bluuebunny/crossref_metadata_2025_split huggingface dataset:
DÉCONVOLUTION DE TRACES RÉELLES*
Authors: D'HOERAENE J. 
Published: April 2006

AbstractThe techniques of deconvolution have been formerly developped and tested on synthetic seismogramms.They are in the present study applied to field records or play backs.Three examples of the result of the deconvolution, i.e. of the reduction of filtering effects caused by the apparatus and the ground, are given.They show that the deconvolution increases the power of resolution and emphasizes thereby the resemblances as well as the differences between traces; consequently it enriches the correlation and improves the picking of the reflections which have a permanent enough character.Besides, it is shown that the comparison between deconvoluted traces and an impulsionnal synthetic seismogramm is, for the same reasons, more significant than between a field record and a filtered synthetic seismogramm.Finally, a section of deconvoluted traces shows that it is possible to obtain a valuable increase of resolution using one and the same inverse filter for a group of field records obtained with the same filter setting, even in locations where subsurface conditions are somewhat variable.
COUPLAGE DES SISMOGRAPHES AVEC LE SOL*
Authors: FAIL J. P. , GRAU G. , LAVERGNE M. 
Published: April 2006

AbstractA series of laboratory and field experiments has proved the validity of theoretical formulae for the geophone‐to‐ground coupling characteristics. Soil properties and geo‐phone mass and size have been studied. It has been shown that soil properties in the immediate vicinity of the geophone determine the coupling, together with geophone mass and size.Statistical studies of coupling characteristics have been conducted on various soils. In some cases the dispersion of resonance frequencies and damping constants is quite large, even when the geophones have been carefully planted.As a rule, it may be said that geophone‐to‐ground coupling is not a source of trouble except ‐in high‐frequency studies. However, the filtering effect of multiple geophones may be affected by the statistical fluctuations of coupling on a given type of soil, even at usual frequencies.
SOME UNUSUAL LOW BOUGUER ANOMALIES OF SMALL EXTENT IN CENTRAL IRELAND AND THEIR CONNECTION WITH GEOLOGICAL STRUCTURE*
Authors: MURPHY T. 
Published: April 2006

AbstractDuring a regional gravity survey in Central Ireland a series of intense Bouguer anomalies of very limited extent was encountered. They are all negative, the largest being ‐6.4 mgal and each covers an area of the order of one square km. Gradients up to 9 mgal/km have been measured. The country rock is Carboniferous Limestone, density 2.7 g/cm3, but outcrops are scarce particularly in the region of the anomalies and the surface is in general covered by glacial gravels, drift and bog. Most of the anomalies lie on an approximate straight line running northeast‐southwest for a distance of 115 km.An analysis indicates that the cause of each anomaly is a mass with a negative density contrast of at least 0.3 g/cm3, probably 0.5 g/cm3, and so positioned that its top is not deeper than 0.5 km from the surface.As no rock with a density less than 2.5 g/cm3 is known to exist in the neighbourhood, it is postulated that the cause of the anomalies lies in a sequence of solution cavities in the limestone now filled with water or lightly packed rock debris and gravel aligned along a large fault. No such system has been known or suspected in Ireland.The presence of such large faults would have serious consequences on the possibility of oil accumulation while the infillings of the cavities might have economic importance.
GEOELECTRICAL PROSPECTING WITH UNDERGROUNDELECTRODES*
Authors: ALFANO LUIGI 
Published: April 2006

AbstractIn many situations, because of the great influence of a surface layer on apparent resistivity values, the interpretation of electrical soundings may be very indeterminate, according to the “equivalence principle”.For these situations, an arrangement which includes an underground electrode has been proposed. With this method, the interpretative indeterminatecy may be often eliminated, as may be seen from the diagrams calculated for some typical situations.
REFLECTION AND TRANSMISSION COEFFICIENTS FOR PLANE LONGITUDINAL INCIDENT WAVES
Authors: KOEFOED O. ,   Institute for Applied Mathematics of the Technological University at Delft
Published: April 2006

AbstractTables are presented giving the two reflection coefficients and the two transmission coefficients resulting from the incidence of a plane longitudinal wave upon a plane boundary between two elastic media, for hundred different combinations of the elastic parameters and the density of the two media. The effect of these parameters upon the change of the reflection or transmission coefficient with the angle of incidence is discussed. For incidence beyond the critical angle the phase shift between the incident wave and the reflected or transmitted wave is also given.
DETERMINATION DE L'EPAISSEUR DES SEDIMENTS MEUBLES A L'AIDE DE LA METHODE DE STATISTIQUES DE ΔT*
Authors: LEENHARDT O. 
Published: April 2006

AbstractOffshore reflection records, even if they are of medium quality, can be used to determine the thickness of unconsolidated sediments. The method is described and its limits are specified. An example of application referring to the Gulf of Lyons is given.
ELASTISCHE ANISOTROPIE IN TEKTONISCH VERFORMTEN SEDIMENTGESTEINEN*
Authors: GIESEL W. 
Published: April 2006

AbstractSedimentary rocks deformed by tectonic forces, especially sandstones, show anisotropy in their elastic behaviour. The velocity of longitudinal ultrasonic pulses in them varies with direction. In three directions perpendicular to each other, velocities are extreme. These directions are parallel to the tectonic axes.In such rocks grains are arranged according to their shape. This special orientation developed during the tectonic deformation, which can also be recognized by deformed fossils.A close relation exists between the anisotropy and the arrangement of the grains. A model of the sediment with grains arranged in a similar manner as in natural sandstones is tested mathematically for its elastic behaviour. Anisotropy similar to that of natural sandstones is exhibited by this model.
SURFACE‐SHIP GRAVITY MEASUREMENTS IN THE NORTH SEA*
Authors: FLEISCHER U. 
Published: April 2006

AbstractModern marine gravimeters enable us to measure gravity at sea with a mean error of 2 to 5 mgals, depending on sea conditions and navigational accuracy.Good results could be obtained, even in rough seas, by means of Graf's ASKANIA Sea Gravimeter mounted on an ANSCHÜTZ gyrostabilized platform.When a DECCA Navigator System is used, the gravity measured at the points of intersection agrees within 5 mgals at wind‐force Beaufort 4 and vertical accelerations of about 60.000 mgals.The southern North Sea has been surveyed with VFS “GAUSS”, the research vessel of the German Hydrographic Institute, Hamburg. Since 1959 about 4.000 miles of continuous gravity measurements combined with simultaneous magnetic measurements have been carried out in this area. Here nearly all remote‐control gravimeter stations of the Netherlands Geodetic Commission were passed once or several times. Hence they could be used as basic points. However, there are a few cases in which the Dutch data could not be confirmed.The results are given as a free air isogam map covering the area between the meridian of Greenwich and 8° east, and between 54° and 56° latitude, with decreasing density of the measurements from east to west.
LA RECHERCHE DE PHOSPHATES PAR RADIOMETRIE AEROPORTEE*
Authors: BOLLO R. , JACQUEMIN M. 
Published: April 2006

AbstractAs a rule, deposits of phosphates contain radioactive elements. Studies made in the laboratory of samples from North America and north Africa had shown that this radioactivity is due to the presence of uranium, and occasionally of thorium, either in the form of vaandate or in a diffuse state. Surface measurements carried out with a portable scintillometer had enabled some deposits to be outlined, but radiometric prospecting was only a supplementary method at this stage. From the results of these surface studies, it could be considered that the relations emitted by phosphates were sufficiently intense to be detected from a certain altitude.Consequently, a scintillometer was installed aboard a helicopter, and experimental tests were carried out on the known deposit of Djebel Honk, Algeria. Three profiles, flown perpendicular to the existing layers at 45 metres, permitted us to ascertain the validity of the method, and to define the working standards. Despite the small width of these outcrops (30 metres at most), it was established that “helicopter radiometry” could be used for phosphate exploration.Fourteen thousand kilometres of profiles were flown in northern Algeria. Since the phosphate deposits known in this area are located at the contact of the Cretaceous and Eocene (Dano‐Maestrichtian, Thanetian, Ypresian), a systematic coverage of these geological series was undertaken. It was then possible to draw up a rapid inventory of the series.Airborne radiometry, and helicopter radiometry in particular, now seems to be the most efficient, quickest, and least expensive method that can be applied to systematic phosphate exploration.
CORRELATION TECHNIQUES –A REVIEW*
Authors: ANSTEY N. A. 
Published: April 2006

ABSTRACTCorrelation techniques are in the process of passing from the research laboratory to the field. This paper seeks to aid the transition. The three main sections of the paper have these objects:

To state in words the basic principles on which correlation techniques are based, and the connection between these principles and more familiar concepts which are already among the tools of the exploration geophysicist.
To review briefly the published applications of correlation techniques in science generally.
To discuss some of the additional applications which are now emerging in exploration geophysics.

The treatment is graphical and illustrative, rather than rigorous. The paper is addressed to the practising exploration geoscientist and to the newcomer to correlation techniques. A list of about 150 references is given.
A NEW TECHNIQUE FOR THE MEASUREMENT OF GEOPHONE PARAMETERS UNDER FIELD CONDITIONS*
Authors: PALMER B. A. 
Published: April 2006

AbstractNormally only operational checks are made on geophones in the field because of the lack of suitable test equipment. The test method described here was developed to enable accurate (better than 1 %) measurements to be made, in the field, of all geophones in common use which have natural frequencies of i c/s or greater.The portable field instrument is simple to operate and can be used to test refraction and reflection geophones, either singly or in series strings.
CHARTS FOR DETERMINING THE GRAVITY EFFECT OF TWO‐ AND THREE‐DIMENSIONAL BODIES BOUNDED BY ARBITRARY POLYGONS*
Authors: COLLETTE B.J. 
Published: April 2006

ABSTRACTCharts are presented for the computation of the vertical component of the attraction of horizontal laminas and of horizontal cylinders bounded by irregular w‐sided polygons. Contrary to older methods no restricting conditions are made for the directions of the sides of the polygons.
A SIMPLE METHOD FOR THE CALCULATION OF STANDARD‐GRAPHS TO BE USED IN GEO ELECTRICAL PROSPECTING*
Authors: VAN DAM J. C. 
Published: April 2006

ABSTRACTThe paper describes a new method for the calculation of standard‐graphs i.e. resistivity‐curves for assumed resistivity profiles. It starts from the integral of Stefanesco and arrives at a system of image poles, similar to, but simpler than earlier developed systems. The advantages of the new method are described, the accuracy is discussed and it is indicated how the accuracy can be improved by a simple artifice.
SYNTHETIC SEISMOGRAMS APPLIED TO THE SEISMIC INVESTIGATION OF A COAL BASIN*
Authors: VAN RIEL W. J. 
Published: April 2006

ABSTRACTIn the present study an attempt is made to relate the general pattern of reflection seismograms obtained over a coal basin to the acoustical properties peculiar to the Coal Measures. The Carboniferous is characterized by a very rapid succession of distinct lithological units, resulting in a surprising variability in their physical properties. Coal seams in particular are conspicuous by their low density and velocity and they produce acoustical contrasts of 35–50 % with respect to country rock. The resulting heavy shielding action prevents the seismic energy from penetrating deeply into this type of formation.With the aid of synthetic seismograms, arranged into synthetic profiles, it is shown that only a minor part of the Coal Measures reflections is of primary origin. The majority has a secondary character brought about by reverberations inside the weathering zone. Thus the conclusion is reached that reflection shooting allows of mapping only the structure of the top section of the Carboniferous, which is sufficient for the purposes of the coalmining industry.
ANALYTICAL AEROMAGNETIC INTERPRETATION THE INCLINED PRISM*
Authors: MOO J. K. C. 
Published: April 2006

ABSTRACTThe problem of the magnetic anomaly due to the induced magnetisation, of a body‐having the form of an inclined prism is treated analytically. The formula for the total intensity anomaly is analysed to yield relations between parameters of the anomaly and the depth, width, and dip of the magnetic model. The treatment is extended to include the case of remanent magnetisation. The numerical results are presented as graphs prepared for use in the interpretation of measured anomalies.
CALCUL D'UN FILM SYNTHETIQUE A PARTIR D'UN TRES GRAND NOMBRE DE COUCHES*
Authors: DELAS C. , TARIEL P. 
Published: April 2006

AbstractIt is considered it might be useful to test the validity of the theoretical study “Sur ľinfluence ?un empilement de couches minces en sismique” by Messrs. I. ?Erceville and G. Kunetz, Geophysical Prospecting, XI, No. 2, June 1963.We chose a borehole of the Compagnie Française des Pétroles where the velocity logs frequently show fine interbedding. Two synthetic records were prepared:a) For the first one, a large step (τ= 3 ms) was selected to preserve the general appearance of the field records (convolution by a Ricker wavelet with a pseudo‐period of 26.6 ms);b) For the second one, a small step (τ= 0.5 ms) was taken, convoluted using the same Ricker wavelet.We observed that the synthetic records without multiples are not dependent on the step taken for calculation, provided this step remains small in relation to the period of the convolution signal (τ, one‐way time, smaller than 1/8 of the period of the signal). Nevertheless, when a small step is used, the high frequencies may be better reflected on the synthetic record.We also noticed that the direct wave attenuates rapidly with depth and is replaced by an accumulation of multiples that restore it exactly, but with a slight time‐lag. We termed this the “pseudo‐wave”. The above‐mentioned delay between the two synthetic records is in good agreement with the results published by Messrs. 1. ?Erceville and G. Kunetz.
SOME NOTES CONCERNING THE FREQUENCY ANALYSIS FOR GRAVITY INTERPRETATION*
Authors: MESKÓ A. 
Published: April 2006

AbstractOne of the most important problems in the interpretation of gravity data is the separation of the data giving information characterizing the different geological structures. Various methods were elaborated to perform this separation (smoothing, removing of residuals, second derivatives, analytic continuation and others). For each operation various sets of coefficients were proposed. All these sets of coefficients may be considered as to provide linear filtering processes applied to the original map. The frequency response of the filter unambigously determines the method and gives good and clear information concerning their advantages (or disadvantages). The knowledge of frequency responses enables the choice of the most suitable method for the interpretation of a given map. Graphs are presented by the author showing:

the effect of radius used in the calculation of residuals
effect of the number of points used in averaging the data on a circle
the effect of the different systems of coefficients used in the various second derivative formulas.
ENERGY DENSITY SPECTRUM AND AUTOCORRELATION FUNCTION OF ANOMALIES DUE TO SIMPLE MAGNETIC MODELS*
Authors: SPECTOR A. , BHATTACHARYYA B. K. 
Published: April 2006

ABSTRACTFormulae of the energy spectrum and autocorrelation function have been derived for magnetic anomalies due to four classes of bodies which can be represented in turn by (a) poles, (b) line of poles, (c) dipoles and (d) line of dipoles. The effects of the depth and dimensions of the magnetized sources on the spectrum and the autocorrelation function have been studied. In the case of the dipole models, the orientation of the polarization vector casts a significant influence on the characteristics of the two functions. In all cases, however, the functions change in size and shape as the inclination and declination of the geomagnetic vector are varied.
HORIZONTAL STACKING AND MULTICHANNEL FILTERING APPLIED TO COMMON DEPTH POINT SEISMIC DATA*
Authors: MEYERHOFF HENRY J. 
Published: April 2006

ABSTRACTThe common depth point method of shooting in oil exploration provides a series of seismic traces which yield information about the substrata layers at one location. After normal moveout and static corrections have been applied, the traces are combined by horizontal stacking, or linear multichannel filtering, into a single record in which the primary reflections have been enhanced relative to the multiple reflections and random noise.The criterion used in optimum horizontal stacking is to maximize the signal to noise power ratio, where signal refers to the primary reflection sequence and noise includes the multiple reflections. It is shown when this criterion is equivalent to minimizing the mean square difference between the desired signal (primary reflection sequence) and the weighted horizontally stacked traces.If the seismic traces are combined by multichannel linear filtering, the primary reflection sequence will have undergone some phase and frequency distortion on the resulting record. The signal to noise power ratio then becomes less meaningful a criterion for designing the optimum linear multichannel filter, and the mean square criterion is adopted. In general, however, since more a priori information about the seismic traces is required to design the optimum linear multichannel filter than required for the optimum set of weights of the horizontal stacking process, the former will be an improvement over the latter. It becomes evident that optimum horizontal stacking is a restricted form of linear multichannel filtering.
NEW FILTERING METHODS WITH “VIBROSEIS”*
Authors: EDELMANN H. 
Published: April 2006

ABSTRACTIn order to obtain high resolution correlograms, it is of importance amongst other things to get reflection signals with large bandwidth. An advantage of the VIBROSEIS*** method is that the frequencies radiated by the vibrators can be matched to the transmission response of the subsurface involved. By choosing the right frequency range, the highest possible amplitude and most favourable form may be given to the reflection signals.In a reflection correlogram, individual signals cannot be considered in isolation. Signals of different origin are interfering with one another. They very often have different amplitudes, so that it may be desirable in many cases to filter out events of certain apparent velocity. With the VIBROSEIS method this may be achieved quite simply. All frequencies of the noise signal are uniformly suppressed. The advantage is that noise signals, e.g. refraction signals, which cannot be sufficiently attenuated by wavelength filtering, may be completely eliminated by this velocity filtering without affecting the bandwith of the desired signal. The total dynamic range of the tape recording can be used for the registration of wanted events. To perform this kind of filtering several vibrators are necessary in the field; each of them is controlled by an individual signal.There is an unavoidable error of static and dynamic corrections which causes the results of reflection measurements to deteriorate when using multiple coverage. High frequency components especially are seriously affected by destructive interference. This difficulty can be avoided by using a VIBROSEIS signal with high frequency component amplitudes supported. For the probability of error of corrections a normal distribution is assumed. A smoothed amplitude characteristic may be achieved after stacking.The amplitude characteristic of seismic devices is commonly reduced to about 100 cps bandwidth. For further improvement of resolution of VIBROSEIS correlograms it is necessary to apply special filtering methods. This is of particular interest when any kind of gain control is used to display weak events more clearly. With increasing amplification the sidelobes of the strong signals may reach the size of the weak events. In order to eliminate this effect, the amplitude characteristic of the VIBROSEIS signal is adjusted for optimum suppression of side‐lobes.
THE TERRAPAK *
Authors: PIEUCHOT M. 
Published: April 2006

ABSTRACTThe Terrapak is a new seismic energy source of the surface energy source type. Essentially, the Terrapak consists of a compressed air piston which transmits a shock to the ground by means of a striker plate attached to the piston rod. The Terrapak is truck‐mounted together with its ancillary equipment. Shocks can be generated at 8 second intervals, and although the weight of the striker is relatively low (approximately 1400 Ibs) the impact velocity exceeds 66 ft/sec. The energy available is about 85,000 ft. lb., which is equivalent to that produced by conventional weight‐dropping methods. The power spectrum of the seismic wave produced by the Terrapak is spread out towards the higher frequencies because its impact velocity is greater than that of a dropping weight.There is a noticeable difference between noise records made with the Terrapak and noise records made with a conventional weight‐dropping technique. The same noise frequencies are found in both cases, but low frequency noise is stronger with weight dropping than with the Terrapak, whereas the intermediate frequency reflections obtained using the Terrapak are more suitable for correlation.The expansion of the compressed air generates a sound wave, the effects of which must be eliminated by the use of multiple geophone arrays. A spectrum analysis of the records has confirmed that the waves produced by the Terrapak are rich in intermediate frequency components. This facilitates the picking of reflections in normal areas where the apparent frequency of the reflections is about 30 to 35 c/s.