bluuebunny/crossref_metadata_2025_split huggingface dataset:
THE MAGNETIZATION OF THE MAGNETITE OREBODY NEAR CORTEGANA, SPAIN*
Authors: BADER K. 
Published: April 2006

AbstractThe magnetic ground survey of ΔZ across the orebody near Cortegana suggests that the direction of the magnetization of the orebody deviates from the present earth field direction in that area. Magnetic measurements of more than 500 specimens of drilling cores of several vertical and one nearly horizontal drill holes showed that the magnetization of the orebody points essentially to the north in the direction of the inclination of the orebody and the banding of the ore. In the central part of the orebody with an average magnetite content of about 50 vol% the magnetization amounts to 0.35 Gauss, the remanent and induced component having the same order of magnitude. The outer parts of the orebody have a much smaller magnetization according to both the smaller magnetite content and greater inhomogeneity of the remanent magnetization, also partly due to their reversed magnetization which is brought about by the stray field of the central part of the orebody. As all drilling cores have been chemically analyzed with respect to their Fe content a logarithmic relationship could be established between the magnetite content, ranging from 25 to 80 vol%, and the susceptibility.
NOUVELLES APPLICATIONS DE LA THEORIE DES MILIEUX ALPHA HARMONIQUES A LA PROSPEGTION ELECTRIQUE EN COURANT CONTINU*
Authors: STEFANESCU SABBA 
Published: April 2006

AbstractThe equation which determines the distribution of the stationary potential ϕ in isotropic heterogeneous conductive media with continuously varying local conductivity σ, takes the symmetrical form
image
if we choose as new variables
image
For certain grounds (half‐spaces) in which α is a harmonic function (Δα=ΔΨ= 0), it is possible to obtain by means of simple calculations the lines of equal apparent resistivity and the geoelectrical apparent cross‐sections for the usual devices of d.c. prospecting methods. Graphical examples are also given.
SUR LA SEPARATION DES ANOMALIES GRAVIMETRIQUES ET MAGNETIQUES*
Authors: BOTEZATU RADU 
Published: April 2006

AbstractOne of the most important aspects in interpretation of gravity and magnetic anomalies, which generally represent the sum of many effects from the subsoil, is that these effects cannot be adequately separated into individual effective anomalies by means of known procedures. Moreover, the concept itself of anomaly separation must be expanded in a certain sense, because the addition of these effects in the mapped anomalies can arise from many structures situated in the subsoil in different relative positions to one another. A combined procedure is proposed, based on Fourier analysis utilising both periodic complex functions and nonperiodic ones, by use of which the number of individual effective anomalies cumulated in the mapped anomalies is obtained. In order to illustrate the use of this procedure and the advantages of obtaining more valuable informations on geological causes of anomalies, one example from Romania is given.
DIFFERENT METHODS OF TIME‐DEPTH CONVERSION WITH AND WITHOUT MIGRATION*
Authors: PATURET DANIEL 
Published: April 2006

AbstractThe increasing use of velocity analysis programs in seismic processing in addition to direct application to normal move out corrections often makes it possible to study the variation of the average velocity versus time and distance. Usually, it is even feasible to compute interval velocities with a good accuracy.We intend to use these velocities to convert the usual time domain displays to the depth domain.An exact conversion requires the knowledge of all interval velocities and all the velocity interfaces.However, when the dips are small, the conversion can be done without considering the dip of all these interfaces, and in some cases migration can even be completely neglected.Three different programs will be described and their use discussed in view of the type of problems to which they are applied.Practical examples of the various methods will be presented.
FIRST EXPERIENCE AND RESULTS WITH A NEW SEISMIC INTERPRETATION METHOD*
Authors: DOHR G. 
Published: April 2006

AbstractAt the EAEG meeting in Venice (May 1969) Linsser presented a new method for the interpretation of seismic measurements (“Transformation of Seismic Data into Geological Models by Digital Template Analysis”). First results were presented during the S.E.G. convention in Calgary (September 1969). Meanwhile some experience concerning the possibility of the application of this method is available.Starting from the fact that the computer is able to store several physical parameters (amplitude, wave‐length, direction of the seismic event, coincidence with a template and the beginning and the end of each reflection), the importance of these data for the investigation of special geophysical questions will be discussed.This method has been tested with several examples on the following problems:

Proving and exact localisation of faults.
Investigation of velocities of interesting layers.
Additional information for the geological interpretation of seismic sections.
Picking of weak reflections in the “Pre‐Zechsteinian” in Northern Germany.

Finally the possibilities of further applications and developments are discussed.
A NEW METHOD OF CANCELLING MULTIPLE REFLECTIONS: “SOUSTON”*
Authors: MICHON D. , WLODARCZAK R. , MERLAND J. 
Published: April 2006

AbstractCancelling of multiple reflections by CDP stacking is generally incomplete. When the order of coverage is low, an improvement may be obtained by the use of special filters (e.g. Schneider et al: Geophysics 1965; D'Hoeraene: Geophysics 1966). But when the order of coverage is high, the efficiency of these filters is less obvious. On the other hand, the higher the order of coverage, the higher the efficiency in the solution presented.Schematically, our method includes three steps:Firstly: Searching for the multiple reflections.For this purpose Move Out corrections corresponding to the multiples are applied to each individual record, then CDP stacking is carried out.Secondly: Cleaning up of the individual records.“Decorrections” are firstly applied, then multiples are subtracted. For this, subtraction is weighed versus the energy of the multiples, that is to say versus the correlation between the original record and the pure multiple reflections.Thirdly: Normal processing with the cleaned records which have been obtained.The different steps of this method are illustrated with the help of theoretical examples. Its efficiency improvement in regard to normal CDP stacking is then demonstrated by means of true examples.
A METHOD FOR INTERPOLATION AND EXTRAPOLATION OF POTENTIAL FIELD DATA*
Authors: CORBYN J. A. 
Published: April 2006

AbstractThe application of automatic methods to the processing of potential field survey results has led to the need for the development of special procedures for the interpolation and extrapolation of such data. A method is proposed which utilizes the mathematical properties of potential field data to achieve a minimum distortion solution to the interpolation/extrapolation problem. The proposed method is suitable for use with any data point distribution. Digital computer programs have been prepared using the method; results obtained through the use of the programs are presented.
A NOTE ON THE LINEAR FILTER METHOD OF INTERPRETING RESISTIVITY SOUNDING DATA*
Authors: KOEFOED O. 
Published: April 2006

AbstractIn the linear filter method of interpreting resistivity sounding data, as developed by Ghosh (1971), it appears that the filter function in the x‐domain approaches an oscillating function for both large positive and large negative abscissa values. In the present note the reason for this oscillating behaviour is derived, and a possible practical application is indicated.
MESURES SISMIQUES PAR TRANSMISSION—APPLICATION AU GENIE CIVIL *
Authors: PORTE M. LA , LAKSHMANAN J. , LAVERGNE M. , WILLM C. 
Published: April 2006

AbstractThe new process of automatic determination of seismic velocities by well to well measurements (Bois et al., 1971, Geophysical Prospecting 19, 42‐73) gives the possibility to increase the knowledge of oil reservoirs, by detecting large inhomogeneities between wells. It can also give useful informations on the mechanical properties of rocks in mining exploitation and civil engineering, by gallery to gallery measurements. An application of the method is given to the search for the proper location of an underground hydroelectric power plant, where the problem was to investigate the rock properties in a horizontal plane between two exploration galleries.
CROSS‐CORRELATION AS AN AID IN SIMULTANEOUS GRAVITY AND MAGNETIC ANALYSIS *
Authors: BOTEZATU R. , CALOTA C. 
Published: April 2006

AbstractThe properties of cross‐correlation functions for the case of gravity and magnetic total field anomalies produced by three geometric models of geological bodies (point‐mass, horizontal line‐mass, and vertical semi‐infinite rectangular prism mass distributions) are studied. This study is carried out on four cases of cross‐correlation: the whole curve of anomalies, a single branch of anomalies, the branch between the two inflexion points and the branch between the apex point and the inflexion point. In all cases, the crosscorrelation function can serve as a good indicator to discriminate the so‐called genetically related anomalies from those produced by different geological bodies situated on the same vertical line; but the best results are obtained using the cross‐correlation of the branches between the apex point and the inflexion point of the two geophysical anomalies.A practical procedure is developed in order to undertake such analysis. The tests in some cases of real gravity and magnetic anomalies mapped in Romania show the validity of this practical procedure.
MATHEMATICAL MODELS OF CONDUCTING ORE BODIES FOR DIRECT CURRENT ELECTRICAL PROSPECTING *
Authors: STEFĂNESCU S. , STEFĂNESCU D. 
Published: April 2006

AbstractThe authors generalize a method expounded in a previous paper (1971, Geoph. Prosp. 18, 786‐799) to the case of a local conductivity σ(M) of the infinite medium satisfying the relation
image
where the Ri's are the distances from the point M to n fixed points Si (i= 1,. n), k is a positive real constant and Ci, Cii are constants ensuring the condition α > O.The sub‐surface conductivity distributions (half‐spaces) complying with (1) provide a wide variety of conducting structures, which can fit quite successfully the rather complicated distributions of conductivity occurring in natural ore bodies.An exact algebraic calculation of the apparent resistivity for these grounds, valid for any dc electrical prospecting devices (Wenner, Schlumberger, dipole, etc.) leads to a set of simultaneous linear equations, with a matrix which is invariant with respect to the position of the quadrupole being used. This greatly simplifies the numerical computation.We also present some examples of cross sections for the real and apparent resistivity obtained by this method.
THE POOR MAN'S SEISMIC SOURCE: A COMPUTER GAME *
Authors: ALTERMAN Z. , CENSOR D. , GINZBURG A. , SCHOENBERG M. 
Published: April 2006

AbstractBasic requirements for a seismic reflection system using a moderate‐power controlled source are discussed. General considerations and computer modelling show promise for geophysical prospecting, especially at low penetration and very high noise level. For many applications, ranging from mineral and water prospecting, to civil and military engineering, and even archeology, a relatively cheap, small and portable device of this kind might be more convenient than conventional explosive sources or sophisticated controlled sources of the vibroseis type. The use of a simple, low frequency periodic signal facilitates rapid data processing procedures and suggests that the mechanical generator will be very simple and cheap.
THEORETICAL RESISTIVITY SOUNDING RESULTS OVER A TRANSITION LAYER MODEL *
Authors: NIWAS SRI , UPADHYAY S. K. 
Published: April 2006

AbstractAn earth model with a transition layer (anisotropic inhomogeneous) is considered. The inhomogeneity in σv (vertical conductivity) of the transition layer is represented by a power law variation. Expressions for potential distribution in the upper layer, transition layer and bottom layer are obtained by solving appropriate differential equation for each layer. By utilizing the boundary conditions, expressions of apparent resistivity for Wenner and Schlumberger configurations are derived. Numerical analysis is performed for linear and quadratic variation of σv. The results are presented in the form of theoretical apparent resistivity curves for both configurations. Negative apparent resistivities are the interesting feature of this analysis.
AFTER‐STACK MULTICHANNEL FILTERS WITHOUT MIXING EFFECTS *
Authors: CASSANO E. , ROCCA F. 
Published: April 2006

AbstractSeveral types of multichannel filters have been introduced in the past with the purpose of rejecting, in a seismic section, coherent noise having a slope different from that of the signal.These filters, generally, tend to introduce a certain amount of mixing and therefore the output trace shows increased horizontal coherence. This is due to the model on which these filters are based, since the hypothesis is posed that the reflectors are continuous. This may be dangerous since it could lead to mistaken interpretations, for example when small faults or breaks are made to disappear in the output section.Other problems that could arise in the application of multichannel filters after‐stack are space‐aliasing and high‐pass filtering. The former occurs when coherent noise is rejected with apparent Velocity V and frequency fa=V/X, where X is the distance between traces. In this case, the signal also is distorted since it is rejected in the same frequency range. The high pass filtering effect occurs when the multichannel filter is designed to remove low coherent noise with high apparent velocity.In the paper a family of multichannel filters is presented based on a model of the seismic section such that minimum mixing effects appear. The filters are designed to give good results even in the case of low frequency and high velocity coherent noise.Some practical examples are shown.
AN EXAMPLE OF THE APPLICATION OF AUTO‐CORRELATION AND SPECTRAL ANALYSIS IN MINING EXPLORATION *
Authors: SARMA D. D. 
Published: April 2006

AbstractThis paper deals with a case study on the application of auto‐correlation and spectral analysis methods to mineral assay data taken along seven drives and two winzes concerning the McTaggart's (West) lode of Kolar gold fields. The general model conceived in this study is: measured (estimated) ore grade at jth location =true value + error at jth location. Employing an auto‐correlation function of the form C e‐ a |k| for signals, the respective contributions of signals and noise to the total logarithmic variances for the data along drives and winzes are analysed. Smoothed spectral density estimates and their 90% confidence limits are computed for the series of data.
APPARENT RESISTIVITY, ANISOTROPY AND STRIKE MEASUREMENTS*
Authors: HABBERJAM G. M. 
Published: April 2006

AbstractIn the search for a descriptive system capable of accounting for the wide variations of earth resistance with orientation of electrode array, which can occur in field measurements, a modified measure of apparent resistivity, based on an anisotropic earth, is proposed.This measure requires the sampling of earth resistance in, at least, three orientations. A practical system, the crossed square array, which effectively samples in four, is considered in detail. A system of reduction of field observations yields, besides the apparent resistivity, apparent measures of anisotropy and strike.Field trials show that the anisotropic analysis not only accounts for the major part of the observed orientational variations in resistance, but also yields sounding curves of resistivity, anisotropy and strike, which vary systematically with electrode spacing.The effects and limitations of applying such techniques in regions of pronounced two dimensional structure are examined.Finally, to avoid unnecessary labour in deploying the crossed square sounding technique at sites where it is not required, a modified single square technique is proposed, which will normally serve but will also alert the observer when crossing is required.
COMPUTATION OF INTERVAL VELOCITIES FROM COMMON REFLECTION POINT MOVEOUT TIMES FOR n LAYERS WITH ARBITRARY DIPS AND CURVATURES IN THREE DIMENSIONS WHEN ASSUMING SMALL SHOT‐GEOPHONE DISTANCES*
Authors: KREY TH. 
Published: April 2006

AbstractIt is well known that interval velocities can be determined from common‐reflection‐point moveout times. However, the mathematics becomes complicated in the general case of n homogeneous layers with curved interfaces dipping in three dimensions.In this paper the problem is solved by mathematical induction using the second power terms only of the Taylor series which represents the moveout time as a function of the coordinate differences between shot and geophone points. Moreover, the zero‐offset reflection times of the nth interface in a certain area surrounding the point of interest have to be known. The n—I upper interfaces and interval velocities are known too on account of the mathematical induction method applied. Thus, the zero‐offset reflection raypath of the nth interface can be supposed to be known down to the intersection with the (n—1)th interface.The method applied consists mainly in transforming the second power terms of the moveout time from one interface to the next one. This is accomplished by matrix algebra.Some special cases are discussed as e.g. uniform strike and small curvatures.
A COMPARISON BETWEEN WIENER FILTERING, KALMAN FILTERING, AND DETERMINISTIC LEAST SQUARES ESTIMATION*
Authors: BERKHOUT A. J. , ZAANEN P. R. 
Published: April 2006

AbstractThe least squares estimation procedures used in different disciplines can be classified in four categories:

Wiener filtering,
b. Autoregressive estimation,
c. Kalman filtering,
d. Recursive least squares estimation.

The recursive least squares estimator is the time average form of the Kalman filter. Likewise, the autoregressive estimator is the time average form of the Wiener filter. Both the Kalman and the Wiener filters use ensemble averages and can basically be constructed without having a particular measurement realisation available.It follows that seismic deconvolution should be based either on autoregression theory or on recursive least squares estimation theory rather than on the normally used Wiener or Kalman theory. A consequence of this change is the need to apply significance tests on the filter coefficients.The recursive least squares estimation theory is particularly suitable for solving the time variant deconvolution problem.
CALCUL DES COURBES DE, SONDAGES ÉLECTRIQUES À L'AIDE DES FONCTIONS D'ÉCHANTILLONNAGE*
Authors: BARANOV W. 
Published: April 2006

AbstractRecently I had an opportunity to apply the theory of sampling functions to the functional transformations of gravity and magnetic anomalies (Baranov 1975). It would be interesting to examine if there is a possibility to use these functions in the electrical prospecting. It seems that the answer might be affirmative.This paper is an attempt to compute the master curves for the electrical vertical sounding with the aid of sampling functions.
PROGRESS IN THE DIRECT INTERPRETATION OF RESISTIVITY SOUNDINGS: AN ALGORITHM*
Authors: KOEFOED O. 
Published: April 2006

AbstractAn algorithm is presented for the direct interpretation of resistivity sounding data. The algorithm is based on the method of successive reductions to lower boundary plane of the resistivity transform function. A novel aspect of the algorithm is that error limits are assigned to the initial values of the resistivity transform, and these error limits are carried through in all the subsequent computations. The width of the error range is then used as the basis for assigning weight factors in the final computation of thicknesses and resistivities of the layers. The errors in the resistivity transform derived from the solution given by the algorithm are usually not more than twice as large as those in the original data.
ELECTROMAGNETIC RESPONSE OF A BROKEN ORE‐VEIN (MODEL STUDIES)*
Authors: PODDAR M. , LAHIRI A. K. , DEB B. K. 
Published: April 2006

AbstractA broken ore‐vein is very common in nature. A small scale model of such a vein has been made by placing two thin metal sheets edge to edge with an air gap between them. The electromagnetic response of this model in a uniform oscillating magnetic field has been measured. The results show that (a) the response of the whole body is not the sum of responses of the constituent parts, (b) the response of the upper part is dominant by virtue of its proximity to the receiving coil and (c) the lower part has the effect of making the upper part appear nearer to the surface and poorer in conductance than it really is.
COMBINED REFRACTION SEISMIC AND GRAVIMETRIC INVESTIGATIONS IN A PALEOGEOGRAPHICAL AND GEOLOGICAL RESEARCH PROGRAM*
Authors: VANDENBERGHE J. 
Published: April 2006

AbstractRefraction seismic and gravity investigations were executed to solve geological and hydrographical problems in recent strata: These loose sediments necessitated a special arrangement for the energy source in the seismic measurements, By the use of a falling weight the refracted wave could be registered from a depth of more than 30 m. Quaternary fluviatile sands are characterized by lower velocities than the Tertiary sediments. Even a marked velocity difference between different Tertiary formations could be observed. Sand‐filled valleys in Tertiary clays give relatively important variations in the gravity field caused by the small differences of densities. Thus buried channels in a clay subsoil can be found by accurate gravity measurements.
HYDROGEOPHYSICAL PROPERTIES OF PARTS OF THE BRITISH TRIAS*
Authors: WORTHINGTON P. F. 
Published: April 2006

AbstractLaboratory studies of Bunter Sandstone specimens from Northwest Lancashire, Shropshire, West Cumberland, and the Vale of Clwyd have indicated that the parameters effective porosity, intergranular permeability, compressional wave velocity, formation resistivity factor, and effective matrix resistivity have significantly different distributions in each of these four regions. Regression analyses have shown that bivariate and trivariate expressions for the prediction of the two hydrological parameters from petrophysical data vary from region to region. It is concluded that, in quantitative geophysical investigations of these formations, each area must be investigated independently.For all four aquifers, and for both horizontally and vertically oriented specimens, effective porosity can be most reliably and readily estimated through a bivariate relationship involving formation resistivity factor. On the other hand, the best estimate of intergranular permeability from geophysical data is obtained through a trivariate expression involving both formation resistivity factor and effective matrix resistivity. The use of hydrogeophysical relationships to estimate hydrological parameters in situ is illustrated by reference to field examples.