix formulae are presented for investigation of further numerical examples.
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LA MESURE DE LA VITESSE VERTICALE PAR LE CAROTTAGE CONTINU (CVL); PRECISION DES MESURES ET DISCUSSIONS DE QUELQUES RÉSULTATS*
More LessThe introduction of the CVL and the “core speed tester” (or ultra sonic velocity meter) have enabled the geophysicist to complement large‐interval, average velocity measurement of sedimentary formations (obtained by conventional well velocity surveys, “Gardner” velocity shots, etc.) by small interval, detailed study of the velocity of particular strata, in situ or in the laboratory. The significance of laboratory velocity measurements on cores is affected by irreversible alterations of the core. At first the integrated time curve of the CVL, calibrated with a skeleton conventional velocity survey, seemed to assure the precision of the interval velocity. Later it was realised that variations of the “Delay Time” (compensation for Mud Travel Time in the single receptor CVL), failure to identify the first energy arrival, etc., could cause errors in the interval velocity measured. These errors can be, detected and reduced by increasing the number of control points of the well survey, running logs down and up the hole, overlapping, and also by the comparison of the Continuous Velocity Logs for neighbouring wells and for various strata in a given well.
Despite these errors, the C VL has been found extremely useful, not only for the determination of average velocity, the identification of reflecting strata, and of refraction markers, but also for geological correlations between wells, the determination of maximum porosity and detailed studies of the parameters affecting the velocity of sedimentary rocks.
The relation between interval velocity and porosity is discussed and a hypothesis that the low velocity of argillaceous, low‐porosity limestones may in part be due to the total fluid contained is put forward.
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SYNTHETIC SEISMOGRAMS FROM CONTINUOUS VELOCITY LOGS*
By H. DÜRSCHNERABSTRACTIn this paper a method of calculating synthetic seismograms from continuous velocity logs (CVL) is presented and described in detail.
The seismic velocities on the CVL are frequently and rapidly changing. Therefore a seismic field‐record consists of a great number of reflections with different sign and amplitude. The sum of all reflections forms the seismogram.
The first part deals with some relations between the log, the reflection‐layers, and the normal field‐record, with special emphasis on the influence of the seismic amplifier.
Then several assumptions are made for the construction of the synthetic seismograms. Finally some examples and applications are given.
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AN ACCURATE GRAPHICAL METHOD FOR INTERPRETING SEISMIC REFRACTION LINES*
By F. W. HALESABSTRACTA method of refraction computing is described which establishes the two points of incidence at the surface of the ray‐paths from any point on the refractor when observed from opposing directions. The distance between these points is used to determine the radius and the centre of a circle to which the refractor must be tangential. The matching of forward and reverse data is intrinsic in the method so that the resulting profile is automatically positioned in depth. It is shown that if the effects of dip are neglected, errors are introduced in the derived radius and also in the position of the centre but these errors are shown to cancel each other almost exactly.
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REVIEWS
The Geophysical Journal of the Royal Astronomical Society, Volume 1, No ‐, March 1958. Published by the Royal Astronomical Society, Price $ 1, Annual Subscription $ 3.
Grundlagen der Geoelektrik by A. P. Krajew. herausgegeben unter der Gesamtredaktion von Prof. Dr. Otto Meisser, VEB‐Verlag Technik, Berlin, 1957, Price D.M. 28.
Grundlagen für die Auswertung von magnetischen Anomalien (insbesondere Z‐Kompo‐nente)– (Fundamentals of the Interpretation of Magnetic Anomalies, Especially of the Vertical Component) by K. Köhler, Freiberger Forschungshefte C41 Geophysik, Akademie‐Verlag, Berlin, 1958.
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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)