bluuebunny/crossref_metadata_2025 huggingface dataset:
ELASTISCHE WELLEN IM ANISOTROPEN MEDIUM NACH EINER MAKROSEISMISCHEN UNTERTAGE‐MESSUNG*
Authors: DUDA S. J.
Published: April 2006

Abstract

In some mines of the Siegerland, besides dilatational and shear waves, an additional direct wave has sometimes been found the velocity of which was somewhat lower than that of the shear wave. Investigations were carried out with the object to establish the directions of oscillations and the velocities of all three kinds of waves. It was the purpose to draw conclusions as to the character and the causes of the appearence of the third wave.

By these investigations the wave having the lowest velocity can be identified as a second shear wave. This points to the fact that double refraction of the shear wave is taking place, the wave of higher velocity being a pure transverse wave and the wave of lower velocity being a quasi‐transverse wave.

As a result of these measurements the examined medium is shown to have a transverse isotropy due to stratification. It is, however, not possible to decide whether there exists also an anisotropy due to schistosity.

Some further calculations show that the wave of lowest velocity can not be explained as a surface wave propagated on the walls of the gallery.
GENERAL METHOD FOR CONSTRUCTION OF TRAJECTORIES AND WAVE‐FRONTS DIAGRAM FOR ANY VELOCITY DISTRIBUTION
Authors: OLHOVICH V. A.
Published: April 2006

Abstract

A graphical method is presented for construction of trajectories and wave‐front diagrams for any velocity distribution.

The analytical solution is given for the case when the time‐depth curve shows a flexure, that is, when the the velocity increases down to a certain depth and, after reaching a maximum, begins to decrease.

A numerical example is considered for the computation of a trajectory.
NOTE ON THE IMPEDANCE OF A GROUNDED WIRE
Authors: OVERHOLT K. J.
Published: April 2006

Abstract

The self‐inductance of a straight grounded wire lying on the surface of the earth is computed from a (slightly corrected) formula given by A. Wolf and compared to approximate formulae.
THE INFLUENCE OF SURFACE FORMATIONS ON THE APPARENT RESISTIVITY VALUES IN ELECTRICAL PROSPECTING*)
Authors: ALFANO L.
Published: April 2006

Abstract

In this first part, 1) we have examined the disturbances on resistivity measurements caused by some simple examples of surface irregularities with a cylindrical structure. The study has been carried out applying a theory developed in a previous paper (Alfano 1959)

In the first place, we have considered the case of measurements carried out with the potential electrodes near the surface irregularities, and the current electrodes more distant from those irregularities. This case is related to those methods of prospecting in which it is preferred to keep the current electrodes fixed and to move the potential electrodes.

One method has been pointed out which will separate, in the measured data, the component of the field due to deep formations, from the components due to surface irregularities. Afterwards, we have considered the case with current electrodes near the dishomo‐geneities and potential electrodes more distant from them. For both cases, numerical examples are shown, both for secondary charge values and for apparent resistivity values.

Finally, asymptotic values of vertical electrical soundings have been calculated for some cases, rigorously showing that they, in the presence of surface disturbances, are not equal, generally, to the true resistivity of a possible infinite substratum.

It follows that the measurement of resistivity of an infinite substratum, by means of the resistivity asymptotic value of only one sounding, is not possible.

The numerical results given have been obtained by means of calculations based on the abovesaid paper, but whose operative details shall be described in the second part of this paper.

The second part also will deal with the cases of surface dishomogeneity with a non‐cylindrical structure.
VARIATION DES VITESSES EN RAPPORT AVEC L'AGE EN LA LITHOLOGIE APPLICATION DE LA LOI DE FAUST*
Authors: AYNARD C. , MITRANI H. , DHINNIN R.
Published: April 2006

Abstract

It was felt that Faust's first law was the best guide in classifying data concerning velocities and their correlation with lithology, even if, on a local basis, other laws fit the observed values better.

Data have been re‐examined which were provided chiefly by borehole measurements, both conventional and continuous, but also by some particularly reliable velocity profiles. “Faust's coefficient” has been computed for a series of geological formations, i.e. the ratio of true velocity to the value resulting from Faust's law, according to the age and present depth of the formation.

Some graphs are shown, in the first place concerning the Sahara, and especially the Palaeozoic. It can be seen that the only formation showing values notably less than I disappears.

On the other hand, values greater than I can be noticed for the quartzitic Ordovician of limited thickness.

This comparison has been continued on a broader basis, using, in particular, data published by Faust and Wyrobek. The data concerning the very homogeneous Westphalian result in an average value slightly less than I.

The Aquitanian basin has been studied in greater detail, owing to the closer spacing of the measurements.

Generally speaking, the Middle and Upper Jurassic, the Cretaceous and the Eocene‐Oligocene show values notably higher than the Palaeozoic in the Sahara. This seems to be connected with the higher proportion of limestones and dolomites. Values as high as 1.7 are observed in compact dolomites.

Four maps are given, concerning the Oligocene, the Eocene‐Paleocene (one of them excluding the Danian) and the Upper Cretaceous (exclusive of Danian), and a cross‐section showing the link with lithology.

Some discrepancies with regard to data from borehole samples are discussed.

The question may be raised as to whether such studies can be carried out at the very beginning of exploration of a basin, on the basis of only a few logged wells. In the Aquitaine basin, data given by velocity profiles are in close agreement with those from wells as regards the Tertiary; but as regards the Mesozoic, information is meagre. In basins of the Sahara type, synthetic records have shown that interference of true and multiple reflections with each other is a major drawback. But on the other hand, the possibilities of a combined use of reflection and refraction in order to define lateral changes in velocities may not have been fully appreciated. Some computed examples are shown, since the results of a survey at present being carried out on this basis cannot yet be published.

Finally, mention is made of the part played by the determination of anisotropy, and an appeal is made for more coöperation between geophysicists in this sphere.
UTILISATION PRATIQUE DES FILMS SYNTHETIQUES DANS LE SAHARA NORD*
Authors: LAHERRERE J.
Published: April 2006

Abstract

The object of this paper is to present 19 synthetic records recorded on 12 wells in the North Sahara by different methods.

A comparaison is made of the synthetic records obtained by different methods:

by analogy: United Geophysical Corporation Seismograph Service Corporation

by computation: Institut Français du Pétrole Compagnie Générale de Géophysique

The method originated by Mr Baranov of the C.G.G. is studied in two cross sections: the first on four wells in the Hassai‐Messaoud field and the second on eight wells in the Anngueur region. The influence of internal and surface multiples on the correlations is very important and explains the reasons for marked variations in the quality of reflections. The problem of the origin of the basis of the stratigraphic correlations furnished by the geologists can be a source of errors.

Finally, the comparison between the synthetic and field records indicates that the best results are not always obtained with a synthetic record including multiples.

In conclusion, on the North Sahara, where the importance of multiples is preponderant and not readily apparent, and where interpretation is primarily based on continuity, the study of synthetic records including multiples on all exploration wells would appear to be indispensable.
AN EXPLANATION FOR THE HIGH ULTRASONIC VELOCITY IN INDIAN ROCKS*
Authors: HAYAKAWA M. , BALAKRISHNA S.
Published: April 2006

Abstract

It has been observed in the course of a detailed investigation that Indian granites exhibit high ultrasonic velocities in contrast to the specimens obtained from other countries. An attempt has been made in this paper to offer an explanation of this peculiar behaviour. Firstly, the initial internal pressure and initial velocity at the time of formation of rocks are calculated by using the experimental results for the changes in velocity with pressure in Indian, American, Japanese and Russian rocks. Besides this, standard curves have been computed using the above named parameters. Also, their possible influence on the high velocity values of Indian rocks, even under atmospheric conditions is studied. The effect of time of the formation of rocks at specific depths is also calculated in detail. As one of the results of this investigation, it comes out that under high pressure (deeper depths) it requires longer time to complete the processes of formation of rocks than under low pressure (shallow depths) and under high pressure a lot of stress energy can be stored i.e., the initial velocity becomes high when the rock is formed at great depths while at shallow depths a less stress energy can be stored and consequently less velocity values. Thus the combined effect of time and physical conditions at the time of formation of rock on the velocity in the rock at a given time is investigated. It can be seen here that the elastic behaviour of rocks with pressure will provide a clue to the possible petrogenetic history and also the approximate age of the rock.
VERSUCHE ZUR AUSNUTZUNG VAGABUNDIERENDER STRÖME IN DER GEOPHYSIKALISCHEN PROSPEKTION.*
Authors: PORSTENDORFER G.
Published: April 2006

Abstract

The experimental recording of the three components of the diurnal intensity of the stray currents in a mine shaft outside the region of mining activity of Freiberg has shown the uninterrupted presence of these currents with periods ranging from a few minutes to a few hours. It is demonstrated from theory and by model experiments that prospection by stray currents, utilizing telluric measuring methods, is feasible when the ratio between the distance to the sources of the stray currents and the size of the surveyed area exceeds a limiting value which depends on the accuracy of the measurements. To obtain an economic procedure it is necessary to replace the classical telluric technique by a vectorial recording method.

From a field example in the vein deposit of Freiberg it is shown that stray currents of arbitrary direction, and also telluric currents, are canalized by veins of anomalous conductivity. Other examples are given of underground measurements of stray currents, which were carried out for studying conductivity anomalies.
THE INFLUENCE OF SURFACE FORMATIONS ON THE APPARENT RESISTIVITY VALUES IN ELECTRICAL PROSPECTING*
Authors: ALFANO L.
Published: April 2006

Abstract

This second part deals with a subject analogous to the one developed in the first part, but related to surface irregularities with a non‐cylindrical structure. In this part we have taken into consideration both the effects due to potential electrodes and the effects due to current electrodes.

The study of these cases has been made with the help of mathematical theory, but it has been necessary to extend this theory from the case of cylindrical bodies to the case of non‐cylindrical ones.

Finally, as conclusion to both parts of the paper, some pages have been dedicated to the details of the calculation procedure, in order to demonstrate its practical htness for the study of this problem.
A DISCUSSION ON THE NATURE AND MAGNITUDE OF ELASTIC ABSORBTION IN SEISMIC PROSPECTING*
Authors: O'BRIEN P. N. S.
Published: April 2006

Abstract

Laboratory measurements indicate that seismic absorbtion in sedimentary rocks lies in the range 0.1 to 1.0 decibel per wavelength. Field measurements on the amplitude attenuation of direct, reflected and refracted pulses give values consistent with this.

If the absorption is linear, dispersion must occur. If it occurs field measurements show that it must be less than 1% over the frequency range 20 c/s to 20 kc/s.

Seismic pulses broaden so slowly with distance that, if the absorbtion is linear it must be less than that measured in the laboratory by a factor of at least ten. This is inconsistent with the amplitude measurements and would mean that emplaced rocks are more perfectly elastic than steel.

Seismic absorbtion must therefore be non‐linear. It is assumed that, for large values of Q, the non‐linear equation of motion may be linearised (Knopoff and MacDonald, 1958) and Fourier synthesis used. If this is valid, then the attenuation per unit distance must be practically independent of frequency and dispersion must be negligible.

Whatever mechanism is acting it must produce an attenuation of roughly one decibel per 1000 feet and a pulse broadening of about 1–2% in the same distance.

It is extremely desirable to make more field and laboratory experiments to determine the physical mechanism by which absorbtion takes place.
CORRELATION A DISTANCE CONSTANTE EN SISMIQUE REFRACTION*
Authors: CLÉMENT A. , LAYAT C.
Published: April 2006

The usual computation methods in refraction seismic in the Sahara often involve considerable shot distances. Therefore, in addition to a high consumption of explosives, difficulties of operation and interpretation arise.

In order to cut down the shot distances, it was necessary to study with great care the refracted waves having the shortest possible traveling path along the marker. Such paths correspond to the zone of great relative energy resulting, on one hand, from the sudden increase of reflected energy beyond the critical angle (total reflection) and, on the other hand, from the sudden appearance of refracted energy. The proposed method is founded on correlations of traces located in this “critical zone” on the different records shot on a profile; in order to get around certain difficulties due to insufficient knowledge of the marker velocity, the interpreter is led to select a constant correlation distance, at least for sections of the profile.

The paper describes in detail the setting up and utilization of the proposed method, analyses a few examples and gives an estimate of the advantages and the restrictions of this method.
ETUDE DES DIAPIRS EN ALSACE ET BADEN‐WURTEMBERG PAR LA METHODE DU RECTANGLE DE RESISTIVITE*
Authors: BREUSSE J. J. , ASTIER J.‐L.
Published: April 2006

Abstract

The study of tectonics of salt and of diapirs in particular is an important problem in the mining field as well as in that of petroleum exploration. This paper describes surveys that were carried out, using the method of the rectangle of resistivities.

After stating the principle of the method, the way it is carried out and its advantages, three examples are discussed: two in the Alsace plain (Hettenschlag‐Oberentzen and Blodelsheim), the third in Baden‐Wurtemberg (Weinstetten‐Heitersheim). Geological conditions are practically the same (resistive alluvia, very conductive marls and resistive salt series); the depth at which the top of the salt was found varied from 100 meters to more than 1000 meters. Maps of resistivities (with current electrode spacing of 6000 meters) and graphs of a few electrical soundings are presented, together with the results obtained under the form of isobath maps of the top of the salt series.

The surveys lasted 26 months and covered 171 square kilometers. The work presented corresponds to three sections totalling 93 square kilometers and was chosen because of the diversity of the tectonics. Four drill holes have been carried out since then and have confirmed the results quite well.

The method may be extended to the survey of the tectonics of a salt series or of a resistive substratum, for instance a limestone formation, that are deeper than the above cases (2000 meters or more), using current electrode spacing of 20 kilometers. Surveys of this type have already been realized in the field.
ETUDE STATISTIQUE DE SISMOGRAMMES*
Authors: AGARD J. , GRAU G.
Published: April 2006

Abstract

The amplitudes of reflection coefficients as computed from well velocity logs are distributed according to approximately normal laws. The distribution in time of the reflection coefficients, the absolute value of which is greater than a certain threshold, is Poissonian. The amplitudes of real seismogram traces obey a normal law.

The autocorrelation of a seismic trace is usually quite different from the autocorrelation of the corresponding impulse.
NOMOGRAMS FOR DETERMINING MAXIMUM ERRORS AND LIMITING CONDITIONS IN SEISMIC REFRACTION SURVEY WITH A BLIND‐ZONE PROBLEM
Authors: HAWKINS L. V. , MAGGS D.
Published: April 2006

Abstract

Nomograms are presented for the determination of the blind‐zone in seismic refraction surveys. The nomograms are calculated for the case where an intermediate velocity is assumed within the blindzone of a recorded refractor which is overlain by a single recorded layer. The nomograms may be used with time‐term or critical distance calculations and yield the depth to the top of the blind‐zone, the thickness of the blind‐zone, and the corrected depth to the recorded refractor. These values represent the maximum or limiting conditions for a layer of the assumed velocity within the blind‐zone.
MESURES D'AMPLITUDE DES ONDES ULTRASONIQUES DANS LES SONDAGES*
Authors: MORLET J. , SCHWAETZER T.
Published: April 2006

Abstract

Since 1955, the continuous velocity measurements in bore holes, made with one, later with more receivers, have become indispensable for the geophysicist, and can be useful to the geologist and the production engineer. From the beginning we have found that the amplitudes of the signals received vary in the course of a single operation. The variations have for a long time been considered as a disturbing phenomenon. It was tried to suppress them by changing the instrument gain.

With increasing precision of the velocity measurements we have sometimes observed anomalies that were hard to explain, discrepancies between the continuous velocity logs and the conventional well velocity survey, as well as between continuous velocity measurements made with different spacings. These phenomena could be observed in cased as well as in uncased holes. The first attempts to explain these phenomena by considering the velocities only, did not lead to an acceptable theory. A further study of these anomalies of the continuous velocity log has shown that in reality they were caused by strong variations of the amplitude which affected the velocity measurements. This result has led us to study the amplitude variations in open as well as in cased holes.

Up to now, the characteristics of the apparatus used in France and in the Sahara have permitted amplitude measurements with a single receiver only. In addition to the “cement bond log” in cased holes, it seems that in open holes correlations can be observed between the measured amplitude and a) the lithology; b) the fluid contained in the pores; c) the continuity of the matrix or, conversely, the permeability. However, it is now certain that numerous factors affect the amplitudes of the signals simultaneously.

In order to study the attenuation of ultrasonic waves in the different formations traversed by a deep well, we have studied the deformations of the signal in the course of its path in the mud and in the formation, restricting ourselves to the P waves. The factors to be taken in consideration are: a) the geometric energy dispersion, inversely proportional to the square of the distance from the source; b) attenuation by absorption and scattering in the mud and in the formation; c) the transmission coefficients at the transition from mud to formation and conversely, as well as at the transition between two formations having different velocities; d) phenomena of signal composition that are due to the fact that the receivers and the transmitters have a non‐infinitesimal length; these last mentioned phenomena have considerable influenc eon the amplitudes of the received signals.

Finally, the practical method for obtaining an attenuation log in an open hole requires the measurement of the ratio of the amplitudes of the first arrivals at the two receivers. Some examples show the importance of amplitude measurements made with two receivers.
MODIFIED TRIPOTENTIAL PROSPECTING METHOD*
Authors: SARMA V. V. JAGANNADHA
Published: April 2006

Abstract

A modification to the tripotential method of Carpenter (1955) and Carpenter and Haberjam (1956) is suggested and its theoretical implications and practical advantages are discussed. A specially designed switchbox is described which enables model tank experiments to be made with the modified tripotential method and with conventional methods. The results broadly show that a horizontal distance of the configuration at which the γ—resistance becomes negative directly corresponds to the depth to the interface. Discrepancies between the observed and actual depths are due to the bottom and wall effects of the wooden tank.
EXPERIENCE WITH THE REFLECTION SEISMOGRAPH IN A MINE WITHIN A SALT‐PLUG *
Authors: WACHSMUTH GÜNTHER , SCHMIDT EDGAR
Published: April 2006

Abstract

Technical development and the introduction of new construction procedures has increased the number of seismic surveys carried out underground. Interesting seismic records in three components are shown and discussed. A vertical section containing results of seismic research investigations and of drilling is shown.
REFLECTION AND REFRACTION OF SPHERICAL COMPRESSIONAL WAVES AT ARBITRARY PLANE INTERFACES *
Authors: BORTFELD R.
Published: April 2006

Abstract

The exact expressions for the reflection and refraction of homogeneous spherical compressional waves at the plane contact between two semi‐infinite media are obtained by a new simple method. Whilst its general ideas were outlined in a previous paper (Bortfeld 1962) dealing with some special interfaces, this method is now applied to all kinds of contact (solid‐solid, solid‐fluid, fluid‐solid, solid‐free, fluid‐fluid, fluid‐free). By some improvements, the treatment of the general case is even more simple than the previous one of the special cases.

Integrating the potentials for sinusoidal excitation over the circular frequency and adding the static potentials yields expressions for the step‐response which consist of (infinite) single integrals of elementary functions. By a single application of Cauchy's theorem, the complete set of wavefronts is obtained and the step‐response is put into forms suitable as a basis for numerical calculations. The responses for arbitrary source excitations are given in the usual way by superposition integrals.
SIMPLIFIED GRAVITY TERRAIN CORRECTIONS*
Authors: WINKLER H. A.
Published: April 2006

Abstract

The method of Far Terrain Corrections is described which permits contouring of terrain effects for distant topography; near terrain effects must be computed separately.

The method is only slightly less accurate than standard graphical techniques and saves computing time. It is most useful in medium size surveys involving 100 to 2,000 observation points where the application of electronic computers is uneconomic.
AIR WAVES IN ENGINEERING SEISMOLOGY
Authors: MOONEY HAROLD M. , KAASA ROBERT A.
Published: April 2006

Abstract

Certain travel time readings in shallow engineering seismology can be attributed to a seismic wave which has propagated through the air, but in which the energy has been transmitted into the ground before reaching the detector. Waveform evidence for this conclusion is presented, based upon the effects of altering the source conditions to delay the direct wave and of embedding the geophone in sound‐absorbent material. Erroneously large depths may be computed if these air wave readings are interpreted as readings produced by direct waves through the ground. Potential difficulty exists only if velocity in the near‐surface material is less than 330 meters/second (1100 feet/second).
EXACT EXPRESSIONS FOR THE GRAVITATIONAL ATTRACTION OF A CIRCULAR LAMINA AT ALL POINTS OF SPACE AND OF A RIGHT CIRCULAR VERTICAL CYLINDER AT POINTS EXTERNAL TO IT
Authors: TALWANI MANIK
Published: April 2006

Abstract

Parasnis' method of obtaining the gravity anomaly of circular laminae can in some cases lead to large errors. The use of the solid angle chart given by Nettleton (1942) is suggested instead.
EFFET DE LA VITESSE ET DE LA CONSTANTE D'INTÉGRATION SUR LA FORME DES ANOMALIES AÉRORADIOMÉTRIQUES*
Authors: GIRET M. R.
Published: April 2006

Abstract

The theoretical radiometric anomalies caused either by a pinpoint source or by a larger one, which could be detected 75 metres above the source by a mobile detector with a very low velocity and time constant, were treated by an analog simulator which gave the curves transformed by the effect of velocity and time constant. The characteristics of these curves are discussed.

An actual airborne survey above a radioactive anomaly of small surface yielded results which are analyzed and compared with the previous theoretical data. The degree of agreement between theoretical and experimental results seems satisfactory.

This study shows that the deformation of curves by velocity and time constant in most actual surveys is small enough when the product of velocity and time constant is less than 75 m for a flying altitude of 75 m.
A METHOD FOR QUANTITATIVE INTERPRETATION OF SELFPOTENTIAL MEASUREMENTS*
Authors: MEISER P.
Published: April 2006

Abstract

The paper deals with the calculation of the potential distribution over various polarized bodies; the potential profiles are plotted on a double‐logarithmic net. For a quantitative evaluation the field graphs, plotted likewise in a logarithmic scale, are compared with model graphs. The method is explained by means of several examples, in which potential graphs of a single, as well as of several disturbing bodies lying close to each other, are interpreted. The practical examples have been derived from selfpotential measurements which were carried out above graphite deposits in the southern Bavarian woods.

This method is generally valid for the interpretation of potential graphs of arbitrary dipoles. Therefore it can also be applied – in a slightly modified form – for the interpretation of magnetic measurements. An appropriate method of interpretation for this purpose is being prepared.
ELABORATION RAPIDE DE CARTES GRAVIMETRIQUES DEDUITES DE L'ANOMALIE DE BOUGUER A L'AIDE D'UNE CALCULATRICE ELECTRONIQUE*
Authors: LA PORTE M.
Published: April 2006

Abstract

A method is described in which various gravity maps (regional, residual, first and second derivatives, upward and downward continuation, etc….) may be quickly constructed, without manual plotting and visual interpolation, which are often a source of error. The coordinates and the g‐values (x, y and g) of the field stations are introduced into the electronic computer on perforated cards. The computations are carried out by means of a hexagonal network. The computed values and their respective positions on the network are plotted directly on a sheet of paper by the electronic computer. The map is obtained by assembling these sheets and contouring.
A GENERAL FORMULA TRIPOTENTIAL PROSPECTING METHOD.*
Authors: SARMA V. V. JAGANNADHA
Published: April 2006

Abstract

The theoretical aspects of a general configuration of the tripotential prospecting method are described while particular cases of the method were described by Carpenter and Haberjam (1956) and Sarma (1961).
THE QUANTITATIVE RECORDING OF SEISMIC EVENTS WITH EXTREMELY LARGE AMPLITUDE VARIATIONS BY DISCONTINUOUS GAIN CONTROL*
Authors: ROSENBACH O. , SCHMITT O. , VEES R.
Published: April 2006

Abstract

A transistorized combination of multivibrators is described, by which the gain is set according to a time programme. This equipment allows quantitative recording of seismic events with extremely large amplitude variations. Some possible applications of this recording system to seismic research are discussed.
A STATISTICAL STUDY OF ISOSTASY*
Authors: NEIDELL NORMAN S.
Published: April 2006

Abstract

Isostasy was regarded as the impulse response to topographic loading, hence convolution with the topography should generate the observed gravity anomalies. Ordinate values of the impulse response were indeterminate but the zeroth, first and second moments were found to be significant. These could be interpreted as the degree of compensation, its spread, and the displacement with respect to the loading.
EVOLUTION DE L'ACTIVITE GEOPHYSIQUE DE SURFACE (PETROLE)*
Authors: DESAINT R. , RICHARD H.
Published: April 2006

Abstract

From data published in various journals, as for instance “Geophysics”, a lot of information can be gathered on the geophysical activity in the world. In this article the evolution of this activity is discussed, as far as it concerns the search for hydrocarbons.

An interesting part of such a study consists of a comparison of the geophysical activity with the activity in drilling and the extent of the discovered reserves. In the USA in particular the amount of data available is sufficient to make a detailed analysis possible.
ETUDE STATISTIQUE DE LA CONTRIBUTION DES MULTIPLES AUX SISMOGRAMMES SYNTHETIQUES ET REELS*
Authors: BOIS P. , HEMON CH.
Published: April 2006

RESUME

Une étude statistique par secteurs des coefficients de réflexion permet de préciser leur homogénéité et de donner des renseignements sur l'importance de la contribution des multiples et de l'atténuation due aux coefficients de transmission.

Elle permet également de montrer que les multiples tendent à rendre normale la répartition des amplitudes des sismogrammes impulsionnels et que le filtrage par l'impulsion provoque le même phénomène sur les amplitudes des sismogrammes syntliétiques.
WAVE FRONT INVESTIGATIONS IN MODEL SEISsMOLOGY*
Authors: BERCKHEMER H. , ANSORGE J.
Published: April 2006

Abstract

A method is described which allows to measure the elastic wave motion in the “interior” of two‐dimensional solid models. It is based on the measurements of the lateral deformations of a plate that are related to the state of compression in the plane of the plate. A capacitive detector measuring the motion has been developed.

Wave front studies have been carried out in a half space, in two half spaces in contact and in a single‐layered half space. The experimental results are compared with theory. Special attention has been paid to the head wave.
FIVE‐LAYER MASTER CURVES FOR THE HYDROGEOLOGICAL INTERPRETATION OF GEOELECTRICAL RESISTIVITY MEASUREMENTS ABOVE A TWO‐STOREY AQUIFER*
Authors: FLATHE H.
Published: April 2006

Abstract

One of the main tasks of geoelectrical techniques in their application to hydrogeological objects is the detection of aquifers with fresh water and the delimitation of such aquifers from impermeable or salt‐water‐bearing beds. In practice it frequently occurs that intercalated clay horizons divide an aquifer into several “storeys” of various thicknesses.

The present paper deals with an aquifer consisting of two storeys (sand and gravel), above a substratum of good electrical conductivity (clay, salt water). By means of a set of 72 computed master curves, the possibilities of interpretation of geo‐electrical measurements above such a substratum are examined with respect to the specific resistivities of the overburden and the intercalated clay horizon. Different thicknesses of the two groundwater storeys are considered. The result gives an idea of the extent to which geoelectrical measurements may help to elucidate hydrogeological conditions; it also provides the geophysicist with practical hints for the performance and the interpretation of such measurements.
EXAMPLES OF SYNTHETIC REFRACTION ARRIVALS AND WIDE‐ANGLE REFLECTIONS*
Authors: BORTFELD R.
Published: April 2006

The exact responses of plane interfaces to incident spherical compressional waves are calculated by an electronic computer. The reflected part of the response is shown for various positions of the ‘shot’ and of the ‘receiver’ as well as for various velocity contrasts. This makes it possible to study some features of the reflection process, especially the behaviour beyond the critical angle.
SERIES FOR THREE‐DIMENSIONAL MIGRATION IN REFLECTION SEISMIC INTERPRETATION*
Authors: SATTLEGGER JOHANN
Published: April 2006

The problem of three‐dimensional migration is solved for arbitrary, three‐dimensional, continuously differentiable velocity functions v=v (x4) by means of series.

The derived formulae are applied to numerical examples.

The possibility of approximating real, discontinuous velocity distributions by continuous functions is mentioned and illustrated by an example.

The application of electronic computers, which is necessary due to the complexity of the formulas, is discussed.
DESIGN OF SUB‐OPTIMUM FILTER SYSTEMS FOR MULTI‐TRACE SEISMIC DATA PROCESSING*
Authors: FOSTER M. R. , SENGBUSH R. L. , WATSON R. J.
Published: April 2006

Using 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.
THE KÖNIGSBERGER RATIO AND THE DIPPING‐DYKE EQUATION*
Authors: HOOD PETER
Published: April 2006

This article deals with the effect that the Königsberger ratio, the ratio of remanent to induced magnetization, has in modifying the dipping‐dyke equation. Many reversed dykes are found on aeromagnetic maps and their presence indicates that remanent magnetism must often play a significant part in the magnetic expression of normally‐polarized dykes. The methods for the measurement of remanent magnetization and susceptibility (k) are outlined, and the relationship between k and volume % magnetite (V) is discussed. It is proposed that a good approximation is k= 0.15 (x−1 ‐ x), where x=1‐V/100. The general equation for the dipping dyke, which includes the contribution of remanent magnetization, is given. A method of obtaining k from the magnetic map is also derived.
SUR LA DEFINITION DE L'ANOMALIE DE BOUGUER ET SES CONSEQUENCES PRATIQUES*
Authors: NAUDY H. , NEUMANN R.
Published: April 2006

When interpreting Bouguer Anomalies, it is important that the location of the point to which the corrected measurement is related, is correctly defined: the station itself or its projection on the datum plane. The consequences of this choice are not negligeable when the topography is rough.
LE MAGNETOMETRE AEROPORTE MP 121 SUD‐AVIATION
Authors: THOMAS J.
Published: April 2006

Abstract

Proton precession magnetometers usually operate discontinuously since thy rely one intermittent impulses. The aerial versions of these magnetometers suffer from relatively high background noise. The type of magnetometer discussed in this paper has solved the two problems of discontinuity of measurements and reduced sensitivity due to background noise.

Comparative texts with an established flux‐gate apparatus have given significant and convincing results.
SPONTANEOUS POLARIZATION STUDIES*
Authors: BECKER ALEX , TELFORD W. M.
Published: April 2006

Self potential measurements, both in drill holes and on surface, have been made in and around sulphide mineralization. Similar measurements were carried out on small scale laboratory models. The potential and current configurations around theoretical sulphide bodies are also described. Results of the model and field work seem to verify, in a qualitative manner, the electrochemical mechanism of spontaneous polarization proposed by Sato and Mooney. Possible causes are suggested for the abnormally large surface anomalies frequently found in the field.
GEOPHONE DISTORTION OF SEISMIC PULSES AND ITS COMPENSATION*
Authors: O'BRIEN P. N. S.
Published: April 2006

An electronic analogue was used to obtain geophone distortion of typical seismic pulses. Some of the results were checked by computation and in all cases agreement was extremely close. For late arrival events estimates of attenuation and phase shift may be made from the steady‐state response curves. It is explained why these curves are not applicable to the first peak, for which one must use the results in Table III.

Ground‐geophone coupling introduces the same distortion as a very lightly damped galvanometer with a natural frequency usually in the range 100c/s—200c/s. In swampy terrain this frequency may reduce to 30c/s—40c/s and coupling effects may be severe.

An electronic unit whose characteristics are the inverse of those of a geophone has been used to improve the first peak amplitude of a seismic refraction record. Since 1c/s geophones are often desirable in refraction survey it may well be more economic to use higher frequency geophones followed by their inverse filter.
MEASUREMENTS ON THE ARRIVAL REFRACTED FROM A THIN HIGH SPEED LAYER*
Authors: DONATO R. J.
Published: April 2006

Abstract

A theory is developed to predict the amplitude and velocity of the first arrival produced by a thin solid refractor embedded in a solid environment. Laboratory experiments on a three dimensional model substantially confirm the theory. The essential conclusion may be found in Figure 8 where it is shown that for a constant wavelength, and for thicknesses up to about one half a wavelength, the attenuation per unit distance decreases monotonically with increase of refractor thickness.

The assumption is made that the amplitude, A, attenuates as (x)‐n exp(‐βx), where x is horizontal distance and n and β are constants. It is emphasised that it is difficult to obtain reliable values for n and β from the initial amplitude measurements.
ETUDE DU “POINT BRILLANT” SUR MODELES SISMIQUES*
Authors: COURONEAU JEAN
Published: April 2006

Abstract

The technique of two‐dimensional seismic models offers a simple solution to the problem of pulse reflection at the interface of two solids. Particular attention is paid to the existence and character of the amplitude increase in the interference zone between PP and PPP. The following points are discussed:

– the considerable deformation of the pulse when such an increase exists.

– the desagreement existing in the neighborhood of the critical points between the amplitude calculated by plane wave theory and the amplitude observed for cylindrical or spherical waves.

– the nonexistence of such an increase when velocity or density contrasts are too great.

– the presence, in the case of very large velocity contrasts, of an increase of the amplitude in the zone of interference, between PP and PSP‐waves.

– the considerable importance of conversion arrivals (PS+SP).

– the necessity of taking into account the emission of distorsional waves so that the observed arrivals of conversion waves can be explained.
P – AND SV – WAVES FROM UPHOLE SHOOTING*
Authors: MEISSNER R.
Published: April 2006

Abstract

Uphole recordings in sediments very often reveal shear waves. With their velocity and that of the P‐waves Poisson's ratio may be determined, this usually has unexpectedly high values.

A number of up‐hole shots were recorded with a linear spread of geophones and with constant gain amplifiers. Calculations were made to show the effect of the free surface and ray divergence (the spread factor). The theoretical, relative amplitudes of the ground motion were plotted together with the observed values. In general, there is good agreement between theory and observation which is better for the P‐waves than for the S‐waves. The reasons for this difference are discussed.

Finally, an absorption coefficient is calculated from the amplitudes measured at the surface.
METHODE DE CALCUL DE LA DERIVEE SECONDE VERTICALE DU CHAMP GRAVIFIQUE OU DU CHAMP MAGNETIQUE UTILISANT ĽINTERVALLE DES ISOGAMMES*
Authors: VAN NGOC PHAM
Published: April 2006

This new method of calculation, of the second vertical derivative of gravity or magnetic fields is appreciably different from the classical methods because it is based upon the variations of the distance between the isogams rather than a regular grid with “constant spacing”. In a certain way, it is a method of “constant interval”. A number of practical advantages are inherent to the method, among these, the possibility to use the cartesian charts with bi‐logarithmic scales which make the calculation much easier, and the creating of iso‐error maps which are indispensable for the interpretation of the derivative maps. Three examples of practical application are given, two of them pertain to gravimetry, the third to aeromagnetism. These results are compared with second derivative maps obtained with other methods.
MULTIPLE EVENTS IN REFRACTION SHOOTING*
Authors: MEISSNER R.
Published: April 2006

A description and classification is given for those later events in seismograms of refraction–and wide angle reflection shooting which travel nearly parallel and at constant time intervals behind the first arrivals and which are frequently observed in field surveys. Multiple events with the velocity V1 of the uppermost layer may be caused by multiple P‐reflections and certain velocity conditions or by PS‐conversions. In addition to these types multiple events with the velocity V2 or Vn may be caused by reflected refractions or by reflected diving waves. The different types will be distinguished mainly by means of travel time–and amplitude‐considerations.
MODEL SEISMIC INVESTIGATIONS ON REFRACTED WAVES*
Authors: GUHA S.
Published: April 2006

The headwave system for an incident P‐wave in a two‐layer case has been traced in the ‘inside’ of a two‐dimensional model and it is found that the measured fronts do not coincide with the wavefronts constructed according to the Huygen's principle. A refraction profile indicates different velocities near the critical distance but shows the true value for the higher velocity medium at greater distances. An error in the intercept time, which is about 6 % too high in the example, should, however, always be present even if extrapolation is done from the region where the profile shows the true velocity of the medium.
RAPID COMPUTATION OF THE GRAVITATION ATTRACTION OF TOPOGRAPHY ON A SPHERICAL EARTH*
Authors: TAKIN MANOUTCHEHR , TALWANI MANIK
Published: April 2006

A brief review of the existing methods of gravity reduction is given and a new method suitable for use on high speed digital computers is described. The method is based on the formula for the gravitational attraction of a frustum of a cone. The topographic contours are represented by polygons and the x and y coordinates of corners of the polygons constitute the input to the computer. The vertical component of the gravitational attraction is calculated by evaluating the cone formula for a number of vertical sections of the topography. Each vertical section is simplified by adopting a procedure of grouping and averaging for the distant points of the section. The effect of the earth's sphericity is taken into account by lowering the distant points of the sections by amounts determined by the curvature. The computations include the area close to the point at which the attraction is required and may be limited to an area defined by a circle centered at this point. The method is therefore compatible with the conventional zone chart methods.

As an illustration of the method the gravitational attraction of Caryn Seamount in the Atlantic Ocean is computed. The total Bouguer correction and the Terrain correction are also computed for an area in northwestern South America and comparisons are made with hand computations by a zone chart method. As an example, for work at sea, the Bouguer corrections for an area near the Island of Mauritius in the Indian Ocean are computed and the effects of sphericity and three‐dimensionality are calculated.

The gravitational attraction of two‐dimensional bodies can be computed in a very similar manner. The attraction of the Puerto Rico Trench model is computed and the results are compared with other methods. The effects of sphericity and assumptions involved in extending the models to infinity are discussed.
AN EVALUATION METHOD FOR GEOMAGNETIC DEEP SOUNDING, ITS DERIVATION AND PRACTICAL USE*
Authors: SCHEUBE H. G.
Published: April 2006

The derivation and application of a new method of geomagnetic deep sounding, that is exploring for underground electrical conductivity anomalies by means of temporal variations of the earth's magnetic field, is presented.

The problem is restricted to two dimensions (horizontal and vertical) and for the case of a nearly homogeneous horizontal component of the disturbance vector as compared with the vertical over the area in question.

The basis of the method is a relationship between both components of the disturbance vector. The first step is a period analysis of the records and from this the construction of so called “characteristic functions”, one for each station, these functions being determined by the conductivity distribution of the earth's interior. The second step consists of a model interpretation of these functions.

The method is applied to simultaneous records from five stations (U. Schmucker, 1959) within the region of the conductivity‐anomaly of Northern Germany. A preliminary model of this anomaly is given.
A PORTABLE PROTON PRECESSION MAGNETOMETER*
Authors: SARMA D. GUPTA , BISWAS S. K.
Published: April 2006

The paper describes a transistorised, portable proton precession magnetometer constructed for surface geophysical prospecting. Constructional and circuit details are furnished. The readout of the instrument is digital. The accuracy of measurement is ± 1 part in 20,000. The maximum gradient of the total field under which a satisfactory measurement can be made is about 1 gamma/cm. The sensing head uses a single coil system with distilled water as the proton sample.
PART II: THE SECTIONAL RETRO‐CORRELOGRAM
Authors: ANSTEY N. A. , NEWMAN P.
Published: April 2006

The retro‐correlation function (or auto‐convolution) of a seismic trace is obtained by correlating the trace against a time‐reversed version, of itself. The Sectional Retro‐Correlogram is obtained by the arrangement of retro‐correlation functions in sectional form, in the manner of the Sectional Auto‐Correlogram.

During the process of retro‐correlation, each primary event on the seismic trace interacts with each primary event on the time‐reversed seismic trace to generate a first‐order surface multiple event. Similarly each primary interacts with each multiple, and each multiple with each multiple, to generate higher‐order surface multiple events. Thus the final appearance of the Sectional Retro‐Correlogram is that of a record section which contains no primary reflections.

The travel‐time and sign of the events displayed on the Sectional Retro‐Correlogram are correct, but the amplitudes of the higher‐order multiples are exaggerated. Nevertheless there is often a remarkable correspondence between the Sectional Retro‐Correlogram and the later parts of the record section from which it was derived.