bluuebunny/crossref_metadata_2025_split huggingface dataset:
SEISMIC MODEL EXPERIMENT ON THIN LAYERS*
Authors: CARABELLI E. , FOLICALDI R. 
Published: April 2006

SummarySeismic two‐dimensional model experiments have been made at the Laboratory of Fondazione Lerici in the Polytechnic School of Milan.For this purpose the Laboratory has developed and constructed a complete equipment including pulse generators, piezoelectric transducers and amplifiers for detecting the waves propagation through the models.We record here experiments concerning reflections from horizontal layers thin in relation to the wave lengths propagated through the media.Layers, with a thickness from a 50th of the total wave length to several wave lengths were used. These strata consist of materials sometimes with lower and sometimes with higher velocities than the homogeneous surrounding medium.The object of this investigation was to clarify the effects of the very thin reflecting layers, individually and in combination, on the reflected arrivals and to determine the influence of the layers upon the reflected energy in comparison with their thickness.We are also studying at what minimum distance, as a fraction of the wave length, the reflection of a horizon appears on the seismogram in an independent event.
THE PULSED VIBRATOR AS A SEISMIC SOURCE*
Authors: EVISON F. F. 
Published: April 2006

ABSTRACTNon‐explosive seismic sources, notably the falling weight and the eccentric machine, have occasionally proved advantageous in experimental and practical seismology in spite of their relative feebleness.Another alternative is the pulsed vibrator, which offers the advantage of a completely controllable waveform. Recent theory shows that such a source is quite well adapted to the radiation of high frequency waves from the surface of the ground; it is estimated, for example, that in typical circumstances reflections should be obtainable from depths of the order of 200 metres. The theory also shows how resonances may be avoided so as to radiate the impulsive waveform unimpaired.
ÉTUDE DE L'ATTÉNUATION DE L'INFLUENCE DES ANOMALIES SUPERFICIELLES DANS LE CALCUL DE LA DÉRIVÉE SECONDE DE LA GRAVITÉ*)
Authors: GOGUEL Jean , LEMOINE Jeannine 
Published: April 2006

ABSTRACTIn order to eliminate the effect of smoothing due to the use of a finite number of grid points, the second derivative is computed by integrating the product of g with a convenient continuous function, which yields the second derivative to the extent to which the first terms of the Taylor expansion of g represent its value correctly. By applying this method to the anomaly caused by an isolated mass, and to that caused by a homogeneous half plane, it is shown that, if the result obtained is interpreted as if it really were a second derivative, erroneous values for the depth and the mass are obtained. If the real depth of the mass is small, a too large apparent depth is obtained. In the case of a half plane the use of a system of grid points gives the same result. These considerations permit the rational choice of the method of computing the second derivative, such that the effects of too shallow mass irregularities are attenuated.
SUR ĽINTERPRÉTATION DES ANOMALIES GRAVIMÉTRIQUES ET MAGNÉTIQUES *)
Authors: DE GERY Jérôme CHASTENET , NAUDY Henri 
Published: April 2006

ABSTRACTFor the interpretation of gravimetric and magnetic maps two types of master curves are proposed: firstly those which apply both to the vertical gradient of g and to the pseudo gravimetric gradient obtained by reduction to the pole of magnetic maps; and secondly those which apply direct to magnetic anomalies.With regard to the first type of master curve, the principle and the advantages of the reduction to the pole are discussed. In the last part of the paper it is shown how a set of master curves, calculated for two‐dimensional east‐west striking structures, can also be used for the interpretation of two‐dimensional structures of arbitrary direction of strike. Practical examples of application are given.
RADON MEASUREMENTS AS A GEOPHYSICAL METHOD *)
Authors: BUDDE E. 
Published: April 2006

AbstractFaults or Uranium‐bearing veins are often to be found by measuring the Radon‐content of the air in the ground through a layer of porous material, even over some distance.It is shown by measurements in the laboratory and in the field, that this distance depends on the character of the porous material (composition of grains with different diameters and water content).A quantitative relation between the composition of grains with different diameters and the coefficient of diffusion of Radon is obtained by comparing the practical measurements with theoretical results.The result of the investigations is, that Uranium‐bearing veins or faults do not cause any measurable anomaly even over a distance of only 5 cm, if they are hidden under fine‐grained material with its natural water content.
REFLECTION SHOOTING TECHNIQUES IN THE NETHERLANDS*
Authors: SNIJDERS G. H. F. 
Published: April 2006

ABSTRACTReflection quality in the Netherlands is extremely variable, ranging from very good to very poor. It is believed that the variation is caused mainly by the changing surface conditions. This suggestion is discussed in the light of available geological data.Several examples are given showing the usefulness of making broad band recordings on normal reflection spreads.The combination of data obtained from the study of the surface conditions and from broad band seismograms is used to select the best shooting method.Some suggestions are made regarding seismometer and shot‐hole patterns, shot medium and the choice of filters.
LA MESURE DE LA VITESSE VERTICALE PAR LE CAROTTAGE CONTINU (CVL); PRECISION DES MESURES ET DISCUSSIONS DE QUELQUES RÉSULTATS*
Authors: SCHWAETZER T. 
Published: April 2006

The introduction of the CVL and the “core speed tester” (or ultra sonic velocity meter) have enabled the geophysicist to complement large‐interval, average velocity measurement of sedimentary formations (obtained by conventional well velocity surveys, “Gardner” velocity shots, etc.) by small interval, detailed study of the velocity of particular strata, in situ or in the laboratory. The significance of laboratory velocity measurements on cores is affected by irreversible alterations of the core. At first the integrated time curve of the CVL, calibrated with a skeleton conventional velocity survey, seemed to assure the precision of the interval velocity. Later it was realised that variations of the “Delay Time” (compensation for Mud Travel Time in the single receptor CVL), failure to identify the first energy arrival, etc., could cause errors in the interval velocity measured. These errors can be, detected and reduced by increasing the number of control points of the well survey, running logs down and up the hole, overlapping, and also by the comparison of the Continuous Velocity Logs for neighbouring wells and for various strata in a given well.Despite these errors, the C VL has been found extremely useful, not only for the determination of average velocity, the identification of reflecting strata, and of refraction markers, but also for geological correlations between wells, the determination of maximum porosity and detailed studies of the parameters affecting the velocity of sedimentary rocks.The relation between interval velocity and porosity is discussed and a hypothesis that the low velocity of argillaceous, low‐porosity limestones may in part be due to the total fluid contained is put forward.
SYNTHETIC SEISMOGRAMS FROM CONTINUOUS VELOCITY LOGS*
Authors: DÜRSCHNER H. 
Published: April 2006

ABSTRACTIn this paper a method of calculating synthetic seismograms from continuous velocity logs (CVL) is presented and described in detail.The seismic velocities on the CVL are frequently and rapidly changing. Therefore a seismic field‐record consists of a great number of reflections with different sign and amplitude. The sum of all reflections forms the seismogram.The first part deals with some relations between the log, the reflection‐layers, and the normal field‐record, with special emphasis on the influence of the seismic amplifier.Then several assumptions are made for the construction of the synthetic seismograms. Finally some examples and applications are given.
ON REFLECTED REFRACTION WAVES*
Authors: BRAUCH W. 
Published: April 2006

ABSTRACTAs an introduction the various ray paths of a refraction wave, which is reflected at a fault, are discussed for the case of an arbitrary angle between the refracting horizon and the fault. Simple geometric considerations lead to the conclusion that the best chances for recording these pulses are encountered, if the angle between the refracting horizon and the fault is either 90° or the critical angle of refraction. In both cases identical travel times of the pulses are to be expected.The case of a fault perpendicular to the refracting horizon is considered in detail for dipping beds. Formulas for the shot point travel time curve and the time contour map are derived. Computed time contour maps show considerable differences between the direction of strike of the contour lines and the strike of the fault, as well as between the recorded apparent velocity and the true velocity of the refracting horizon. Finally, alignment charts and computing procedures are given by which the position of the fault and the velocity of the refracting horizon can be obtained from the recorded shot point travel times or the time contour map.
A NOTE ON THE SEISMIC PULSE RECORDED FROM A MINE EXPLOSION
Authors: ANSTEY N. A. 
Published: April 2006

ABSTRACTIt is not easy to record a seismic pulse at distances of interest to oil prospectors without there being reflected or refracted pulses superimposed on the direct arrival. Accordingly the record illustrated is considered worth publishing, although it was taken fortuitously during a normal survey and cannot claim to be a controlled experiment. A comparison with the filtered pulse to be expected from a theoretical Ricker‐type wavelet is presented.
GEOPHYSICAL EXPLORATION IN MINING BY INDUCED POLARIZATION*
Authors: ŠUMI F. 
Published: April 2006

AbstractThe present paper deals with various causes giving rise to potential differences caused by induced polarization. In order to obtain the induced polarization effect of ore bodies it is necessary to determine the effect of the barren rock and substract it from the total observed effect.Results of field measurements carried out by this method in the mercury mine of Idrija, as well as those in the lead‐zinc mine of Mežica and the Kankberg ore district are in good agreement with the geological data. A theoretically calculated profile is compared with an actual field profile.
REMANENT MAGNETIZATION AND THE INTERPRETATION OF MAGNETIC ANOMALIES
Authors: GREEN R. 
Published: April 2006

AbstractLavas and intrusives are often permanently magnetized in a direction different from the direction of the present geomagnetic field and this can make the interpretation of a magnetic intensity map difficult. However, the profiles over a permanently magnetized body are identical with the profiles over an inductively magnetized body of the same shape provided the direction and dip of the geomagnetic field in the induced case is appropriately changed. In which case, the shape of the body can be deduced by the well‐known methods of interpretation of induced anomalies. Examples of the application of this method to Australian Kainozoic basalts, Tertiary basalts from Australia and Tasmania, and the classical Pilansberg dykes have been worked out. This article stresses the fact that the apparently confused patterns obtained by magnetic surveys over volcanic rocks can often be explained with little difficulty as the juxtaposition of normal and reversely magnetized rocks.
SOME PRESSURE EFFECTS ON THE BEHAVIOUR OF WORDEN GRAVITY‐METERS *
Authors: GANTAR C. , MORELLI C. 
Published: April 2006

AbstractSome tests carried out on a Worden “Educator” gravimeter (n. E 302) showed that pressure variations had a significant effect on the readings.The changes of pressure cause changes in readings of the same sign. Corrections are given which may be applied to the instrument readings to compensate for this effect.
ANOMALE ULTRASCHALL‐GESCHWINDIGKEITEN IN GESTEINSBOHRKERNEN *
Authors: BAULE H. 
Published: April 2006

AbstractThe velocity of supersonic pulses in cylindrical drill cores and rock samples is measured as a function of the frequency or wave length λ of the pulses. If λ is very much lower than the diameter D of the drill core –λ < D– the higher velocity of the longitudinal waves vl appears; on the other side we get the lower velocity of the rod waves vd (Stabdehnungswellen) if λ > D.Some drill cores from the carbon were found the velocities of which for sonic and supersonic pulses do not follow the above rule. It is shown that these cores have a constant velocity both for short and for long wave lengths in a frequency range between 5 kHz and 2 MHz.
SEISMIC WAVES IN TRANSITION LAYERS*
Authors: BORTFELD REINHARD 
Published: April 2006

AbstractA transition layer is a layer in which the velocity changes linearly with depth from va to ve and we consider it embedded between two layers of constant velocity va and ve, respectively. A plane displacement wave of arbitrary shape is supposed to come out of the upper v”‐layer, and to meet the transition layer at vertical incidence. Using methods of elementary calculus only, the subsequent events are derived for both inside and outside the transition layer.The transition layer can be regarded as the limit of a sequence of constant‐velocity‐layer divisions. Thus, after computing the first few multiples of the incident wave for these divisions, the respective multiples of the transition layer are obtained as the limit of these multiples. Then, with the help of recurrence formulae, the multiples of the transition layer of any order are computed. The sum of all multiples defines the complete response of the transition layer and satisfies the differential equations of the problem.The solution has the form of a superposition integral, and it is seen that the transition layer has the properties of a linear filter. The superposition integral is built up out of the incident wave and a conglomerate of Bessel functions, the latter being the corresponding response to an incident spike impulse in a mathematical sense. The reflected and transmitted responses to the spike impulse are shown for two values of the velocity ratio. For large values of this ratio, both these responses have a‘wave‐like’shape and it is seen that the transition layer may effect a serious change of shape of incident waves.
DIFFRACTION PROBLEMS IN FAULT INTERPRETATION*
Authors: KUNZ BRUNO F. J. 
Published: April 2006

AbstractDistinguishing between diffractions and true reflections is often difficult and may lead to misinterpretations. In the Molasse zone of Upper Austria, numerous faults were established by seismic surveying. Diffractions were observed at several antithetic faults but not at synthetic faults. As an example, a seismic record section of the Steindlberg structure is shown. The reflections from the base of Tertiary arid from the Cretaceous‐Jurassic contact run parallel over long distances, and so do the less important reflections lying above and between. If, contrary to the general trend, the reflection from the base of the Tertiary approaches the underlying reflection from the Cretaceous‐Jurassic contact, or if the latter diverges from the former, this is considered a criterion for a diffraction.
THE USE OF AMPLITUDES IN REFRACTION SHOOTING – A CASE HISTORY*
Authors: O'BRIEN P. N. S. 
Published: April 2006

AbstractOn a group of seismic refraction records there occurs a late arrival with the same apparent velocity as an earlier arrival. It was first thought that the late arrival travelled along the same refractor as the earlier one but had been delayed in the overburden either by multiple reflection or by P‐S (dilatation to shear) conversion. Either of these two mechanisms could be made to fit the time‐distance data. A study of the ratio of the amplitudes of the two events showed that the observed ratio was about ten times that to be expected on either of these hypotheses. Also, the rate of attenuation of the earlier arrival (3.7 ± 1.0 db/1000 ft) was appropriate to a thin layer while the rate for the later arrival (0.74 ± 0.30 db/1000 ft) was appropriate to a thick layer. Accordingly, the later arrival was identified as a refraction from a deeper layer.The subsequent depth section agreed very well with that found by drilling.
ELASTISCHE WELLEN IM ANISOTROPEN MEDIUM NACH EINER MAKROSEISMISCHEN UNTERTAGE‐MESSUNG*
Authors: DUDA S. J. 
Published: April 2006

AbstractIn some mines of the Siegerland, besides dilatational and shear waves, an additional direct wave has sometimes been found the velocity of which was somewhat lower than that of the shear wave. Investigations were carried out with the object to establish the directions of oscillations and the velocities of all three kinds of waves. It was the purpose to draw conclusions as to the character and the causes of the appearence of the third wave.By these investigations the wave having the lowest velocity can be identified as a second shear wave. This points to the fact that double refraction of the shear wave is taking place, the wave of higher velocity being a pure transverse wave and the wave of lower velocity being a quasi‐transverse wave.As a result of these measurements the examined medium is shown to have a transverse isotropy due to stratification. It is, however, not possible to decide whether there exists also an anisotropy due to schistosity.Some further calculations show that the wave of lowest velocity can not be explained as a surface wave propagated on the walls of the gallery.
GENERAL METHOD FOR CONSTRUCTION OF TRAJECTORIES AND WAVE‐FRONTS DIAGRAM FOR ANY VELOCITY DISTRIBUTION
Authors: OLHOVICH V. A. 
Published: April 2006

AbstractA graphical method is presented for construction of trajectories and wave‐front diagrams for any velocity distribution.The analytical solution is given for the case when the time‐depth curve shows a flexure, that is, when the the velocity increases down to a certain depth and, after reaching a maximum, begins to decrease.A numerical example is considered for the computation of a trajectory.
THE INFLUENCE OF SURFACE FORMATIONS ON THE APPARENT RESISTIVITY VALUES IN ELECTRICAL PROSPECTING*)
Authors: ALFANO L. 
Published: April 2006

AbstractIn this first part, 1) we have examined the disturbances on resistivity measurements caused by some simple examples of surface irregularities with a cylindrical structure. The study has been carried out applying a theory developed in a previous paper (Alfano 1959)In the first place, we have considered the case of measurements carried out with the potential electrodes near the surface irregularities, and the current electrodes more distant from those irregularities. This case is related to those methods of prospecting in which it is preferred to keep the current electrodes fixed and to move the potential electrodes.One method has been pointed out which will separate, in the measured data, the component of the field due to deep formations, from the components due to surface irregularities. Afterwards, we have considered the case with current electrodes near the dishomo‐geneities and potential electrodes more distant from them. For both cases, numerical examples are shown, both for secondary charge values and for apparent resistivity values.Finally, asymptotic values of vertical electrical soundings have been calculated for some cases, rigorously showing that they, in the presence of surface disturbances, are not equal, generally, to the true resistivity of a possible infinite substratum.It follows that the measurement of resistivity of an infinite substratum, by means of the resistivity asymptotic value of only one sounding, is not possible.The numerical results given have been obtained by means of calculations based on the abovesaid paper, but whose operative details shall be described in the second part of this paper.The second part also will deal with the cases of surface dishomogeneity with a non‐cylindrical structure.
VARIATION DES VITESSES EN RAPPORT AVEC L'AGE EN LA LITHOLOGIE APPLICATION DE LA LOI DE FAUST*
Authors: AYNARD C. , MITRANI H. , DHINNIN R. 
Published: April 2006

AbstractIt was felt that Faust's first law was the best guide in classifying data concerning velocities and their correlation with lithology, even if, on a local basis, other laws fit the observed values better.Data have been re‐examined which were provided chiefly by borehole measurements, both conventional and continuous, but also by some particularly reliable velocity profiles. “Faust's coefficient” has been computed for a series of geological formations, i.e. the ratio of true velocity to the value resulting from Faust's law, according to the age and present depth of the formation.Some graphs are shown, in the first place concerning the Sahara, and especially the Palaeozoic. It can be seen that the only formation showing values notably less than I disappears.On the other hand, values greater than I can be noticed for the quartzitic Ordovician of limited thickness.This comparison has been continued on a broader basis, using, in particular, data published by Faust and Wyrobek. The data concerning the very homogeneous Westphalian result in an average value slightly less than I.The Aquitanian basin has been studied in greater detail, owing to the closer spacing of the measurements.Generally speaking, the Middle and Upper Jurassic, the Cretaceous and the Eocene‐Oligocene show values notably higher than the Palaeozoic in the Sahara. This seems to be connected with the higher proportion of limestones and dolomites. Values as high as 1.7 are observed in compact dolomites.Four maps are given, concerning the Oligocene, the Eocene‐Paleocene (one of them excluding the Danian) and the Upper Cretaceous (exclusive of Danian), and a cross‐section showing the link with lithology.Some discrepancies with regard to data from borehole samples are discussed.The question may be raised as to whether such studies can be carried out at the very beginning of exploration of a basin, on the basis of only a few logged wells. In the Aquitaine basin, data given by velocity profiles are in close agreement with those from wells as regards the Tertiary; but as regards the Mesozoic, information is meagre. In basins of the Sahara type, synthetic records have shown that interference of true and multiple reflections with each other is a major drawback. But on the other hand, the possibilities of a combined use of reflection and refraction in order to define lateral changes in velocities may not have been fully appreciated. Some computed examples are shown, since the results of a survey at present being carried out on this basis cannot yet be published.Finally, mention is made of the part played by the determination of anisotropy, and an appeal is made for more coöperation between geophysicists in this sphere.