bluuebunny/crossref_metadata_2025 huggingface dataset:
SYSTEM APPROACH TO AIR‐GUN ARRAY DESIGN *
Authors: GILES B. F. , JOHNSTON R. C.
Published: April 2006

Abstract

To specify intelligently a nondynamite source in a marine seismic data‐collection system, it is important to use all known parameters of the system—source, receiver, and recording‐system characteristics. A technique has been developed to design the far‐field pressure pulse of an air‐gun array by taking these parameters into account.

Important source variables to consider are interaction among guns in the array and the depth of the array. Near‐field pressure signatures of individual guns, which are relatively unaffected by boundaries, have been used to‘construct’the far‐field pressure pulse of the array by considering these variables. Comparison between constructed pulses and measured far‐field pulses shows substantial agreement.

Streamer depth and recording‐system bandpass should also be considered when designing an air‐gun array. Comparison of far‐field pressure pulses for several bandpasses clearly shows the importance of considering this variable; e.g., the initial pulse is severely attenuated when a high‐cut filter is used. Likewise, an additional filtering effect due to the streamer's proximity to the surface should be taken into account.

Design of an air‐gun array using the principles just outlined are illustrated by an example.
ACOUSTIC WAVES ALONG OILFILLED STREAMER CABLES *
Authors: WEICHART H. F.
Published: April 2006

Abstract

There are different types of acoustic noise induced in streamer cables. One type consists of pulsed waves preferentially generated by vertical motions of the towing ship or of the tail buoy. The pulsed waves travel along the streamer with low attenuation and a velocity about 15% less than the velocity of water. Frequencies observed lie between 5 and 15 Hz.

These pulsed waves are well known and for the last few years acoustic isolator sections have been used to reduce their generation. But under bad weather conditions and especially in cold water these waves become stronger. Recent investigations demonstrated that the pulsed waves are able to produce a high noise level even in new streamers with acceleration cancelling hydrophones. We point out that the material of the hoses has a dominant effect on the amplitude picked up by the hydrophones.

Acoustic theory is applied to understand the phenomenon of these waves.
A NEW PARAMETER FOR THE INTERPRETATION OF INDUCED POLARIZATION FIELD PROSPECTING (time‐domain) *
Authors: PATELLA D.
Published: April 2006

Abstract

In a previous paper it has been shown that we can relate the transient IP electric field Ep, existing in a rock after a step wave of polarizing current, with the steady‐state current density Jss during the current step wave as follows: Ep=ρ'Jss.

This relation may be interpreted as a generalized Ohm's law, valid in linear cases, in which ρ’(fictitious resistivity) is defined as the product of the true resistivity ρ with the chargeability m.

Supposing Ep=—grad Up and applying the divergence condition div Jss= o, one can, for a layered earth, obtain a general expression for the depolarization potential Up as a solution of Laplace's equation ∇2Up= o.

Since the mathematical procedure for the solution of this last equation is identical to that used in resistivity problems, we propose now the introduction of an apparent fictitious resistivity ρ'a (defined as the product of the apparent resistivity ρa with the apparent chargeability ma) as a new parameter for the interpretations of IP soundings carried out over layered structures with a common electrode array.

The most general expression of ρ'a as a function of the electrode distance turns out to be mathematically identical to the general expression of ρ'a. Therefore it is possible to interpret a ρ'a field curve using the same standard graphs for resistivity prospecting with the usual method of complete curve matching.

In this manner a great deal of work is saved since there is no need to construct proper ma graphs for the interpretation of IP soundings, as it has been done up to now.

Finally some field examples are reported.
INDUCTIVE SOUNDING OF A STRATIFIED EARTH WITH TRANSITION LAYER RESTING ON DIPPING ANISOTROPIC BEDS *
Authors: NEGI J. G. , SARAF P. D.
Published: April 2006

Abstract

The 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 parameters m (coefficient of anisotropy), h (thickness of the transition layer), α (angle of inclination of the dipping beds), and b (conductivity ratio between substratum and upper layer) modify the amplitude and phase‐variation curves (with skindepth) significantly.
MAGNÉTOMÈTRE DIFFÉRENTIEL À HAUTE SENSIBILITÉ*
Authors: COLLIN C. R. , SALVI A. , LEMERCIER D. , LEMERCIER P. , ROBACH F.
Published: April 2006

Abstract

The 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 (10‐7 Oe).

— 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 measuring technique.
SOME IMPLICATIONS OF SIMPLE GEOMETRIC ANALYSIS OF MARINE CABLE FEATHERING IN SEISMIC EXPLORATION *
Authors: RENICK H.
Published: April 2006

Abstract

Cable 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

Summary

A 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

Abstract

Common‐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

Abstract

In 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

Abstract

A 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

Abstract

Section 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

Abstract

A 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

Abstract

Approximate 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

Abstract

Theoretical 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

Abstract

In 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

Abstract

Gravity 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

Abstract

Magneto‐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

Abstract

A 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

Abstract

For 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

Abstract

Variations 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

Abstract

The 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

Abstract

The 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.
THE GRAVITATIONAL ATTRACTION OF VERTICAL TRIANGULAR PRISMS*
Authors: WOODWARD D. J.
Published: April 2006

Abstract

Formulae for the gravitational attraction, at a point, of vertical triangular prisms with oblique ends are presented. They are suited to computation on an electronic computer and are useful for determining the thickness of sediments in a sedimentary basin by iterative means.
TEST OF RECIPROCITY AND SUPERPOSITION IN TIME DOMAIN INDUCED POLARIZATION MEASUREMENTS*
Authors: HABBERJAM G. M. , KHAN M. A.
Published: April 2006

Abstract

The 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

Abstract

The 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

Abstract

An 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

Abstract

The 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

Abstract

A 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

Abstract

The 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

Abstract

An 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

Abstract

Dip 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

Abstract

A 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

Abstract

A 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.
THE RADIATION OF ACOUSTIC WAVES FROM AN AIR‐GUN*
Authors: SAFAR M. H.
Published: April 2006

Abstract

A theoretical model is developed for predicting three important parameters of the pressure pulse radiated by an air‐gun, namely the rise time, the amplitude of the initial pulse, and the period of the bubble pulse. A knowledge of these three parameters is essential for the efficient design of air‐guns arrays.

The prediction of the amplitude of the initial pulse is based on the assumption that the initial pulse is radiated by a spherical source with surface area equal to that of the air‐gun ports and not by a spherical source with initial volume equal to that of the air‐gun chamber, as has been assumed previously.

A simple equation is obtained for predicting the period of the bubble pulsation, taking into account the effect of the air‐gun body, boundaries such as the sea‐surface and seabed and the presence of a number of identical air‐guns placed at the same depth and fired simultaneously.
A COMPARATIVE STUDY OF THE SHORTENING OPERATORS USED IN VARIOUS DATA PROCESSING TECHNIQUES IN GRAVITY INTERPRETATION*
Authors: AGARWAL B. N. P. , SINGH Jagdeo
Published: April 2006

Abstract

Discrete Fourier transform analysis provides an infinite number of weight coefficients for filters like upward and downward continuation. For practical applicability, the lengths of such filters have been reduced to a manageable number by various shortening operators, viz. those by Peters, Martin, Mufti, v. Hann, Hamming, and the truncation operator. A comparative study for choosing an operator which approximates the theoretical filter response best has indicated that Martin's shortening operator and the truncation operator are best, respectively, for normalized and non‐normalized sets of weight coefficients.
ESTIMATION OF DEPTH TO CONDUCTORS BY THE USE OF ELECTROMAGNETIC TRANSIENTS*
Authors: LEE T.
Published: April 2006

Abstract

The transient response of a layered structure to plane wave excitation can be considered to be composed of a series of waves and a ground wave. For the case of a half‐space of conductivity σ and permeability μ the maximum in the electric field is found at a depth z and time t when t=z2σμ/2.

This formula can be used to estimate the depth to a buried horizontal conductor with an accuracy that depends upon the resistive contrast at the conductor's surface.

The above ray type of solution can be converted to a solution composed of a number of modes by the use of a Poisson transform and the transformed solutions yield decay constants that are consistent with the previously reported results.

In the case of a finite source, the maximum in the electric field is strongly directed. The direction depends upon the geometry of the source and the air‐earth interface. Although the maximum varies with direction it can be shown that in some directions similar laws to that above are valid.

The depth to a conductor can be estimated from the early part of the transients when the ground wave is removed. The removal of the ground wave from the transient is facilitated by the use of an apparent conductivity formula.

Although these results were obtained under restrictive conditions they do provide some insight into the electrical transients that are encountered by studying more complex models.
INDUCED POLARIZATION RESPONSE OF A HORIZONTALLY MULTILAYERED EARTH WITH NO RESISTIVITY CONTRAST*
Authors: ELLIOT C. L. , LAURITSEN E.
Published: April 2006

Abstract

The induced polarization response of a horizontally multilayered earth with no resistivity contrast can rapidly be calculated on a desk calculator or minicomputer for any electrode array. The formulation is a simple series summation of the products of weighting coefficients and the true induced polarization responses for each of the layers. The coefficients are directly derivable from the corresponding resistivity model. This series approach to IP formulation was originally described by Seigel but has not been treated extensively in the present‐day geophysical literature. This method can be applied to either time or frequency domain induced polarization measurements. Once the coefficients are known, apparent induced polarization response can readily be obtained by judicious substitution of known, suspected, or assumed values of the true induced polarization of each layer.

Basic formulation is presented for the IP potential coefficients (pole‐pole or two array) with no resistivity contrast between the layers. From these coefficients, response of any number of layers for any electrode array can be obtained by suitable differentiation. Some examples of Wenner array for a three‐layered earth and dipole‐dipole array for a four‐layered earth are used to illustrate the application.

The results of this technique are valid for many natural situations of modest resistivity contrast. However, they definitely cannot be used if there are highly contrasting resistivity layers present. Such an approach is conceptually simple and is useful for survey planning, checking or setting the “depth‐of‐penetration”of a given array. For field induced polarization data that fits reasonably well to the no‐resistivity‐contrast model, this simple approach facilitates quantitative interpretation.
ON THE MIGRATION OF REFLECTION TIME CONTOUR MAPS*
Authors: KLEYN A. H.
Published: April 2006

Abstract

After the sampling of a reflection time contour map, i.e. after times and time gradients at the grid points of a square sampling grid have been determined, its conversion into true depth contours can be performed by normal incidence ray tracing.

At each grid point the spatial orientation of the ray is uniquely defined by a corresponding time gradient vector, whereas its continuation into the subsurface is controlled by Snell's law. For arbitrarily orientated velocity interfaces the 3 – D ray tracing problem can systematically be solved with the aid of vector algebra, by expressing Snell's law as an equation of vector cross products. This allows to set up a computer algorithm for migration of contour maps.

Reliable sampling of reflection time contour maps in the presence of faults is essential for the realization of a practical map migration system. A possible solution of the relevant sampling problem requires a special map editing and digitization procedure.

Lateral migration shifts cause a translation and distortion of the original sampling grid. On the transformed grid the true positions of faults can be related to their apparent ones on the reflection time contour map.

Errors in the time domain correlations or an incorrect velocity distribution or a combination of both these effects may cause migration failures due to total reflection and time deficiencies, or give rise to an anomalous distortion of grid cells, the latter signifying a violation of the maximum convexity condition.

Emphasis is placed upon the significance of map migration as an interpretive tool for solving time to depth conversion problems in the presence of severely faulted or salt intruded overburdens.
SHORT RANGE DISTANCE MEASUREMENT BY ELECTRO‐MAGNETIC PHASE COMPARISON TECHNIQUE*
Authors: GREENE J. R.
Published: April 2006

Abstract

The contribution of electromagnetic phase comparison techniques to distance measuring is reviewed in an historical context. Special emphasis is accorded the new class of near infra‐red electro‐optic instruments suited to the measurement of distances under 2 km with an accuracy of a few millimetres. Principles of operation, sources of error, and practical applications are discussed.
QUELQUES CONSIDÉRATIONS SUR LA DIGITALISATION DES SIGNAUX MAGNÉTOTELLURIQUES — DESCRIPTION D'UN ÉQUIPEMENT*
Authors: ILICETO V.
Published: April 2006

Abstract

A magnetotelluric digital equipment has been designed and built for operation in geophysical and applied geophysical research. The five components of the natural electromagnetic field can be digitized in the frequency range 1/1000 Hz (magnetic sensor's response limits) to some tens Hz.

The magnetotelluric (MT) data are directly digitized in the field and stored in a cassette tape recorder.
HORIZONTALLY STRATIFIED MEDIUM AS A REFERENCE LARGE SCALE SYSTEM*
Authors: SZARANIEC E.
Published: April 2006

Abstract

The geophysical system of horizontal layers may be considered as a large scale system. A large class of systems is identified which are equivalent to the geophysical processes in horizontal layering. The property of hierarchical aggregation of layers forms a convenient framework within which the peculiarities of such systems can be studied. Geophysical processes in multilayered media may serve as a reference physical model for a specified class of large scale systems, in order to take advantage and to apply geophysical methods of data processing, system analysis, and parameter identification.

Specified large scale systems are decomposable, like geophysical systems, by use of recursive schemes. A category particulary susceptible to such a decomposition is any polynomial which is stable inside the unit circle. Sophisticated geophysical concepts, such as anisotropy, equivalence, and disappearance, can be used to approximate or to simplify the system by vanishing or adjusting the decomposition coefficients.
EFFECT OF VERTICAL CONTACT ON WENNER RESISTIVITY SOUNDINGS*
Authors: KUMAR RAKESH , CHOWDARY M. V. RAMANAIAH
Published: April 2006

Abstract

The allowance for the influence of a vertical contact is evaluated on Wenner resistivity sounding curves, which are graphically constructed on bilogarithmic paper over simple composite earth models consisting of a vertical contact separating two‐ or three layered earth on one side and a homogeneous medium on the other side. The error incurred in the graphical constructions is explored.

Finally, the use of these graphically constructed sounding curves is shown in the interpretation of two Wenner field soundings measured in a complex geologic area.
THE CONCEPT OF APPARENT RESISTIVITY IN LATEROLOG 7*
Authors: ROY A.
Published: April 2006

Abstract

It appears that Doll (1951) and N. N. (1958, 1969, 1972) on the one hand, and Roy (1975) and Roy and Apparao (1976) on the other, used different formulas for computing the apparent resistivity for the Laterolog 7 sonde. This would partly explain the contra‐dictory nature of LL7 results from these two groups of workers.

The first group use a formula that relates the measured potential to a system of currents that are largely fictitious and non‐existent in the ground at the time of measurement. The second group, on the other hand, employ a formula that combines the observed signal with the currents that actually exist in the ground and produce that signal. We believe that the second procedure is the right one.
AN ULTRASONIC PROFILING INVESTIGATION ON SOME FRESH AND WEATHERED GRANITES OF HYDERABAD, INDIA*
Authors: RAGHAVA M. S. VIJAYA , JAWAHAR G. , SHERBAKOVA T. V.
Published: April 2006

Abstract

The ultrasonic profiling method of measuring the compressional and shear wave velocities in cylindrical rock samples is extended to measurements in some weathered and fresh granite blocks collected from the Hyderabad (India) region. This possibility of the method provides a means of investigating the elastic properties of the less compact rocks, of which the near‐surface formations are particularly important.

In this article the important parts of the ultrasonic profiling instrument developed are described and the relevant aspects of the seismic wave fields and identification of the individual waves in the wavetrain responses to longitudinal excitation are considered. Compressional, shear and surface (Rayleigh) wave velocities in some fresh and weathered granites are detailed. The compressional velocities range from 4.8 km/s to 5.5 km/s in fresh granites and lie between 1.1 km/s and 2.5 km/s in weathered granites. Young's modulus and Poisson's ratios computed from the measured velocities are also presented. An empirical relation of the form log E= 4.27 + 2.11 log Vp between Young's modulus E and compressional velocities Vp in the fresh granites studied is deduced. The versatility of the approach is thus demonstrated.
TRANSFORMATION OF DIPOLE TO SCHLUMBERGER SOUNDING CURVES BY MEANS OF DIGITAL LINEAR FILTERS*
Authors: KUMAR R. , DAS U. C.
Published: April 2006

Abstract

Linear relationship between dipole and Schlumberger sounding resistivities leads to the use of digital filters to transform the former to the latter. This transformation is of importance from the viewpoint that Schlumberger interpretational techniques and know‐how could then be applied to the pseudo‐Schlumberger field curve. Filters for this transformation are presented for the radial, perpendicular, and parallel (30°) dipole method. The characteristics of these filters are similar to the ones for transforming dipole data to the kernel and are favourable in that they do not amplify noise. A sampling interval of (In 10) /6 has been used in determining the filter yielding good accuracy. Like previous filters the present one is handy and fast in operation.
ENCODING TECHNIQUES FOR THE VIBROSEIS * SYSTEM **
Authors: BERNHARDT T. , PEACOCK J. H.
Published: April 2006

Abstract

The use of certain codes for the Vibroseis system of exploration has been investigated. The codes considered are well‐known in communication theory. The effect of coding the Vibroseis input signal is the suppression of correlation noise and therefore an improvement of the signal to noise ratio.

It is believed that, during the course of research, a new property of one of the codes used has been discovered.
CARTOGRAPHIE DES “PSEUDO‐RESISTIVITES APPARENTES’ PAR PROFILAGE TELLURIQUE‐TELLURIQUE ASSOCIE A LA MAGNETO‐TELLURIQUE *
Authors: VAN NGOC PHAM , BOYER D. , CHOUTEAU ET M.
Published: April 2006

Abstract

The magneto‐telluric and telluric‐telluric profiling techniques are presented, and then a new method which combines these two techniques for mapping a parameter defined as the “apparent pseudo‐resistivity”.

The results obtained for the uranium structures in the Cluff Lake district (Saskatchewan Canada) indicate the use of these different techniques in the detection of zones of conduction for surface zones and for deeper zones, and demonstrate the advantages of these methods over the usual electrical methods in problems of structural research.
SELF‐MATCHING DECONVOLUTION IN THE FREQUENCY DOMAIN *
Authors: DEREGOWSKI S. M.
Published: April 2006

Abstract

In a previous paper the author showed how, by computing an inverse filter in the frequency domain, an automatic compromise could be made between the conflicting requirements to spike a wavelet and to keep the attendant noise amplification within bounds. This paper extends the technique to take account of errors in the estimated shape of the wavelet defined to the deconvolution process. The drastic effects which such errors can have if they are ignored are demonstrated. A novel form of filter–called the “self‐matching filter”–is defined which allows the user to limit not only the noise amplification but also the sensitivity of the filter to random uncertainties in the estimated wavelet. This is achieved by whitening the spectrum only within automatically selected pass bands whilst suppressing other noise‐dominated or uncertainly defined frequency components. Conventional Wiener filtering is shown to be a special case of this more general filter, namely one in which the wavelet uncertainty is completely ignored. The type of phase spectrum which the output pulse should be designed to possess (e.g. zero phase or minimum phase) is briefly discussed.
TRANSIENT ELECTROMAGNETIC FIELD OF A POLARIZABLE HALF‐SPACE DUE TO VARIOUS CURRENT PULSES *
Authors: RATHOR B. S.
Published: April 2006

Abstract

In this paper, the expressions for the induced voltage function V(T) and mutual impedance function Zm(T) have been derived for specific range of time T and specific values of induced polarization parameters a for ramp and saw‐tooth type of current pulses. The computed results for various cases are also presented. The low values of induced polarization parameter a represent the medium possessing membrane polarization, whereas high values exhibit electrode polarization medium. The method has practical applicability and is best suited for the interpretation of transient electromagnetic fields over a polarizable half‐space.
TRANSFORMATION OF SCHLUMBERGER APPARENT RESISTIVITY TO DIPOLE APPARENT RESISTIVITY OVER LAYERED EARTH BY THE APPLICATION OF DIGITAL LINEAR FILTERS *
Authors: KUMAR R. , DAS U. C.
Published: April 2006

Abstract

A simple extension of our previous work in which digital filters were developed to transform dipole resistivity measurements over layered earth to Schlumberger ones leads us to the development of filters for transforming the latter to the former. As in the previous work we use a sampling interval of 1/6 In 10 in designing the filters that are both accurate and fast in operation.