bluuebunny/crossref_metadata_2025 huggingface dataset:
ω‐k FILTER DESIGN*
Authors: WIGGINS RALPH A.
Published: April 2006

Abstract

Two‐dimensional band‐pass filters can be constructed by a simple extension of the theory of one‐dimensional band‐pass filters. Similarly to the one‐dimensional analogue the shape of the two‐dimensional filter is important in determining its effectiveness. The band‐pass filter formulation can be further refined so that the filter will concentrate its rejection energies in certain areas of the ω, k plane. Such band‐pass, band‐reject filters are found by solving a set of simultaneous equations.
REFRACTION LE LONG DES BANCS MINCES RAPIDES ET EFFET D'ECRAN POUR LES MARQUEURS PROFONDS *
Authors: LAVERGNE M.
Published: April 2006

Refraction along thin high velocity layers and along basement is investigated in two cases.

a) high velocity layer just on the basement.

b) high velocity layer higher above.

Period and attenuation of refracted waves are givers as a function of the layer thickness H. Refracted arrivals along thin high velocity layers are visible at significant distances if the layer thickness is not smaller than A/6, where A is the longitudinal wavelength in high velocity medium. The pseudoperiod is proportional to the layer thickness H. The attenuation at large distance follows an x‐ne‐k1x law, where n is close to I and k1 is inversely proportional to H.

Refracted arrivals along the basement are observable even in the case of thin high velocity layers situated in the overburden; their intensity is smaller and their pseudo‐period larger than when no layer exists in the overburden. The intensity of the basement arrival decreases and the pseudoperiod increases with increasing layer thickness.

The pseudoperiod and the attenuation of refracted arrivals along high velocity layers and along the basement are also highly dependent on acoustic contrasts.

Both arrivals from a high velocity layer and from the basement can be recorded simultaneously, provided the frequency spectrum of the seismic chain is sufficiently broad. In all cases layer arrivals show a character very different from basement arrivals.
ON THE ELECTROMAGNETIC RESPONSE OF CONDUCTORS IN THE INDUCTIVE METHOD OF PROSPECTING (MODEL STUDIES)*
Authors: PODDAR M. , BHATTACHARYA P. K.
Published: April 2006

In the inductive method of prospecting, information on conductivity and size of conducting ore‐bodies located in non‐conducting host rocks, can be conveniently obtained by studying amplitude‐frequency relation or amplitude‐phase relation of their response with the help of suitable Master‐curves. Experiments carried out in the laboratory on the scale‐model method show these Master‐curves to be different depending on the type of primary excitation and the shape of conductor. Cases of sphere, plate and disc in uniform field, field of line source and dipole field have been studied with an Amplitude‐Phase Meter specially constructed in the laboratory for this purpose.
REFRACTION LE LONG DES BANCS MINCES RAPIDES ET EFFET D'ECRAN POUR LES MARQUEURS PROFONDS*
Authors: Lavergne M
Published: April 2006

Refraction along thin high velocity layers and along basement is investigated in two cases.

a) high velocity layer just on the basement.

b) high velocity layer higher above.

Period and attenuation of refracted waves are given as a function of the layer thickness H. Refracted arrivals along thin high velocity layers are visible at significant distances if the layer thickness is not smaller than A/6, where A is the longitudinal wavelength in high velocity medium. the pseudoperiod is proportional to the layer thickness H. The attenuation at large distance follows an x−n e−k1x law, where n is close to I and R1 is inversely proportional to H.

Refracted arrivals along the basement are observable even in the case of thin high velocity layers situated in the overburden; their intensity is smaller and their pseudoperiod larger than when no layer exists in the overburden. The intensity of the basement arrival decreases and the pseudoperiod increases with increasing laer thickness.

The pseudoperiod and the attenuation of refracted arrival along high velocity layers and along the basement are also highly dependent on acoustic contrasts.

Both arrivals from a high velocity layer and from the basement can be recorded simultaneously, provided the frequency spectrum of the seismic cbain is sufficiently broad. IN all cases layer arrivals show a character very different from basement arrivals.

RESUME

La refraction le long des bancs minces rapides et du socle moins rapide sous‐jacent, est etudiee sur modeles dans deux cas:

a) banc rapide reposant directement sur le socle;

b) banc rapide situe plus haut dans le recouvrement.

La period et l'attenuation des ondes rerractees sont donnees en fonction den l'epaisseur H du banc rapide. Les arrivees refractees le long des bancs rapides ne sont pas visibles sur une distance importante si l'espaisseur de ces bancs est inferieure a A/6 A designant la longueur d'onde longitudinale dans le milieu rapide. La pseudoperiode est proportionnelle a l'epaisseur H du banc. L'attenuation a grande distance suit une loi eb x−n e−k1x avec n voisin de l et k1 inversement proportionnel a H.

Les arrivees refractees le long du socle sont observables en presence de bancs minces rapides dans le recouvrement, mais avec des internsites plus faibles que dans le cas d'unrecouvrement homogene. La pseudoperiode des impulsions refractees du socle augmente avec l'epaisseur H du banc rapide. L'attenuation en fonction de la distance est superieure a l'attenuation observee pour un recouvrement homogene, et elle croit avec H.

La pseudo‐periode et l'attenuation des arrivees refractees le long des bancs rapides et des marqueurs sous‐jacents sont largement fonction des impedances acoustiques des milieux en presence.

Les arrivees d'un banc mince rapide et socle peuvent etre observees simultanement a condition que la chaine d'enregistrement ait un spectre en frequence suffisamment large. On constate dans tous les cas que le caractere des arrivees des bancs est tres different du caractere des arrivees du socle.
SIGNIFICANCE AND IMPLICATIONS OF SHINGLING IN REFRACTION RECORDS *
Authors: CASSINIS R. , BORGONOVI L.
Published: April 2006

The occurrence of shingling in. long range refraction records often makes the task of the seismic interpreter heavier, especially when several refractors are encountered and the velocity contrasts are small.

The explanation of the phenomenon given by the existing literature is examined and the theoretical results are compared with the observed data on field records.

In field seismograms shingling must be separated from the effect of geological structures or lateral discontinuities.

If an appropriate analysis of shingling is possible, this phenomenon can be related to the type of refracting layer, being a useful tool to a qualitative approach.

On the other hand the implications of shingling are examined on the side of the geometrical interpretation
SPECIFICATION OF TWO MODULI OF A VISCOELASTIC MATERIAL *
Authors: THOMSON KER C.
Published: April 2006

In order to adequately understand the complicated, anelastic processes governing wave propagation in soils or highly weathered rock it seems desirable first to have available a convenient laboratory material for such propagation studies the frequency dependent rheological parameters of which are known beforehand. A property measurement program has been conducted to determine the complex Young's modulus and the complex shear modulus of a commercially available viscoelastic material over a broad spectral region.
SOME RESULTS OF THE GEO‐ELECTRICAL RESISTIVITY METHOD IN GROUND WATER INVESTIGATIONS IN THE NETHERLANDS*
Authors: VAN DAM J. C. , MEULENKAMP J. J.
Published: April 2006

In the year 1958 the Service for Water Management of the „Rijkswaterstaat” started its program of geo‐electrical resistivity prospecting in the western part of the Netherlands. The aim of this program was to obtain data on the salinity distribution of the ground water.

The ground water regime in this part of the Netherlands is most intricate. This is due to the geological and geo‐hydrological conditions and to the low elevation of the land. Many reclaimed areas are up to several metres below mean sea level.

The resistivity data obtained are closely related to the salinity of the ground water. On the basis of bore hole data it was even possible to arrive at calibration curves for the salinity of the ground water in sand deposits. Under special conditions it was also possible to draw conclusions with respect to the presence of less permeable formations as e.g. clay layers.

Some remarks are given on the practical performance and the interpretation of the measurements.

A review is given of the work done until now. Some results are shown by means of maps of the salinity distribution of the ground water in the western and northern parts of the Netherlands.

Two examples are described of the use of the data obtained during the survey in the province of Zuid‐Holland.

Another two examples are presented of detailed investigations for special purposes in relatively small areas.
TOPOGRAPHIC AND ISOSTATIC CORRECTIONS TO GRAVITY SURVEYS IN MOUNTAINOUS AREAS*
Authors: JOHN V. P. st , GREEN RONALD
Published: April 2006

In mountainous areas it is an inadequate procedure to reduce gravity observations by merely subtracting the effect of an infinite flat slab of material between the station and sea‐level, and adding a terrain correction. A programme is described which directly computes the effect of masses above sea‐level, and mass‐deficiencies below it; as well as the effect of compensating masses under the Pratt and Airy isostatic systems. As an example, the method has been applied to a regional gravity survey of Papua and New Guinea where it is seen to remove the usually high correlation of the Bouguer anomaly with local topography.
GRAPHICAL EVALUATION OF MAGNETIC AND GRAVITY ATTRACTION OF THREE‐DIMENSIONAL BODIES*
Authors: SHARMA P. VALLABH
Published: April 2006

A nomogram is presented which enables evaluation of the components of magnetic attraction of a homogeneous finite rectangular prism, and of gravitational attraction due to a uniform rectangular lamina.

In practice any three‐dimensional body could be approximated by a number of right rectangular prisms of varying dimensions governed by the shape of the body. The magnetic attraction of the whole body is then obtained by numerical summation of the effects of the constituent prisms.

For evaluating the gravitational effect, the cross‐section of the body corresponding to each elevation contour is approximated by a number of rectangular laminae (or by a stepping polygon) the attraction of which can be determined with the aid of the same nomogram. The total gravitational attraction of the body is obtained by a process of graphical integration along the vertical axis.
THE ANALYSIS AND DESIGN OF TWO‐DIMENSIONAL FILTERS FOR TWO‐DIMENSIONAL DATA *
Authors: DARBY E. K. , DAVIES E. B.
Published: April 2006

Some of the methods such as regional removal and second derivative calculations which can be used to outline anomalies on potential data maps can be thought of as a filtering operation. The analysis and design of such two‐dimensional filters by means of direct and inverse two‐dimensional Fourier transforms have been considered.

An analysis of several published sets of second derivative coefficient sets indicates that, in general, they are not a good approximation to the theoretical second derivative filter. Alternate methods of designing regional removal and second derivative filters are discussed. The properties of various two‐dimensional filters are further illustrated by means of maps obtained from the convolution of several of these filters with a set of observed field data. These maps show the large changes in anomaly shape which can result from the inclusion or rejection of various wavelength components.
SHIP‐TOWED MAGNETICS IN PETROLEUM EXPLORATION*
Authors: PRINDLE ROBERT O.
Published: April 2006

In one geophysical survey over a salt dome in the Gulf of Mexico, data taken from a single magnetic and seismic shipborne traverse demonstrated significantly the importance of magnetic measurements. The reduced magnetic and seismic profiles were integrated with gravity measurements from an earlier survey demonstrating the value of obtaining simultaneous geophysical data. The traverse was approximately 25 miles in length, 135 miles southeast of Galveston, Texas. The observed gradient averaged approximately 2 gammas per 1000 feet and crosses the southwest corner of a large shallow salt dome called the Way Dome. The recorded magnetic profile over the salt dome shows a negative magnetic anomaly extending for approximately 12 miles with a maximum amplitude of approximately 20 gammas. This negatively anomaly is due to the negative susceptibility contrast between the salt and cap rock that truncates the surrounding parent sediments. The shape of the negative anomaly correlates well with the continous seismic record and clearly delineates the topographical and structural features of the salt dome. The recorded analog magnetic profile was replotted, with both the regional gradient and time variations removed, which makes the observed anomaly much sharper than is noticeable on the original recorded strip chart record. A theoretical magnetic anomaly was calculated using a computer program for comparison to the observed anomaly. The results showed good correlation.
BEDROCK DEPTH FROM SURFACE POTENTIAL MEASUREMENTS*
Authors: ROY AMALENDU
Published: April 2006

When, in a two‐layer earth, the substratum is insulating or infinitely conducting, the thickness of the top layer can be determined from surface potential measurements along a radius from a single point power electrode. The observed potential needs to be numerically integrated in a direction perpendicular to the said radius, and Figure 4 can then be used to find the thickness. A field example is included.
DETERMINATION DE L'IMPULSION SISMIQUE*
Authors: BOIS P.
Published: April 2006

Determining the shape of a pulse generated by an explosion solely from the data provided by the recorded seismic trace is a difficult and even ambitious task.

Knowledge of parameters such as length and number of “arches” of the pulse under study is, in fact, indispensable in solving this problem.

These parameters cannot be found directly in the seismic trace, which nevertheless contains a great amount of information. Autocorrelation, with its mathematical and statistical properties, is an efficient way of making the best of this information.

We compute all the autocorrelations of reflections having a given number of arches which fulfil certain conditions determined in advance. Then, after statistical testing of some parameters pertaining to the autocorrelations (abcissae of zeros, of extrema …), we select only those with a maximum likelihood. It is sufficient to consider only the reflections whose autocorrelations have been selected and to arrange them in groups according to their shape and arch number in order to obtain average pulses.

In so doing several solutions are arrived at, but when considering a given number of traces, a single record for instance, it is possible by comparing these results with each other to considerably reduce their number.

In the last part of the paper the nature of the impulse obtained with our method is examined in order to find out whether it is “minimum phase” for carrying out deconvolutions.
ÜBER DIE GENAUIGKEIT GEOMAGNETISCHER FELDREGISTRIERSTATIONEN*
Authors: FANSELAU G. , RITTER E. , WOLTER H.
Published: April 2006

The accuracy of the magnetic registrations of a new field station constructed at Niemegk Observatory is described. The most important aspects for the construction were good mechanical stability, a good constancy of all physical data and the fact, that the station is ready in the field for solid registration ere long. The apparatus was proved during geomagnetic survey in the field, especially in view of the variability of the geomagnetic variations. The results obtained by field work and by comparison at observatories are good. It is planned to enlarge the registrations by means of photocellcompensators.

Der Plan zur Konstruktion einer transportablen und schnell aufstellbaren geomagnetischen Feldregistrierstation geht schon auf das Jahr 1939 zurück. In diesem Jahr wurde von Fanselau ein Plan für eine solche Station den Askania‐Werken in Berlin‐Friedenau unterbreitet und zur Konstruktion empfohlen. Der Krieg verhinderte eine rasche Durchführung der Fertigungsarbeiten, so daß erst nach Beendigung des Krieges die Askania‐Werke den auf diesen Vorschlägen beruhenden Magnetographen fertigen konnten. Am Adolf‐Schmidt‐Observatorium für Erdmagnetismus in Niemegk wurden dann weitere geomagnetische Feldregistrierstationen entwickelt [1, 2, 3]. Bei der Konstruktion des Gerätes wurde bewußt auf Robustheit und Stabilität Wert gelegt, während der Gesichtspunkt, ein möglichst leichtes und kleines Gerät zu haben, nicht so sehr im Vordergrund stand. Von dem neuen Typ der Station sind inzwischen schon eine ganze Reihe von Exemplaren in Betrieb genommen worden, so daß es an der Zeit ist, einige Bemerkungen über Zuverlässigkeit in der Konstanz der Skalen‐ und Basiswerte sowie über andere instrumentelle Daten der Geräte zu machen. Auf Grund eingehender Messungen am Observatorium und im Gelände liegt genügend umfangreiches Material vor, um diese Fragen sicher beantworten zu können.
EIN AUTOMATISCHES VERFAHREN ZUR INTERPRETATION MAGNETISCHER ANOMALIEN NACH DER METHODE DER KLEINSTEN QUADRATE*
Authors: BOSUM W.
Published: April 2006

Die Interpretation magnetischer Anomalien durch Modellkörper geschieht bevorzugt nach der indirekten Methode (trial und error). Dieses von Hand aufwendige Verfahren läβt sich mit Hilfe der Ausgleichsrechnung nach der Methode der kleinsten Quadrate Rechenautomaten übertragen.

Die allgemeinen Grundlagen des Verfahrens werden beschrieben. Wesentliche Voraus‐setzungen sind:

die Annahme bestimmter Körperformen

das Vorhandensein von Näherungswerten der Unbekannten (Lage, Magnetisierung etc.)

eine genügend groβe Anzahl von Meβwerten, um den Ausgleichsprozeβ durchführen zu können.

Die Vorteile der Methode sind:

weitgehende Automatisierung und schnelle Arbeitsweise bei Verwendung von Rechenautomaten

Ermittlung der Fehler der Unbekannten

Die Methode wurde angewandt auf die Interpretation 2‐dimensionaler ΔZ‐ und ΔT‐Anomalien. Drei Körpertypen werden dem Rechenprogramm zugrunde gelegt, und zwar die unendliche und endliche diinne Platte und der Kreiszylinder. In die Maschine ein‐gegeben werden nur die Meβwerte. Die Interpretation erfolgt im einzelnen in folgenden Schritten:

Ermittlung von Näherungswerten

Bestimmung der Körper bester Annäherung

Iteration für den Körper bester Annäherung.

Die Maschine gibt die Endwerte der Unbekannten (Lage, Einfallen, Magnetisierung etc.) mit Angabe der mittleren Fehler sowie die hierzu gehörigen Modellanomalien aus. Diese Endwerte werden einem Zeichenautomaten übergeben, der die gemessene Kurve, die theoretische Kurve und die gesuchten Modellkorper zeichnet.

Interpretationsbeispiele werden vorgeführt.
A POSSIBLE WAY OF TRACING GROUNDWATER FLOWS IN KARST*
Authors: ARANDJELOVI DUŠAN
Published: April 2006

In designing as well as in the construction of hydro‐electric power plants and water‐supply projects in karst, the knowledge of the location of groundwater flows is invaluable. Attempts made so far in this direction have not produced the desired results and all the methods known so far have shown to be more or less ineffective, especially with respect to deep‐seated underground flows.

An interesting suggestion on the possible determination of the groundwater flow location by using a specific geophysical prospecting procedure is based on the studies and knowledge of groundwater flows in the karstland of Yugoslavia. The procedure is as follows: a time‐bomb thrown down a swallow‐hole travels down to the groundwater flow and explodes at a predetermined moment. Elastic waves generated by the explosion propagate reaching the surface, where they are detected by properly arranged geophones that are connected with a standard seismic apparatus. By a specific graphical or arithmetical method the coordinates of the epicentre and hypocentre of the underground explosion can be worked out, and thus the location of the groundwater flow determined. By successive repetition of the experiment, i.e. by different time activation of underground explosion of the time‐bomb, the location of the groundwater flow can be defined over longer paths.

The success of the experiment depends upon a number of factors all of which must be met. If only one of them is overlooked, the experiment will not succeed. All this calls for great care both in preliminary work and in the course of the experiment. Substantial funds invested in and considerable time required in executing the experiment are multiply recompensed by the success of the experiment. The information obtained about the location of groundwater flows will directly affect the maximum operating pool adopted for hydro‐electric power projects and the most favourable point in cutting off groundwater flows and bringing them to the surface for water‐supply purposes.
GEOELECTRICAL INVESTIGATIONS IN EAST AFGHANISTAN*
Authors: HOMILIUS J.
Published: April 2006

During the years from 1965 until 1967, a German/Afghan team carried out a number of geoelectrical resistivity measurements according to the “Four‐Point‐Method” within the framework of Technical Assistance to Afghanistan.

On two selected objects of investigation, i.e. Kabul (69°10 E, 34°30′N) and Zarkašan (67°40′E, 32° 54.5′N), the possibilities and limits of the resistivity method in the exploration of useful groundwater resources, of the geological structure, and in the treatment of problems pertaining to mineral deposits in Afghanistan are demonstrated. In connection with geological mapping these geophysical investigations provided certain conceptions on the structure and the stratigraphy of the intramontane basins in the region south of the Hindukush mountains. Field interpretations are checked by boreholes and by computed model graphs.
SOME EXPERIMENTS CONCERNING THE PRIMARY SEISMIC PULSE*
Authors: O'BRIEN P. N. S.
Published: April 2006

Recordings were made with three types of detector of the primary compressional (P) and shear (S) wave pulses generated by explosions in boreholes. Charge weights varied from 0.08 kg to 9.5 kg and detector distances varied from about 3 m to about 80 m. Scaling by the simple factor W1/3 where W is the charge weight, enabled observations from different sized charges to be fitted to a single expression.

Experiments were carried out in the Bunter sandstone and the London clay and both fluid and solid tamping were used. This variation in tamping had no significant effect on the P‐waves but it may have affected the generation of SV‐waves. In both media the P‐wave energy carried at 30 m from the shot by frequencies less than 100 Hz decreased rapidly with depth and was usually 1–2 % of the available chemical energy for a shot depth of 15 m. The S‐wave energy was much less than this, but was highly directional.

The P‐wave pulse had the appearance of a damped sinusoid in very good agreement with the predictions of the ‘equivalent radiator’ hypothesis. However, the surface of this radiator should be identified not with the blown cavity but with the surface at which the tensile stresses associated with the stress wave become less than the tensile strength of the rock.

The predominant frequency for a 1 kg charge at a depth of 15 m was 24 Hz in the clay and 52 Hz in the sandstone. In these and similar media, therefore, an effort should be made to keep individual charges less than 1 kg in reflection shooting and less than 10 kg in refraction shooting.

The value of Q was about 50 in clay and about 25 in the sandstone. These estimates are rather uncertain because of the small distances over which the pulses were observed.

The Z‐transforms of the sampled pulses indicated that they were all of minimum phase, or very near to it.
REMARKS ON THE SIGNAL TO NOISE RATIO IN THE VIBROSEIS SYSTEM*
Authors: KREY TH.
Published: April 2006

Abstract

The paper presents a discussion of some of the noise features of the VIBROSEIS SYSTEM*** and their bearing on the determination of the optimally weighted stack.
UNE METHODE D'ANALYSE FINE DES PROFILS AEROMAGNETIQUES *
Authors: NAUDY HENRI
Published: April 2006

A method to analyse aeromagnetic profiles is proposed: several horizontal (width‐) and vertical (amplitude‐) parameters are deduced from the anomalies. These parameters are then compared with diagrams drawn on a logarithmic scale. The comparison yields depth and magnetization of the causative bodies.

The method lends itself equally well to a quick estimate and to a thorough interpretation, depending on the number of parameters deduced and on the number of diagrams. It can be applied also to the anomalies of the total field and its vertical gradient.
CENTRAL FREQUENCY SOUNDING IN SHALLOW ENGINEERING AND HYDRO‐GEOLOGICAL PROBLEMS*
Authors: PATRA H. P.
Published: April 2006

Abstract

The paper deals with the early stages of development of a convenient form of electromagnetic induction method of sounding referred to as ‘Central Frequency Sounding’ and abbreviated as CFS. The method is introduced as a rapid and useful technique for investigation of shallow engineering and hydro‐geological problems. Sets of theoretical two‐layer master curves, suitable for interpretation of field data involving measurement of the vertical magnetic component of the field induced at the center of a loop placed on a two‐layer earth, have been presented.

The approximate but reasonably accurate solutions for a two‐layer earth of any arbitrary resistivity contrast have been considered for the purpose and expressed in a form suitable for computation. The computed results have been presented in sets of curves useful for interpretation of field data.
APPLICATION OF REFRACTION SEISMICS TO SUBSALT TECTONIC PROBLEMS IN A DEEP SALTDOME BASIN*
Authors: KREY TH. , NODOP I.
Published: April 2006

Abstract

Despite the use of CDP and digital methods the Zechstein base is still the deepest horizon in the vast salt‐dome basin of Central Europe for which continuous information can be obtained by reflection seismics. Thus in North‐western Germany, in addition to reflection seismics, the refraction seismic method has been increasingly used for a reliable survey of deeper horizons.

The first part of the paper deals with the investigation of the various possibilities and limitations of refraction seismics with regard to the investigation of Pre‐Zechstein layers in a basin with a tectonically very complicated overburden. The recording techniques specially developed for continuous profiling of the desired refraction seismic arrivals and the data processing methods are described.

The main problems of interpretation are then discussed, in particular with regard to depth representation. The advantages and disadvantages of the various methods, e.g. Gardner's, Hales' and Wyrobek's, and of the wave‐front method, are compared. On account of the tectonically complicated overburden Thornburgh's wave‐front method proved to be the most useful.

In a further section the various possibilities for velocity determinations are mentioned, e.g. Wyrobek's determination of the overburden velocity, for which the wave‐front method automatically furnishes the necessary corrections to a deep datum.

Finally, some examples are given for the results obtained, including some incidental information on the deeper crust.
RELATIVE CONTRIBUTION TO SIGNAL BY GROUND ELEMENTS IN TWO‐COIL INDUCTION LOGGING SYSTEM*
Authors: ROY A. , DHAR R. L.
Published: April 2006

Abstract

A two‐coil induction logging system in an infinite homogeneous medium has been theoretically analysed for the relative contributions of various ground elements to the total signal at the receiver. Unlike an earlier approximate treatment by Doll (1949), the present analysis takes skin effect into account (while neglecting displacement currents). Contour diagrams depicting relative contributions from every ground point and diagrams for vertical and radial/lateral investigation characteristics are presented. The results differ significantly from Doll's in the following points:

The relative contribution is frequency and conductivity dependent;

It does not show symmetry with respect to the center of coil system;

It alternates between positive and negative values with distance;

Real and imaginary contributions for a given conductivity and frequency are different from each other.

The possibilities of a horizontal‐horizontal sonde is briefly examined and found to be inferior to the usual sonde because of its higher sensitivity to the mud column and the invaded zone.
DETECTION OF SOLUTION CHANNELS IN LIMESTONE BY ELECTRICAL RESISTIVITY METHOD*
Authors: DUTTA N. P. , BOSE R. N. , SAIKIA B. C.
Published: April 2006

Abstract

The results of geophysical surveys carried out in the Kopili Hydel Project site in the United North Cachar and Mikir Hills district, Assam, to locate and trace underground caverns in limestone are presented. Electrical resistivity observations over known limestone caverns showed significant anomalies (high resistivity). In the course of the systematic electrical resistivity survey conducted at the eastern fringe of the Umrong basin to study the competency of the proposed reservoir, a number of indications of possible caverns in limestone were obtained and a few of them have been verified by drilling. An analysis of the electrical resistivity data also suggests that the deep seated caverns are aligned along an axis trending NNW‐SSE, which may represent a zone of weakness– presumably a fault–that has influenced the formation of the caverns in preferred direction. Drilling over a few of the geophysical indications have corroborated the presence of a fault along the eastern fringe of the Umrong basin.
ARRAYS AND NOMOGRAMS FOR ELECTRICAL RESISTIVITY EXPLORATION*
Authors: MEIDAV TSVI
Published: April 2006

Abstract

A number of electrical resistivity arrays are available to the exploration geophysicist in the conduct of vertical or horizontal profiling. The advantage of using central‐type arrays which produce large potential drops, such as the Wenner or the Schlumberger, must be weighed against the ease of acentral arrays such as the polar and equatorial arrays.

A series of nomograms has been designed to provide a means of rapid calculation of the potential drop to be obtained by any of the various central and acentral arrays, as a function of apparent resistivity, electrode spacings and available transmitter power. The same nomograms may also be used for approximate computation of the apparent resistivities in routine surveys. However, the accuracy of resistivity calculation is directly related to the accuracy of drawing lines between the scales and hence is rather limited in reduced‐size nomograms in this paper.
A PULSE COMPRESSION TECHNIQUE USING COHERENT LIGHT*
Authors: BARBIER M. , POULEAU J.
Published: April 2006

Résumé

Les méthodes sismiques à signaux longs du type Vibroseis réclament un traitement qui consiste en la crosscorrélation des signaux reçus avec le signal émis. Cette opération qui est effectuée par des ordinateurs puissants, équipés de convolueurs, est aussi réalisée de manière analogique. Lorsque le volume des données à traiter devient trés important comme c'est le cas en sismique marine, il peut être intéressant ?avoir recours au principe décrit dans cet article, qui utilise une source de lumière cohérente. Une étude de la dyna‐mique et des exemples synthétiques sont montrés.
MAGNETOTELLURIC SOUNDING ON A LAYERED EARTH WITH TRANSITIONAL BOUNDARY*
Authors: MALLICK K.
Published: April 2006

Abstract

This work deals with a theoretical investigation of the magnetotelluric sounding where the horizontal layers of a geological section do not have a sharp but a transitional boundary. The ratio of the horizontal electric to the horizontal magnetic components gives a measure of “Cagniard impedance”, which together with the phase relationship between them, enables one to determine the subsurface geometry and the true resistivities.

Utilising the principle of similitude a set of Resistivity Master Curves and the corresponding phase relationships are presented here for the case where the lower half‐space is infinitely resistive. The relation between the relative transition thickness and the cut‐off period is illustrated.
APPROXIMATION OF THE GRAVITATIONAL ATTRACTION OF GEOLOGICAL BODIES*
Authors: BOTEZATU R. , VISARION M. , SCURTU F. , CUCU G.
Published: April 2006

Abstract

The gravitational attraction produced by a geological body of irregular shape can be easily determined by dividing it into cubes of small size. The exact expression of the effect of a cube is very complicated, but it can be calculated by using an electronic computer.

4851 values of the gravitational attraction were determined for different positions of a cube with the side of 2l and the center in M(x0, y0, z0), for x0∈[0;20], y0∈[0;20] and z0∈[0;10]. Using these values, templates in double logarithmic representation were drawn, with x0 and z0 as parameters and y0 as abscissa, and with x0 and y0 as parameters and z0 in abscissa; this double set of templates permits a good interpolation for all cubes in the considered domain of M.

The use of templates was tested to approximate the effect produced by a theoretical model of spherical shape and in a real case of a three‐dimensional salt body of known shape based on a large number of boreholes. In both cases very good results were obtained.
MULTICOVER MEASUREMENTS IN REFRACTION SHOOTING*
Authors: HIRSCHLEBER U.
Published: April 2006

Abstract

Multicover measurements in refraction shooting are comparable to long‐spread reflection shooting. Of course, spread length, distance of traces and offset may be larger than in reflection shooting and depend on the, depth, the velocity and the dipping of the refractors to be detected. For later processing an equation for the refractor velocity is derived in case of flat and steep dipping refractors. The depth and the angle of dip will be computed from delay times. An outlook to digital processing is given.
VERTICAL MAGNETIC DIPOLE OVER TRANSITIONAL EARTH*
Authors: MALLICK K. , ROY A.
Published: April 2006

Abstract

Harmonic steady‐state solutions for magnetic and electric vector components are obtained for a layered transitional earth in a vertical magnetic dipole field. The conduction currents dominate the displacement currents. The time factor eiωt is implied. MKS units are used.
THE USE OF COMPUTER GRAPHICS IN GRAVITY INTERPRETATION*
Authors: ARAB N.
Published: April 2006

Abstract

Computer‐Graphics, the visual display of data in digital and analog form, allows immediate interaction between man and machine. This interaction facility is valuable when the user is engaged in model design. By using such a device in gravity interpretation, the geophysicist can overcome the slow process of model simulation constrained by the conventional input/output devices, also maximum control over running programmes can be exerted if needed.
RESISTIVITY ANALYSIS FOR MODELS OF A SPHERE IN A HALF‐SPACE WITH BURIED CURRENT SOURCES*
Authors: MERKEL R. H. , ALEXANDER S. S.
Published: April 2006

Abstract

Boundary‐value problems in steady‐state current flow were solved numerically in bispherical coordinates for a sphere of arbitrary conductivity in a half‐space. Solutions for the potential on the surface of the half‐space were examined for the cases where both current sources were on the surface, one source on the surface and the second between the surface and the sphere, and one source on the surface and the other in the sphere. Results show a great similarity with the layered case when the buried electrode is placed between the surface and the conducting region. Such a buried electrode configuration makes it possible to obtain an accurate measurement of the depth to the conductor in both cases. A model with the current electrode placed in a conductive sphere is compared with a three‐layered model with the source in a conductive intermediate layer, and results indicate that the lateral extent of a finite anomalous zone can be estimated using these limiting curves. The validity of these theoretical calculations for buried spheres was confirmed experimentally by tests conducted on an analog model.
ABOUT A METHOD OF REPRESENTATION OF IP‐VALUES OBTAINED OVER SEDIMENTARY FORMATIONS (TWO LAYER CASES).*
Authors: MONGELLI F. , PATELLA D.
Published: April 2006

Summary

An operative technique is described along with a method of representation of Induced Polarization values obtained over homogeneous rocks against the electrical power per unit volume.

The results of similar experiments over two‐layer ground, are shown according to the same operative technique and method of representation.

With the method of representation suggested in this paper it is possible to distinguish discontinuities and to get information about the thickness of the upper medium.
THERMAL NEAR‐SURFACE EXPRESSION OF SHALLOW GEOLOGICAL FEATURES*
Authors: POLEY J. PH. , VAN STEVENINCK J.
Published: April 2006

Abstract

It has been customary in geothermal studies to assume the surface to be an isothermal plane, though difficulties existed to explain the magnitude of thermal anomalies observed in the field under this assumption. Detailed investigations of temperatures at depths between 5 cm and 230 cm show that—after removal of the strong diurnal variations—sizeable anomalies persist right to the surface. Thus, the effective heat transfer (coefficient) at the surface might be lower than commonly assumed.
ADAPTIVE SIGNAL PROCESSING THROUGH STOCHASTIC APPROXIMATION*
Authors: WANG R. J. , TREITEL S.
Published: April 2006

Abstract

One of the problems in signal processing is estimating the impulse response function of an unknown system. The well‐known Wiener filter theory has been a powerful method in attacking this problem. In comparison, the use of stochastic approximation method as an adaptive signal processor is relatively new. This adaptive scheme can often be described by a recursive equation in which the estimated impulse response parameters are adjusted according to the gradient of a predetermined error function.

This paper illustrates by means of simple examples the application of stochastic approximation method as a single‐channel adaptive processor. Under some conditions the expected value of its weight sequence converges to the corresponding Wiener optimum filter when the least‐mean‐square error criterion is used.
OPTIMUM DIGITAL FILTERING AND INVERSE FILTERING IN THE FREQUENCY DOMAIN*
Authors: DEREGOWSKI S. M.
Published: April 2006

Abstract

Two distinct filters are developed in the frequency domain which represent an attempt to increase the resolution of fine structure contained in the signal whilst keeping the expected filtered noise energy within reasonable bounds. A parameter termed the White Noise Amplification is defined and used together with a measure of the deconvolved pulse width in order to provide a more complete characterisation of the filters. Each of the two main types of frequency domain filters discussed varies in properties with respect to a single adjustable parameter. This may be contrasted with a time domain Wiener filter which in general has three variables: length, delay and an adjustable noise parameter or weight. The direct frequency domain analogue of the Wiener filter is termed a gamma‐Fourier filter, and is shown to have properties which span the range from those of a spiking filter with zero least square error at one extreme, to those of a matched filter at the other extreme of its variable parameter's range. The second type of filter considered—termed the modulated Gaussian filter—is similarly shown to be a perfect spiking filter at one extreme of its parameter range, but adopts the properties of an output energy filter at the other extreme.
INVERSE FILTER COEFFICIENTS FOR THE COMPUTATION OF APPARENT RESISTIVITY STANDARD CURVES FOR A HORIZONTALLY STRATIFIED EARTH*
Authors: GHOSH D. P.
Published: April 2006

Abstract

In this paper a fast method is developed for computing apparent resistivity curves for known layer configurations. The method is based on the application of a linear filter to determine the apparent resistivity curve from, the kernel function.
A NOTE ON THE USE OF NOMOGRAMS FOR APPARENT RESISTIVITY COMPUTATION*
Authors: CHAN SIEW HUNG
Published: April 2006

Abstract

Nomograms are presented for the purpose of rapid computation of the apparent resistivity functions from the field data for symmetrical and unsymmetrical linear electrode arrays.
CORRECTION OF ACCURATE GRAVITY SURVEYS BY CAREFULLY OBSERVED VERTICAL GRADIENTS OF GRAVITY*
Authors: THYSSEN‐BORNEMISZA S , GROTEN E. , BAZHAW W. O.
Published: April 2006

Abstract

Gravity surveys in western Texas with station spacing of about 400 m were complemented by carefully observed vertical gradients of gravity making use of specially designed and automated instrumentation. The presented areal surveys of 51 and 52 stations taken in relatively flat terrain are parts of a large survey of close to 1000 stations complemented by an equal number of vertical gradient measurements. Quite irregular anomalous vertical gravity gradients surpassing 10 microgal/m were often encountered. Assuming the causative density contrasts to be located not more than 10 m below ground surface then free air correction errors of ± 0.1 mgal and more must be accepted. From a practical point of view there seems to be no other way to control such unpredictable errors than to carefully observe the local variation of vertical gravity gradients with adequate equipment. Making use of very closely spaced gravity measurements to derive these anomalous features seems more costly and cumbersome.
SEISMIC NOISE MEASUREMENTS IN A GEOTHERMAL AREA*
Authors: GOFORTH T. T. , DOUZE E. J. , SORRELLS G. G.
Published: April 2006

Abstract

Generation of electrical power through the use of natural steam obtained from the Earth has the potential to be a significant source of pollution‐free power. Successful future exploitation of geothermal power depends upon the development of cost‐effective exploration techniques. A field experiment in the Imperial Valley of California indicates that there is a close empirical relationship between hot water deposits at depth and an anomalously high seismic background level at the surface. If this relationship proves to be a general one, it will serve as the basis of a simple and inexpensive method of geothermal exploration.
RESISTIVITY PROFILES OVER SOME DYKES OF DHANBAD*
Authors: SINGH J. , JHA B. P.
Published: April 2006

Abstract

A number of resistivity profiles over dolerite and metadolerite dykes have been taken using Wenner and Schlumberger configurations around Dhanbad in order to find the potential of these for water accumulation. These dykes give rise to both resistivity highs and lows as compared to the background. The results are discussed in the light of known theories. Some suitable sites for water accumulation have been delineated.
“REMOTE SENSING”— AN EVALUATION OF ITS IMPACT ON EARTH SCIENCE—*
Authors: CASSINIS R.
Published: April 2006

Summary

“Remote sensing” techniques have been used for many years as an exploration tool; broadly speaking, any method using sensors not directly connected to the earth's surface falls into this group.

It is preferable, however, to use the term solely with reference to a number of new sensors which have recently become available to earth scientists for the detection of various radiations of the electromagnetic spectrum in the wave length range from 0.1 micron (UV) to some centimeters including the visible and infrared regions.

Radiations artificially induced in the earth (active sensing) or spontaneous radiations (passive sensing) can be detected. Some of the bands investigated seem promising for application to geological surveys, especially using sensors on aircraft and satellites, which allow synoptic and large scale investigations.

A brief account is given of the results already achieved and of future developments such as the ERTS and manned satellite (post Apollo) “earth observation” programmes.

The potential role of Europe in the field is discussed.

Details are given of some applications of thermal I.R. imagery to geological and vulcanological problems, with special emphasis on the research carried out in Italy.
LES COURBES DAR ZARROUK ET LES SONDAGES DIFFÉRENTIELS DE RÉSISTIVÉ*
Authors: SZARANIEC E.
Published: April 2006

Abstract

Differential and difference soundings of resistivity for real, imaginary and complex values of the newly introduced parameters ν and μ are considered. The transverse and longitudinal differential soundings, known up to the present, correspond with the values ν= 1 and ν=— 1.

The point of departure is the generalization of the concept of Dar Zarrouk parameters and the dimensional analogy between D.Z. resistivity and transverse and longitudinal differential resistivities. Properties of generalized D.Z. curves as well as the method of their construction are given. The examples of differential and difference curves are presented and the properties of these curves are discussed; particulary the effective spacings are determined. The problems of the realization of differential and difference soundings are considered; the bisymmetrical and asymmetrical arrays are proposed as a practical ones.
THE EFFECTS OF ANISOTROPY ON SQUARE ARRAY RESISTIVITY MEASUREMENTS*
Authors: HABBERJAM G. M.
Published: April 2006

An account is given of the use of the square array technique in investigating the surface effects of rotational anisotropy when the axes of anisotropy are inclined to the surface. It is shown that, as with other arrays, two anisotropy parameters and n can be derived by varying the array orientation.

On the basis of these considerations, the effects of such anisotropy on the values of the mean apparent resistivity and azimuthal inhomogeneity ratio normally obtained in square array measurements is reviewed.

Particular attention is paid to the variation of resistivity with orientation and it is noted that, in areas of moderate anisotropy, this variation is lower for the square than for the Schlumberger array.

In addition to this advantage, the azimuthal inhomogeneity ratio obtained from square array measurements may be used to indicate the severity of anisotropy in an area and two field examples of this use are given.

Where anisotropy is severe, gross variations of apparent resistivity with orientation are obtained with either square or collinear arrays. In these circumstances, the use of crossed measurements is considered and the particular stability of the crossed square array demonstrated.
RESISTIVITY SOUNDING ON A THREE‐LAYER TRANSITIONAL MODEL*
Authors: JAIN S. C.
Published: April 2006

Abstract

The expression for the potential due to a point source of current, placed on the surface of a horizontal three‐layer earth, has been derived when conductivity in the second layer varies linearly with depth and changes abruptly at the boundaries. Master curves for Wenner and Schlumberger configurations have been presented for an insulating basement and for one value of conductivity gradient in the second layer.
ELECTRICAL SOUNDING ON THE WATER SURFACE AT KHOR KUNDI EL‐BAHARI IN EGYPT*
Authors: BOULOS F. K.
Published: April 2006

Abstract

Electrical resistivity sounding was attempted with success in 1960 on the surface of the Nile water in Khor Kundi El‐Bahari, the starting place for the construction of the offset channel of the High Dam. The method was applied to determine the depth to the upper surface of the granite below the alluvium and Nile water. The success of the method conducted at two stations in the Khor is attributed to the favourable geological conditions of the section which consists of nearly homogeneous layers besides the good earthing conditions of electrodes dipped in water. The high resistivity contrast between water and granite facilitates interpretation of sounding curves. Factors interfering with the results of interpretation are mentioned.