bluuebunny/crossref_metadata_2025 huggingface dataset:
DEPTH OF INVESTIGATION IN WENNER, THREE‐ELECTRODE AND DIPOLE‐DIPOLE DC RESISTIVITY METHODS*
Authors: ROY A.
Published: April 2006

Abstract

Using a method and definition given earlier (Roy and Apparao, 1971), this paper computes the depths of investigation in homogeneous ground for (a) the Wenner α, β and γ configurations, (b) the three electrode system and (c) the dipole‐dipole arrangements when the dipole lengths are not infinitesimally small. The results for (a) and (b) have been summarised in a table, while those for (c) are shown as contour diagrams. In all the dipolar arrangements examined in this paper, except the equatorial, the depth of investigation decreases (and the vertical resolution increases) with increase in any or both of the dipole lengths. For the equatorial set up, this decrease (or increase) is very small.
RESISTIVITY MEASUREMENTS IN VALLEYS WITH ELLIPTIC CROSS‐SECTION*
Authors: MUNDRY E. , HOMILIUS J.
Published: April 2006

Abstract

In this paper an idealized valley of a semi‐elliptic cross‐section is considered. For a Schlumberger configuration on the axis, sets of master curves are calculated for the ratio of semi‐axis a/b= 1, 2, 3, 4, 5 in corresponding to various resistivity ratios of surrounding rocks and valley sediments. For small resistivity ratios, these model curves have the shape of three‐layer curves for horizontal bedding and are often equivalent to them within the accuracy of measurements. The axial ratio a/b considerably affects the depth determination of valley sediments. In the special case of a circular cross‐section (a/b= 1) the influence of the position of the electrodes on the sounding curve is studied in more detail.

The application of the master curves in practice shows that the influence of the specific shape of the valley on soundings should not be neglected. In general, the valleys have a greater “true” depth than can be seen from the interpretation of a sounding by master curves corresponding to the horizontal bedding.
MAGNETIC SUSCEPTIBILITY ANISOTROPY OF VARIOUS ROCK TYPES AND ITS SIGNIFICANCE FOR GEOPHYSICS AND GEOLOGY*
Authors: JANÁK F.
Published: April 2006

Abstract

In the interpretation of magnetic anomalies and in paleomagnetism, the anisotropy of magnetic susceptibility is commonly neglected. Nevertheless, this property has basic significance, because, owing to susceptibility anisotropy, the directions of the vectors of induced and remanent magnetization are deflected from the direction of the Earth's magnetic field. Almost all rock types investigated possess higher or lower degree of the susceptibility anisotropy. Effusive and sedimentary rocks have the lowest degree of anisotropy. For the latter, the “masking effect” of the paramagnetic mineral components has some influence on the anisotropy degree due to the low mean susceptibility of sedimentary rocks. Metamorphic and plutonic rocks usually exhibit a considerable degree of anisotropy. The highest degree of anisotropy has been found in the rocks containing ferromagnetic minerals with mimetic fabric.

The dependence of the degree of the susceptibility anisotropy on the degree of metamorphism proved to be very complicated; of the rock sequence from slates to gneisses, the transient rocks (roofing slates and mica‐schist‐gneisses) showed the highest degree of anisotropy. This result can be used in geology for reliable determination of these rock types.
SIGNAL ENHANCEMENT OF VIBRATORY SOURCE DATA IN THE PRESENCE OF ATTENUATION*
Authors: GURBUZ B. M.
Published: April 2006

Abstract

Amplitude spectra of input FM signals used in the vibratory source method of seismic exploration often show undesirable oscillations near the initial and terminal frequencies. These oscillations have an effect on the correlation background and distort the output signal. Considerable improvement in reducing the amplitude of these oscillations is obtained using a proper taper fuction. Attention is given to the relation between the tapering time and bandwidth of the spectrum.

Analyses of the spectra of the received data from vibratory sources show considerable attenuation in comparison with the original field sweep. Since the matched filtering process will result in a series of waveforms which have the shape of the autocorrelation of the input signal, consideration is given to the autocorrelation function and its zero‐lag coefficient of the FM signal in the presence of attenuation. A method has been developed which compensates for the attenuation and recovers the distortion of waveforms when the received data is correlated.

The design of a waveform shaping filter for vibratory source data is given to reduce the influence of phase distortion on the received waveforms as well as to increase S/N ratio resolution. Parameters used for this filter are based on the properties of the FM signal and its autocorrelation function.

Several examples from field data are presented to illustrate the methods. The results indicate that the use of the above techniques yields sections with good frequency resolution and improved S/N ratio.
INTERPRETATION QUANTITATIVE EN GRAVIMETRIE OU MAGNETISME A PARTIR DE CARTES TRANSFORMEES DE GRADIENT VERTICAL*
Authors: GERARD A. , GRIVEAU P.
Published: April 2006

Abstract

A discussion is given of the requirements, the advantages and the methods to be considered in attempting the quantitative interpretation of gravity or magnetic fields from computed maps of the vertically derived field.

The transform which is used here is the first vertical derivative (or vertical gradient) with or without downward continuation, but the computed maps are in fact obtained by a controllable Fourier method in which two kinds of operations can be simultaneously performed in complete independance: on one hand the separation of any part of the data by frequency cut‐off, and on the other hand the transformation by vertical derivation or continuation of the part which is retained.

Taking as raw data either actual surveys or artificially constructed maps, it is first shown how separated and transformed maps of this type can be efficiently obtained under quite flexible conditions, using a special computer program. It is further seen that for correctly controlled filterings the accuracy of the computed maps actually permits to take them as the basis for quantitative interpretation.

To effect this, any one of the conventional methods which make use of equivalent model computations may in the first place be adapted to the interpretation of gradients, with the benefits, however, of an enhanced lateral separation of the anomalies and of a large attenuation of the regional effects.

Particularly, the delineation of horizontal contours for even fairly complex models can often be made directly in a sufficiently safe way on the anomalies as they show on the vertical gradient maps. This greatly accelerates the process of determining equivalent model bodies.

More special methods of interpretation can also be designed by taking into account first the fact that the vertical derivation of the field amounts to an operation of separation on the field's sources themselves, and in addition the availability of the frequency form of the information as a result of using a Fourier method of transform computation.

Trial utilisations of various such interpretation processes of either the conventional or the less conventional type, are presented especially in connection with an interpretation study on transformed maps of parts of an offshore aeromagnetic survey (English Channel).
ANALYSE SEQUENTIELLE*
Authors: BOIS P.
Published: April 2006

Abstract

Various authors have recently studied the Walsh and Hadamard transforms for functions with one or two variables. Like the Fourier transform they may be obtained by using the Cooley‐Tukey algorithm. They can be calculated all the faster because Walsh functions have only values equal to + 1 or − 1. The complex number multiplications in the Fourier transform are replaced by additions and subtractions of real numbers.

These transforms are more general than that of Fourier because the concept of sequency, i.e. the mean number of zeros per time unit, is substituted for that of frequency.

These transforms already have numerous applications to signal transmission. We describe some in the field of seismic prospecting, in particular the compression of the information contained in seismic traces.
DIGITAL PROCESSING OF REFRACTION DATA STUDY OF FIRST ARRIVALS*
Authors: PERALDI R. , CLEMENT A.
Published: April 2006

Abstract

It has been necessary to resort to the use of “long‐line” refraction marine operations in certain areas where it proved impossible to eliminate singing from reflection records despite the number and variety of programs at our disposal for this purpose.

Experience has shown that manual processing of offshore refraction records takes a disproportionate length of time in comparison with the surveys themselves, and this is incompatible with the requirements for choosing the site of an exploration well. It thus became necessary to find an “industrial approach” to the solution of this processing problem.

It was apparent that automatic picking could also facilitate the interpretation of land refraction data, and that in the case of both marine and land work the interpretations would be more accurate when factors were taken into account which could not be considered when working without the aid of a digital computer.

For these reasons a set of programs was developed for automatic picking and interpretation of refracted arrivals.

The picking itself consists in searching for the maximum values of the normalized cross‐correlation functions of the traces with a “model” trace. The first results thus supplied are: “picked” times, intercept times, maximum values of the correlations, and the values of the tie constants between overlapping spreads.

Next, the construction of the relative intercept time curves is performed; a statistical analysis of these curves then allows the determination of the offset distance.

From these elements,

⊙ either the delay time curve is produced, after ensuring correct reciprocal times by means of additional minor corrections.

Such work is carried out in order to enable the geophysicist to gain a sound idea of the quality of the interpretation. To assist in this aim, part of the trace on both sides of the pick is plotted on the final documents. Valid groupings of several traces involving the same amount of refraction data are thus possible.

⊙ or the refractor depth is constructed with the wavefront method, making use of the relative intercept times.

Such a procedure, which is normally applied to first breaks, can also be used for later arrivals exhibiting slight interference and should represent an important step towards processing secondary arrivals with high interference.

The development of this package, in response to a need which is shared by both SNPA and CGG, is the result of the joint efforts of the Geophysical Group of SNPA's Pau Research Center and CGG's Technical and Scientific Departments.
AN INTERPRETATION THEORY FOR INDUCED POLARIZATION VERTICAL SOUNDINGS (TIME‐DOMAIN)*
Authors: PATELLA D.
Published: April 2006

Abstract

In this paper it is shown how one may obtain a generalized Ohm's law which relates the induced polarization electric field to the steady‐state current density through the introduction of a fictitious resistivity defined as the product of the chargeability and the resistivity of a given medium.

The potential generated by the induced polarization is calculated at any point in a layered earth by the same procedure as used for calculating the potential due to a point source of direct current.

On the basis of the definition of the apparent chargeability ma, the expressions of ma for different stratigraphie situations are obtained, provided the IP measurements are carried out on surface with an appropriate AMNB array. These expressions may be used to plot master curves for IP vertical soundings.

Finally some field experiments over sedimentary formations and the quantitative interpretation procedure are reported.
COMPARISON OF TIME, FREQUENCY, AND PHASE MEASUREMENTS IN INDUCED POLARIZATION*
Authors: ZONGE K. L. , SAUCK W. A. , SUMNER J. S.
Published: April 2006

Abstract

In comparing the similarity between time, frequency, and phase measurements as used in the induced polarization method of geophysical prospecting, parameters must first be defined and the basis for comparison established. The conditions for mathematical equivalence then follow in a natural sequence. Laboratory measurements are made on a variety of rock samples to indicate the type of comparison and correlation expected from field measurements.

Results indicate that frequency domain and phase measurements are equivalent, but two frequency domain measurements are needed to produce the same amount of polarization information as a single phase measurement. Frequency and time domain measurements will be similar but never equivalent due to the basic differences in their respective parameter definitions.
INFLUENCE OF NUMBER AND SPACING OF SENSORS ON THE EFFECTIVENESS OF SEISMIC ARRAYS*
Authors: HARTENBERGER R. A. , Van NOSTRAND R. G.
Published: April 2006

Résumé

De préférence, les sismographes seront disposés dans un lieu sans bruit, oú il n'y aurait pas besoin de patternes. Par contre, si les bruits sont tels qu'une patterne est nécessaire, l'objectif de la patterne est d'améliorer le rapport signal/bruit et donc de rendre le signal le plus utile possible. La patterne sera dessinée en fonction des charactéristiques du signal, des charactéristiques du bruit, et de la géologie du site.

Il a été démontré que, dans le sens pratique, l'opération optimum sur les données d'une patterne est représentée par le proces “delai et somme”. L'augmentation du nombre N de senseurs sur une surface donnée diminue les espacements entre les senseurs et peut augmenter la coherence entre les bruits enrigistrés aux senseurs voisins, donnant donc moins d'amélioration au rapport signal/bruit que la √N anticipée. L'augmentation du nombre de senseurs par l'augmentation proportionnelle de la surface de la patterne peut resulter en la détérioration du signal, et peut également donner moins d'amélioration que la √N Ces deux effets, ainsi que l'élément économique, combinent à limiter le nombre de senseurs qui peuvent être employés.

Bien que les données sur lesquelles l'on a basé ces conclusions soient tirées de la sismologie conventionnelle, ces principes sont également valables pour l'exploration sismique et pour d'autres mesures géophysiques qui emploient des dispositifs dans lesquelles plusieurs senseurs sont requis.
IMPEDANCE OF A PLANE ELECTROMAGNETIC WAVE AT THE SURFACE OF A LAYERED CONDUCTING EARTH WITH DIPPING ANISOTROPY*
Authors: NEGI J. G. , SARAF P. D.
Published: April 2006

Abstract

The problem of a plane wave incident on a non‐isotropic dipping layer lying over an isotropic conducting substratum has been studied and some numerical results are presented to show the effects of

degree of anisotropy m,

conductivity contrast between the substratum to the upper layer b,

angle of inclination of the axis of anisotropy α,

on the variation of amplitude and phase difference of the wave impedance with the normalized skin‐depth (d/δ1).
TRANSIENT ELECTROMAGNETIC RESPONSE NEAR A FAULT ZONE*
Authors: GEYER R. G.
Published: April 2006

Abstract

Recent improvements in instrumentation and field techniques have made time domain electromagnetic methods more acceptable. This acceptance has prompted further theoretical work for use in the interpretation of field data.

The asymptotic solutions for the transient electromagnetic field components in the vicinity of a fault zone separating two media of high resistivity contrast are obtained for low frequency or late time. Excitation is by normally incident plane waves at the earth's surface. Because of the slow convergence of the asymptotic time series expansions, a numerical polygonal inversion is performed on the real part, or in‐phase term, of the time‐harmonic surface expressions for the electric and magnetic field components.

For both impulsive and step excitation the transient electric field normal to the contact is more sensitive to changes in the structural attitude of the fault plane than the transient electric field parallel to the contact. The transient anomalous vertical magnetic field for either impulsive or step excitation appears to be most diagnostic of dip angle, although waveform shape does not seem to be significantly dependent on the slope of the fault. For dip angles greater than 90 degrees, as measured on the poorly conducting side of the contact, all field components become more insensitive as indicators of the structural attitude. The results presented here should be useful in obtaining several geologic parameters descriptive of a fault zone or lateral resistivity inhomogeneity from transient electromagnetic soundings; they should also provide an aid to differentiating with available geological information between layering effects on transient electromagnetic responses and effects largely due to lateral changes in resistivity.
CONDUCTING INFINITE HORIZONTAL CYLINDER IN ELECTROMAGNETIC INPUT FIELD *
Authors: MALLICK K.
Published: April 2006

Abstract

With the help of the principle of superposition the Input response of a conducting infinite horizontal homogeneous cylinder is synthesised from its step‐function response. The variation of transient peaks and the time lag between the secondary and primary fields with the cylinder constitution parameter are illustrated.
A NEW ENERGY SOURCE FOR MARSH AREAS *
Authors: BADGER A. S. , GUNDLACH W. J.
Published: April 2006

Abstract

Many practical energy sources are available for land use and likewise a goodly number for marine operations. However, the transitional region between navigable water and negotiable land is poorly served. The vehicles that are capable of operating amphibiously are limited in the pay‐load they can transport, and in the bulk of apparatus that can be operated from the space available. The Flex‐O‐Gun (Trademark of Geo Space Corporation) is a new, lightweight gas exploder designed to meet the requirements for operation in rivers, bays, and marsh areas not generally accessible to the larger, heavier systems such as the Dinoseis (Trademark of Atlantic Richfield Company), Vibrator and Air Guns. Weighing less than 70 kilograms, the Flex‐O‐Gun requires only modest sources of oxygen and propane and the associated firing equipment for operation.

The gun delivers energy by the sudden introduction into the water of high pressure gases resulting from detonation. The device is unique in that the underwater gun assembly contains no gas mixing or firing elements. A flexible, metallic hose conveys the charge of mixed gases and subsequent detonating flame to the gun from control and firing mechanisms located above the surface. With its small weight and total space requirements, the Flex‐O‐Gun can be operated from small boats, buggies, or trucks, and is easily transported.

In this paper the features of the gun are described and the results given of tests of its operations. An implanting device is also discussed which extends its application to viscous formations. The device employs water jets mounted below the gun to wash down a hole and insure placement of the gun at depths to obtain maximum energy output.
ELECTROMAGNETIC RESPONSE PATTERN OF A CONDUCTING VEIN *
Authors: JAIN SHEEL C.
Published: April 2006

Abstract

Dividing a vertical conducting vein into horizontal strips, response of each of them is obtained for various transmitter receiver orientations.
SEISMIC REFRACTION ON CONTINENTAL SHELVES WITH DETECTORS ON SEA FLOOR *
Authors: AVEDIK F. , RENARD V.
Published: April 2006

Abstract

Seismic refraction at sea and on continental shelves requires most of all a precise positioning of the shooting and receiving stations and a good signal to noise ratio.

A new system has been developed using detectors anchored on the sea floor and radio transmission of signal for refraction work on continental shelves. This technique satisfies both requirements. The system has been tested in the western Channel in December 1971.
ELECTROMETRIC OBSERVATIONS OF ANTIFILTRATIONAL CEMENTATION CURTAINS *
Authors: BOGOSLOVSKY V. A. , OGILVY A. A.
Published: April 2006

Abstract

Creation of antifiltrational cementation curtains needed to prevent increased seepage from water reservoirs is a rather labour‐consuming and costly measure. High cost of such curtains necessitates careful checking of the quality of cementation as well as the strength and stability of the solidified cement which is being formed in the pores and fissures of injected rocks.

The traditional methods of control are rather labour‐consuming and do not allow observations during process of cementation. The advantage of electrometric observations of cementation curtains lies in the possibility of making measurements on the surface from the moment of pumping slurry into a borehole up to the termination of cement hardening.

The laboratory investigations carried out by the authors demonstrate an increase in the specific electrical resistivity of a cement in the course of hardening as well as the existence of a functional dependence between the electrical and strength parameters which allows to use the resistivity method for checking the cement strength.

Methods of electrometric observations of cementation curtains are dependent on the particular features of cementation and the curtain dimensions. The observations are usually conducted in a network of profiles parallel to the curtain axis. The cement slurry spreading in the space is studied on the maps of ρa and geoelectrical sections obtained at different distances from the feed line. Zones of the strongest absorption of cement slurry are indicated by resistivity minima. The electrometric observations should be compared with the data on cement expenditure in the boreholes.

The cement strengthening is monitored by comparing the results of control observations consecutively conducted in 1‐2 months following the cementation, with utilization of the ρa maps and graphs. If the specific resistivities of the skeleton of the enclosing rocks and the filler of cavities are known, one can approximately evaluate the changes in the cement strength in absolute units (kg/cm2).

By way of example, the authors give the results of electrometric observations conducted to evaluate the quality of an antifiltrational curtain on one of the high‐mountain water reservoirs in Armenia.
THREE‐DIMENSIONAL SEISMIC MODELING FOR ARBITRARY VELOCITY DISTRIBUTIONS *
Authors: DOBECKI T. L.
Published: April 2006

Abstract

The growing awareness of the significance of three‐dimensional interpretation of seismic reflection data carries with it a need for better understanding of the role of the velocity configuration in the production of reflection patterns. Modeling the reflection responses of a simple dipping plane reflector through velocity models of various degrees of complexity demonstrates the importance of overlying velocities in determining the reflection pattern.

Modeling is accomplished using a raytracing technique which determines total travel time of the normal incidence raypath through an arbitrary iso‐velocity layer model.
COMPUTATION OF THE TIME‐DISTANCE CURVE FOR A DIPPING REFRACTOR AND VELOCITY INCREASING WITH DEPTH IN THE OVERBURDEN *
Authors: LASKI J. D.
Published: April 2006

Abstract

The paper presents the method and algorithm for computing the time‐distance curve for head waves in the case of a dipping refractor and velocity increasing with depth in the overburden. The method is illustrated by an example.
A STUDY ON THE DIRECT INTERPRETATION OF DIPOLE SOUNDING RESISTIVITY MEASUREMENTS OVER LAYERED EARTH *
Authors: DAS BY U. C. , GHOSH D. P.
Published: April 2006

Abstract

Dipole sounding resistivity measurements over layered earth can be interpreted directly by adapting the procedure given by Koefoed (1968) for Schlumberger system. To carry out the first step of the interpretation leading to the determination of the raised kernel function, partial resistivity functions for the dipole method are derived and given in the form of standard curves. The second step involving the derivation of layering parameters from the kernel being independent of the electrode configurations remains unaltered. The applicability and limitations of the method are discussed.
AN INTERPRETATION SYSTEM FOR GEO‐ELECTRICAL SOUNDING GRAPHS *
Authors: DEPPERMANN K.
Published: April 2006

Abstract

For the two and three layer cases geo‐electrical sounding graphs can be rapidly and accurately evaluated by comparing them with an adequate set of standard model graphs. The variety of model graphs required is reasonably limited and the use of a computer is unnecessary for this type of interpretation.

For more than three layers a compilation of model graphs is not possible, because the variety of curves required in practice increases immensely. To evaluate a measured graph under these conditions, a model graph is calculated by computer for an approximately calculated resistivity profile which is determined, for example, by means of the auxiliary point methods. This model graph is then compared with the measured curve, and from the deviation between the curves a new resistivity profile is derived, the model graph of which is calculated for another comparison procedure, etc. This type of interpretation, although exact, is very inconvenient and time‐consuming, because there is no simple method by which an improved resistivity profile can be derived from the deviations between a model graph and a measured graph.

The aim of this paper is, on the one hand, to give a simple interpretation method, suitable for use during field work, for multi‐layer geo‐electrical sounding graphs, and, on the other hand, to indicate an automatic evaluation procedure based on these principles, suitable for use by digital computer.

This interpretation system is based on the resolution of the kernel function of Stefanescu's integral into partial fractions. The system consists of a calculation method for an arbitrary multi‐layer case and a highly accurate approximation method for determining those partial fractions which are important for interpretation. The partial fractions are found by fitting three‐layer graphs to a measured curve. Using the roots and coefficients of these partial fractions and simple equations derived from the kernel function of Stefanescu's integral, the thicknesses and resistivities of layers may be directly calculated for successively increasing depths.

The system also provides a simple method for the approximative construction of model graphs.
EXEMPLES D'APPLICATION DE TRAITEMENTS AUTOMATIQUES À L'INTERPRÉTATION DE SONDAGES ELECTRIQUES *
Authors: DUPRAT A. , GOLÉ F. , ROCROI J. P.
Published: April 2006

Résumé

Il est maintenant courant d'employer l'ordinateur pour interpréter les sondages électriques. Cependant, le problème à résoudre en prospection électrique n'admettant pas une solution unique, le but des traitements automatiques consiste simplement à fournir plusieurs hypothèses qui aident à bâtir une interprétation géologique des mesures géophysiques. C'est, d'ailleurs, ce qu'on recherche aussi par la comparaison visuelle des courbes de terrain avec des abaques précalculés. Mais, tandis que l'interprétation manuelle, pour conduire à des solutions qui respectent les mesures faites sur le terrain, exige un temps très long, le traitement automatique fournit immédiatement des solutions compatibles avec les courbes àétudier.

Les procédés employés s'adaptent aux divers besoins de la prospection: ils peuvent traiter aussi bien la station isolée que les profils de sondages électriques. C'est ce qu'on se propose de montrer, à l'aide de quelques exemples tirés d'études récentes.
RESISTIVITY TYPE CURVES OVER OUTCROPPING VERTICAL DYKE—I *
Authors: KUMAR RAKESH
Published: April 2006

Abstract

The theoretical horizontal resistivity profiles over an outcropping vertical dyke for various parameters‐electrode spacing, vein‐width and resistivity contrast—with inline alpha, beta and gamma‐Wenner electrode systems are described. The resistivity profiles present a most bewildering variety of shapes as compared to those in resistivity soundings. The analysis of type curves suggests suitable electrode configuration for detection of wide, moderately wide, and thin veins. The negative apparent resistivity values on the gamma anomalies for resistive vein over certain vein‐widths of higher positive values of resistivity reflection factor contradict the concept of apparent resistivity hitherto held.
RESISTIVITY TYPE CURVES OVER OUTCROPPING VERTICAL DYKE—II *
Authors: KUMAR RAKESH
Published: April 2006

Abstract

The theoretical horizontal resistivity profiles Over an outcropping vertical dyke with two‐electrode and Schlumberger electrode systems are discussed. The two‐electrode array seems very useful in locating the highly conducting thick or thin vein, while the Schlumberger (gradient) array is suited to detect the conducting vein of low and moderately high resistivity contrast and as well as the resistive vein of all widths and resistivity contrasts. Besides, the inline gradient array has a distinction of establishing a clue to evaluate the resistivity contrast of the vein.
RAPID DETERMINATION OF CUBE'S GRAVITY FIELD *
Authors: MUFTI I. R.
Published: April 2006

Abstract

Gravity modeling involves the evaluation of gravity field due to bodies of irregular shape. This is commonly accomplished by dividing the body into smaller units of regular shape whose field can be determined analytically.

Cubes are ideal building blocks for constructing bodies of irregular shape. However, the exact expression defining the gravity field of a cube‐shaped body is very long and requires tedious numerical work. Approximation formulas for rapid evaluation of the cube's gravity field are presented and discussed in detail. Their use for computing the field for small distances leads to large errors in the results; on the other hand, using the exact formula for large distances where approximation formulas yield practically identical results, is waste of time. After a detailed analysis about the nature of the cube's gravity field, certain criteria are established for suitably combining the two alternatives. This results in tremendous reduction in the task of computations without affecting the accuracy of data.
PHYSICAL AND COMPUTER MODELING OF INDUCED POLARIZATION *
Authors: AIKEN C. L. , HASTINGS D. A. , STURGUL J. R.
Published: April 2006

Abstract

The Laboratory of Geophysics of the University of Arizona was presented with an exploration problem by Falconbridge, Ltd. of Canada. Massive mineralized hemispherical “pods” are in the vicinity of a tuff layer of high conductivity and induced polarization response, covered by large thicknesses of resistive volcanics. The initial approach was to utilize electrolytic tank modeling. The extreme resistivity and IP contrasts proved to be difficult to recreate. Two dimensional modeling was attempted next with conductive paper, using copper and silver paint for anomalous masses. This method also proved inadequate. Finally, mathematical equations were solved which could model any arbitrary anomalous body in any steady state electrical field. Plane waves as well as point current sources producing non‐plane waves are possible. Finite difference equations were derived for the non‐linear partial differential equations under consideration. The equations were solved using a digital computer. Initially, the boundary conditions had to be satisfied at the boundaries of resistivity changes, severely restricting possible geometric shapes for anomalous bodies. The final and successful solution was to apply numerical techniques to obtain solutions of equations which require only that the relative resistivities through the area be specified. The Falconbridge problem and its solution are analyzed.
NEW POSSIBILITIES FOR REFLECTION SEISMICS BY UNDERSHOOTING BODIES WITH COMPLICATED TECTONICS *
Authors: BADING R. , ECHTERHOFF J. , KREY TH. , MARSCHALL R.
Published: April 2006

Abstract

In modern oil exploration layers of prospective interest with rather simple structural features are often overlain by very complicated bodies as e.g. saltdomes or other kinds of diapirs, olistostromes, or front zones of overthrusted blankets. In all these cases normal reflection seismic investigations, where downgoing and upgoing rays are rather close to each other, mostly fail, either because no reflections from underneath the complicated bodies are obtained, or because a reliable migrated depth presentation becomes practically impossible due to the inhomogeneity of the overlying bodies.

The undershooting technique avoids these difficulties by using ray paths which do not traverse the complicated bodies e.g. by shooting on one side of a saltdome and recording on the other side. On account of the large shot‐geophone distances in this method special considerations and computer processes were developed concerning moveout corrections for common depth point stacking and migrated depth presentation.

In many cases the location of the disturbing complicated bodies is known in advance. The shooting and recording program can then be adjusted to this knowledge and thereby kept to a minimum. If the location of the complicated bodies is unknown a more extended seismic program has to be carried out encompassing a great variety of shot‐geophone distances. But in this case the approximate location of the complicated bodies can be deduced from the survey too.

Results are presented in order to give an idea of the efficiency of the new seismic tool.
THE STABILITY OF THE SOLUTIONS OF THE POTENTIAL FIELD TRANSFORMATIONS *
Authors: IANĂṠ M. , MOLDOVEANU N.
Published: April 2006

Abstract

The quantitative analysis of the potential fields leads to the solution of some operational equations which sometimes have unstable solutions representing fictitious anomalies. A general method to find numerically stable solutions of such problems is presented in this paper. The subject of the downward analytical continuation is also discussed. The method has been checked on a theoretical model and applied to a gravity map.
PULSE CODING IN SEISMIC PROSPECTING SOSIE AND SEISCODE *
Authors: BARBIER M. G. , VIALLIX J. R.
Published: April 2006

Abstract

The conventional seismic technique is subject to a recording time following each transmission of energy, in which it is forbidden to release any new pulse. The recording time depends on the deepest reflection of interest, and is often 10 seconds or more in actual practice. To each transmission corresponds one record, i.e. a fixed amount of data which cannot be increased in a given time.

Pulse coding allows us to go beyond this limit, by transmitting several times during the normal recording time. The procedure gives as many records as there are pulses, but they overlap, each event being repeated every time there is a pulse. It is possible to process the composite record back to its usual appearance with all events in their proper place if the time breaks are accurately known and make up a code such that the unavoidable noise generated by the process be kept, on the final section, below the ambient noise. The processing is quite similar to that of records made from vibrating sources, though faster in practice.

The additional information can be devoted to a saving of time and money as the same profile may be recorded in a shorter time; or to an improvement of quality of the section due to a higher order of coverage, a multiplication of the ray paths and a closer sampling of the reflectors. It is also possible to record information in several planes at the same time, and to work out a 3‐dimensional restitution, without loss of production.

The process applies to all kinds of sources provided they can be triggered according to the code with sufficient accuracy. Depending on the source and conditions of implementation, the method benefits from other advantages such as better resolution, increased flexibility, and better coupling.

Two different names have been given to the process, Sosie and Seiscode, which apply to slightly different parameters for the sequence of pulses. Sosie is more useful at sea, while the normal scope for Seiscode is onshore. Both names are trademarks for SNPA.
DEPTH OF INVESTIGATION IN RESISTIVITY METHODS USING LINEAR ELECTRODES *
Authors: APPARAO A. , RAO T. GANGADHARA
Published: April 2006

Abstract

Depths of investigation for normal (bipolar) and focusing (unipolar) linear electrode arrays have been computed following the method given earlier (Roy and Apparao 1971) both in homogeneous and layered earth. The focusing arrangement is found to be superior to normal arrangement both in regard to depth of investigation and zone of uniform depth of investigation. This analysis holds good in layered media too. Further, the depth of investigation increases with the increase in the length (2M) of the electrode and reaches a limit, 0.29L for normal and 0.50L for focusing, when the electrode attains an optimum length to satisfy the infinite condition. This optimum length of the electrode is six times the distance L of the observation point from the electrode for normal and about ten times for focusing. A contour diagram for contributions of individual ground elements to the total signal measured at the centre of focused system is also discussed.
TWO‐DIMENSIONAL POWER SPECTRAL ANALYSIS OF AEROMAGNETIC FIELDS *
Authors: MISHRA D. C. , NAIDU P. S.
Published: April 2006

Abstract

A study of probability distribution function and spectrum of the Airborne Total Intensity Map for an area of 3000 Squ. miles covered by the Bundelkhand granite in India has revealed a close correlation between the Gaussian or non‐Gaussian nature of distribution and the shape of unite value contour on the spectrum plot. Further studies of radial spectrum plots suggest that the surface magnetic sources are mainly responsible for the non‐Gaussian character of the distribution function and as well as for irregular spectrum shape. The histogram of depth values for magnetic sources obtained from radial spectrum plots show three horizons, namely (i) surface (ii) 410 m(1400′) and (iii) 1000 m (3400′).

Based on these informations blocks with ferromagnetic composition at the surface can be identified from those which are non magnetic at the surface.
APPROXIMATE RULES FOR THE COMPOSITION OF APPARENT RESISTIVITY SECTIONS *
Authors: HABBERJAM G. M. , JACKSON A. A.
Published: April 2006

Abstract

Consideration is given to the form of apparent resistivity sections obtained by varying electrode array position and spacing over two dimensional features.

Since basic solutions exist for horizontally layered media and for vertical or dipping single interfaces, simple rules are proposed whereby these solutions can be directly combined to give solutions for more complex sections. Substantial approximations may be involved as the rules do not fully allow for interactions between the constituents.

The range of error incurred in application of the rules is explored, with particular reference to the square array system of resistivity measurement. The two extremes‐ of orientation of the square array with respect to the line of section are separately considered in this survey.

Within appropriate limits, the rules appear extendable to a wide variety of simple structures for which rigorous solutions would be formidable. The rules are finally discussed in relation to practical applications.
TRANSFORMATION OF DIPOLE RESISTIVITY SOUNDING MEASUREMENTS OVER LAYERED EARTH BY LINEAR DIGITAL FILTERING *
Authors: DAS U. C. , GHOSH D. P. , BIEWINGA D. T.
Published: April 2006

Abstract

The technique of linear digital filtering as developed for the direct interpretation of Schlumberger and Wenner soundings (Ghosh 1971) has been applied here for the derivation of the resistivity transform function from the field dipole measurements as the first step in directly interpreting dipole data. Filter coefficients for this transformation have been worked out for the radial‐polar, perpendicular and parallel (30°) arrays of dipole sounding. The procedure combines speed with accuracy.
NAVIGATION REQUIREMENTS FOR GEOPHYSICAL EXPLORATION *
Authors: SHERIFF R. E.
Published: April 2006

Abstract

Marine geophysical work requires accurate navigation on a continuous basis. A repeatability of 150 m CEP (circular error probable) with sequential positioning of 15 m CEP is usually acceptable. Quoted figures for many presently available navigation systems yield nearly the required accuracy. In actual operations, however, such accuracies may not be achieved, and usually the performance actually realized cannot be determined for want of independent measurements for comparison. If more redundancy in navigation measurements were available on an integrated basis, the limitations of individual systems would no longer be so critical and the accuracy of measurements could be assessed in real time. Failures in navigation continue to occur. Such failures usually result from ignorance of the capabilities of the navigation system and limitations and consequent choice of a system which is not appropriate to the demands of a particular survey. The points to be covered in work standards are listed.
A CONTRIBUTION TO THE QUANTITATIVE ERROR ANALYSIS IN MAGNETIC AND GRAVIMETRIC INTERPRETATION *
Authors: HJELT S. E.
Published: April 2006

Abstract

The paper discusses the smallest obtainable parameter errors (variances) in the interpretation with the least‐squares method. Useful approximations of the sum of squares contained in the minimum error expressions are obtained using results of numerical integration. The approximations lead to especially simple results for long interpretation profiles, when the parameter errors are proportional to the square root of the point separation.

Formulae are developed and examples shown for minimum error calculation in gravimetric interpretation with the cylindrical model and in magnetic interpretation with the two‐dimensional plate model. Smallest errors are obtained when the interpretation profile is chosen around the anomaly maximum except for dip and depth extent interpretation of magnetic plates.
STACKING FILTERS AND THEIR CHARACTERIZATION IN THE (f—k) DOMAIN *
Authors: HUBRAL P.
Published: April 2006

Abstract

The implementation of a stacking filter involves the filtering of each trace with an individual filter and the subsequent summing of all outputs. The actual position of a trace in space as well as certain simultaneous shifts of traces and filter components in time do not influence the process. The resulting output is consequently invariant to various arbitrary coordinate transformations. For a certain useful class of ensembles of non‐linear moveout arrival times for signals a particular transformation can be found which transforms a given ensemble into one consisting only of straight lines. It is thus possible to reduce, for instance, the analysis of a stacking filter designed for hyperbola‐like moveout curves to the analysis of a velocity filter with linear moveout curves. As the (f—k) transform is a very useful concept to describe a velocity filter, it can consequently be applied to characterize a stacking filter in regard to its performance on input signals with non‐linear moveout.
THE INTERPRETATION OF GRADIENT ARRAY CHARGEABILITY ANOMALIES *
Authors: QUICK D. H.
Published: April 2006

Abstract

Empirical equalities derived from time domain induced polarization scale modelling with the gradient array over simple geometries, and from the potential field functions for equivalent simple charge configurations are similar. The function for the dyke like body is analogous to the magnetic case allowing both total and vertical magnetic field interpretation techniques to be applied to gradient array chargeability anomalies.
THE DETERMINATION OF FILTER COEFFICIENTS FOR THE COMPUTATION OF STANDARD CURVES FOR DIPOLE RESISTIVITY SOUNDING OVER LAYERED EARTH BY LINEAR DIGITAL FILTERING *
Authors: DAS U. C. , GHOSH D. P.
Published: April 2006

Abstract

The technique of linear digital filtering developed for the computation of standard curves for conventional resistivity and electromagnetic depth soundings is applied to the determination of filter coefficients for the computation of dipole curves from the resistivity transform function by convolution. In designing the filter function from which the coefficients are derived, a sampling interval shorter than the one used in the earlier work on resistivity sounding is found to be necessary. The performance of the filter sets is tested and found to be highly accurate. The method is also simple and very fast in application.
COMPATIBILITY OF EM AND IP SURVEYS *
Authors: VOGELSANG D.
Published: April 2006

Abstract

Methods and typical case histories of EM and IP surveys are compared in order to check their compatibility for the investigation of large areas for base metal sulphides. It is demonstrated that the fast, low cost EM may miss sulphide concentrations which cause no reduction of apparent resistivity, or which act like horizontal slabs, where EM anomalies occur marginally. In such cases only IP can recognize the whole extent of the mineralization. The misleading role of graphite exists for both methods.

The conclusion is that EM remains the only economical method to survey whole ore districts, but that the shortcomings should always be taken into account in the interpretation. They can be overcome by employing geological, geochemical or other geophysical indicators in selecting promising targets for follow‐up IP. Even if less than 20% of the area is covered by the expensive IP, there is a fair chance that all sulphide bearing rocks will be found. Therefore, the question is not whether to apply EM or IP methods, but how to combine them best.
THE USE OF FOURIER SERIES METHOD IN UPWARD CONTINUATION WITH NEW IMPROVEMENTS*
Authors: TSAY L. J.
Published: April 2006

Abstract

This paper shows how to reduce the errors near edges of potential field data that result from using Fourier series in the computation of upward continuation of potential field anomalies. This kind of error, if uncorrected, can lead to erroneous geological interpretation.

The errors that occur at both edges of potential field data after upward continuation originate from the representation of data by using Fourier series from which data becomes periodic with discontinuities or sharp changes between each period. In order to reduce this type of error, we propose, either 1) to use only the cosine series, or 2) to add a certain number of constant data to both edges of the original data before continuation. Using these new schemes, we have demonstrated the improvement on the accuracy near edges of continued anomalies with profiles of magnetic anomaly computed from an assumed model.
EFFECTS OF DATA ERRORS AND ACCURACY IN SECOND DERIVATIVE COMPUTATION BY RATIONAL APPROXIMATION*
Authors: AGARWAL B. N. P. , SINGH J.
Published: April 2006

Abstract

The effects of systematic (constant) and random errors in the observed data have been investigated analytically for rational approximation method of computing second derivative involving a summation of the products of the averages of the gravity field with the corresponding weight coefficients, both in numerator as well as in denominator. A theoretical gravity anomaly over three spheres has been analyzed to demonstrate the high accuracy in the approximation. Since the sums of the weight coefficients in numerator and denominator are zero and one respectively, the regional gravity anomaly, even though approximated by a constant value over the entire area under computation, can produce substantially large error in the calculated derivative value. This is happening because of the contribution of the regional field in the denominator. Thus, inspite of the high accuracy in rational approximation, the method has limited application to field cases where a combined gravity field consisting of regional and residual anomalies is usually used. Master curves are presented for the constant and random errors by which a rough estimate of the percentage of error in second derivative computation can be made provided one has some idea of the magnitudes of the regional field and random error.