bluuebunny/crossref_metadata_2025_split huggingface dataset:
A STUDY OF ABYSSAL FRACTURES IN THE UKRAINIAN SHIELD BY GEOPHYSICAL METHODS*
Authors: TYAPKIN K.F. 
Published: April 2006

AbstractAccording to data presented by YU.A. Kosigin, 84% of all endogenous mineral deposits are in some direct or indirect relation with the fractures of the earth's crust. Therefore the discovery and the study of the spatial disposition of the fractures is the most important object for geophysicists. Abyssal fractures are of particular interest.By geophysical methods one can find the geometrical parameters of abyssal fractures such as their extent, the depth of formation, the breadth of the zones, and the amplitude of the relative displacement of separated blocks.The methods determining these parameters are widely known. A calculation of the difference in the levels of the erosion cuts of the blocks are of particular interest under shield conditions. A method to calculate this difference by gravity interpretation of “step” anomalies and by using the gradient model of the earth's crust is proposed.A comparision of the results of gravimetry and magnetometry with those of deep seismic soundings shows that the fractures of the first and the second order in the Ukrainian shield cut the earth's crust and part of the upper mantle so they can be qualified as abyssal fractures.In the Ukrainian shield the spatial regularities of the fractures determined by geophysical methods can be used for the prognosis of the ore deposits.
THE QUANTITATIVE INTERPRETATION OF DIPOLE SOUNDINGS BY MEANS OF THE RESISTIVITY TRANSFORM FUNCTION*
Authors: PATELLA D. 
Published: April 2006

AbstractIn this paper a theorem is demonstrated which allows—after the introduction of a suitable dipole kernel function or dipole resistivity transform function—to write the apparent resistivity function as an Hankel transformable integral expression.As a practical application of the theorem a procedure of quantitative interpretation of dipole soundings is suggested in which the dipole resistivity transform function obtained after inversion of the original dipole apparent resistivity data is used to control the goodness of the set of layering parameters which have been derived with our previous method of transformation of dipole sounding curves into equivalent Schlumberger diagrams.
THE INTERPRETATION OF THE VERTICAL FAULT PROBLEM IN GEOELECTRICS USING HANKEL INTEGRAL*
Authors: PATELLA D. 
Published: April 2006

AbstractIt is shown how to interpret, without curve‐matching, Schlumberger resistivity soundings carried out with the array parallel to the surface trace of a vertical boundary plane separating two media with different resistivities (the vertical fault problem). To this end, it is demonstrated that the apparent resistivity function can be expressed as an Hankel‐transformable integral that allows to invert the apparent resistivity curve into an associated resistivity transform curve. The study of the asymptotical properties of this function and of some mathematical properties of a related reduced transform function allows to realize a simple procedure for deriving the parameters of the model. In practice, this procedure consists in fitting a straight‐line to a semi‐logarithmic plot of the reduced transform function and in evaluating the intercept along the vertical axis and the slope.
REDUCTION OF HARMONIC DISTORTION IN VIBRATORY SOURCE RECORDS*
Authors: RIETSCH E. 
Published: April 2006

AbstractDue to non‐linear effects, the swept frequency signals (sweeps) transmitted into the subsurface by vibrators are contaminated by harmonics. Upon correlation of the recorded seismograms, these harmonics lead to noise trains which are particularly disturbing in the case of down‐sweeps. The method described in this paper—which can be regarded as a generalization of Sorkin's approach to the suppression of even order harmonics—allows elimination, from the final vibratory source seismogram, of harmonics of the sweep up to any desired order. It requires that not one single signal but rather a series of M signals is employed where each signal has an initial phase differing from that of the previous one of the series by the phase angle 2πM. Prior to stacking, the seismograms generated with the different signals have to be brought into the form they would have if they had been generated with the same signal.The method seems also to be capable of reducing the correlation noise if sign‐bit recording techniques are used.
ZERO MEMORY NON‐LINEAR DECONVOLUTION*
Authors: GODFREY R. , ROCCA F. 
Published: April 2006

AbstractA type of iterative deconvolution that extracts the source waveform and reflectivity from a seismogram through the use of zero memory, non‐linear estimators of reflection coefficient amplitnde is developed. Here, we present a theory for iterative deconvolution that is based upon the specification of a stochastic model describing reflectivity. The resulting parametric algorithm deconvolves the seismogram by forcing a filtered version of the seismogram to resemble an estimated reflection coefficient sequence. This latter time series is itself obtained from the filtered seismogram, and so a degree of iteration is required. Algorithms utilizing zero memory non‐linearities (ZNLs) converge to a family of processes, which we call Bussgang, of which any colored Gaussian process and any independent process are members. The direction of convergence is controlled by the choice of ZNL used in the algorithm. Synthetic and real data show that, generally, five to ten iterations are required for acceptable deconvolutions.
THE AMPLITUDE AND PHASE RESPONSE OF A SEISMIC VIBRATOR*
Authors: Lerwill W.E. 
Published: April 2006

AbstractThe amplitude and phase response of a simple model is compared with the performance of a real vibrator working in the field. The field results show a characteristic phase response which confirms that the real drive force applied to the baseplate and its load impedance is faithfully represented by the acceleration of the reaction mass. It follows that all the parameters necessary to calculate the load impedance and the true power dissipated in the earth can be measured at the output of the vibrator. It also follows that the current method of baseplate phase compensation should be reconsidered.
SYSTEMATIC CLASSIFICATION OF LAYER‐INDUCED TRANSVERSE ISOTROPY*
Authors: HELBIG K. 
Published: April 2006

AbstractWaves propagating through a sequence of layers that are thin compared with the wavelength show effects of anisotropy: velocity and displacement direction depend on the angle between the plane of layering and the wave normal, and shear waves split up into two distinct types of different velocity. The layered medium can thus be replaced by a transversely isotrophic medium the parameters of which depend on the parameters of the individual constituent layers.A survey of the anisotropy effects possible in such a medium is generally done by varying the layer parameters in order to obtain different replacement media. This approach guarantees that the replacement medium is realistic, but it does not guarantee adequate sampling of the set of replacement media. To this end one has to begin by selecting the replacement media and then check whether the chosen media possess stable (and eventually realistic) representations by layer sequences. In general, there is an infinite number of layer representations for any transversely isotropic medium that can at all be represented. However, if one restricts the solutions to those requiring the minimal number of layers and the minimum number of different layer parameters, the set of solutions has only one free parameter (i.e., it is a one‐dimensional manifold), and an important subset even has a unique solution. A simple algorithm exists for the determination of these “simplest representations”.Aside from sampling the set of representable transversely isotropic media for survey purposes, the method can be applied to the problem of determining the cause of observed anisotropy effects (or lateral changes in such effects). If this method can be applied to real data, it would for instance allow to determine changes in relative thickness or lithology on a scale smaller than the limit of resolution of the seismic method.
DETERMINATION OF THE NATURE OF RESERVOIRS BY USE OF PATTERN RECOGNITION ALGORITHM WITH PRIOR LEARNING*
Authors: BOIS P. 
Published: April 2006

AbstractThe determination of the nature of reservoirs containing hydrocarbons is approached via a pattern‐recognition method with prior learning. This method consists of comparing the nature of a reservoir that has been drilled into with an unknown reservoir. The known reservoir plays the part of a monitor for the learning process. To this end an algorithm is compiled using the Burg method of the features represented by different portions of traces contained in the reservoirs. An analysis of the dots representing these different features serves as a criterion for deciding whether the two reservoirs have identical or different natures.
SOIL CONSOLIDATION BEHAVIOR ASSESSED BY SEISMIC VELOCITY MEASUREMENTS*
Authors: HAMDI FALAH A.I. , SMITH D. TAYLOR 
Published: April 2006

AbstractLarge gravity platforms are often used as alternatives to the more conventional pilesupported structures in hydrocarbon exploitation. A gravity structure, as opposed to the piled structure, is sitting on the sea floor by virtue of its weight and base width; as such it poses considerable problems for the site investigation engineer. One such problem is the calculation of the settlement of the structure and its time history; these depend upon the permeability and compressibility of the soil and its drainage conditions. The required data are usually obtained by sampling for subsequent laboratory testing. The collection of an undisturbed sample is beset by problems so that the consolidation behavior of the foundation material can only be inadequately assessed by laboratory testing. However, a series of laboratory consolidation experiments during which seismic velocities have been measured on the sample as consolidation proceeds shows that it is possible to reconstruct the stress‐strain and time‐dependent curves from the seismic data, once the initial void ratio and permeability of the soil are known. This leads the way to an in situ technique for predicting settlement using a combination of geophysical techniques (electrical resistivity and seismic velocities) to obtain the required engineering properties.
ASPECTS OF VERTICAL SEISMIC RESOLUTION*
Authors: KOEFOED O. 
Published: April 2006

AbstractIt is proposed that the vertical resolving power of a seismic signal is controlled by three aspects: the width of the central lobe, the side lobe ratio, and the side‐tail oscillations. A comparative study of zero‐phase signals covering the same frequency range shows that improvement of any one of these aspects inevitably leads to deterioration of one of the other aspects.An analytical simulation model is proposed of zero‐phase signals free from side‐tail oscillations, in which both the width of the central lobe and the side lobe ratio are adjustable. Analysis of the spectra of this model shows that, while the high frequency content of the spectrum is essential for obtaining a small width of the central lobe, the low frequency content of the spectrum plays an essential part in causing a low value of the side lobe ratio.
A NOTE ON THE USE OF A NOMOGRAM FOR SELF‐POTENTIAL ANOMALIES*
Authors: BHATTACHARYA B.B. , ROY N. 
Published: April 2006

AbstractA nomogram has been devised for situations, in which the source of a self‐potential anomaly can be approximated by an obliquely polarized sphere or horizontal cylinder embedded in a homogeneous half space. The nomogram can be used for rapid determination of three parameters of the target: (1) depth to the centre, (2) angle between the axis of polarization and the horizontal, (3) shift of the point vertically above the centre of the body from zero potential value.The nomogram has been tested and the parameters determined for SP results obtained over ore bodies Weiss and Süleymanköy in the Ergani Copper district, Turkey. The curves computed for the estimated parameters match the field curves well.
A STRATIGRAPHIC CASE HISTORY USING THREE‐DIMENSIONAL SEISMIC DATA IN THE GULF OF THAILAND *
Authors: BROWN A. R. , DAHM C.G. , GRAEBNER R.J. 
Published: April 2006

AbstractA three‐dimensional marine seismic survey was conducted in the Gulf of Thailand to aid in the development of a gas field indicated by three wildcat wells. The results and interpretation reported previously demonstrated improved fault resolution and better structural definition.Five successful appraisal wells have now been drilled, and these show that most of the sands have limited extent. Widespread character changes in the seismic data also support stratigraphic variations in many of the sands.Several new methods of 3D stratigraphic interpretation have been developed while investigating the depositional history of this area. Anomalous seismic amplitudes, tied to sands penetrated by wells and mapped from SeiscropTM horizontal sections in time and depth, have indicated the distribution of bars and channels. Horizon Seiscrop sections, each sliced through a single bed, have been used to delineate these depositional features directly. G‐LOGTM sections, displaying seismic logs derived by rigorous wave equation inversion, confirm the existence of these features. Sands greater than 10 m thick have proved mappable.
A SIMPLE DERIVATION OF SEIGEL'S TIME DOMAIN INDUCED POLARIZATION FORMULA *
Authors: Roy A. , Poddar M. 
Published: April 2006

AbstractIt is advantageous to postulate the phenomenological equivalence of chargeability with a slight increase in resistivities rather than a similar reduction in the conductivities. Substitution of these increments in the expression for the total differential of apparent resistivity leads directly to Seigel's formula. Included also are (i) an equally simple demonstration that, for a homogeneously chargeable ground with arbitrary resistivity distribution, the apparent chargeability ma, equals the true homogeneous value m, and (ii) a direct derivation of the completely general resistivity relation
image

where the symbols have the usual meanings.
DIRECT INTERPRETATION OF RESISTIVITY DATA OVER TWO‐DIMENSIONAL STRUCTURES*
Authors: LEE T. 
Published: April 2006

AbstractA direct interpretation scheme is developed which is capable of determining most of the geological features of a ground which can be assumed to be two dimensional in structure. This scheme extends the earlier work of Pekeris (1940) and Koefoed (1968) to the case where the basal layer of a ground is undulating. It also has a limited use for finding the parameters of a dipping dyke in the lower medium. Though the top and dip of the dyke can be determined, this is not true for the thickness.
MIGRATION OF SEISMIC INTERFACES*
Authors: SATTLEGGER J. 
Published: April 2006

AbstractMost interpretation work is still based on stacked and not on migrated sections. In the case of heavy faulting and considerable velocity contrasts between formations, migration of interpreted interfaces poses a problem. In more detail, the problem may be specified as follows:— a given interpretation of a number of interfaces along with a given heterogeneous velocity field may not always have a plausible solution in the form of migrated interfaces in depth;— fault planes, salt boundaries, etc., are, in most cases, not directly interpretable in a section and are plotted by intuition using interface terminations as a guide;— the velocity field in fault zones is, in most cases, hard to determine.The interpreter may arrive at a plausible solution by repeating the migration process with various possible interpretations and various velocity assumptions.The subject of this paper is an algorithm based on ray‐theory which allows one:— to handle faults and velocity variations at faults properly;— to perform migration in steps, working a particular geological unit at a time and proceeding to the next unit once the foregoing one has been properly migrated;— to display ray‐paths, where necessary, for investigation of interface distortions, e.g., below fault areas.The algorithm is designed and implemented for application in an interactive environment. Inspection of intermediate and final results, investigation of interface distortions and modifications are performed on a graphics screen. Thus, various possible interpretations and velocity assumptions may be investigated within a short time.Interfaces interpreted on migrated sections may be over‐migrated because of neglection of the influence of refraction in most section migration programs. This over‐migration may also be corrected using the above algorithm in the “image ray” mode.
A FREQUENCY DOMAIN MAPPING APPROXIMATION OF MOVEOUT FILTERS WITH APPLICATIONS*
Authors: ÖZDEM˙IR H. 
Published: April 2006

AbstractWavenumber aliasing is the main limitation of conventional optimum least‐squares linear moveout filters: it prevents adequate reject domain weighting for efficient coherent noise rejection. A general frequency domain multichannel filter design technique based on a one‐to‐one mapping method between two‐dimensional (2D) space and one‐dimensional (1D) space is presented. The 2D desired response is mapped to the 1D frequency axis after a suitable sorting of the coefficients. A min‐max or Tchebycheff approximation to the desired response is obtained in the 1D frequency domain and mapped back to the 2D frequency domain. The algorithm is suitable for multiband 2D filter design. No aliasing damage is inherent in the linear moveout filters designed using this technique because the approximation is done in the frequency‐wavenumber (f, k)‐domain.Linear moveout filters designed by using the present coefficient mapping technique achieve better pass domain approximations than the corresponding conventional least‐squares filters. Compatible reject domain approximations can be obtained from suitable mappings of the origin coefficient of the desired (f k)‐response to the 1D frequency axis. The (fk)‐responses of linear moveout filters designed by using the new technique show equi‐ripple behavior. Synthetic and real data applications show that the present technique is superior to the optimum least‐squares filters and straight stacking in recovering and enhancing the signal events with relatively high residual statics. Their outputs also show higher resolution than those of the optimum least‐squares filters.
IN‐SITU INVESTIGATION OF SEISMIC BODY WAVE ATTENUATION IN HETEROGENEOUS MEDIA*
Authors: NEWMAN P. J. , WORTHINGTON M. H. 
Published: April 2006

AbstractField experiments have been carried out to study the nature and magnitude of seismic wave attenuation for a variety of lithologies. In each survey two three‐component sets of geophones with wall clamping mechanisms were lowered down boreholes and signals originating from surface compressional and shear‐wave sources were recorded. The data collected were corrected for spherical divergence and analyzed to determine intrinsic attenuation. For situations of anomalous wavefront expansion and in cases where multiple reflection losses may be significant, corrections were supplied by a synthetic seismogram programme to improve the estimates of intrinsic attenuation.Values of attenuation were obtained for pure sandstone, sandstone‐marl sequences and fissured‐unfissured chalk sequences. These formations were all near surface and relatively porous. Significant differences in the relative values of compressional and shear‐wave attenuation in the various lithologies were noted. In particular compressional absorption in the fissured zones of chalk was twice the absorption associated with the seismic velocities and the absorption of shear waves fluctuated much less. A large contrast in P‐wave attenuation was also observed between pure Bunter Sandstone and the sandstone‐marl sequence (absorption was over three times as small in the former). A smaller contrast was noted for shear attenuation.The results obtained suggest that, for the relatively homogeneous formations such as pure sandstone and “unfissured” chalk, “shear” absorption was dominant over “bulk” absorption. In contrast bulk absorption was larger than shear absorption for other formations, e.g. the “fissured” chalk sequences and a “partially saturated” chalk section. Attenuation was found to be approximately proportional to frequency in all experiments.
THE POTENTIAL OF SHEAR‐WAVE OBSERVATIONS*
Authors: HELBIG K. , MESDAG C. S. 
Published: April 2006

AbstractShear waves can today be generated and observed, though not with the flexibility and the technical standard of compressional waves, and they can be identified in seismograms by various means. Their potential lies not so much in their lower velocity (corresponding—for the same frequency—to shorter wavelength and higher resolution) but in the fact that they probe the earth with stresses and strains that differ from those of compressional waves. Full utilization of the information potential of shear waves, therefore, requires combined use of P‐and S‐waves.Complications in the combined use of different wave types should be regarded as opportunities to obtain additional information. A typical example is the observation that the depth of one and the same interface estimated on the bases of P‐ and SH‐reflections, respectively, can differ significantly. This discrepancy may be due to the anisotropy of a finely layered medium. Under favorable circumstances some of the parameters describing this anisotropy can be deduced from the different depth estimates and the curvature of the squared‐offset/squared‐time representation of the different reflections. Since in anisotropic media vertically polarized shear waves are significantly different from horizontally polarized ones, the combined observation of all three waves opens up additional possibilities.
UPSWEEP SIGNALS WITH HIGH‐FREQUENCY ATTENUATION AND THEIR USE IN THE CONSTRUCTION OF VIBROSEIS® SYNTHETIC SEISMOGRAMS*
Authors: GURBUZ B. M. 
Published: April 2006

AbstractAn analytical relationship for the autocorrelation function of an upsweep with high‐frequency attenuation is used in the construction of synthetic seismograms.Field experiments were conducted in two areas to investigate the attenuation of upsweep where the near‐surface materials were different. The results showed that the attenuation of high frequencies occurs at the source point depending on the near‐surface lithology.The attenuation effect is usually neglected in the construction of the input wavelet of synthetic seismograms for Vibroseis data. In this study, the high‐frequency attenuation of upsweep was considered in the construction of the input wavelet for the synthetic seismogram in an area where the Vibroseis technique was used. The synthetic seismogram generated in this manner had a better correlation with the Vibroseis section than that of corresponding synthetics using minimum‐phase and the unattenuated autocorrelation wavelet of the upsweep.
A LINEAR MODEL FOR VELOCITY ANOMALIES*
Authors: LOINGER E. 
Published: April 2006

AbstractVariations of seismic interval velocities within the cable length cause anomalies in the stacking velocity analyses. Utilizing the approximation of rectilinear ray propagation, i.e. supposing that the velocity changes cause time delays only, it is shown that the stacking velocity anomalies are linearly related to the interval velocity variations. In particular, the stacking velocity anomaly is calculated when the interval velocity of an intermediate layer undergoes a stepwise variation. The amplitude of the anomaly increases with the ratio between horizon depth and cable length.From the forward model, a program for the inversion is derived in order to identify lateral changes of interval velocities from unsmoothed stacking velocity analyses.Some examples of the application of this technique to synthetic and real data are presented.