ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00036.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00037.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00038.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractFor the two and three layer cases geo‐electrical sounding graphs can be rapidly and accurately evaluated by comparing them with an adequate set of standard model graphs. The variety of model graphs required is reasonably limited and the use of a computer is unnecessary for this type of interpretation.For more than three layers a compilation of model graphs is not possible, because the variety of curves required in practice increases immensely. To evaluate a measured graph under these conditions, a model graph is calculated by computer for an approximately calculated resistivity profile which is determined, for example, by means of the auxiliary point methods. This model graph is then compared with the measured curve, and from the deviation between the curves a new resistivity profile is derived, the model graph of which is calculated for another comparison procedure, etc. This type of interpretation, although exact, is very inconvenient and time‐consuming, because there is no simple method by which an improved resistivity profile can be derived from the deviations between a model graph and a measured graph.The aim of this paper is, on the one hand, to give a simple interpretation method, suitable for use during field work, for multi‐layer geo‐electrical sounding graphs, and, on the other hand, to indicate an automatic evaluation procedure based on these principles, suitable for use by digital computer.This interpretation system is based on the resolution of the kernel function of Stefanescu's integral into partial fractions. The system consists of a calculation method for an arbitrary multi‐layer case and a highly accurate approximation method for determining those partial fractions which are important for interpretation. The partial fractions are found by fitting three‐layer graphs to a measured curve. Using the roots and coefficients of these partial fractions and simple equations derived from the kernel function of Stefanescu's integral, the thicknesses and resistivities of layers may be directly calculated for successively increasing depths.The system also provides a simple method for the approximative construction of m

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00039.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractApplication of statistical methods of analysis of geophysical data is often helpful for the detection of weak anomalies against a noisy background. The processing and analysis of areal geophysical data by two such methods are presented. The advantage of these methods are illustrated with the help of two field examples.

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00040.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

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 practi

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00041.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractNumerical solutions of the wave equation for a particular type of non‐linear “constantQ” medium were carried out. These solutions were obtained after the transformation of the space derivatives in finite differences; power series of the time are used to express the solutions.The medium is characterized by a not single valued stress‐strain relation; the stresses are greater when the absolute values of strain are increasing (passive work), and are less when they are decreasing (active work). A loss of energy follows which is constant for every cycle and independent of frequency. This model represents the simplest type of medium in agreement with the laboratory data on rock samples. For a similar medium the stress’values do not depend only on the instantaneous value of the strain, but also on the previous strain values, i.e. the history of the medium. All these characteristics are not compatible with linearity and require particular types of computing procedures similar to the one shown in this paper.The results of calculations here shown refer both to the propagation of an isolated wave and to the generation of a wave in a spherical hole by change of pressure. They refer particularly to the shape, the amplitude and the width of the isolated wave along the propagation path. The most important results for this type of medium are the following:a) for a plane single isolated wave, the displacement amplitude wave does not change along the propagated distance. The width increases linearly as function of the distance;b) the corresponding particle velocity decreases in amplitude;c) for single isolated spherical waves the displacement amplitude decreases with propagated distance only due to the geometric factor, i.e. inversely proportional to the propagated distance; its width increases in the same way as for plane waves.The comparison between these theoretical results with the field and seismological data show a sufficiently good agreement as far as the value interval of wave width and frequencies is concerned. Less satisfactory is the comparison regarding a linear dependence of the wave width on the distance. This fact happens probably because in the field often long trains of waves and not isolated waves occur. In effect, for trains of waves the behaviour is different than that of an isolated wave; particularly, for the former the frequency variations along the travelled path is less and the displacement variations greater.However, it seems likely that a further similar theoretical research for trains of waves propagating in this type of non‐linear medium might be carried out to complete the prese

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00042.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractRao, K. G. C. and D. N. Avasthi, 1973, Analysis of the Fourier Spectrum of the Gravity Effect Due to Two‐Dimensional Triangular Prism, Geophysical Prospecting 21, 526‐542.Fourier Transform of the theoretical gravity effect due to a two‐dimensional isosceles triangular prism has been derived. Evaluation of the model parameters from the analysis of the Fourier Spectrum has been outlined. Application of this method to synthetic gravity anomalies is

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00043.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

RésuméIl est maintenant courant d'employer l'ordinateur pour interpréter les sondages électriques. Cependant, le problème à résoudre en prospection électrique n'admettant pas une solution unique, le but des traitements automatiques consiste simplement à fournir plusieurs hypothèses qui aident à bâtir une interprétation géologique des mesures géophysiques. C'est, d'ailleurs, ce qu'on recherche aussi par la comparaison visuelle des courbes de terrain avec des abaques précalculés. Mais, tandis que l'interprétation manuelle, pour conduire à des solutions qui respectent les mesures faites sur le terrain, exige un temps très long, le traitement automatique fournit immédiatement des solutions compatibles avec les courbes àétudier.Les procédés employés s'adaptent aux divers besoins de la prospection: ils peuvent traiter aussi bien la station isolée que les profils de sondages électriques. C'est ce qu'on se propose de montrer, à l'aide de quelques exem

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00044.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractThe theoretical horizontal resistivity profiles over an outcropping vertical dyke for various parameters‐electrode spacing, vein‐width and resistivity contrast—with inline alpha, beta and gamma‐Wenner electrode systems are described. The resistivity profiles present a most bewildering variety of shapes as compared to those in resistivity soundings. The analysis of type curves suggests suitable electrode configuration for detection of wide, moderately wide, and thin veins. The negative apparent resistivity values on the gamma anomalies for resistive vein over certain vein‐widths of higher positive values of resistivity reflection factor contradict the concept of apparent resistivity hith

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00045.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY