bluuebunny/crossref_metadata_2025_split huggingface dataset:
CONTINUOUS ANALYSIS OF THE VELOCITY FUNCTION AND OF THE MOVE OUT CORRECTIONS*
Authors: GAROTTA ROBERT , MICHON DOMINIQUE 
Published: April 2006

ABSTRACTSeveral papers presented at the last SEG Convention in Houston by Schneider, Backus et al have shown how important and fruitful it was to obtain a continuous knowledge of the velocity functions and they have solved their problem by a Dynamic Correlation Analysis. Our purpose is to introduce here a method based on the best summation of a set of traces instead of the best correlation.Practically, this approach has several advantages:1) Two traces only can be correlated at each step whereas the summation can bear on any number of them;2) Optimizing the summation is actually what we are looking for since, at the long end, the success of the improvement is evaluated from the compositing of several traces either weighted or not.On the other hand, an advantage of correlation is the possibility of adding correlations obtained at several places in a same neighbourhood in order to improve the results. With the summation method this is feasible only when dips are inexistent: we shall see that the difficulty due to the dip effect can be turned around.The basic principle of the method can be summed up as follows: traces relating to a same reflection point are considered; several composites are made, each after applying different move out corrections ranging widely around an estimated adequate velocity function. At each time coordinate, the best adapted velocity function, i.e. the one that yields the best phase relation between reflected events, corresponds to the composite trace the average amplitude of which is the largest.This way, the velocity function corresponding to primary reflections as well as those corresponding to multiple reflections can be established accurately.Some examples are shown.
THE ELECTRICAL CURRENT PATTERN INDUCED BY AN OSCILLATING MAGNETIC DIPOLE IN A SEMI‐INFINITE THIN PLATE OF INFINITESIMAL RESISTIVITY*
Authors: KOEFOED O. , KEGGE G. 
Published: April 2006

ABSTRACTSeveral papers have been published in which the electromagnetic anomalies are described that are produced by conductive ore bodies of different shapes. No publications are available, however, in which the electrical current pattern is described that is induced in these ore bodies. Yet an insight in this electrical current pattern would be valuable in order to assess the possibilities of different electromagnetic techniques, for instance with regard to the determination of the dip and of the depth extent of plate shaped ore bodies.In the present paper computations are given of the electrical current pattern induced by an oscillating magnetic dipole in a semi infinite plate shaped orebody of infinitesimal thickness, in which the penetration depth of the current is infinitesimal to a higher order than the thickness of the plate. The computations are based upon an equation derived by Wesley for the magnetic field produced in these conditions, combined with the relation between the electrical current density in a laminar sheet and the magnetic field produced by this current at the surface of the sheet.The results of the computations show that, if the horizontal distance between the dipole source and the sheet is sufficiently small, the maximum current density of the return current may occur at a depth below the upper edge of the sheet which is appreciably smaller than the depth of the upper edge of the sheet below the surface. The depth of the return current becomes large when the horizontal distance between the source and the sheet is large.
COMPUTATIONS OF NETWORK MODELS OF POROUS MEDIA*
Authors: RINK MANFRED , SCHOPPER JÜRGEN R. 
Published: April 2006

ABSTRACTIn a paper presented at last year's Amsterdam meeting (viz. Geophysical Prospecting 14 (1966), 3, 301–341), J. R. Schopper derived formulas relating formation factor, permeability and porosity, by means of a statistical‐network approach and by treating the electric and hydraulic resistance analogously.The model of the porous medium consists of a network of branch resistors, their values being statistically distributed about a mean Ro with a relative standard deviation (variation coefficient) s. A properly defined total resistance R of the network can be expressed by the relationship:

image

Here α is a geometrical factor dependent only on the shape of the network (i.e. the number of meshes in the longitudinal and transversal direction), ε is a characteristical constant dependent only on the individual mesh shape (i.e. the number of nodes and branches within a mesh).This network constant ε enters the equations relating formation factor, permeability and porosity, ε had been found to be in the range zero to one by calculating algebraically two special limiting network cases. However, for a better understanding of which value exactly this constant will have in actual porous media, networks with various mesh shapes have to be treated generally.Because of the basically statistical approach, the networks have to be large so that a general algebraic treatment is precluded. Hence numerical methods using digital computers must be applied.The determination of the total resistance R of any resistance network leads to the problem of solving a system of linear, inhomogeneous equations; i.e. Ohm's law written in matrix form:

image

(R) is the matrix of the coefficients, composed of the individual branch resistances.
(I) is the column vector, its components being fictitious circular mesh currents.
(U) is the inhomogeneity column, its components being source voltages within the individual meshes.

The matrix (R) has characteristic properties that depend on the mesh shape on the one hand and on the number and arrangement of the meshes on the other hand. With the regular arrangement of identical meshes investigated here, the matrix always has a banded structure and is symmetrical with respect to the main diagonal, positive definite, and non‐singular.For the numerical determination of the wanted constant ε the coefficients matrix is provided with values having a known distribution. Here, in particular, a computer‐generated pseudorandom homogeneous distribution is used. The system, of equations is solved for R by a modified Cholesky method. Equation (1′) can then be solved fore. The main features of an ALGOL program written for this purpose and optimized with respect to storage space requirement and computer time are discussed.Networks of triangular, square and hexagonal meshes have been investigated. The results are discussed.
THE INFLUENCE OF LATERAL INHOMOGENEITIES ON THE DIPOLE METHODS*
Authors: FRÖHLICH R. K. 
Published: April 2006

ABSTRACTThe theory of electrical dipole soundings proved that this method can produce resistivity measurements, which are comparable with those obtained by electrical soundings of the Wenner or Schlumberger type. Their main advantage is the use of short cable lengths, which is important if the depth of penetration should be large.A considerable disadvantage of the dipole method is the great sensitivity to lateral discontinuities. Though these have an influence on the Schlumberger arrangement as well, they can disturb a dipole sounding to such an extent than an interpretation based on a horizontal layer case is no more possible.There are six different dipole arrays, which differ from each other with respect to the angle enclosed by the two dipole orientations‐the current dipole AB and the measuring dipole MN. The theoretical comparison of the dipole arrays with the Schlumberger array concerning their sensitivity to lateral discontinuities is a useful basis for the choice of the most suitable configuration.Considering geological subsurface conditions the right choice of a dipole array can give an optimal result, i.e. a dipole sounding for which the sensitivity to lateral discontinuities is as small as possible under the given circumstances.
RESISTIVITY PROSPECTING IN A UNITED NATIONS GROUNDWATER PROJECT OF WESTERN ARGENTINA*
Authors: SERRES Y. F. 
Published: April 2006

AbstractResistivity surveys including surface measurements and electric well logging are at present carried out as routine techniques by a Groundwater Project of the United Nations Special Fund in arid valleys of the Argentine eastern Andes.The aims of the Project are the evaluation of ground water supplies in 5 pilot areas and the training of Argentine professionals in modern techniques of groundwater investigation.In Zonda and Tulüm Valleys, one of the five pilot areas, the groundwater body is essentially represented by alluvium of San Juan River and upper Tertiary gravels lying upon impervious clayey Tertiary sediments.Profiles of electrical soundings—spread in the valleys normal to the structural trends—were completed as a broad reconnaissance type investigation. In the outwash plain, a thick clayey overburden sometimes covered by saline material produces a masking effect on the deep sands and gravels and makes the evaluation of true resistivities difficult. Under certain conditions, appropriate use of electric well logging results helps solving the ambiguities found in the interpretation of the electrical soundings. Two examples are discussed.Also a typical development of surface resistivity interpretation as a whole is presented. Emphasis is placed upon the significance of the transverse resistance values to better interpret the hydrogeological picture. The last stage in data processing, presented on a map of the resistive fill and the conductive basement, provides evidence of the strong structural control of the valleys and shows the main variations in the ground water body constitution.
DIE SEISMISCHEN GESCHWINDIGKEITEN DER JUNGEREN MOLASSE IM OSTSCHWEIZERISCHEN UND DEUTSCHEN ALPENVORLAND*
Authors: LOHR J. 
Published: April 2006

AbstractAccording to a study of seismic velocities in the Alpine Foreland of Eastern Switzerland, the initial velocity is rather high in comparison with other Tertiary basins and shows an exceptionally high increase rate. When analysing the average and the interval velocities, especially of Tertiary strata, and when comparing them with velocities of strata of the same age and a very similar facies of the Northern Rheintalgraben, it has been found that the increase of velocity is closely related to the distance to the Subalpine Molasse. The conclusion is that the velocity of the Tertiary strata is strongly influenced by the folding pressure of the Subalpine Molasse or of the Alps. The same method has been applied to a relatively large number of wells in the area of the “German Molasse”. Not only the results in Eastern Switzerland have been confirmed, but also it has been proved that the diagenesis of the Tertiary strata and, hence, their velocities are influenced only partially by the specific depth of the basin. Velocities increase towards the Folded Molasse or the Alps. Consequently they depend on lateral folding pressure, which decreases from west to east with the increasing width of the basin. The tertiary strata of the basin have been affected by lateral folding pressurefrom south to north. However, structures with lateral compression have not been discovered yet in the German Alpine Foreland.
AN ANALYSIS OF EQUIVALENCE IN RESISTIVITY SOUNDING*
Authors: KOEFOED O. 
Published: April 2006

AbstractA mathematical analysis is given of the phenomenon of equivalence in resistivity sounding, which is based upon the properties of the raised kernel function. Analysis of this function instead of the apparent resistivity function is justified because, as has been shown in a previous publication, variations in the apparent resistivity function lead to variations in the raised kernel function with relative values of the same order of magnitude The expression for the raised kernel function is expanded into a Mac Laurin series. Equivalence can occur only if the second order term of this series is negligible. The coefficient of the first order term depends on the resistivity and the thickness of the layer under consideration. There is an infinite set of combinations of values for these two quantities, for which the coefficient of the first order term has the same value. All these combinations represent equivalent layer distributions.
COUPLAGE SOL‐GEOPHONE*
Authors: LAMER A. 
Published: April 2006

AbstractThe seismometer‐ground system is represented by a damped oscillatory system. Relatively simple approximation formulas are derived to express the coupling between ground and seismometer. These expressions are applicable in seismic exploration. The coupling is that of a mass, suspended by a spring, to the surface that the ground would have in absence of the seismometer. It results in a low‐pass filtering of the ground motion, which is due to the presence of the seismometer. This effect is expressed in a unit‐impulse response. It appears that, over a sufficiently homogeneous ground and for low frequencies, one has a true coupling between ground and seismometer. To obtain a sufficiently large pass‐band, a low seismometer housing‐mass together with a not too small housing radius are necessary.
A RESPONSE OF A RANDOMLY LAYERED EARTH TO AN ELECTRIC POINT OR DIPOLE SOURCE*
Authors: NAIDU PRABHAKAR S. 
Published: April 2006

AbstractA point source or a dipole source of electric current, placed on a randomly layered semi‐infinite medium, produces an inhomogeneous random potential field on the surface. The variance of the random potential, normalized with reference to the normal field (that is, a field due to a point source or a dipole source on a homogeneous medium), falls off inversely as the distance from the source. The conductivity of the layers is assumed to vary randomly about a mean value (unity) such that the variations can be represented by a zero mean homogeneous random function. Further the variations are assumed to be small compared to the mean so that the first order perturbation is adequate. The analysis shows that the dipole field is more sensitive than the single pole field to the conductivity variations.
ANALYSIS OF SOME MULTI‐FREQUENCY, MULTI‐SEPARATION ELECTROMAGNETIC SURVEYS*
Authors: PARASNIS D. S. 
Published: April 2006

AbstractIn the interpretation of anomalies obtained with moving source‐receiver dipole electromagnetic surveys, use is frequently made of the so‐called phasor or vector diagrams. Most such diagrams are based on model experiments or theoretical calculations on bodies of simple geometry. If the anomaly at some given coil‐separation and frequency is known it is possible to predict the anomaly at some other separation and frequency. While the results of such predictions often agree admirably in the laboratory experiments, wide, systematic discrepancies are observed in full‐scale field work. Some of the discrepancies can be explained by various phenomenological arguments and in this respect the effect of overburden conductivity appears to be more serious than is generally supposed. The effect of phase rotation due to the overburden is discussed in detail.The paper is mainly a cautionary note based on some full‐scale data of multi‐frequency, multi‐separation surveys against the blind use of vector diagrams, but it also discusses the extent of the extra information and interpretation aid provided by such surveys.
TWO‐DIMENSIONAL MASS DISTRIBUTIONS FROM GRAVITY ANOMALIES: A COMPUTER METHOD*
Authors: QURESHI I. R. , MULA H. G. 
Published: April 2006

AbstractA gravity anomaly profile, considered to be associated with a two‐dimensional mass distribution of constant density contrast, may be interpreted with the help of a digital computer. Using the infinite slab formula and anomaly values at selected points of the profile, an initial model of the anomalous mass is built. The gravity effect of the model is computed with a simplified version of the formula derived by Talwani, Worzel and Landisman (1959) for line‐integration. After the effect is computed at a point, the model is adjusted depending upon the residual anomaly. The effect of the adjusted model is computed at the following point. Within one cycle of computation the model is adjusted as many times as the number of the selected points. Five such cycles are sufficient to minimize residuals in most cases. A final cycle is computed without adjustment.Local anomaly profiles have been interpreted to obtain the shape of a sedimentary basin and of a faulted block. A regional anomaly profile has been interpreted to obtain crustal structure.
DISCOVERY OF DIRECT‐SHIPPING IRON ORE BY GEOPHYSICAL METHODS IN THE CENTRAL PART OF THE LABRADOR TROUGH*
Authors: SEGUIN MAURICE K. 
Published: April 2006

AbstractThe deposits of the central sector of the Labrador Trough are magnetite‐rich iron ores subjected to enrichment by the process of leaching. In spite of the fact that some ore types are porous and low in density, most of the ore zones have undergone a net increase in density brought about by enrichment. In the course of their formation, the magnetic characteristics of the rocks have changed and a great deal of the magnetite was altered to relatively non‐magnetic iron oxides and hydrous iron oxides. Consequently, induced as well as remanent magnetization decreased, but the ratio of the latter with respect to the former increased substantially. All drift‐covered areas underlain with iron‐formation are potential ore producing areas. From measurements of the first two physical properties and determination of the thickness of overburden by means of a combined gravity‐magnetic‐seismic or resistivity survey, it is possible to detect and distinguish the iron formations and potential ore zones from the country rocks.In spite of the fact that the iron formations are a complex assemblage of rock types, each having different physical and chemical properties, a qualitative and semi‐quantitative correlation between the results of the surveys and the geology as well as the structure of the area could be established. Consequently, in order to increase the chances of success, first a mathematical correlation of the amplitude of the gravity anomalies with the specific gravity, the iron content, the silica content, the porosity factors and the dimensions of the underlying orebodies, and secondly, a quantitative correlation of the ground magnetic intensity relative to the reference lithologie unit with the percentage of Fe3 O4 recovery and the volume magnetic susceptibility were done for many deposits.A few discoveries were made with this method. Finally, a fully quantitative interpretation of the geophysical data using a multimodeling analysis led to the discovery of additional direct‐shipping iron ore deposits in the Schefferville mining district of Canada.
THE UTILITY OF CARBORNE RADIOMETRIC SURVEYS IN PETROLEUM EXPLORATION OF GLACIATED REGIONS*
Authors: SHIDELER GERALD L. , HINZE WILLIAM J. 
Published: April 2006

AbstractCarborne gamma radiation surveys over petroleum reservoirs and faults in the glaciated Michigan Basin suggest that this mobile technique may be useful in reconnaissance subsurface exploration, especially in fault detection. This conclusion assumes favorable surface conditions, as well as proper instrumentation, field procedures, and interpretive techniques. Glaciated regions are relatively undesirable terrains for gamma radiation surveys. Thick deposits of glacial drift appear to repress the detection of subsurface features. Furthermore, extremely heterogeneous soil conditions, which are characteristic of many glaciated regions, result in excessive radiation interference. The operational conditions which produced optimum results consisted of continuous profiling on unconsolidated roads, employing two simultaneously operated scintillation counters. Optimum detection was obtained during relatively cool nighttime traverses.
FINITE‐ELEMENT ANALYSIS OF SHALLOW TEMPERATURE ANOMALIES*
Authors: GEERTSMA J. 
Published: April 2006

AbstractFinite‐element analysis has been used in calculating shallow temperature anomalies due to both the presence of salt domes and near‐surface faults. The results of the numerical analysis are in good agreement with field observations reported earlier by Poley and van Steveninck. The calculations show how surface emissivity must be responsible for the pronounced temperature anomalies above salt domes.Faulting is a mechanism that disorders the layering sequence of sedimentary deposits. If the disordered sedimentary layers show notable differences in heat conductivity, the layers are thick enough and the displacements along the fault plane large enough, temperature anomalies close to the free surface may be apparent because of the surface‐emissivity mechanism.In order to explain certain characteristic temperature anomalies where a fault reaches or approaches the free surface, an additional mechanism has to be assumed; namely a distortion of texture, and consequently a change in the heat conductivity of the rock material surrounding the fault plane. The consequences of both a reduced and an increased heat conductivity of the surroundings of a near‐surface fault have been calculated, and they show remarkable agreement with temperature anomalies observed in various parts of the world.
INTERPRETATION OF GRAVITY ANOMALIES BY NON‐LINEAR OPTIMISATION*
Authors: AL‐CHALABI MAHBOUB 
Published: April 2006

AbstractThe interpretation of a gravity anomaly in terms of the shape of the anomalous body is a non‐linear problem and may, therefore, be carried out using non‐linear optimisation techniques. The formulation is extended to include cases where the density contrast and the regional background are also unknown. For a given model the objective function is provided by the discrepancy between the observed anomaly and the calculated anomaly due to the model. Given an initial model, the optimisation procedure searches for a minimum of the objective function by an iterative adjustment of the parameters. A number of suitable objective functions is given. The behaviour of these functions in the parameter hyperspace is quite complex. Accordingly, direct search methods should be employed at the early stages of the search, changing to gradient methods at later stages. The use of constraints is also necessary to ensure the geological feasibility of the model. The required computer time may be largely reduced by careful programming. Two examples of interpretation by optimisation methods are given.
THE STUDY OF STREAMING POTENTIALS ON FISSURED MEDIA MODELS*
Authors: BOGOSLOVSKY V. A. , OGILVY A. A. 
Published: April 2006

AbstractIn massive rocks ground waters mainly flow in fracture zones whose permeability greatly changes depending on their filling. When studying ground‐water flow in fissures, the results of observations of the electric fields of filtrational origin—which, in this case, considerably differ from those in porous media—can be used. Therefore the authors have made experiments on fissured media models. The measurements have been made in a special filtration tube with the fissured media simulated by a system of quartz glass plates. The spacings between plates were regarded as fissure widths. The observations have been made in fully open “fissures” and in those partially filled with sand or sandy‐clay material.These experiments have resulted in establishing a dependence between the values of streaming potentials and pressure drops. The SP values have particularly been found to decrease with the opening of “fissures”. The most intensive electro‐filtrational fields were observed at 40 per cent filling with medium grained sand. Additions of argillaceous material to the sand filler brought about sharp reductions in the intensity of electro‐filtrational potentials.