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- Volume 11, Issue 3, 1963
Geophysical Prospecting - Volume 11, Issue 3, 1963
Volume 11, Issue 3, 1963
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ORIGIN OF OIL*
More LessAbstractAll sorts of organic matter preserved under anaerobic conditions and transformed in reducing environments may form components of natural crude oils; such oils are linked to sapropel deposits by their contents in porphyrins and trace metals.
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CALCUL DE LA FORME ?UNE STRUCTURE HOMOGENE A PARTIR DE SON CHAMP GRAVIMETRIQUE*
By M. LA PORTEAbstractA given gravity field is considered; it is assumed to be due to a homogeneous structure.
The method of computation presented here makes it possible to determine one of the limits of such a structure (upper or lower), provided the other limit and the density contrast of the structure are known.
Among the various applications of this method, location of the upper limit of buried palaeo‐reliefs can be mentioned.
The calculation is designed for electronic computers, and uses one of the properties of the downward continuation of the gravity field. The process is iterative and takes place at the corners of a regular grid.
Modern computers can handle several thousand points at a time.
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TWO METHODS APPLICABLE TO COMPUTERS FOR EVALUATING MAGNETIC ANOMALIES DUE TO FINITE THREE DIMENSIONAL BODIES*
More LessAbstractTwo methods applicable to computers are described which are designed to evaluate the vertical, horizontal and total intensity magnetic anomalies due to finite three‐dimensional bodies of uniform polarisation contrast. The direction of polarisation need not be co‐linear with the Earth's field, thus allowing for a remanent component; and the calculation may be performed for a given model for several different directions of polarisation concurrently. The first programme depends on the transformation from a volume integral to a surface integral and the approximate representation of the surface by a series of plane polygonal faces. The second programme is based on an extension of Vacquier's graphical method.
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A LABORATORY INVESTIGATION INTO THE ELASTIC PROPERTIES OF LIMESTONES*
Authors O. KOEFOED, M. M. OOSTERVELD and I. J. G. ALONSAbstractMeasurements have been made by the resonance method of the longitudinal bar velocities and the transverse velocities of 29 chemically pure limestones of varying porosity. The elastic anisotropy factors of the limestones were found to vary over a wide range. For the isotropic limestones, both the longitudinal and the transverse velocity decrease in general with increasing porosity, but this decrease is somewhat irregular. The irregularities in the velocity were found to correlate with the irregularities in the electrical resistivity of the samples when saturated with a standard salt solution, and with those in their tensile strength. This correlation indicates an influence on the velocity of the geometry of the pore space of the rock and of its counterpart: the geometry of the matrix. Indications have been obtained that a condition akin to weathering may be partly responsible for the irregularities in the velocities.
Saturating the samples with water was found to result in a decrease of their velocities. An investigation of the available literature, combined with measurements made in our laboratory with a low frequency pulse method, indicate that water saturation results in a decrease of the velocity at low frequencies and in an increase of the velocity at high frequencies.
Since other investigators have shown that the velocities of dry rock are hardly effected by the frequency, one must conclude that the velocities of water saturated rock do change appreciably with frequency.
The values of Poisson's ratio were found to decrease with increasing porosity, but more so for the dry samples than for the water saturated samples. A possible explanation is that the cross‐contraction and cross‐dilatation is partly consumed in changing the diameters of the pores, thus reducing the effect on the outer diameter of the sample; this mechanism would be partly resisted by water filling the pores.
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ETUDE STATISTIQUE DE LA CONTRIBUTION DES MULTIPLES AUX SISMOGRAMMES SYNTHETIQUES ET REELS*
More LessAbstractA statistical study of reflection coefficients by sections permits evaluation of the coefficients' homogeneity, of the contribution of the multiples, and of the attenuation due to the coefficients of transmission.
Such a study also shows that the multiples tend to make distribution of the amplitudes of impulsional seismograms comply with normal laws, and that filtering by an impulse produces the same phenomenon on the amplitudes of synthetic seismograms.
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DETERMINATION DE L'EPAISSEUR DES SEDIMENTS MEUBLES A L'AIDE DE LA METHODE DE STATISTIQUES DE ΔT*
By O. LEENHARDTAbstractOffshore reflection records, even if they are of medium quality, can be used to determine the thickness of unconsolidated sediments. The method is described and its limits are specified. An example of application referring to the Gulf of Lyons is given.
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BOOK REVIEWS
Books reviewed in this article:
E. Hardtwig, Theorien zur mikroseismischen Bodenunruhe
Physics and Chemistry of the Earth
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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)