摘要:

AbstractField experiments in the vicinity of a tabular body of nearly massive magnetite have demonstrated that the body may respond in either of two ways; it may react as a permeable mass, or it may react as an eddy current inductor, depending upon the frequency employed. If several frequencies, spanning a broad range, are employed, both types of response will be experienced. The transition from one type of response to the other would appear to have considerable significance. Based upon theoretical and empirical work to date, it seems possible to establish a relationship between transition frequency and percentage magnetite at any given section of a deposit.

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1961.tb01506.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

AbstractLaboratory investigation has shown that the resistivity of massive sulphide ores at specimen dimensions is of the order of 0–10 ohmcm. Several writers, on the basis of field results obtained with various electromagnetic methods, deny the possibility that natural orebodies could have correspondingly low resistivities. The question is of interest, since such conductors, because of their small imaginary response, would be undetectable by electromagnetic methods measuring only imaginary components or phase shifts.In the present paper anomalies obtained with the Loop‐Frame electromagnetic method on massive sulphide bodies in different parts of Canada are discussed. It is shown, by means of model experiments, that the conductors all have very low resistivities which, where the effective thickness can be determined, appear to correspond to the order of magnitude of specimen resistivity. It is demonstrated that confusion of the total width of a conductor with its effective thickness may lead to erronous resistivity determinati

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1961.tb01507.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

AbstractThis 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 prob

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1961.tb01508.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1961.tb01509.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

AbstractLaboratory 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

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1961.tb01510.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1961.tb01511.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

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 met

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1961.tb01512.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

Book reviews in this article:Overvoltage Research and Geophysical Applications, Editor JamesR. Wait.HermannReich,Grundlagen der Angewandten Geophysik für Geologen.BOOKS RECIVEDThe Rotation of the Earth, a geophysical discussion by Walter H. Munkand Gordon J. F. MacDonald

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1961.tb01513.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY