bluuebunny/crossref_metadata_2025_split huggingface dataset:
A METHOD OF TACKLING SOME SEISMIC PROBLEMS AND ITS APPLICATIONS *
Authors: ALFANO L. 
Published: April 2006

ABSTRACTThe theory is explained and practical applications are shown for a numerical procedure in seismology. Particularly the problems concerning the generation of waves under the action of external pressures, and their propagation, in non‐homogeneous, both elastic and absorbing media, have been carried out. These problems have been assumed mono‐dimensional and refer to plane and spherical waves.The procedure is based on the solution, by means of series, of the wave differential equation, non‐homogeneous, and with non‐constant coefficients. It is a direct numerical method whose advantage is, mainly, the possibility of tackling, without great difficulties, problems regarding non‐homogeneous elastic and absorbing media.On the contrary the methods which require the theoretical expression of the solutions by means of formulae, generally, present conceptual and numerical difficulties.As examples of application of this procedure, the following cases have been carried out by means of numerical calculations.a) Propagation of a wave, initially of symmetrical shape, in a viscoelastic medium; from the results it appears that the wave propagates without losing its symmetry, i.e. without sensible dispersion. A theoretical analysis has been carried out to justify this result, showing that the dispersion in viscoelastic media is noticeable only for relatively high frequencies. It seems that the practical absence of dispersion in field experiments do not exclude necessarily the viscoelastic character of absorption.b) Generation of plane waves under the effect of a uniform pressure distributed on the plane surface of a medium. The way the length and the shape of the generated wave depends not only on the type of pressure acting on the surface but also on the near surface impedance variations has been studied.c) Generation of a spherical wave under the action of a pressure in a spherical hole.The examples treated show how the length and shape of the wave depends on the radius of the hole. Particularly the frequencies of the wave spectrum are proportional to this radius, for a given type of pressure acting in the hole.The characteristics of this procedure would also permit the study of media for which the stress‐strain relations are not univocal and linear (non linear absorption). This study, interesting for the wave propagation in rocks, is worth while to be carried out in a special paper.
THE USE OF A SQUARE CONFIGURATION IN RESISTIVITY PROSPECTING *
Authors: HABBERJAM G. M. , WATKINS G. E. 
Published: April 2006

ABSTRACTConsideration is given to the use of a configuration of four electrodes set in a square array for resistivity measurements.It is found that, by passing current successively between different pairs of electrodes, an apparent resistivity can be determined which is both more sensitive to the position of the array centre and less dependent on orientation than the measures usually obtained with colinear arrays of electrodes. At the same time the observations made enable the degree of the departure of local conditions from conditions of lateral homogeneity to be assessed.Theoretical and practical examples of the use of this electrode system are given and the use of the system both as a tool in mapping and in depth investigations is considered.It is shown that provided electrode spacings are suitably arranged the results of a probe carried out using the square array can be interpreted by conventional methods.The system is shown to have particular advantages in the investigation of lateral resistivity variations and the reduced dependence on orientation makes possible the recasting of interpretation data in an orientationally invariant form with a consequent drastic reduction in the number of type curves required for a particular problem.
SOME ASPECTS OF INDUCED POLARIZATION (TIME DOMAIN)*
Authors: BERTIN JACQUES 
Published: April 2006

ABSTRACTIn the first part, the author, recalling the principle of d/c current measurements, shows by means of some examples, different experimental results relative to the induced polarization phenomenon. He presents the case of the negative induced polarization which can be explained by geometric effects. He gives some examples of saturation curves and discusses the problem of the linearity of the I.P. phenomenon. Then he shows some aspects which demonstrate that I.P. decay curves do not always conform to the general law. He concludes by showing the influence of the current electrodes, the position of which, relative to the polarizable bodies, may alter the shape of the I.P. anomalies.In the second part, the author presents different case histories of I.P. mineral surveys where I.P. is compared to other geophysical methods and drilling results.
REALIZATION OF SHARP CUT‐OFF FREQUENCY CHARACTERISTICS ON DIGITAL COMPUTERS
Authors: MEYERHOFF H. J. 
Published: April 2006

ABSTRACTIt was found in Part I of this paper that approximating the sharp cut‐off frequency characteristic best in a mean square sense by an impulse response of finite length M produced a characteristic whose slope on a linear frequency scale was proportional to the length of impulse response, but whose maximum overshoot of ±9% was independent of this length (Gibbs' phenomenon). Weighting functions, based on frequency tapering or arbitrarily chosen, were used in Part II to modify the truncated impulse response of the sharp cut‐off frequency characteristic, and thereby obtain a trade‐off between the value of maximum overshoot and the sharpness of the resulting characteristic. These weighting functions, known as apodising functions, were dependent on the time‐bandwidth product Mξ, where 2ξ, corresponded to the tapering range of frequencies.Part III now deals with digital filters where the number 2N–1 of coefficients is directly related to the finite length M of the continuous impulse response. The values of the filter coefficients are taken from the continuous impulse response at the sampling instants, and the resulting characteristic is approximately the same as that derived in Part II for the continuous finite length impulse response. Corresponding to known types of frequency tapering, we now specify a filter characteristic which is undefined in the tapering range, and determine the filter coefficients according to a mean square criterion over the rest of the frequency spectrum. The resulting characteristic is dependent on the time bandwidth product Mξ= (N–1/2)ξ up to a maximum value of 2, beyond which undesirable effects occur. This optimum partially specified characteristic is an improvement on the previous digital filters in terms of the trade‐off ratio for values of maximum overshoot less than 1%. Similar to the previous optimum characteristic is the optimum partially specified weighted digital filter, where greater “emphasis is placed on reducing the value of maximum overshoot than of maximum undershoot”. Such characteristics are capable of providing better trade‐off ratios than the other filters for maximum overshoots greater than 1/2%. However these filters have critical maximum numbers 2.NC–1 of coefficients, beyond which the resulting characteristics have unsuitable shapes. This type of characteristic differs from the others in not being a biassed odd function about its cut‐off frequency.
TRANSFORMATION OF MAGNETOMETRIC DATA INTO TECTONIC MAPS BY DIGITAL TEMPLATE ANALYSIS*
Authors: LINSSER HELMUT 
Published: April 2006

ABSTRACTResults of gravimetric surveys can be interpreted by comparing the Bouguer field values with master curves based on simplified geological models. It has been shown in a previous paper how this procedure can be transformed into routine processes which can be computerized. The application of this method has yielded useful results in detailed gravity surveys.The present paper discusses the application of the same interpretation principles to magnetic data. After some modifications, the method elaborated for the gravimetric data can be used for the interpretation of magnetometric survey results. Magnetometric‐tectonic maps are obtained which show the structural picture by common geological symbols. In the case of faults, the dimensions of depth of burial and throw are indicated on the maps.The method is illustrated by an example where these procedures have been applied to gravimetric and magnetometric data of the same area. Two different maps are obtained: One shows the tectonics according to density contrasts and the other map depicts the tectonic situation on the basis of magnetic susceptibility contrasts.
REALIZATION OF SHARP CUT‐OFF FREQUENCY CHARACTERISTICS ON DIGITAL COMPUTERS*
Authors: MEYERHOFF H. J. 
Published: April 2006

AbstractIn Part I of this paper, we examined the properties of the best mean square approximation to the sharp cut‐off frequency characteristic by an impulse response of finite length. It was found that the sharpness of cut‐off for the resulting frequency characteristic depended on the length of the impulse response–but because of the discontinuous nature of the specified frequency characteristic, this best mean square approximation always had a maximum overshoot of ± 9%, independent of the length of the impulse response (Gibbs phenomenon).In Part II, we investigate ways of reducing this ± 9% overshoot at the expense of a reduced sharpness of cut‐off. The discontinuous frequency characteristic is first approximated by a continuous characteristic with linear or cosine frequency tapering. The impulse response for such tapered characteristics consists of the impulse response of the discontinuous frequency characteristic weighted by a certain function corresponding to the type of tapering employed. The best mean square approximation to the tapered characteristic by an impulse response of finite length M will produce a frequency characteristic whose properties are now dependent on the time‐band width product Mζ, where 2ζ is the tapering range.A trade‐off exists between the maximum overshoot and the sharpness of cut‐off for the resulting characteristic for both forms of frequency tapering. Instead of considering other forms of tapering in the frequency domain, we now investigate arbitrarily chosen weighting functions in the time domain to determine the minimum length of impulse response for a minimum value of maximum overshoot and a maximum value of sharpness of cut‐off.Part III will discuss the digital realization of the above finite length impulse responses together with the optimum partially specified digital filter approximation to the desired frequency characteristic.
VERFAHREN ZUR AUSWERTUNG REFLEXIONSSEISMISCHER UNTERTAGEMESSUNGEN NACH DER SPIEGELPUNKTMETHODE*
Authors: SCHMIDT EDGAR 
Published: April 2006

ZUSAMMENFASSUNGBei reflexionsseismischen Untertagemessungen werden die Geophonaufstellungen und die Schußpunkte im Bergwerk angelegt. Die Möglichkeiten hierzu sind durch das Grubengebäude und durch die Meßmethode eingeschränkt. Ungeachtet dessen werden oft Aussagen über die Lage eines Reflektors im dreidimensionalen Raum benötigt. Es müssen daher hohe Anforderungen an die Konstruktionsmethoden gestellt werden können.Zunächst ist es im Hinblick auf die Meßgenauigkeit erforderlich, zwischen günstigen und ungünstigen Anordnungen von Aufstellungen und Schußpunkten zu unterscheiden. Diese Frage wird in der Einleitung kurz behandelt.Die Beschreibung von allgemeingültigen Konstruktionen ist das eigentliche Ziel dieser Arbeit in ihrer hier vorliegenden Fassung. Es wird gezeigt, wie mit Hilfsmitteln der Darstellenden Geometrie beliebig im Raum gelegene ebene reflektierende Flächen‐elemente nach der Spiegelpunktmethode konstruiert werden können. Dies kann, je nach der Korrelation, auf zwei verschiedenen Wegen geschehen, die in den Abschnitten I und 2 getrennt beschrieben werden.Im ersten Abschnitt wird der Fall zweier Geophonaufstellungen behandelt, welche wie die Schenkel eines Winkels aneinandergefügt sind. Sie können von einem beliebig gelegenen Schußpunkt aus beschossen werden (siehe den linken Teil der Abbildung I). Anhand eines Beispiels aus der Kaligrube Salzdetfurth bei Hildesheim wird dies etwas näher erläutert. Bei bekannter Streichrichtung oder bei bekanntem senkrechten Einfallen des Reflektors führt bereits eine Geophonaufstellung zum Ziel und es vereinfacht sich die Konstruktion.Der zweite Abschnitt bringt den Fall zweier nicht notwendig zusammenhängenden Aufstellungen, die nicht in einer gemeinsamen Ebene zu liegen brauchen. Durch Anwendung der Technik des Gegenschießens gelingt es auch so, ein reflektierendes Flächen‐element zu erhalten (siehe den rechten Teil der Abbildung I). Naturgemaß ist die Lage der beiden Schußpunkte hierbei nicht beliebig.
HEAD WAVES IN TWO‐DIMENSIONAL SEISMIC MODELS*
Authors: DATTA S. , BHOWMICK A. N. 
Published: April 2006

ABSTRACTStudies made on head waves in a large number of two‐dimensional horizontal and inclined layer seismic models are described. The assumption that the amplitude of head wave decreases exponentially with distance is found to be valid in horizontal layers. For the correct estimation of the head wave decay coefficient, the decrease of amplitude due to the divergence of wave energy should always be considered.The variations of head wave amplitude at large distances from the source appear to follow the theory of Heelan (1953). It is, however, concluded that the theory can only be verified from the measurements in models which have large velocity contrast and thick layer at the top.A prominent interference phenomenon between the direct and head wave has been observed near the critical distance. This is more marked for up‐dip profile in the case of inclined layer models. The rate of head wave amplitude decrease with distance beyond the zone of interference is found to depend on dip angle, direction of the dip, and velocity contrast.
VELOCITY SPECTRA AND THEIR USE IN STRATIGRAPHIC AND LITHOLOGIC DIFFERENTIATION*
Authors: COOK ERNEST E. , TANER M. TURHAN 
Published: April 2006

ABSTRACTVelocity Spectra which were originally developed for the optimum stacking of seismic data have been found to give considerable information concerning lithologic and stratigraphic changes in the geologic section. In the Gulf of Mexico shale sections and sand bodies have been recognized on the Velocity Spectra display, and in the Caribbean last year a first attempt was made to utilize Velocity Spectra information for the determination and mapping of lithology. Since that time, a new program has been developed which takes dip into account when computing the interval velocity. This program has been applied to a seismic section in the North Sea which has resulted in a geologic model derived from interval velocities which were found to be quite consistent. Such a model can be of great value in geological interpretation.
QUANTITATIVE INTERPRETATION OF TRANSIENT ELECTROMAGNETIC FIELDS OVER A LAYERED HALF SPACE*
Authors: MORRISON H. F. , PHILLIPS R. J. , O'BRIEN D. P. 
Published: April 2006

AbstractThe transient fields from a finite horizontal loop excited by a half sine wave current pulse have been computed numerically for a particular source receiver configuration at a height of 100 meters above a layered ground. The amplitude of the vertical component of the magnetic field has been chosen for the interpretation. Curves of apparent conductivity vs. time, plotted during the off‐time of the signal, show that layering is easily resolved, that resonance effects are present and that polarization effects are detectable for certain types of polarization.
OPTIMUM DIGITAL FILTERS FOR SIGNAL TO NOISE RATIO ENHANCEMENT*
Authors: TREITEL SVEN , ROBINSON ENDERS A. 
Published: April 2006

SummaryOne of the main objectives of seismic digital processing is the improvement of the signal‐to‐noise ratio in the recorded data. Wiener filters have been successfully applied in this capacity, but alternate filtering devices also merit our attention. Two such systems are the matched filter and the output energy filter. The former is better known to geophysicists as the crosscorrelation filter, and has seen widespread use for the processing of vibratory source data, while the latter is. much less familiar in seismic work.The matched filter is designed such that ideally the presence of a given signal is indicated by a single large deflection in the output. The output energy filter ideally reveals the presence of such a signal by producing a longer burst of energy in the time interval where the signal occurs. The received seismic trace is assumed to be an additive mixture of signal and noise. The shape of the signal must be known in order to design the matched filter, but only the autocorrelation function of this signal need be known to obtain the output energy filter. The derivation of these filters differs according to whether the noise is white or colored. In the former case the noise autocorrelation function consists of only a single spike at lag zero, while in the latter the shape of this noise autocorrelation function is arbitrary.We propose a novel version of the matched filter. Its memory function is given by the minimum‐delay wavelet whose autocorrelation function is computed from selected gates of an actual seismic trace. For this reason explicit knowledge of the signal shape is not required for its design; nevertheless, its performance level is not much below that achievable with ordinary matched filters. We call this new filter the “mini‐matched” filter.With digital computation in mind, the design criteria are formulated and optimized with time as a discrete variable. We illustrate the techniques with simple numerical examples, and discuss many of the interesting properties that these filters exhibit.
ESTIMATION OF SPECTRUM AND CROSS‐SPECTRUM OF AEROMAGNETIC FIELD USING FAST DIGITAL FOURIER TRANSFORM (FDFT) TECHNIQUES*
Authors: NAIDU PRABHAKAR S. 
Published: April 2006

AbstractAn efficient method of computing spectrum and cross‐spectrum of large scale aero‐magnetic field (or of any other two‐dimensional field) has been developed and programmed for a digital computer. The method uses fast Fourier transform techniques. Briefly, the method is as follows: a digitized aeromagnetic map is divided into a number of rectangular blocks. Fourier transforms of these blocks are computed using a two‐dimensional fast Fourier transform method. Finally, the amplitude of the Fourier transforms is averaged to give the desired spectrum. Computation of cross‐spectrum follows the same lines. In fact, the same programme may be used to a compute the spectrum as well as cross‐spectrum. The method has a number of computational advantages, in particular it reduces greatly computational time and storage requirements. The programme has been tested on synthetic data as well as on real aeromagnetic data. It took less than 30 seconds on an IBM 360/50 computer to compute the spectrum of an aeromagnetic map covering an area of approximately 4500 square miles.
THE ASSOCIATION OF RESISTIVITY SOUNDINGS*
Authors: HABBERJAM G. M. 
Published: April 2006

AbstractA simple measure, the association parameter, is proposed for directly comparing the results of two electrical soundings. The use of this measure to classify field results and to gain some insight into geological structure before extensive depth interpretation is discussed. In particular it is shown that when used with soundings conducted using the tripotential technique the combined use of association parameter arid lateral inhomogeneity index can allow structural patterns to be discerned where otherwise they might be obscured.Possible extension of the technique is considered.
SIMULTANEOUS ESTIMATION OF PARAMETERS OF REFLECTION EVENTS (DEPTH, DIP, VELOCITY) AND RELATIVE STATIC CORRECTIONS*
Authors: LASKI J. D. 
Published: April 2006

SummaryIt is pointed out that after identifying reflection events from the same horizon on two records obtained on the same spread from two different shotpoints, one can simultaneously estimate parameters of reflection events and relative static corrections. The parameters of reflection events are treated as quantities to compute whereas relative static corrections are treated as quantities to minimize by the least squares method. Static corrections obtained from different horizons for the same point on the spread are averaged.The case of more than one pair of records for the same spread (or part of the spread), vital for multiple coverage, is also discussed.
AN INVESTIGATION OF THE RELATIVE ACCURACY OF THE MOST COMMON NORMAL‐MOVEOUT EXPRESSIONS IN VELOCITY ANALYSES*
Authors: ROBINSON JOHN C. 
Published: April 2006

AbstractThree common expressions for the normal moveout of recorded seismic events are investigated by numerical simulation procedures for accuracy in predicting the root‐mean‐squared (RMS) or mean, as the case may be, subsurface velocity function from seismic data. The principal investigation, for which detailed error curves are shown, was derived for a stochastic subsurface model composed of strata with thicknesses ranging up to 91.4 m (300 ft) and boundary velocity contrasts ranging up to 45.7 m/sec (150 ft/sec); there was a 95 percent chance of velocity increase with increased depth. The effects of changes in the basic statistical subsurface model are discussed.The results appear to confirm the judiciousness of the choices of to and (x/z') as plotting parameters to be used with the respective percent errors in the three expressions, where are, respectively, the zero‐offset arrival time of, the offset distance of, and the mean‐squared velocity encountered by a seismic ray. Out of the three normal‐moveout expressions examined, the “straight‐raypath” expression with the RMS velocity substituted as its velocity term proved to be the most accurate in the determination of velocities.
NUMERICAL INTERPRETATION OF RESISTIVITY SOUNDINGS OVER HORIZONTAL BEDS*
Authors: MEINARDUS HANS A. 
Published: April 2006

AbstractThe digital computer technique described for interpreting resistivity soundings over a horizontally stratified earth requires two steps. First, the kernel function is evaluated numerically from the inverse Hankel transform of the observed apparent resistivity curve. Special attention is given to the inversion of resistivity data recorded over a section with a resistant basement. The second step consists in the least‐squares estimation of layer resistivities and thicknesses from the kernel function. For the case of S or T‐equivalent beds only one layer‐parameter can be obtained, either the longitudinal conductance, or the transverse resistance respectively.Two examples given in the paper show that a wide tolerance is permitted for Choosing the starting values of the layering parameters in the successive approximation procedure. Another important feature for practical applications is good convergence of the iterations. The method is probably best suited for interpreting profiles of electrical soundings with the purpose of mapping approximately horizontal interfaces at depth.
METHODE DE FILTRAGE DU FANTOME: APPLICATION A DES CAS REELS*
Authors: FAIL J. P. , LAYOTTE P. C. 
Published: April 2006

RésuméAprès avoir essayé?analyser, par voie optique, ľeffet de la réflexion fantôme sur des enregistrements sismiques, on montre ľapplication de deux méthodes de filtrage de ce fantôme sur des exemples réels.La première méthode utilise là mise à feu séquentielle de charges situées à différentes profondeurs dans un même trou; il s'agit ?un filtrage réalisé sur le terrain. Le deuxième procédé consiste à filtrer, au central, des enregistrements réalisés à des profondeurs de tir différentes avant de les sommer.