bluuebunny/crossref_metadata_2025_split huggingface dataset:
SOME IMPLICATIONS OF SIMPLE GEOMETRIC ANALYSIS OF MARINE CABLE FEATHERING IN SEISMIC EXPLORATION *
Authors: RENICK H. 
Published: April 2006

AbstractCable feathering is defined as the angle between a line connecting the cable end points and the line of the seismic profile. It is shown that an average reflection point map is more accurate than a shot point location map for geologic interpretation. Geologic resolution is degraded by feathering and this degradation is a function of the number of channels recorded. Feathering in areas of dipping reflectors produces non‐standard normal move‐out because the depth points are not common, and the perpendicular distances to the reflecting surfaces vary among traces in the c.d.p. gather. An example of a profile shot across a large river is discussed.
CONTROLE OPTIQUE DES TRAITEMENTS NUMÉRIQUES DÉCONVOLUTION OPTIQUE DES TRACES SISMIQUES *
Authors: BOURROUILH B. 
Published: April 2006

SummaryA checking method of digital multiple elimination and of deconvolution processing using computers and based on optical autocorrelation is first presented. Comparison between autocorrelograms before and after a single or several processing steps allows to estimate, on one hand, the strength of the deconvolution obtained, known by the study of the central parts which is in fact the signal autocorrelation, on the other hand, the multiple elimination given by the study of side parts of the autocorrelogram.Further, an optical deconvolution procedure, is presented. For this, it is supposed that the signal is known and optically reproduced in the same way as the one of a trace. This is achieved by sphero‐cylindrical optics allowing trace to trace processing. Deconvolution is carried out in the spectral domain by inserting a filter in the Fourier plane of the optical unit, the transmission law of which expresses the Fourier transform of the antisignal. This filter device introduces a holographic technique called Fourier holography, in such a way phases as well as amplitudes are preserved.Several results are presented from a synthetic section and also from field sections.
OBTAINING INTERVAL VELOCITIES FROM STACKING VELOCITIES WHEN DIPPING HORIZONS ARE INCLUDED *
Authors: EVERETT J. E. 
Published: April 2006

AbstractCommon‐depth‐point stacking velocities may differ from root‐mean‐square velocities because of large offset and because of dipping reflectors. This paper shows that the two effects may be treated separately, and proceeds to examine the effect of dip. If stacking velocities are assumed equal to rms velocities for the purpose of time to depth conversion, then errors are introduced comparable to the difference between migrated and unmigrated depths. Consequently, if the effect of dip on stacking velocity is ignored, there is no point in migrating the resulting depth data.For a multi‐layered model having parallel dip, a formula is developed to compute interval velocities and depths from the stacking velocities, time picks, and time slope of the seismic section. It is shown that cross‐dip need not be considered, if all the reflectors have the same dip azimuth.The problem becomes intractable if the dips are not parallel. But the inverse problem is soluble: to obtain, stacking velocities; time picks, and time slopes from a given depth and interval velocity model.Finally, the inverse solution is combined with an approximate forward solution. This provides an iterative method to obtain depths and interval velocities from stacking velocities, time picks and time slopes. It is assumed that the dip azimuth is the same for all reflectors, but not necessarily in the plane of the section, and that the curvature of the reflecting horizons is negligible.The effect of onset delay is examined. It is shown that onset corrections may be unnecessary when converting from time to depth.
THE INFLUENCE OF ELECTRICAL ANISOTROPY ON MISE À LA MASSE SURVEYS *
Authors: ASTEN M. W. 
Published: April 2006

AbstractIn a transversely electrically anisotropic rock mass of arbitrary dip, the potential distribution about an electrode at arbitrary depth is the sum of the whole‐space potential about that electrode, plus the whole‐space potential about a postulated image electrode displaced up‐dip from the source position. Equipotential lines on the rock‐air surface are ellipses, elongated parallel to strike, and with centers displaced up‐dip from the surface projection of the electrode position. In metamorphosed rocks frequently encountered in mining geophysics, anisotropy is such that elongation is most marked in steeply dipping rocks, with displacement most evident in low to moderate dip.Graphs relating the anisotropy coefficient to displacement and elongation assist in separation of the anisotropy‐related effects from those of a significant subsurface conductive body, particularly if surface resistivity sounding establishes the coefficient of anisotropy.
A WIDE‐BAND DIGITAL MAGNETOTELLURIC RECORDING SYSTEM *
Authors: ALLSOPP D. F. , BURKE M. D. , RANKIN D. , REDDY I. K. 
Published: April 2006

AbstractA six‐channel wide‐band digital system for magnetotelluric measurements is described The system is designed to operate in the frequency band 10‐.0001 Hz. The recording is made on a 7 track tape in an IBM compatible 12 bit format. The amplitude and phase responses of the system and sample records are presented.
SECTION MIGRATION, BEFORE STACK, AFTER STACK, OR INBETWEEN *
Authors: SATTLEGGER J. W. , STILLER P. K. 
Published: April 2006

AbstractSection migration after stack has been widely accepted by the industry. From a theoretical point of view, section migration before stack should provide superior results, the improvement warranting the drastically increased cost is not realized in most cases.There are a number of reasons that explain the discrepancy between actual and theoretically expected quality: Long period statics, refraction of rays, two‐dimensional treatment of an actually three‐dimensional problem.The section migration package subject to this paper allows(i) to take refraction into account,(ii) to discriminate against noise with a variety of statistical and geometrical criteria,(iii) to adapt processing time to problem complexity by a special process called SEMI‐STACK.A number of examples will demonstrate the effects of section migration.
ON THE TRANSFORMATION OF DIPOLE TO SCHLUMBERGER SOUNDING CURVES *
Authors: PATELLA D. 
Published: April 2006

AbstractA method is described to transform a dipole sounding curve, obtained with any one of the common dipole arrays over a horizontally layered earth, to the form of a Schlumberger sounding curve. Starting from the general expression which relates the dipole apparent resistivity to the Schlumberger apparent resistivity and its derivative with respect to the spacing, it is possible with some approximations to derive an easy numerical computation procedure in order to perform the transformation. The applicability of the method is discussed briefly.
WAVELET SHAPING AND NOISE REDUCTION *
Authors: DE VOOGD N. 
Published: April 2006

AbstractApproximate deconvolution by means of Wiener filters has become standard practice in seismic data‐processing. It is well‐known that addition of a certain percentage of noise energy to the autocorrelation of the signal wavelet leads to a filter that does not increase, or even reduces, the noise level on the seismogram. This noise addition will, in general, cause a minimum phase signal to become mixed phase. A technique is presented for the calculation of the optimum‐lag shaping filter for a contaminated signal wavelet. The advantages of this method over the more conventional approach are that it needs less arithmetic operations and that it automatically gives the filter with the optimum combination of shaping performance and noise reduction.
THEORETICAL BROADSIDE RESISTIVITY PROFILES OVER AN OUTCROPPING DYKE
Authors: JAIN SHIKHAR C. 
Published: April 2006

AbstractTheoretical broadside resistivity profiles over an outcropping dyke of infinite depth extent with three Wenner configurations (namely Alpha, Beta and Gamma), Schlumberger, and two‐electrode configurations of various electrode spacings and for various reflection factors are presented. The broadside profiles qualitatively indicate that the shape of the anomaly is invariant with the electrode configurations. The various electrode configurations can be arranged in decreasing order of magnitude of anomalies as Beta Wenner, Alpha Wenner, Schlumberger, Gamma Wenner, and two‐electrode. The broadside Wenner profiles also show larger anomalies compared to those in inline profiles.
RELATED PROPERTIES OF MINIMUM‐PHASE AND ZERO‐PHASE TIME FUNCTIONS *
Authors: BERKHOUT A. J. 
Published: April 2006

AbstractIn this paper properties of the discrete zero‐phase time function are derived and compared with related properties of the discrete minimum‐phase time function.The two‐sided minimum‐length signal is introduced and it is derived that, for any given amplitude spectrum, the two‐sided minimum‐length signal and the signal with zero‐phase spectrum are identical signals. A comparison is made between the one‐sided minimum‐length signal (minimum‐phase signal) and the two‐sided minimum‐length signal (zero‐phase signal).A computational scheme is discussed which determines the zero‐phase correspondent of a given signal.A method is proposed to compute zero‐phase least‐square inverse filters. The efficiency of minimum‐phase and zero‐phase least‐square inverse filters is shown on signals with different phase properties.A criterion is derived which determines whether a symmetric time function has the zero‐phase property. The close relationship with the minimum‐phase criterion is discussed.Finally the relationship between signal length and resolving power is illustrated on numerical examples.
GRAVITY COMPUTATIONS BY FLUX DENSITY SUMMATIONS*
Authors: JACKSON P. L. 
Published: April 2006

AbstractGravity profiles can be computed by summing flux lines uniformly radiating from source elements within a density distribution. Digital computations are performed efficiently, irregular density distributions modeled, and alterations easily made to the model to alter the profile by recomputation of only the altered elements. The concept applies to both two‐ and three‐dimensional models and the corresponding datum plane contours. Two‐dimensional computations are described and illustrated.
EXEMPLES D'APPLICATION DE LA METHODE MAGNETOTELLURIQUE DE PROSPECTION GEOPHYSIQUE A L'ETUDE DE STRUCTURES OU DE FORMATIONS GEOLOGIQUES SITUEES SOUS UN TRES FAIBLE RECOUVREMENT*
Authors: GUINEAU B. 
Published: April 2006

AbstractMagneto‐telluric radio frequency measurements can be developped in shallow applications in civil engineering, mining exploration hydrogeology and even archeology.In the V.L.F. and L.F. ranges the depths usually encountered range from 4 or 5 meters to nearly 50 meters.Specially designed equipment allows rapid work—in some cases even continuous profiling.Field data obtained over a fault, a cavity, and sedimentary ore deposits agree well with data from conventional electric surveys.
RESOLUTION OF RESPONSES DUE TO CONDUCTIVE OVERBURDEN AND ORE‐BODY THROUGH TIME‐DOMAIN ELECTROMAGNETIC MEASUREMENTS—A FIELD EXAMPLE*
Authors: VERMA S. K. 
Published: April 2006

AbstractA technique is suggested to separate the effect of conductive overburden from the recorded time‐domain electromagnetic anomalies. Such a separation leads one to construct a relatively undistorted picture of the conductor underlying a conductive overburden. A parameter τ (with dimensions of time) is introduced to characterize various conductors. To illustrate the applicability of the technique, four ‘Input’ (Mark V) anomalies obtained over the Cuddapah District, A.P., India have been analyzed and different values of the time‐parameter τ corresponding to the overburden and the mineralized zones are obtained.
LOCATING A DIFFRACTOR BELOW PLANE LAYERS OF CONSTANT INTERVAL VELOCITY AND VARYING DIP*
Authors: HUBRAL P. 
Published: April 2006

AbstractFor a two‐dimensional situation, a direct solution exists to the problem of locating a point diffractor below plane layers of constant interval velocity and varying dip. The required surface measurements are obtainable from an arbitrary portion of the observed diffraction curve on the stacked section. The method resembles the computing of plane dipping layers of constant interval velocity from common depth point surface measurements.
FUNDAMENTAL NOISE AFFECTING SIGNAL‐TO‐NOISE RATIO OF RESISTIVITY SURVEYS*
Authors: HOOGERVORST G. H. T. C. 
Published: April 2006

AbstractVariations of the spontaneous electrical field appear to be a fundamental noise in geoelectrical resistivity surveying, irrespective of the origin of these variations. The signal‐to‐noise ratio can decrease to such an extent that investigations to large depths are impossible in some regions. Description of the character and magnitude of the noise recorded in Spain and Holland (1973) and the correlation between simultaneous recorded data at different locations form the subject of this paper.
QUANTITATIVE INTERPRETATION OF A COMBINED ELECTROMAGNETIC AND MAGNETIC HELIPORTED SURVEY FOR THE SEARCH OF ECONOMIC MAGNETIC TACONITE*
Authors: SEGUIN M. K. 
Published: April 2006

AbstractThe present paper shows the practical use of a combined electromagnetic and magnetic helicopter transported system in the search for steeply dipping high‐grade magnetic taconite bodies (magnetic ribbons). The principles of operation of the heliported system and the essential parts of the instrumentation are described. The quantitative interpretation of the data allows the geophysicist to calculate the tonnage of magnetite within the iron ores and to obtain an approximate idea of their grade. According to the tonnage and grade calculations obtained from the surveys, three regions in the west‐central sector of the Labrador trough (Wishart Creek, Knob Lake Ridge, and Swampy Bay areas) appear to be the most interesting locations for the site of a magnetic taconite deposit (the Howells River area, which has been evaluated previously, is excluded from the discussion). The tonnages calculated by this geophysical method are not to be compared with probable or possible mineable ore reserves, but are only rough estimates in terms of mining engineering standard.The physical parameters determined with such a system are also used as a tool for indirect geological mapping of the areas flown when interpreted carefully. Practical examples related to results obtained on the magnetic iron formations of the Schefferville mining district are presented.
TRANSIENT ELECTROMAGNETIC RESPONSE OF A SPHERE IN A LAYERED MEDIUM*
Authors: LEE T. 
Published: April 2006

AbstractThe Galerkin method of solving integral equations is well suited to the solution of the integral equations describing the transient response of a sphere embedded in a layered medium, which is excited by a large co‐axial loop.The transient response is calculated by transforming the steady state solutions obtained in the frequency domain.The analysis shows that the scattering matrix is extremely diagonally dominant and the maximum number of modes required to obtain convergence does not rapidly increase with frequency. The number of modes required is about eight. This type of scattering matrix can be taken to be an expression of the principle of elementary superposition. This principle is reflected in the decay curves. These show that the early part of the decay curves asymptotically approach the decay curves to be expected for a layered structure without the sphere. The slope of the latter stages of the decay curve gives a decay constant that is the same as was obtained for spheres in free space excited by planar or dipolar sources.The point of departure in time of these curves from the layered ground curves is delayed either by placing the sphere at a greater depth or by placing a more conductive overburden above the sphere.
TEST OF RECIPROCITY AND SUPERPOSITION IN TIME DOMAIN INDUCED POLARIZATION MEASUREMENTS*
Authors: HABBERJAM G. M. , KHAN M. A. 
Published: April 2006

AbstractThe principles of reciprocity and superposition, which hold in normal resistivity measurements, are sometimes considered to apply also to Induced Polarisation measurements.In this paper, an account is given of experiments designed to test how far such a proposition is justified. The experiments comprise a limited field test and more extensive observations using a tank analogue.Within acceptable limits, both tests showed that these basic theorems are applicable to I.P. potentials provided that these are measured at the same instant after switch off and that identical charging regimes are used.The implications of these findings are discussed.
HIDDEN LAYER PROBLEM IN SEISMIC REFRACTION WORK*
Authors: BANERJEE B. , GUPTA S. K. 
Published: April 2006

AbstractThe hidden layer problem in seismic refraction work has been studied for three velocity configurations – the intermediate layer having (a) lower, (b) intermediate and (c) higher velocity than the underlying and overlying beds. It has been shown that conventional methods fail to locate the presence of the intermediate layer for the cases (a) and (c) and lead to errors in calculating the depth to the bedrock. For the case (b), it is possible to interpret the first arrival travel time analytically as an alternative to Green's graphical approach. It has been suggested that the hidden layer may be detected in all the three cases if converted S waves are also recorded in the seismogram.
ERROR PROPAGATION AND UNCERTAINTY IN THE INTERPRETATION OF RESISTIVITY SOUNDING DATA*
Authors: KOEFOED O. 
Published: April 2006

AbstractAn analysis is made of the propagation of the measuring error in the different stages of the interpretation by the linear filter and reducing method.This analysis leads to an understanding of the range of possible values of the layer parameters and of the nature of the relation between them.It is shown that this relation is not always adequately described by the equivalence expressions of Maillet.
ELECTRICAL SOUNDING OF A HALF SPACE WHOSE RESISTIVITY OR ITS INVERSE FUNCTION VARIES LINEARLY WITH DEPTH*
Authors: SAMPAIO E. S. 
Published: April 2006

AbstractThe solution for the potential distribution about a point source of current placed at the surface of a continuous half‐space is obtained for two cases: (1) the resistivity increases linearly with depth; (2) the conductivity increases linearly with depth. In each case, an expression for the apparent resistivity is established and master curves are presented for both the Wenner and the Schlumberger configurations. The results can be used in the interpretation of electrical sounding data in specified geologic situations. Furthermore, they may be used as a first step in the development of solutions for the more complex electric sounding problems.
INTERPRETATION OF GRAVITV ANOMALIES BY MEANS OF LOCAL POWER SPECTRA*
Authors: CIANCIARA B. , MARCAK H. 
Published: April 2006

AbstractA statistical model of the medium is introduced as source of a gravimetric anomaly. On the basis of this model the estimation of the parameters of the medium is proposed based on the statistically transformed power spectrum of the gravity anomaly. The method permits to associate the estimated depths to the disturbing limit with the profile points. Practical examples illustrate usefulness of this method to interpretation.
FUNDAMENTAL FUNCTIONS FOR HORIZONTALLY STRATIFIED EARTH*
Authors: SZARANIEC E. 
Published: April 2006

AbstractThe potential distribution and the wave propagation in a horizontally stratified earth is considered and the analogy of the mathematical expression for seismic transfer function, electromagnetic and electric kernel functions, and magnetotelluric input impedance is discussed. Although these specific functions are conveniently treated by a separate expression in each method, it is indicated that the function for seismic and electromagnetic methods is mathematically the same with a change in the physical meaning of the variables from one method to the other. Similarly, the identity of the mathematical expressions of the resistivity kernel function and magnetotelluric input impedance is noticed.In each method a specific geophysical function depends on the thickness and the physical properties of the various layers. Every specific function involves two interdependent fundamental functions, that is Pn and Qn, or Pn and P*n, having different physical meaning for different methods. Specific functions are expressible as a ratio Pn/Qn or P*n/Pn. Fundamental functions may be reduced to polynomials.The fundamental polynomials Q*n and P*n describing the horizontally stratified media are a system of polynomials orthogonal on the unit circle, of first and second order, respectively. The interpretation of geophysical problems corresponds to the identification of the parameters of a system of fundamental orthogonal polynomials. The theorems of orthogonal polynomials are applied to the solution of identification problems. A formula for calculating theoretical curves and direct resistivity interpretation is proposed for the case of arbitrary resistivity of the substratum.The basic equation for synthetic seismograms is reformulated in appendix A. In appendix B a method is indicated for the conversion of the seismic transfer function from arbitrary to perfectly reflective substratum.
AN APPROXIMATE METHOD OF RESISTIVITY SOUNDING INTERPRETATION*
Authors: KOEFOED O. 
Published: April 2006

AbstractAn approximate method of interpretation of resistivity sounding is presented, which may be described as a very crude manner of application of the exact direct interpretation method. The accuracy of this method is fairly low, the errors being in the order of 25%. The method is very fast in application and well suited for application to multilayer cases. The main advantage of the method is that it is in close and clear relation to the exact theory.
DIP SELECTIVE MIGRATION VELOCITY DETERMINATION*
Authors: SATTLEGGER J. W. , STILLER P. K. , ECHTERHOFF J. A. 
Published: April 2006

AbstractDip selective migration velocity determination calculates coherency of energy migrating into an output trace or ‘MVD‐axis’ as a function of the three variables time, velocity, and dip. In doing so, it provides additional information, the dip information, relative to standard MVD.
INTERPRETATION GRAPH FOR VERTICAL TABULAR CONDUCTORS IN E.M. IN‐LINE DIP‐ANGLE MEASUREMENTS*
Authors: KETELAAR A. C. R. , DE VENTE C. P. 
Published: April 2006

AbstractA graphical interpretation method is presented by which separately the depth and the product of conductivity and thickness of a vertical plate‐shaped conducting orebody can be determined. The method is based on the result of model experiments.
RECONNAISSANCE DES HORIZONS SISMIQUES PAR ANALYSE FACTORIELLE DISCRIMINANTE*
Authors: BOIS P. 
Published: April 2006

AbstractA complicated geological structure may make it difficult to recognize seismic horizons. This may be the case when blind zones are present, when horizons have to be identified on both sides of a fault, or when lithological facies exhibit a lateral variation.A method for the recognition of seismic reflections is described. The process takes the dynamic range of seismic information into account as well as the extensive logical possibilities of modern computers. The method implements a factorial discriminant analysis of seismic traces by means of a stepwise iterative process. The reliability of results is studied by examining the a posteriori discrimination between different horizons. If the classification is good, a percentage of well classified reflections is given for each horizon.