bluuebunny/crossref_metadata_2025 huggingface dataset:
CHANGES OF SHAPE OF SEISMIC IMPULSES IN HOMOGENEOUS VISCOELASTIC MEDIA
Authors: POSTMA G. W.
Published: April 2006

Changes of shape of seismic waves provide information on the properties of the material in which the waves propagate. Ricker (1953) has attempted to explain the changes of shape on the basis of a simple viscoelastic theory. His conclusions are at variance with those of others who find a dependence of the attenuation on frequency which could be explained only by a much more complicated linear theory or by nonlinear theories.

To provide a basis for discussion, the essentials of the theory of viscoelasticity are briefly reviewed. If a relaxation spectrum, rather than one or very few relaxation times, is admitted, a great variety of experimental results can be described by the linear theory of viscoelasticity. A linear theory is indicated when no obvious violations of the principle of superposition occur.

Ricker's theory is presented with some modifications which allow for a finite duration of the initial pulse and for the approximate character of his basic assumptions. There do not appear to be serious discrepancies between his theory and his experimental results. Some of the objections to his theory can be met by assuming a finite duration of the initial pulse. However, more direct measurements made under similar circumstances by McDonal et al. (1958) at the same location lead to a conclusion on the nature of the material not in accordance with Ricker's. This casts doubt on the sensitivity of his method.

Laboratory measurements usually yield results which are not explainable in terms of simple viscoelastic models. Whether a linear theory with a relaxation spectrum or a nonlinear theory should apply depends much on the experimental conditions. We must also consider the possibility of nonlinear mechanisms which are active at small amplitudes. No stand is taken in this controversy, but it is pointed out that the question linear or nonlinear could be decided experimentally without considering the details of the theories.
LABORATORY DETERMINATIONS OF ELASTIC PROPERTIES OF SOME LIMESTONES
Authors: KUIPER J. , VAN RYEN W. M. L. , KOEFOED O.
Published: April 2006

Abstract

Using a resonance method, determinations have been made of the longitudinal bar velocity and of Poisson's ratio of thirteen different chemically pure limestones. The relation between the velocity and the density showed far less scatter than in the determinations previously published; this is primarily attributed to the high purity of the specimens used. The measurements further showed a tendency of the values of Poisson's ratio to increase with increasing density.
TIME VARIATIONS OF THE CALIBRATION OF THE WORDEN GRAVITY‐METER*
Authors: INGHILLERI G.
Published: April 2006

Abstract

Precision calibration tests carried out with a Worden gravimeter in environment conditions as varied as possible have led to the following conclusions. The secular variation curve of the calibration shows that the secular relative variation has been very appreciable in the first year of life of the instrument, precisely of 1.3 × 10−3 in 13 months, while it has been practically zero in the second year. This must be ascribed to the fact that at the beginning of the operations the gravity‐meter had just arrived from the factory with its measuring body renewed.

On the other side the effect of 24°C of temperature difference between two series of determinations reveals itself in a variation of 0.0022 of the value of the calibration, so that it can be established that the variation of the calibration is I‰ for each 10°C of temperature variation.
APPLICATION OF THE CONTINUOUS VELOCITY LOG TO ANISOTROPY MEASUREMENTS IN NORTHERN SAHARA; RESULTS AND CONSEQUENCES
Authors: DE SEGONZAC PH. DUNOYER , LAHERRERE J.
Published: April 2006

Abstract

Anisotropy measurements were carried out in two wells 300 km apart in the Northern Sahara, in order to improve the interpretation of seismic refraction surveys.

These measurements were based on; the shortening of experimental oblique travel‐times with respect to theoretical, travel‐times computed by disregarding anisotropy. A perfect knowledge of the velocity distribution is required in order to eliminate all influence of refraction; therefore a continuous velocity log is indispensable.

The results in the two wells are in agreement, and show that anisotropy is essentially a function of lithology. The following values were obtained:

image

Consequences pertaining to seismic refraction are as follows:

— Depths computed without anisotropy are too small by 8 % to 9 %, i.e. about 300 meters.

— The error on offsets reaches 70 %.

— Depth computations carried out by assigning anisotropy factors at the sight of lithology gave very satisfactory results.

— High velocity, highly anisotropic formations such as anhydrite play a very important part in the propagation of refracted waves and in interpretation.

Consequences pertaining to seismic reflection are as follows:

— Velocity profiles yield velocities closer to horizontal velocities than to vertical velocities.

— Depth and migration computations are significantly influenced by high velocity, highly anisotropic formations such as anhydrite.
WELL VELOCITY DETERMINATIONS IN THE ENGLISH TRIAS, PERMIAN AND CARBONIFEROUS
Authors: WYROBEK S. M.
Published: April 2006

Abstract

To obtain inferences useful in predicting the overburden velocities, a statistical study of velocity data was undertaken on 46 well velocity surveys confined mainly to Eastern England. Five formations were particularly studied: Keuper, Bunter, Permian, Coal Measures and Millstone Grit. Their interval velocities plotted against the mean depth of the interval below the surface supplied five equations of the form V=k. H1/n, which cover the range of depth explored down to 7000 ft. Comparison of these results shows that the interval velocities increase with depth and in the Keuper and Permian attain a maximum value nearly twice that in the remaining three formations. The interval velocities of these formations are confined within a relatively narrow band of 9000–12000 ft/sec. and the formations cannot be distinguished satisfactorily by their interval velocities alone. More practical results were obtained considering the relation between the vertical time and depth to the top of the Permian, Coal Measures, Millstone Grit and Carboniferous Limestone. For each of these a linear relation T=k. H+ To, was obtained from which the vertical time T can be predicted from the known depth with a probable error of ± 4 millisecs.
RESULTS OF UNDERGROUND‐SEISMIC REFLECTION INVESTIGATIONS IN THE SIDERITE DISTRICT OF THE SIEGERLAND*
Authors: SCHMIDT G.
Published: April 2006

Abstract

The iron ores of the Siegerland district are found in lodes occurring in schists of Lower Devonian age. These lodes, normally dipping almost perpendicularly, could be traced only by seismic reflection measurements underground, up to distances of approximately 500 m. The geophones were attached to the walls of the galleries. The frequencies of the recorded longitudinal and transverse waves ranged from 200 to 500 c.p.s. By this method a new siderite lode was discovered.
A EUROPEAN FIELD OF THE NORMAL GEOMAGNETIC VERTICAL INTENSITY AND ITS SECULAR VARIATION
Authors: BOCK R.
Published: April 2006

Summary

A uniform field of the normal geomagnetic vertical intensity and its normal dependence on the first and second powers of latitude and longitude are derived for Europe and represented by sketches. The epochs of 1938.5, 1941.5, 1944.5, 1947.5, 1950.5, 1953.5, and 1956.5 have been chosen.

It is suggested that anomalies of the vertical intensity should be given according to this field in order to obtain, in course of time, a coherent image of the magnetic effects of the European continent.
A GENERALIZED CAGNIARD GRAPH FOR THE INTERPRETATION OF GEOELECTRICAL SOUNDING DATA
Authors: KOEFOED O.
Published: April 2006

Abstract

The Cagniard method of interpreting geoelectrical sounding data is based on the use of an empirical graph which expresses the relation between the resistivity and thickness of the second subsurface layer on one side, and on the other side the replacement resistivity and replacement thickness which are derived from the two‐layer sounding curve which is asymptotic to the second branch of the observed sounding curve. In his method separate graphs of this type are required for different values of the resistivity of the third subsurface layer. In the present paper a generalized Cagniard graph is derived which has the advantage of being independent of the value of the resistivity of the third subsurface layer. Finally, the accuracy of the method is discussed, and a procedure is described for extending its use to cases where more than three subsurface layers intervene.
A SHOCK WAVE THEORY FOR THE GENERATION OF THE SEISMIC SIGNAL AROUND A SPHERICAL SHOT HOLE
Authors: PEET W. E.
Published: April 2006

Abstract

The shape of the seismic signal generated by an explosive charge is assumed to be governed by shock‐wave phenomena in a non‐linear region around the shot hole.

The dimensions of this shock‐wave region are shown to depend on the weight of the explosive charge and the properties of the medium in which the shot is fired.

The presented theory enables us to elucidate the power law relationship between the amplitude of the seismic pulse and the weight of the charge fired, in the literature often denoted by A = c.Qn, in which A is the pulse amplitude, Q the charge weight and c a constant.

Experiments have been made to check the theory and the results are promising.
SOME FORMULAE FOR INTERPRETING LOCAL GRAVITY ANOMALIES
Authors: SMITH R. A.
Published: April 2006

Abstract

Let Oxyz be a system of rectangular axes with origin at the earth's surface and with the z axis pointing vertically downwards. If a body B lies wholly] between the planes z=h, z=I then for all x, y and for n= 1, 2, 3 it is proved that

image

where a=h/d, β=l/d and K is the gravitational constant. Dn are very easily computed from the Bouger anomaly and Jn are tabulated in this paper.
CALCUL DE L'ATTRACTION D'UN POLYGONE HORIZONTAL DE DENSITÉ UNIFORME*
Authors: GOGUEL JEAN
Published: April 2006

Abstract

The vertical component of the attraction exerted by a horizontal homogeneous polygon is obtained as the sum of terms proportional to the difference, for each of the vertices, between the external angle and its spherical perspective. A set of computation charts is presented, each for a fixed value of the angle of the polygon (22° 30′, 30°, 45°, 67° 30’ and 90°). These charts give the difference between the external angle and its spherical perspective as a function of the quotient of the distance from the sides to the vertical through the station over the depth. The chart for the right angle is an alignment chart, permitting a more accurate reading; the others are graphs in rectangular coördinates.

For a remote station the result would be obtained as a small difference between relatively large quantities, and consequently with a not quite satisfactory precision. For these stations it is preferable to assume the entire mass to be concentrated in the centre of gravity.
THE ELECTROMAGNETIC RESPONSE OF A MAGNETIC IRON ORE DEPOSIT
Authors: WARD STANLEY H.
Published: April 2006

Abstract

Field experiments in the vicinity of a tabular body of nearly massive magnetite have demonstrated that the body may respond in either of two ways; it may react as a permeable mass, or it may react as an eddy current inductor, depending upon the frequency employed. If several frequencies, spanning a broad range, are employed, both types of response will be experienced. The transition from one type of response to the other would appear to have considerable significance. Based upon theoretical and empirical work to date, it seems possible to establish a relationship between transition frequency and percentage magnetite at any given section of a deposit.
ENERGIE DES VIBRATIONS ET FILTRAGE NON LINEAIRE*
Authors: BARANOV V.
Published: April 2006

Abstract

A filtered seismic trace often appears as an almost sinusoidal curve. The reflected energy arrivals are superimposed and interfere with the continuous oscillations of the trace, and are therefore often difficult to distinguish. This is the chief difficulty in picking reflections. The situation is similar to that met with in gravimetry when a strong regional anomaly conceals small local anomalies. However, a regional anomaly is regular and broad, and owing to these two characteristics it can be removed. In reflection seismology batches of energy may also be concealed by oscillations of a continuous character. The main difference lies in the fact that the background of continuous seismic vibrations is not static, as is the case in gravimetry, but variable with time. However, a fairly constant physical quantity corresponds to these vibrations, which are composed partly of noise, partly of undesired secondary reflections. This quantity is the energy of motion of the surface layer of the ground. It is this troublesome energy that we intend to remove, in order to keep only the useful, actually reflected, energy.

These remarks clearly demonstrate the importance of an investigation of the energy contained in the surface layer of the ground. After showing that, in the simplest case, the density of this energy can be expressed almost exactly by the formula

u
′2−uu′′

in which u′ is the velocity of a ground particle, we show how the non‐linear filtering defined by this formula can be realized, and we provide a few examples.
SEISMIC WAVES IN A MATHEMATICAL MODEL OF THE SURFACE LAYER*
Authors: BORTFELD REINHARD
Published: April 2006

Abstract

The surface layer is replaced by a layer in which the velocity changes linearly with the depth, i.e. by a transition layer. A plane irrotational wave of arbitrary shape travels vertically upward and hits this layer. The multiples produced by differential reflections in the layer and by reflections at the free boundary are computed. From the third order on, these multiples look exactly like empirical reflections. The sum of all multiples is the solution of the differential equations of the problem, and has some formal mathematical similarity to diffraction phenomena known from optics.
SOME THEOREMS CONCERNING LOCAL MAGNETIC ANOMALIES
Authors: SMITH R. A.
Published: April 2006

Abstract

Formulae are derived and discussed. They can be applied to magnetometer observations, with negligible computation, to yield limits to the depth and intensity of magnetisation of the bodies causing the anomaly.
THE RELATIVE CONTRIBUTIONS OF REMANENT AND INDUCED MAGNETISM TO THE OBSERVED MAGNETIC FIELD IN NORTHEASTERN ALBERTA
Authors: WATKINS N. D.
Published: April 2006

Abstract

The ratios of induced to remanent magnetic intensities have been determined for samples of Precambrian rock from part of the Canadian Shield in northeastern Alberta.

The relatively insignificant contribution of remanent magnetism to the observed field indicates that interpretation techniques based on the assumption of zero remanent intensity can be used.

Other implications of the magnetic measurements are discussed briefly.
THE GENERATION OF SEISMIC WAVES BY EXPLOSIONS*
Authors: LINSSER HELMUT
Published: April 2006

Abstract

In the mathematical treatment of the propagation of seismic waves the process in the medium surrounding the point of explosion is introduced as initial condition into the differential equation. It is the purpose of this paper to contribute to the knowledge of this process.

The treatment of the process of explosion is a difficult one because the elastic limit is exceeded in the surroundings of the point of explosion. To gain a better view on the acting forces the space concerned is replaced by a simplifying model. It is shown that a permanent deformation is caused by the explosion. This deformation will be especially intensive if the rock does not offer any resistance to tensile forces.

To determine the extent of such a permanent deformation a sudden release of pressure — the opposite of an explosion — was recorded by seismographs. It has been proved that any seismic waves of measurable magnitude are not produced. This leads to the conclusion that permanent deformation plays an essential part in the generation of seismic waves.
EXEMPLES D'APPLICATION DE LA REPRESENTATION CONFORME A L'INTERPRETATION DU CHAMP TELLURIQUE*
Authors: KUNETZ G. , DE GÉRY J. CHASTENET
Published: April 2006

Abstract

The method of conformal transformation is applied to determine the distribution of telluric current density at the surface for several subsurface situations. To this end one starts of from a configuration of boundaries between media of different resistivities and of two equal and opposite current poles, for which the potential distribution can be easily determined. Then a suitable conformal transformation is applied, by which the two current poles are displaced to infinity, and the boundary between the media are made to correspond to typical layer configurations in the subsurface. Several examples of the method are discussed in detail, leading to typical subsurface structures as well as to typical topographic conditions.
MESURES D'AMPLITUDE DANS LES SONDAGES: LE LOG D'ATTENUATION *
Authors: MORLET J. , SCHWAETZER T.
Published: April 2006

Resume

Parmi les différents facteurs agissant sur l'amplitude des signaux acoustiques enregistrés au cours des mesures continues de vitesse dans les puits, le coefficient d'atténuation semble présenter beaucoup d'intérêt pour la détermination des qualités mécaniques des roches, en particulier la continuité de la matrice, donc dans une certaine mesure la perméabilité.

Afin d'éliminer les facteurs secondaires agissant sur l'amplitude, nous avons été amenés à enregistrer le rapport des amplitudes aux deux récepteurs de la sonde C.V.L. Nous avons donc étudié un appareil permettant d'enregistrer les amplitudes des premières arrivées aux deux récepteurs, ainsi que le rapport de ces amplitudes.

Nous présentons ici les premiers résultats obtenus par la mesure continue de l'atténuation des ondes acoustiques dans différents types de formations. Des comparaisons sont faites avec les diagraphics de vitesse, de résistivité et de radioactivité.

Le log d'atténuation semble permettre la détermination de la lithologie et plus particulièrement la localisation des zones fracturées et perméables. Bien que nous n'ayons que peu d'expérience de ce nouveau type de diagraphie, il nous semble que les premiers résultats obtenus soient très prometteurs.
THE HYPERBOLIC INCREASE OF DEPTH WITH TIME
Authors: KUNZ BRUNO
Published: April 2006

Abstract

The geometric description of wave fronts and ray paths has previously always started from the velocity distribution which has been chosen as simple as possible in order to be able to solve the integrals occurring in the basic equations. As the velocity is derived from the measured values of path and time, it is preferable to start from the path‐time function. There are exponential, parabolic and hyperbolic path‐time functions; the first and the second case correspond to the known linear and parabolic velocity functions. The hyperbolic case, on the other hand, has not yet been covered in literature. In the first two cases, two parameters–a and vo–can be chosen arbitrarily. In the hyperbolic case, we have 3 parameters (a, b and v)o at our disposal; this makes for a better approximation to actual conditions. A special advantage is seen also in the fact that the velocity does not become infinite with increasing depth but approaches a finite limit.
IN PURSUIT OF THE ERRANT SEISMIC PULSE*
Authors: HAGEDOORN J. G.
Published: April 2006

Abstract

The results obtained from a series of geophones extending vertically from the surface down to a particularly strong reflector 450 m deep have provided an insight into the properties of the various types of wave generated by an explosion in the ground and have shown how these waves are converted into other types near the surface and at a reflector. The direct shear pulse generated by an explosion was observed to be quite simple and to penetrate to the deepest geophone even from large horizontal distances, but to be much more attenuated and broadened on its way through the earth than the compressional pulse. This shear pulse was found to be the cause of the ground‐roll commonly observed at the surface. A clear PS reflection, of the same magnitude as the PP reflection, was observed from the reflector 450 m deep. This shear event starts out from the reflector as a short and simple pulse, but does not persist as such on its way to the surface. It loses its sharpness well before reaching the base of the weathered layer, whereas the reflected compressional pulse is hardly affected at all.
HIGH SPEED CALCULATION OF GRAVITY AND MAGNETIC PROFILES ACROSS TWO‐DIMENSIONAL BODIES HAVING AN ARBITRARY CROSS‐SECTION*
Authors: MORGAN N. A. , GRANT F. S.
Published: April 2006

Abstract

A method is found for programming the calculation of gravity and magnetic profiles across two‐dimensional bodies of arbitrary cross‐section for high‐speed computers. It is based upon an idea applied recently by Worzel, Landisman and Talwani, of approximating the cross‐section with an n‐sided polygon. The gravity and magnetic formulae are functions of the coordinates of the vertices. A profile of each kind takes only a few seconds to compute, and the accuracy appears to be at least as good as that of graticules.
APERçUS STATISTIQUES SUR L'INTERPRETATION EN AEROMAGNETISME*
Authors: CHEREAU J. Y.
Published: April 2006

Abstract

When inspecting maps that were obtained a few years ago as a result of the interpretation of aeromagnetic surveys, one is divided between feelings of satisfaction about well confirmed predictions, of regret about unfortunate choices or errors that could have been avoided by present experience and of confusion in regard to certain still poorly understood phenomena.

Some documents of the Bureau de Recherches de Pétrole have been examined in order to evaluate the precision of aeromagnetic interpretations and to find possible sources of the observed discrepancies.
LA SURFACE D'ONDE DANS UN MILIEU ELASTIQUE ANISTROPE*
Authors: LOEB J.
Published: April 2006

Abstract

The present work was initiated by an account given by Messrs. Kunetz and ?Erceville. It is greatly inspired by the article of G. W. Postma: Wave propagation in a stratified medium. There a construction of the “wave front” is given, starting from the surface of the velocities. This latter surface is the pedal of the wavefront. This theory is based on a certain section of Love's Treatise on the Mathematical Theory of Elasticity (Ch. XIII, sect. 209). However, no proof of this theory has been provided, neither in Postma's article nor in Love's work.

It is the intention of this article to supply such a proof. Also the construction is proved to be valid only for distances from the point source which are large compared with the wavelength.
SOME THEORETICAL ASPECTS OF ELECTRODE POLARIZATION IN ROCKS*
Authors: BHATTACHARYYA B. K. , MORRISON H. F.
Published: April 2006

Abstract

A study has been made on the influence of the several variables of an electrode‐electrolyte system on the different parameters usually measured in connection with the induced polarization method of geophysical exploration. Both the reaction resistance and the Warburg impedance of the system are found to vary appreciably with active ion concentration. The activation energy barrier exerts a predominant influence only on the former, whereas the salt concentration is important to a small degree in the determination of only the latter.

With a simple equivalent electrical circuit to represent the complex mechanism of conduction of electrical currents through mineralized rocks, the amplitude and phase of the metal factor are evaluated at a frequency of 10 cps. An analysis is then made to determine the build‐up and decay characteristics of the transient signal in the rock induced by a rectangular current pulse. All these measurable quantities are highly dependent on the salt and active ion concentrations. It is interesting to note that the build‐up or decay time of the transient signal increases normally as the square of the solution resistance and inversely as the square of the Warburg impedance. The activation energy barrier exerts, practically no influence on the metal factor nor on the transient signal.
CALCUL DE LA FORME ?UNE STRUCTURE HOMOGENE A PARTIR DE SON CHAMP GRAVIMETRIQUE*
Authors: LA PORTE M.
Published: April 2006

Abstract

A 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.
TWO METHODS APPLICABLE TO COMPUTERS FOR EVALUATING MAGNETIC ANOMALIES DUE TO FINITE THREE DIMENSIONAL BODIES*
Authors: BOTT M. H. P.
Published: April 2006

Abstract

Two 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.
THE USE OF GEOPHONE GROUPS TO IMPROVE THE SIGNAL‐TO‐NOISE RATIO OF THE FIRST ARRIVAL IN REFRACTION SHOOTING*
Authors: DENHAM DAVID
Published: April 2006

Abstract

For a group of n geophones at a single station, a signal‐to‐noise improvement of √n can only be expected when the background noise, between the individual detectors in the group, is completely uncorrected. This paper gives results, from four different sites, for the variation of correlation coefficient with distance between the detectors. It is found that at these locations the geophone spacings required to reduce the correlation coefficient to zero varied from 30 to 300 feet.

These results are in agreement with the predictions of the theoretical model of a two‐dimensional isotropic noise field described by Hills and Faran (1952). This model provides estimates of the spacing required between geophones to reduce the correlation coefficient to zero, provided that the velocity of the noise is known and that its spectrum is of a simple form.

Often it is impractical to reduce the correlation coefficient to zero because of the large spacing required between the geophones in the group. For this case a simple method is described in which the signal‐to‐noise improvement can be calculated given that the correlation coefficients between the geophones in the group are known. This procedure can easily be used in the field because the correlation coefficients can rapidly be computed from paper records by using Tomoda's method (Tomoda, 1956) which gives values of sufficient accuracy to be used for on‐the‐spot calculation.
CONTRIBUTION AU CALCUL SIMPLIFIE DES CORRECTIONS DE RELIEF A GRANDE DISTANCE EN GRAVIMETRIE*
Authors: NEUMANN R.
Published: April 2006

Abstract

In a recent paper, H. A. Winkler developed a suitable method for determining longdistance terrain corrections in gravity by interpolation. Such a technique implies that it is necessary to take into account the changes of the correction g not only with the location (X, Y) but also with the elevation Z of a station. Study of the function g(Z) shows that its curve, with amply sufficient accuracy, may be represented as a parabola. Moreover, the parabolas corresponding to different stations are all equal. From these properties a method has been derived which saves computing time and yields long‐distance terrain corrections with convenient accuracy.
EIN NÄHERUNGSVERFAHREN ZUR BERECHNUNG VON GRAVITATIONS‐ANOMALIEN FÜR BELIEBIG GEFORMTE INHOMOGENE MASSEN MIT DEM DIGITAL‐RECHNER*
Authors: SZELÉNYI GY.
Published: April 2006

By 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.
AMELIORATION DU RAPPORT SIGNAL / BRUIT A L'AIDE DU FILTRAGE EN EVENTAIL*
Authors: FAIL J. P. , GRAU G. , LAYOTTE P. C.
Published: April 2006

Case history of the use of fan filtering for improving reflection continuity without destroying their character. The field technique is described: wide‐band, large dynamical range recording with a programmed gain control and a very slow A.G.C., small distance between trace centers, high cutoff wave‐number.

Although the total amount of mixing due to fan filtering is rather high, a broad spectrum was obtained and inverse convolution filtering was used to improve trace resolution.
A METHOD OF QUANTITATIVE INTERPRETATION OF THE ELECTRICAL FIELDS OF INFINITELY LONG SINKS AND HORIZONTAL CIRCULAR CYLINDRICAL BODIES*
Authors: JAIN SUDHIR
Published: April 2006

Using a simple integral transform suggested by Roy and Jain (1961), methods of interpretation of electrical potential data for a point source in the presence of one or two infinitely long horizontal cylinders are developed. The methods are applicable to electrical surveys of long filled channels of semi‐circular cross‐section or of buried cylindrical ore bodies.
SUR LA REPONSE TRANSITOIRE DES FORMATIONS RESISTIVES*
Authors: LOEB J.
Published: April 2006

This paper deals with transient response of resistive formations to pulse sources. Computation of solutions of equations such as:

image

is linked to computation of solutions of equations such as:

image

It can be used in the case where several media exist, the conductivities of which are σ1 σ2.

The method consists in establishing a correspondence between the case to be dealt with and a fictitious region of space with the same interfaces, in which the propagation of a disturbance obeys Equation (2).

Velocities C1 C2. are related to conductivities by the condition

image

At the interfaces, the distribution of incident energy between transmitted and reflected energy is related to the ratio of characteristic impedances, i.e.

image

in the real case (ω is the angular frequency) and C1/C2 in the fictitious case.

These ratios are the same because of Equation (3).

Time variation g(θ) of solution of (1) in a given point is computed from time variation of solution of (2) at the same point by means of the transformation

image

(in which τ is the actual time and T the time unit).

Equation (4) originates from a formula of symbolic calculus, that allows the Laplace transform of F(Vp) to be calculated from the known Laplace transform of F(p). This correspondence is the one that allows passage from in (1) to in (2)

Equation (4) becomes considerably simpler when the response to the unit impulse consists (as happens most often) of the sum of a finite or infinite number of pulses The results is then a sum of functions such as:

image

Hence, this procedure appears as an extension to systems that obey Equation (1) of the image theory very often used when Equation (2) is applied.
ON THE CORRELATION OF GRAVITY WITH TIDAL ANOMALIES*
Authors: GROTEN E.
Published: April 2006

Tidal deformations of the solid earth show remarkable regional fluctuations. Mean gravity anomalies reveal strong positive correlation with the regional variations in the vertical tide component, if the effect of topography on the gravity field is reduced by isostatic proceedings. The correlation of these “tidal anomalies” with the lower harmonics of the gravity field is weaker. Heterogenities of the upper mantle may be a source of these differences in the deformations.
SECURITE EXAMEN STATISTIQUE DE 1200 ACCIDENTS GEOPHYSIQUES*
Authors: RICHARD H.
Published: April 2006

More than 1200 cards on geophysical accidents have been accumulated since 1957. Classification of these cards into various categories reveals relative stability in terms of time. It is possible to determine a highly significant severity rating for each category. The greatest hazards are explosion and electrocution.
UN NOUVEAU MAGNETOMETRE AERIEN LE MAGNETOMETRE A VAPEUR DE CAESIUM
Authors: GIRET R. , MALNAR L.
Published: April 2006

Compagnie Générate de T.S.F. (C.S.F.) has recently developed a new magnetometer based on the optical pumping of caesium vapour.

After carrying out a systematic programme of ground and in‐flight tests, Compagnie Générale de Géophysique (C.G.G.) has put several of the airborne models into service.

Following a discussion of the fundamental principles involved, the instrument is described and its specifications are given. The two forms of read‐out are: an analog recording, of the conventional type, and a digital version, recorded on magnetic tape.

The instrument measures the total intensity of the earth's magnetic field with a sensitivity of 0.03 gamma. Temperature compensation is provided, making possible operation between — 20 and + 45 degrees centigrade. Performance is not affected by an inhomogeneous field as long as the gradient is less than 10 gammas per centimetre.

The range of the instrument is from 20,000 to 70,000 gammas and the values are obtained automatically, without the intervention of an operator.

There is no danger of instrumental drift, and the selection of caesium vapour and the components of the detector guarantee that the absolute value of the field, throughout the range of the instrument and regardless of the circumstances, is measured to within one gamma.

The first large‐scale project making use of these magnetometers, carried out by C.G.G., is the Magnetic Map of France, which has been compiled for the Centre National de la Recherche Scientifique. The characteristics of this project are given.
UTILISATION D'UN CENTRAL DE DIGITALISATION D'ENREGISTREMENTS SISMIQUES*
Authors: MILLOUET J. , MORLET J.
Published: April 2006

Until such time as digital seismic recording techniques are in widespread use in the field and partly because it cannot afford digital equipment, C.E.P. has decided to build a processing system which can digitize and process seismic information in analog form on magnetic tapes.

C.E.P. was prompted to adopt the digital technique to enable it to proceed with its stratigraphical investigations, starting with the elaboration of synthetic records and followed by the study of signals and deconvolution.

Though the analog form of recording is not too suitable for digital processing owing to its low dynamic range, it seemed to us that it was nevertheless perfectly feasible to enhance the analog information by processing it digitally through an automatic computer.

This approach to the problem of data enhancement is more satisfactory than the (conventional) analog method, which is more complicated and less accurate.

The digital processing system comprises:

a magnetic playback system

a two‐channel reproduction device

an analog‐digital converter

a 1620 IBM computer

an automatic plotting device for graphical presentation of results.

Examples of different processing forms are presented:

cancellation of A.G.C. action

computation of seismic signal

deconvolution

correlation techniques

anti‐singing

study of the response of the various items of equipment.

We have come to the conclusion that very interesting results have been obtained in spite of the low dynamic range of the analog tapes.

With this equipment it is possible to study and process the data in digital form and compare results with those obtained by analog processing. Also, the experience gained will be very useful when digital field crews start operating.

Unfortunately, it is not possible for the time being to operate the equipment on a commercial production basis, but only to develop working methods, to conduct short studies or to guide and control analog processing techniques.

At present our efforts are therefore aimed at shortening the time required for processing and plotting.
SEISMIC REFRACTION AND SCREENING BY THIN HIGH‐VELOCITY LAYERS *
Authors: POLEY J. Ph. , NOOTEBOOM J. J.
Published: April 2006

The screening effect of thin, relatively shallow high‐velocity layers often presents considerable problems in seismic exploration. Such layers prevent the greater part of the seismic energy from travelling to greater depths and introduce additional refraction arrivals, confusing the seismogram still further.

In order to investigate both the screening and refractive properties of high‐velocity layers, scale‐model experiments have been made over a wide range of layer‐thickness/ wavelength ratios (0.05 < d/λ < 2) for suitably chosen material contrasts. The results may be summarised as follows.

Refraction arrivals from thin layers in the field may be recognised by their relatively rapid amplitude decay. Furthermore, the “echeloning”‐effect observed for refraction first arrivals may be due to the presence of a (thin) layered structure. Since the apparent refraction velocity varies with d/λ when d/λ < 1, differences between vertical well‐log velocities and velocities observed along the surface may be expected, making time/depth conversion using surface velocity data inaccurate.

Transmission of elastic energy may be expected, if anywhere, only near the shotpoint, at small geophone offset, and for relatively thin screens (d/λ < 0.1). The transmitted signal shape is then independent of the layer thickness. This transmitted energy may be registered either in a reflection set‐up with geophones near the shotpoint, or in long‐distance refraction work.

Three possibilities are offered for overcoming the screening effect of thin high‐velocity layers: Use longer‐wavelength signals

Apply short‐spread reflection shooting

Apply long‐distance refraction shooting

The experimental results obtained in scale‐model arrangements of such set‐ups confirm the potentialities of these methods.
IMPORTANCE OF AEROMAGNETICS IN EVALUATION OF STRUCTURAL CONTROL OF MINERALIZATION*
Authors: DOMZALSKI W.
Published: April 2006

The term “structure”, as used here, includes synclinal and anticlinal folds and folding in general, faults, cross fractures and various conditions associated with intrusions. Structure, both regional and local, has a very important role in emplacement of mineralization. Under certain circumstances which occur fairly commonly, structural conditions are reflected significantly in the trends and intensities apparent on aeromagnetic maps. A number of documented illustrations based on Canadian Shield conditions are discussed. Illustrations are drawn from areas of known geology and from proven mining camps, as well as from loci of recent discoveries. Canadian examples are chosen because of existence and availability of extensive aeromagnetic cover, although it is logical to extend the argument to other shields and indeed to regions of other geological, but similar magnetic character.

The importance of aeromagnetics in structural approach to exploration and the correctness of such approach seem to be fully substantiated by results discussed.
A THEORETICAL INVESTIGATION ON THE FORMATION FACTOR/PERMEABILITY/POROSITY RELATIONSHIP USING A NETWORK MODEL*
Authors: SCHOPPER JÜRGEN R.
Published: April 2006

The knowledge of hydraulic and electric properties of porous media and the relations between them is essential for the quantitative evaluation of electric well logs and the solution of other reservoir engineering problems. The state of the art in this field is not yet satisfying. Theories still show considerable discrepancies with practice due to oversimplified model approaches. Empirical relations are either too coarse, not fully determined, or valid under specific geological and geographical conditions only. This article deals with the development of a general theory of the electric and hydraulic resistance behavior of porous media on the basis of a very general statistical network model. A general solution of the relations between formation factor, permeability, and porosity is presented by means of a rigorous mathematical treatment of two limiting cases of such a network. The solution shows that the product of the formation factor and the permeability can be expressed in the expectation values and the variation coefficients of pore channel cross section and shape factor and by a network factor, that depends on the mesh texture of the network. This network factor is in the range zero to one. It is further shown that the path length increase enters both the electric and the hydraulic tortuosity by its square.
THE SECTIONAL AUTO‐CORRELOGRAM AND THE SECTIONAL RETRO‐CORRELOGRAM *
Authors: ANSTEY N. A.
Published: April 2006

The auto‐correlation function of a seismic trace contains information on all the multiple reflection activity present in the trace.

The interpretation of this information is facilitated by the arrangement of autocorrelation functions in cross‐sectional form, in the manner of a normal record section. This is the concept of the Sectional Auto‐Correlogram.

Specifically, the Sectional Auto‐Correlogram will.

Show if the record section does not include significant multiples, thus allowing confident picking of the primary reflections.

Show if the record section does include significant multiples, giving their travel times and inclinations (and, under certain circumstances, their reflection coefficients).

Indicate by what process the multiples should be treated.

Yield an authoritative measure of the success of a multiple‐attenuating treatment.

Delineate shallow horizons, even those whose primary reflections are too early to be recorded satisfactorily.

Give the true travel time of a primary reflector, and the sign of its reflection coefficient.

The Sectional Auto‐Correlogram allows the study of primary reflectors by consideration of the multiples generated by them, and in this sense may be said to turn multiple reflections to advantage. Thus a primary reflection at a certain time is defined if we find that every reflection on the record is followed by a multiple after this certain time. Alternatively, a primary reflection at a certain time is defined if, after that certain time, we can find a repetition of the entire record.

The Sectional Auto‐Correlogram also has secondary uses in fault identification, crustal studies and weathering problems.
ω‐k FILTER DESIGN*
Authors: WIGGINS RALPH A.
Published: April 2006

Two‐dimensional band‐pass filters can be constructed by a simple extension of the theory of one‐dimensional band‐pass filters. Similarly to the one‐dimensional analogue the shape of the two‐dimensional filter is important in determining its effectiveness. The band‐pass filter formulation can be further refined so that the filter will concentrate its rejection energies in certain areas of the ω, k plane. Such band‐pass, band‐reject filters are found by solving a set of simultaneous equations.
TWO COMPUTER PROGRAMS FOR THE CALCULATION OF STANDARD GRAPHS FOR RESISTIVITY PROSPECTING*
Authors: ARGELO S. M.
Published: April 2006

This paper includes publication of two algorithms, to be processed on a digital computer. The algorithms are based upon the two mathematical denotations, presented by Dr. J. C. van Dam in this same issue. The computer programs are written in Algol, in the form of procedures (i.e. subroutines to be activated from a surrounding Algol program).

Each of the two procedures is preceded by a numerical analysis. Some remarks are made about the reliability of each of the two procedures, the production and the computing time required.
LA GRAVIMETRIE DE HAUTE PRECISION APPLICATION AUX RECHERCHES DE CAVITES*
Authors: NEUMANN ROBERT
Published: April 2006

High precision gravity surveys have to be examined at different points of view: the accuracy which one can expect on the final results, regardless to their distribution, the shape and amplitude of the expected anomalies, depending on these factors, which grid of stations is convenient in each particular case.

Under certain condition, using an appropriate procedure, involving strict criteria, it is possible to get on the Bouguer map the same accuracy as the reading one.

However an accuracy closed to 0,01 mgal does not imply that anomalies as 0,01 or 0,02 mgal deserved attention. Numerous factors limit our appreciation of significant anomalies to 0,05 mgal, may be a little less.

When cavites are concerned, it is always necessary to define the extreme dimensions an depth of volumes which may give detectable anomalies.

Some example are given illustrating different aspects of this particular type of geophysical prospecting.
A NEW PARAMETER FOR AEROMAGNETIC SURVEYING*
Authors: THYSSEN‐BORNEMISZA STEPHEN
Published: April 2006

The author proposes the parameter Δ2/ΔT1 for possible application in aeromagnetic surveying making use of already available gradiometer systems equipped with sensors separated vertically.
FITTING OBSERVED PROFILES TO A MAGNETIZED DYKE OR FAULT‐STEP MODEL*
Authors: POWELL D. W.
Published: April 2006

The symmetry shown, by the function describing the magnetic anomaly due to a dyke or vertical fault step leads to a method by which an observed profile may be adjusted to conform with that symmetry. By making these adjustments a minimum the ideal dyke or fault profile closest to the observations is constructed. In three of four possible situations this is interpreted by simple geometry.

Parallelpiped models may be transformed into two dykes for symmetry analysis. Depth limited models are not so amenable, even in special cases.