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- Volume 18, Issue 4, 1970
Geophysical Prospecting - Volume 18, Issue 4, 1970
Volume 18, Issue 4, 1970
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POINTE AUTOMATIQUE*
Authors P. BOIS and M. LA PORTEAbstractThe automatic picking of seismic sections replaces the slow and painstaking task of manual reflection plotting with rapid and economical processing by computer. Essentially, reflection picking is a decision‐making problem which also can be considered as a sort of filtering. Mathematically this means multiplying the seismic data matrix by a more or less complex decision operator.
For the sake of economy, we give an initial solution for simple cases which only require easily automatized decision‐making criteria.
We describe another more elaborate method for use in examining seismic phenomena which are more difficult to spot.
The process used is based on the recognition of shapes and consists first of all of determining a series of characteristics capable of identifying each reflection on each trace and then of comparing these different characteristics from trace to trace so as to be able to judge the continuity or discontinuity of the reflections.
Automatic picking thus leads to a schematic time‐section in which only the horizons found by calculation are retained. An automatic migration program then transforms this time‐section into a depth‐section.
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SUR LA CORRELATION EXISTANT ENTRE POROSITE ET FAGTEUR DE FORMATION DANS LES SEDIMENTS NON CONSOLIDES*
By E. ACCERBONIAbstractThe relationship between porosity and formation factor in unconsolidated homogeneous and anisotropic sediments without granule‐liquid interaction is investigated by introducing a parametric model that simulates a variable cellular structure.
In this hypothesis, porosity φ and F‐factor are calculated for some fixed values of the parameter, solving numerically two integral expressions.
From these calculations the form of the function φ=f(F), corresponding to the proposed model, has been deduced. This relation is in very good agreement with Archie's empirical law for unconsolidated sands which requires that F=φ‐‐1,3. Therefore it seems that the validity of Archie's law is theoretically confirmed for the unconsolidated sediments considered in this paper.
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DETERMINATION OF ELECTRIC ROCK PARAMETERS FROM THE FIELD STRUCTURE OF A MAGNETIC DIPOLE*
Authors W. BITTERLICH and A. W. KELLNERAbstractIn the theoretical part of the present paper, formulas have been analyzed for a magnetic dipole in a homogeneous and unbounded medium. The magnetic field is elliptically polarized in the region between the quasistatic zone and the far field. Since the position and the shape of the polarization ellipses depend on the complex wave number, k, it is possible to determine k by measuring the polarization ellipses. From k, the conductivity and the dielectric constant of the medium are easily calculated. The functions required for the measuring method have been computed and plotted in graphs.
In the experimental part it was examined how far the theory may be applied to measurements of propagation through rock at frequencies ranging from 100‐1000 kHz. These measurements showed that reasonably defined mean values of rock parameters can be given only if the deviations of the field from the theoretically expected field are not too high. These deviations have been named field distortions and have been examined by means of statistical methods (variance ratio tests). Gallery cavity and inhomogeneity or anisotropy of the medium account for these distortions.
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ARRAYS AND NOMOGRAMS FOR ELECTRICAL RESISTIVITY EXPLORATION*
By TSVI MEIDAVAbstractA number of electrical resistivity arrays are available to the exploration geophysicist in the conduct of vertical or horizontal profiling. The advantage of using central‐type arrays which produce large potential drops, such as the Wenner or the Schlumberger, must be weighed against the ease of acentral arrays such as the polar and equatorial arrays.
A series of nomograms has been designed to provide a means of rapid calculation of the potential drop to be obtained by any of the various central and acentral arrays, as a function of apparent resistivity, electrode spacings and available transmitter power. The same nomograms may also be used for approximate computation of the apparent resistivities in routine surveys. However, the accuracy of resistivity calculation is directly related to the accuracy of drawing lines between the scales and hence is rather limited in reduced‐size nomograms in this paper.
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A FAST METHOD FOR DETERMINING THE LAYER DISTRIBUTION FROM THE RAISED KERNEL FUNCTION IN GEOELEGTRICAL SOUNDING*
By O. KOEFOEDAbstractIn a previous publication (Koefoed 1968) a function called the “raised kernel function” has been introduced as an intermediate function in the interpretation of resistivity sounding data, and methods have been described both for the determination of the raised kernel function from the apparent resistivity function, and for the determination of the layer distribution from the raised kernel function.
In the present paper a procedure is described by which the second step in this interpretation method–i.e. the determination of the layer distribution from the raised kernel function–is considerably accelerated. This gain in interpretation speed is attained by the use of a standard graph for a function which defines the reduction of the raised kernel function to a lower boundary plane.
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A PULSE COMPRESSION TECHNIQUE USING COHERENT LIGHT*
Authors M. BARBIER and J. POULEAUAbstractSeismic methods of the Vibroseis type require a cross‐correlation between received and transmitted signals. This process is now carried out with computers with convolvers but was first analogically realized. When the amount of data to be processed becomes very important as for marine seismic, it might be worth considering the principle described in this article. Dynamic range determination and synthetic examples are shown.
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A PNEUMATIC SEISMIC ENERGY SOURCE FOR SHALLOW WATER / MARSH AREAS*
Authors E. C. BREDE, R. C. JOHNSTON, L. B. SULLIVAN and H. L. VIGERAbstractNon dynamite seismic energy sources have shown only limited success in difficult shallow‐water or marsh prospect areas, and none have applicability to both environments. Recently, a method has been devised to adapt a marine pneumatic source for operation in abrasive surroundings. A system composed of four of these modified sources together with associated emplacement and retrieval mechanisms has been developed and has proven to be a reliable and efficient seismic energy source for both shallow‐water and marsh applications.
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SISMIQUE REFLEXION EN EAU PROFONDE*
Authors J. CASSAND, J. P. FAIL and L. MONTADERTAbstractReflection seismic profiles from the South‐East part of the Bay of Biscay are shown. They where shot in deep waters with continuation of some of the lines on the continental shelf.
Flexotir with one or two guns was used with 300% CD.P. Total charge weight per shot was 50 or 100 grams according to the number of guns. Ship speed was 6.5 knots and 1000 kilometers were recorded in 9 days. Trace intervals being 60 meters, good detail can be seen on the sections.
Good reflections were obtained in places where water was 4000 meters deep. Penetration is often 5 seconds (2 way‐time) below sea bottom.
Flexotir is a seismic method well suited for oceanographic surveys.
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ULTRA DEEP SCHLUMBERGER SOUNDING AND CRUSTAL CONDUCTIVITY STRUCTURE IN SOUTH AFRICA*
Authors J. S. V. VAN ZIJL, P. L. V. HUGO and J. H. DE BELLOCQAbstractA second deep Schlumberger sounding has been carried out in South Africa, this time using a newly completed power transmission line, not yet in sevice, as emission line. The maximum current electrode separation attained was 600 km. The sounding was situated on a shield area with a thin cover of sedimentary rocks (Karroo System) overlying the archaean granite. The center was chosen near to the village of Dealesville.
It is shown that lateral effects at large AB spacings are unlikely, but due to numerous dolerite intrusions in the sediments surface electrode effects must be guarded against; thus AB positions were chosen by geologists. Because of a low signal/noise ratio at large AB spacings the measurements were treated statistically; in particular, the elimination of non‐random events improved the measuring accuracy.
Although a thin conducting layer at the base of the sedimentary succession decreased the resolution of the sounding curve, the results, which were interpreted with the aid of a computer, show positively that
- (a). the crust is multi‐layered with a highly resistant portion having a minimum resistivity of 15000 ohm.m and
- (b). a good, thick conductor appears as the final layer.
The Dealesville results are in complete agreement with those obtained from the first deep Schlumberger sounding at Pofadder (Van Zijl 1969) except that the transverse resistance of the lowermost resistant crust is about 100% larger at Pofadder due probably to a second period of metamorphism. Both electrical studies support the view of a dehydrated lower crust (granulite facies).
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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)