摘要:

ABSTRACTUntil such time as digital seismic recording techniques are in widespread use in the field and partly because it cannot afford digital equipment, C.E.P. has decided to build a processing system which can digitize and process seismic information in analog form on magnetic tapes.C.E.P. was prompted to adopt the digital technique to enable it to proceed with its stratigraphical investigations, starting with the elaboration of synthetic records and followed by the study of signals and deconvolution.Though the analog form of recording is not too suitable for digital processing owing to its low dynamic range, it seemed to us that it was nevertheless perfectly feasible to enhance the analog information by processing it digitally through an automatic computer.This approach to the problem of data enhancement is more satisfactory than the (conventional) analog method, which is more complicated and less accurate.The digital processing system comprises:a magnetic playback systema two‐channel reproduction devicean analog‐digital convertera 1620 IBM computeran automatic plotting device for graphical presentation of results.Examples of different processing forms are presented:cancellation of A.G.C. actioncomputation of seismic signaldeconvolutioncorrelation techniquesanti‐singingstudy of the response of the various items of equipment.We have come to the conclusion that very interesting results have been obtained in spite of the low dynamic range of the analog tapes.With this equipment it is possible to study and process the data in digital form and compare results with those obtained by analog processing. Also, the experience gained will be very useful when digital field crews start operating.Unfortunately, it is not possible for the time being to operate the equipment on a commercial production basis, but only to develop working methods, to conduct short studies or to guide and control analog processing techniques.At present our efforts are therefore aimed at shortening the time required for processing and plo

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1965.tb01938.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractElectronic circuits are described which simulate the effects of galvanometers and geophones. By placing these circuits in the feedback loop of an operational amplifier it is possible to obtain transfer functions which are the inverse of those of the transducers. That is, they will remove the distortion on the signal which was produced by the geophone or the galvanometer.Both a geophone simulator and its inverse filter have been built and used (O'Brien, 1965). The simulator is accurate over at least seven octaves and the inverse filter restores the ground signal to what it would have been if the recording geophone had had a natural frequency √n+1 times that of the actual geophone, whereAis the gain of the operational amplifier used in the circui

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1965.tb01939.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractA theory is developed to predict the amplitude and velocity of the first arrival produced by a thin solid refractor embedded in a solid environment. Laboratory experiments on a three dimensional model substantially confirm the theory. The essential conclusion may be found in Figure 8 where it is shown that for a constant wavelength, and for thicknesses up to about one half a wavelength, the attenuation per unit distance decreases monotonically with increase of refractor thickness.The assumption is made that the amplitude,A, attenuates as (x)‐nexp(‐βx), wherexis horizontal distance andnand β are constants. It is emphasised that it is difficult to obtain reliable values fornand β from the initial amplitude measur

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1965.tb01940.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractThe technique of two‐dimensional seismic models offers a simple solution to the problem of pulse reflection at the interface of two solids. Particular attention is paid to the existence and character of the amplitude increase in the interference zone betweenPPandPPP. The following points are discussed:1)– the considerable deformation of the pulse when such an increase exists.2)– the desagreement existing in the neighborhood of the critical points between the amplitude calculated by plane wave theory and the amplitude observed for cylindrical or spherical waves.3)– the nonexistence of such an increase when velocity or density contrasts are too great.4)– the presence, in the case of very large velocity contrasts, of an increase of the amplitude in the zone of interference, betweenPPandPSP‐waves.5)– the considerable importance of conversion arrivals (PS+SP).6)– the necessity of taking into account the emission of distorsional waves so that the observed arrivals of conversion waves c

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1965.tb01941.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractUphole recordings in sediments very often reveal shear waves. With their velocity and that of theP‐waves Poisson's ratio may be determined, this usually has unexpectedly high values.A number of up‐hole shots were recorded with a linear spread of geophones and with constant gain amplifiers. Calculations were made to show the effect of the free surface and ray divergence (the spread factor). The theoretical, relative amplitudes of the ground motion were plotted together with the observed values. In general, there is good agreement between theory and observation which is better for theP‐waves than for the S‐waves. The reasons for this difference are discussed.Finally, an absorption coefficient is calculated from the amplitudes measured at the

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1965.tb01942.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractIt is considered it might be useful to test the validity of the theoretical study “Sur ľinfluence ?un empilement de couches minces en sismique” by Messrs. I. ?Erceville and G. Kunetz, Geophysical Prospecting, XI, No. 2, June 1963.We chose a borehole of the Compagnie Française des Pétroles where the velocity logs frequently show fine interbedding. Two synthetic records were prepared:a) For the first one, a large step (τ= 3 ms) was selected to preserve the general appearance of the field records (convolution by a Ricker wavelet with a pseudo‐period of 26.6 ms);b) For the second one, a small step (τ= 0.5 ms) was taken, convoluted using the same Ricker wavelet.We observed that the synthetic records without multiples are not dependent on the step taken for calculation, provided this step remains small in relation to the period of the convolution signal (τ, one‐way time, smaller than 1/8 of the period of the signal). Nevertheless, when a small step is used, the high frequencies may be better reflected on the synthetic record.We also noticed that the direct wave attenuates rapidly with depth and is replaced by an accumulation of multiples that restore it exactly, but with a slight time‐lag. We termed this the “pseudo‐wave”. The above‐mentioned delay between the two synthetic records is in good agreement with the results published by Messrs. 1. ?

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1965.tb01943.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractOne of the most important problems in the interpretation of gravity data is the separation of the data giving information characterizing the different geological structures. Various methods were elaborated to perform this separation (smoothing, removing of residuals, second derivatives, analytic continuation and others). For each operation various sets of coefficients were proposed. All these sets of coefficients may be considered as to provide linear filtering processes applied to the original map. The frequency response of the filter unambigously determines the method and gives good and clear information concerning their advantages (or disadvantages). The knowledge of frequency responses enables the choice of the most suitable method for the interpretation of a given map. Graphs are presented by the author showing:a.the effect of radius used in the calculation of residualsb.effect of the number of points used in averaging the data on a circlec.the effect of the different systems of coefficients used in the various second derivative formulas.

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1965.tb01944.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Book reviewed in this article:State of Stress in the Earth's Crust, Proceedings of the International ConferenceF. A. VeningMeinesz, The Earth's Crust and Mantle (Development in Solid Earth Geophysics)

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1965.tb01945.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY