bluuebunny/crossref_metadata_2025_split huggingface dataset:
A GENERALIZED METHOD OF COMPUTING SECOND DERIVATIVE OF GRAVITY FIELD*
Authors: AGARWAL B. N. P. , LAL T. 
Published: April 2006

AbstractThe unsuitability of a particular method of computation of second derivative to varying types of field problems evinces the need of a method by which it may be possible to obtain a wide range of filters. This requirement is achieved by incorporating a mathematical smoothing operator, e‐λρ2, λ and ρ being the smoothing parameter and radial frequency respectively, in the theoretical frequency response of second derivative operation. A few sets of weights for various smoothing parameters, are presented. The analysis of Bouguer gravity anomaly map of Los Angeles Basin, California, U.S.A., is carried out by Elkins's (1951) and Rosenbach's (1953) methods and the sets of weights given in this paper which clearly establishes their filtering equivalence.
A NOTE ON SIGNAL DISTORTION DUE TO DYNAMIC (NMO) CORRECTIONS*
Authors: BUCHHOLTZ H. 
Published: April 2006

AbstractBy applying dynamic corrections a seismic trace recorded at a distance x from the energy source should be varied in such a way as to obtain a trace which would be recorded at zero‐distance, i.e. at the source itself. Only such a zero‐offset‐trace contains the correct sequence of reflection coefficients (reflectivity function), whilst all other traces contain a distorted reflectivity function. In the simplest case, the reflectivity function is compressed over a shorter time whereas in more complicated cases a partial inversion of the reflectivity function results. This happens when some of the reflection hyperbolae intersect one another.The reconstruction of the true zero‐offset reflectivity function by the application of dynamic corrections can only be an approximative process. In the first case mentioned we must expect a decrease in accuracy of the corrected trace in comparison with a zero‐offset‐trace. In the second case, where intersections of the hyperbolae occur, accurate reconstruction is clearly impossible.The problems are discussed with the help of theoretical and practical examples.
THE AUTOMATIC FITTING OF A RESISTIVITY SOUNDING BY A GEOMETRICAL PROGRESSION OF DEPTHS *
Authors: MARSDEN D. 
Published: April 2006

AbstractThe problem of interpretation of geoelectrical resistivity soundings has been studied and a compromise method of interpretation developed. A simple depth sequence of increasing bed thickness is taken and resistivities assigned to the various layers so that a good fit is obtained to the observed apparent resistivity curve. An initial estimate of the resistivities is made by a direct method but the model is then altered to give an improved fit by the indirect method of curve matching. The whole method is computerized and input data to the computer program consists of spacings and apparent resistivities. The method is extremely rapid, about one third of the computation time is devoted to obtaining the resistivity transform by the method of convolution. A normal type of solution, incorporating additional information if necessary, can also be obtained.
SEISMIC WAVES IN ANELASTIC NON‐LINEAR MEDIA—A THEORETICAL CONTRIBUTION *
Authors: ALFANO L. 
Published: April 2006

AbstractNumerical solutions of the wave equation for a particular type of non‐linear “constant Q” medium were carried out. These solutions were obtained after the transformation of the space derivatives in finite differences; power series of the time are used to express the solutions.The medium is characterized by a not single valued stress‐strain relation; the stresses are greater when the absolute values of strain are increasing (passive work), and are less when they are decreasing (active work). A loss of energy follows which is constant for every cycle and independent of frequency. This model represents the simplest type of medium in agreement with the laboratory data on rock samples. For a similar medium the stress’values do not depend only on the instantaneous value of the strain, but also on the previous strain values, i.e. the history of the medium. All these characteristics are not compatible with linearity and require particular types of computing procedures similar to the one shown in this paper.The results of calculations here shown refer both to the propagation of an isolated wave and to the generation of a wave in a spherical hole by change of pressure. They refer particularly to the shape, the amplitude and the width of the isolated wave along the propagation path. The most important results for this type of medium are the following: a) for a plane single isolated wave, the displacement amplitude wave does not change along the propagated distance. The width increases linearly as function of the distance; b) the corresponding particle velocity decreases in amplitude; c) for single isolated spherical waves the displacement amplitude decreases with propagated distance only due to the geometric factor, i.e. inversely proportional to the propagated distance; its width increases in the same way as for plane waves.The comparison between these theoretical results with the field and seismological data show a sufficiently good agreement as far as the value interval of wave width and frequencies is concerned. Less satisfactory is the comparison regarding a linear dependence of the wave width on the distance. This fact happens probably because in the field often long trains of waves and not isolated waves occur. In effect, for trains of waves the behaviour is different than that of an isolated wave; particularly, for the former the frequency variations along the travelled path is less and the displacement variations greater.However, it seems likely that a further similar theoretical research for trains of waves propagating in this type of non‐linear medium might be carried out to complete the present research.
ANALYSIS OF THE FOURIER SPECTRUM OF THE GRAVITY EFFECT DUE TO TWO‐DIMENSIONAL TRIANGULAR PRISM *
Authors: RAO K. G. C. , AVASTHI D. N. 
Published: April 2006

AbstractRao, K. G. C. and D. N. Avasthi, 1973, Analysis of the Fourier Spectrum of the Gravity Effect Due to Two‐Dimensional Triangular Prism, Geophysical Prospecting 21, 526‐542.Fourier Transform of the theoretical gravity effect due to a two‐dimensional isosceles triangular prism has been derived. Evaluation of the model parameters from the analysis of the Fourier Spectrum has been outlined. Application of this method to synthetic gravity anomalies is shown.
SHAPED CHARGE—A POWERFUL EXPLOSIVE SURFACE SEISMIC SOURCE *
Authors: BAHIA R. R. , SILVA W. F. 
Published: April 2006

AbstractThe directional effect of shaped charge is a well‐known feature used for a long time in military weapons, oil well guns, and steel industry. This charge was successfully applied as a seismic energy source by Petrobrás during the past three years under different surface and geological conditions.Preliminary amplitude measurements taken with fixed gain shallow refraction instruments showed a consistent difference between conventional and shaped charges. Lately, a similar difference has been noted in deep reflection energy recorded with digital binary gain instruments as well as in deep oil well velocity surveys.Direct comparisons along more than 50 km of multiple coverage field reflection shooting are in agreement with these results and have proved the practical advantage of this source as compared to conventional dynamite.This source has been used since 1971 in routine seismic operation in the Amazon jungle with 300 gram unit charges distributed in small and large shot arrays increasing substantially the coverage and halving the cost at a higher record quality. A large amount of production seismic field work has been carried out in several other areas attesting the successful application of the shaped charges.
SERIES APPROXIMATION IN VELOCITY AND TRAVELTIME COMPUTATIONS *
Authors: AL‐CHALABI M. 
Published: April 2006

AbstractA rigorous proof is presented to show that over a horizontally layered ground the rms velocity cannot exceed the stacking velocity. The proof helps to illustrate the difference between stacking and rms velocities in a quantitative manner. The series of Taner and Koehler (1969) is used for the purpose. Convergence of this series is tested. Including more terms will not necessarily improve the convergence. Although the series is rapidly convergent when the spread length/depth ratio is small, strong oscillations are observed when this ratio is high.
HOW TO WRITE FOR “GEOPHYSICAL PROSPECTING”*
Authors: HELBIG K. 
Published: April 2006

AbstractThe acceptance of articles in Geophysical Prospecting is strictly based on the originality and relevance of the contents. In order to be published a paper has to satisfy additional requirements on its external form and on its style and language: it should be written preferably in English though articles in French and German are permitted. A paper should consist of (i) a title page, (ii) an abstract, (iii) the text, (iv) list of references, (v) captions to illustrations, if any, (vi) tables, if any, and (vii) illustrations, if any. These seven parts should be mailed together but be physically separable and should be prepared according to rules which are either based on printing necessities or on the editorial style of the Journal.Failure to comply with these rules may result in delay in further processing of the article. Since Geophysical Prospecting is edited with a minimal budget correspondence with authors is kept to a minimum.
ESTIMATION OF THE PRIMARY SEISMIC PULSE *
Authors: WHITE R. E. , O'BRIEN P. N. S. 
Published: April 2006

AbstractA seismic trace after application of suitable amplitude recovery may be treated as a stationary time‐series. Such a trace, or a portion of it, is modelled by the expression
image
where j represents trace number on the record, t is time, αj is a time delay, α (t) is the seismic wavelet, s(t) is the reflection impulse response of the ground and nj is uncorrelated noise. With the common assumption that s(t) is white, random, and stationary, estimates of the energy spectrum (or auto‐correlation function) of the pulse α(t) are obtained by statistical analysis of the multitrace record. The time‐domain pulse itself is then reconstituted under the assumption of minimum‐phase. Three techniques for obtaining the phase spectrum have been evaluated: (A) use of the Hilbert transform, (B) Use of the z‐transform, (C) a fast method based on inverting the least‐squares inverse of the wavelets, i.e. inverting the normal time‐domain deconvolution operator. Problems associated with these three methods are most acute when the z‐transform of α(t) has zeroes on or near the unit circle. Such zeroes result from oversampling or from highly resonant wavelets. The behaviour of the three methods when the energy spectra are perturbed by measurement errors is studied. It is concluded that method (A) is the best of the three. Examples of reconstituted pulses are given which illustrate the variability from trace‐to‐trace, from shot‐to‐shot, and from one shot‐point medium to another. There is reasonable agreement between the minimum‐phase pulses obtained by this statistical analysis of operational records and those estimated from measurements close to the source. However, this comparison incorporates a “fudge‐factor” since an allowance for absorption has to be made in order to attenuate the high frequencies present in the pulse measured close to the shot.
STRESS WAVE VELOCITY AND CRACK SYSTEM OF A MEDIUM *
Authors: SCHENK V. , SCHENKOVÁ Z. 
Published: April 2006

AbstractTwo in situ measurements of stress wave velocity in a granodiorite massif were made. Firstly, the velocities close to the source were investigated (for elimination of the influence of cracks), and secondly, the velocities in different horizontal directions over a large area were studied from the viewpoint of their dependence on the crack system of the medium. A correlation between the mutual orientation of the cracks and the maximum or minimum values of the stress wave velocities was obtained.
INTER‐BOREHOLE ACOUSTIC MEASUREMENTS AND THEIR USE IN ENGINEERING GEOLOGY*
Authors: McCANN D. M. , GRAINGER P. , McCANN C. 
Published: April 2006

AbstractWell–to‐well seismic measurements are adapted to civil engineering problems by use of a sparker as a source of seismic signals and an 80 kHz hydrophone as a receiver. For display a Tektronix 549 oscilloscope is used.Field application shows that the delineation of interfaces between homogeneous strata and the detection and delineation of localized and irregular features is possible from inter‐well travel times. In‐situ measurement of the compressional wave velocity in a medium is often complicated by refraction and wave guide effects. The degree of fracturing cannot be estimated from travel time measurements alone in a tightly jointed, saturated, rock mass, but it may be possible to correlate variations in pulse shape and length with this parameter.
BOUNDARY CONDITIONS FOR THIN IMPERFECT CONDUCTORS AND INSULATORS*
Authors: HURLEY D. G. 
Published: April 2006

AbstractConsider a thin, plane, finite sheet of material of thickness 2t whose electrical resistivity is σ2. It is surrounded by a medium of resistivity σ1 in which there is an electric field whose length scale is L. We consider the limit t/L→ o with , or fixed. In the former case the sheet is an imperfect conductor and it is shown that it may be modelled by a surface on which the boundary condition is , where φ and Z are the (nondimensional) electrical potential and distance measured normal to the surface, and the subscripts + and − denote values on either side of the surface.In the latter case the sheet is an imperfect insulator and the boundary condition is
FACTORS AFFECTING SEISMIC AMPLITUDES*
Authors: SHERIFF R. E. 
Published: April 2006

AbstractThe amplitude of seismic energy varies over a tremendous range. Some of the factors responsible for such variation do not contain subsurface information; these include source strength and coupling, geophone sensitivity, array directivity, instrument balance, scattering in the near‐surface, for example. Others depend on subsurface factors but do not convey information about lithology or hydrocarbon accumulation in a form from which we are able to extract it; these include spherical divergence, ray‐path curvature, loss in transmission through intervening reflectors, peg‐leg multiples, reflector rugosity, and curvature. The amplitude‐governing factors we are primarily interested in are reflection coefficient, the interference of reflections from the top and base of a sand, and absorption.
VIBROSEIS DECONVOLUTION*
Authors: RISTOW D. , JURCZYK D. 
Published: April 2006

AbstractVibroseis deconvolution can be performed either before or after correlation. As regards the deconvolution before correlation, the Vibroseis deconvolution operator can be described as convolution of a spike deconvolution operator with a minimum‐phase filter operator with bandpass properties. As regards the deconvolution after correlation, the deconvolution operator can be shown to be the convolution of three operators: spike deconvolution operator and two‐fold convolution with a minimum phase operator. Time‐varying Vibroseis deconvolution can particularly well be described and performed after correlation.
MICROGRAVIMETRY FOR ENGINEERING APPLICATIONS*
Authors: ARZI A. A. 
Published: April 2006

AbstractMicrogravimetric surveys for verifying bedrock soundness at the foundation of a nuclear power plant and for delineating a zone of small cavities and tracing grout emplacement at the foundation of a large cooling tower are described and used to illustrate an analysis of the method.It is pointed out that the difference between the usual large scale gravity surveys and microgravimetric surveys for engineering applications involves significantly more than a mere scaling down of grid spacings and precision tolerances. In addition to the smaller scale, the special physical environments for such microgravimetric surveys as well as strict timing and economy considerations and the demand for conclusive answers to specific questions require careful revisions of field procedures as well as data reduction and interpretation.Where properly applied, microgravimetric surveys—usually in conjunction with selective drilling—yield reliable subsurface information with a high resolution that is still limited by the gravimeter noise. Costly extensive drilling can thus be avoided. The method offers special advantages over other subsurface exploration methods in a wide variety of applications.
FLAT SPOT EXPLORATION*
Authors: Backus M. M. , Chen R. L. 
Published: April 2006

AbstractThe hydrocarbon‐brine contact produces a flat reflection, unconformable with the lithologic reflections from the trap boundaries, and over a limited area bounded by structural contours. When it can be reliably detected and mapped, the flat spot can provide (i) a reasonably unambiguous indication and areal extent of a reservoir and (ii) an estimate of reservoir thickness.The gas‐brine contact in thick reservoirs in offshore elastic sections is the easiest target. An example of gas mapping is presented in the paper. Other reservoirs represent a continuum of increasingly elusive targets.Increasing the range of applicability of flat spot exploration will require (i) increases in signal/noise and multiple ratio, increases in the three dimensional depth point density (or grid density), increased resolution and static and dynamic correction accuracy, and (ii) processing and interpretation aimed directly at flat spot mapping.Low relief structural and stratigraphic traps should provide the most attractive targets. The approach should be at least theoretically feasible, though not necessarily cost effective, for most major reservoirs with a well‐behaved hydrocarbon brine contact.
SIGN REVERSALS IN THE TRANSIENT METHOD OF ELECTRICAL PROSPECTING (ONE‐LOOP VERSION)*
Authors: LEE T. 
Published: April 2006

AbstractThe transient electromagnetic fields observed by the MPPO‐1 equipment in practice over geological structures cannot always be adequately explained by Maxwell's equation when the imaginary part of the conductivity of the rocks is neglected.If, for any reason, the conductivity of the rocks is a complex function of frequency such that the imaginary part is appreciable the model calculations must include this. This explains why some observed transient electromagnetic decay curves change sign with time.
CONTINUATION OF TOTAL INTENSITY ANOMALY ON AEROMAGNETIC PROFILES WITH CONSTANT ELEVATION CHANGE*
Authors: TSAY L. J. 
Published: April 2006

AbstractA new scheme for continuing aeromagnetic data along a profile with constantly changing elevation to a horizontal level is presented in this paper. It only requires some modifications of the conventional methods which are designed to continue potential field data from one horizontal level to another level.The new scheme procedes in the following steps: (1) digitization of anomaly along flight level, thus giving distance and elevation to the desired horizontal level at each station. (2) upward continuation at each digitized point from the corresponding elevation to a desired horizontal level. The validity and usefulness of the scheme is shown with theoretical and real data.
THE WAVE EQUATION APPLIED TO MIGRATION*
Authors: LOEWENTHAL D. , LU L. , ROBERSON R. , SHERWOOD J. 
Published: April 2006

AbstractClaerbout's method has been implemented for the migration of stacked seismic data. A simplified description of the method is given together with an account of some of the practical programming problems and the types of inaccuracy encountered. Routine production results are considered to be comparable or superior to the results derived from alternative migration techniques. Particular advantages are 1) the possibility of using a detailed velocity model for the migration and 2) the preservation of the amplitude and character of the seismic events on the migrated time section.
MAGNETOMETRIC AND ELECTROMETRIC METHODS FOR THE INVESTIGATION OF THE DYNAMICS OF LANDSLIDE PROCESSES*
Authors: BOGOSLOVSKY V. A. , OGILVY A. A. , STRAKHOVA N. A. 
Published: April 2006

AbstractGeophysical methods for the investigation of the dynamics of landslide processes are most effective in long‐term observations. Magnetometric and electrometric methods for observing the displacement of man‐made and natural markers are most sensitive and most highly developed at the present time.A detailed magnetic survey carried out near boreholes where magnets have been emplaced makes it possible to establish the direction and velocities of the displacement of landslide masses at different depths.Observations of the dislocation of the stable anomalies of the natural electric field allow us to elucidate the character of landslide deformations in the zone of capillary uplift of ground waters.
ANALYSIS OF THE GRAVITY EFFECT OF TWO‐DIMENSIONAL TRAPEZOIDAL PRISMS USING FOURIER TRANSFORM*
Authors: BHIMASANKARAM V. L. S. , MOHAN N. L. , RAO S. V. SESHAGIRI 
Published: April 2006

AbstractThe gravity effect of an infinite horizontal trapezoidal prism is derived and its Fourier spectrum is analyzed so as to yield information about four parameters of the causative structure, namely the depths to the upper and lower surfaces, width of the upper surface, and the inclination of the sides. In order to test the applicability of the method, synthetic data are constructed by digitizing the theoretical gravity effect. Subsequently, the corresponding Discrete Fourier Transform (DFT) is obtained. The parameters evaluated from the DFT are observed to be sufficiently close to the chosen values.
COMPUTERIZED ANALYSIS OF VIBROSEIS SIGNAL SIMILARITY*
Authors: RIETSCH E. 
Published: April 2006

AbstractComputerized evaluation of Vibroseis similarity test data is the logical consequence of the increasing quality requirements for signal reproducibility and for synchronization of vibrators. The differences in start time and phase as well as an indication of local phasing problems between any two Vibroseis signals can be obtained from an analysis of the difference of their respective phase spectra. This method appears to be accurate and stable with respect to harmonics which usually plague the signals from transducers monitoring the motion of the vibrators'base plates.
A MAN/COMPUTER INTERPRETATION SYSTEM FOR RESISTIVITY SOUNDINGS OVER A HORIZONTALLY STRAFIFIED EARTH*
Authors: JOHANSEN H. K. 
Published: April 2006

AbstractThe proposed system works as follows:

By a trial‐and‐error procedure using a graphic display terminal a geologically relevant layer sequence with parameters (ρj, dj) is adjusted to yield roughly the measured curve.
The resulting layer sequence is used as starting model for an iterative least squares procedure with singular value decomposition. Minimization of the sum of the squares of the logarithmic differences between measured and calculated values with respect to the logarithms of the resistivities and thicknesses as parameters linearizes the problem to a great extent, with two important implications:

a considerable increase in speed (the number of iterations goes down), thus making it cheap to achieve the optimum solution;
the confidence surfaces in parameter space are well approximated by the hyper‐ellipsoids defined by the eigenvalues and eigenvectors of the normal equations.

Since these are known from the singular value decomposition we do in fact know all possible solutions compatible with the measured curve and the geological concept.

It is possible to “freeze” any combination of parameters at predetermined values. Thus extra knowledge and/or hypotheses are easily incorporated and can be tested by rerunning step (2). The overall computing time for a practical case is of the order of 10 sec on a CDC 6400.