摘要:

AbstractThe theoretical horizontal resistivity profiles Over an outcropping vertical dyke with two‐electrode and Schlumberger electrode systems are discussed. The two‐electrode array seems very useful in locating the highly conducting thick or thin vein, while the Schlumberger (gradient) array is suited to detect the conducting vein of low and moderately high resistivity contrast and as well as the resistive vein of all widths and resistivity contrasts. Besides, the inline gradient array has a distinction of establishing a clue to evaluate the resistivity contrast of the v

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00047.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractFive test profiles in time‐domain induced polarization measurements over conducting sulphide and graphite mineralisations were run with the two‐electrode, three‐electrode, modified unipole, pole‐dipole, dipole‐dipole, Schlumberger, and Wenner α and β configurations. The results show that, compared to the other electrode systems, the simplest two‐electrode array produces the largest anomalies with the smalles

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00048.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractThe generalised three layer boundary value problem with a transition layer sand‐witched between an isotropic overburden and dipping anisotropic substratum is discussed assuming that plane electro‐magnetic waves are incident normally over the air‐earth inter‐face. The tangential electric (Ey) and magnetic (Hx) fields and the expression for surface‐impedance (Ey/Hx) have been evaluated at the earth's surface. Through numerical analysis it is shown that changes in the values of the parametersm(coefficient of anisotropy),h(thickness of the transition layer), α (angle of inclination of the dipping beds), andb(conductivity ratio between substratum and upper layer) modify the amplitude and phase‐variation curves (with skindepth) s

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00049.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractMaster diagrams for electromagnetic responses of nine dipole dipole systems are presented for various depths of a vertical infinitely conducting vein. TheYYsystem gives the minimum anomaly for both the inline and broadside arrays. Among other inline systems, it is difficult to decide the clearcut superiority of one system over the other, whereas theXXsystem in broadside array gives maximum anomaly.

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00050.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractA seismic trace recorded with suitable gain control can be treated as a stationary time series. Each trace, χj(t), from a set of traces, can be broken down into two stationary components: a signal sequence, αj(t) *s(t—τj), which correlates from trace to trace, and an incoherent noise sequence,nj(t), which does not correlate from trace to trace. The model for a seismic trace used in this paper is thus χj(t) =αj(t) * s(t—τj) +nj(t) where the signal wavelet αj(t), the lag (moveout) of the signal τj, and the noise sequencenj(t) can vary in any manner from trace to trace. Given this model, a method for estimating the power spectra of the signal and incoherent noise components on each trace is presented.The method requires the calculation of the multiple coherence function γj(f) of each trace. γj(f) is the fraction of the power on traced at frequencyfthat can be predicted in a least‐square error sense from all other traces. It is related to the signal‐to‐noise power ratio ρj(f) bywhereKj(f) can be computed and is in general close to 1.0. The theory leading to this relation is given in an Appendix.Particular attention is paid to the statistical distributions of all estimated quantities. The statistical behaviour of cross‐spectral and coherence estimates is complicated by the presence of bias as well as random deviations. Straightforward methods for removing this bias and setting up confidence limits, based on the principle of maximum likelihood and the Goodman distribution for the sample multiple coherence, are described.Actual field records differ from the assumed model mainly in having more than one correctable component, components other than the required sequence of reflections being lumped together as correlated noise. When more than one correlatable component is present, the estimate for the signal power spectrum obtained by the multiple coherence method is approximately the sum of the power spectra of the correlatable components. A further practical drawback to estimating spectra from seismic data is the limited number of degrees of freedom available. Usually at least one second of stationary data on each trace is needed to estimate the signal spectrum with an accuracy of about 10%. Examples using synthetic data are presented to

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00051.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractThe aim of this article is to describe the double resonance magnetometer system designed and built by the Division de Magnétométrie of the C.E.N. Grenoble, and used by the Département des Recherches Minières du CE.A.For the measurement of magnetic anomalies of geological origin it is necessary to make differential measurements between a mobile instrument which scans the region of interest and a fixed compensatory instrument.The apparatus described here features the following main characteristics:— it gives a direct numerical measurement of the differential magnetic field between the two instruments with an accuracy of 0.01 gamma (10‐7Oe).— it is designed to be easily operated in geological field work (light weight, low power, possibility to make continuous measurements along a given profile, the measuring signals being radio‐linked there are no wires connecting the instruments).Firstly we describe the components of the magnetometer itself namely: double resonance magnetometer heads and differential numerical magnetometer. Secondly we describe the measurin

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00052.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractThe paper deals with the electro‐filtrational fields formed near the drainage structures. Main laws of deformation of these fields above vertical and horizontal drains are considered and practical examples supplie

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00053.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractGravity modeling involves the evaluation of gravity field due to bodies of irregular shape. This is commonly accomplished by dividing the body into smaller units of regular shape whose field can be determined analytically.Cubes are ideal building blocks for constructing bodies of irregular shape. However, the exact expression defining the gravity field of a cube‐shaped body is very long and requires tedious numerical work. Approximation formulas for rapid evaluation of the cube's gravity field are presented and discussed in detail. Their use for computing the field for small distances leads to large errors in the results; on the other hand, using the exact formula for large distances where approximation formulas yield practically identical results, is waste of time. After a detailed analysis about the nature of the cube's gravity field, certain criteria are established for suitably combining the two alternatives. This results in tremendous reduction in the task of computations without affecting the accuracy of dat

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00054.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractDuring the last ten years data processing has enabled the geophysicist to seriously attack the problem of how to improve the quality of seismic sections. For instance new processing methods have been proposed for improving the resolving power of the seismic pulse. These methods are based on deconvolution and they require lengthy computations.The method discussed here for pulse contraction is based on the use of Hadamard transforms. It is very fast but nevertheless the quality of the result stands comparison with that of conventional methods.

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00055.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractThe directional effect of shaped charge is a well‐known feature used for a long time in military weapons, oil well guns, and steel industry. This charge was successfully applied as a seismic energy source by Petrobrás during the past three years under different surface and geological conditions.Preliminary amplitude measurements taken with fixed gain shallow refraction instruments showed a consistent difference between conventional and shaped charges. Lately, a similar difference has been noted in deep reflection energy recorded with digital binary gain instruments as well as in deep oil well velocity surveys.Direct comparisons along more than 50 km of multiple coverage field reflection shooting are in agreement with these results and have proved the practical advantage of this source as compared to conventional dynamite.This source has been used since 1971 in routine seismic operation in the Amazon jungle with 300 gram unit charges distributed in small and large shot arrays increasing substantially the coverage and halving the cost at a higher record quality. A large amount of production seismic field work has been carried out in several other areas attesting the successful application of the shaped charg

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1973.tb00056.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY