bluuebunny/crossref_metadata_2025_split huggingface dataset:
THE PROPAGATION OF ATTENUATED SH CHANNEL WAVES*
Authors: BUCHANAN D. J. 
Published: April 2006

AbstractThe problem of detecting discontinuities which interrupt coal seams is of great importance to the coal mining industry. One possible method of detecting such discontinuities is that of in‐seam seismology where both source and detectors are placed under‐ ground on the coal face. In this paper the propagation of SH waves from a line source in the seam is investigated. There exists a particular set of waves–channel waves–, confined to the coal seam. These waves are dispersive and have an associated Airy phase whose geometrical attenuation is least. However, if absorption of energy within the coal is included then the Airy phase is the dominant wavegroup only for distances less than a certain maximum. If a detection criterion proposed by Dresen and Freystätter applies, then there is a lower limit to the frequency that should be used for exploration. This requirement may be in conflict with attenuation considerations.
A NOTE ON CONVOLUTION AND PADDING FOR TWO‐DIMENSIONAL DATA*
Authors: GUPTA V. K. , RAMANI N. 
Published: April 2006

AbstractGupta, V. K., and Ramani, N., 1978, A Note on Convolution and Padding for Two‐Dimensional Data, Geophysical Prospecting 26, 214–217.Filtering of gridded data by means of two‐dimensional generalized convolution results in a loss of data along the edges of the map. This loss can be counteracted by ‘padding’– filling the surrounding of the input map with some kind of data. Padding by algebraic extrapolation is assumed to be better than surrounding the maps with zeroes. A Føsrtran IV routine for padding by algebraic extrapolation is available from the authors.
SUPERSTACK—AN ITERATIVE STACKING ALGORITHM*
Authors: NÆSS O. E. 
Published: April 2006

AbstractAn algorithm for separation of signals according to their coherency is proposed. The algorithm, called Superstack, is used on common depth point data after normal moveout corrections have been applied. The algorithm can be regarded as an iterative stacking procedure. After each stack, input values are changed depending on the consistency of the output of the previous stack.The Superstack algorithm is able to provide better separation of signals showing a different degree of horizontal consistency (coherency) than the normal horizontal stack.All noise signals in a CDP‐gather may be assumed to show less horizontal consistency than the primary reflections. On this basis the algorithm will give an improved primary/multiple and an improved primary/noise ratio.The Superstack is very general, should not be especially expensive in terms of computer time, and can easily be implemented in routine processing.
DETERMINATION OF RESISTIVITY SOUNDING FILTERS BY THE WIENER‐HOPF LEAST‐SQUARES METHOD*
Authors: KOEFOED O. , DIRKS F. J. H. 
Published: April 2006

AbstractIt has been found that the Wiener‐Hopf least‐squares method is a very successful tool for the determination of resistivity sounding filters. The values of the individual filter coefficients differ quite appreciably from those obtained by the Ghosh procedure. These differences in the filter coefficients, however, have only a negligible effect on the output of the filter. It seems that these differences in the coefficients correspond to a filter function of a rather narrow frequency band around the Nyquist frequency, which is only very weakly present in the input and output functions.
SEISMIC CLASSIFICATION OF ROCK MASS QUALITIES*
Authors: SJØGREN B. , ØFSTHUS A. , SANDBERG J. 
Published: April 2006

AbstractCorrelations between longitudinal velocities and rock mechanic parameters such as fracture frequencies and “Rock Quality Designation” (RQD) values have been studied, based upon velocity data from various rock types and different geographical locations.The dispersion of values at different sites studied is on average ± 0.8 cracks per meter and for the RQD values ± 3.5%. Within sites the dispersion of individual values relative to the average for the site is ± 1.0 – 2.0 cracks per meter and ± 2 – 6% for the RQD values.The deviations are rather moderate, especially when considering the variation of rock type involved in the studies: amphibolite, granite, gneiss, meta‐anorthosite, pegmatite, porphyry, quartzite, and mylonite. The studies thus confirmed earlier assumptions that there is a strong correlation between longitudinal velocity and fracturing and that the velocities can be used to give rather accurate predictions of the quality of rock masses for construction purposes. The accuracy of the predictions increases if the velocity level of the more competent rock is taken into account.The correlation between velocity and fracturing is related to jointed but unweathered igneous and metamorphic rock and cannot be applied without introducing serious errors to a site where the rocks present a higher degree of alteration and weathering.Comparisons between rock permeability and longitudinal velocity proved that a more reliable general correlation is not likely to be found.By comparing the elastic moduli Edyn, μ, and k with ø, Vp/V8, and k/μ, indications have been obtained where the optimum rock conditions for a certain site are to be encountered. This has been verified by a similar comparison where the elastic moduli have been replaced by fracturing values.The value of the longitudinal velocity as a means to evaluate rock quality increases if the position of the velocity in the range of the Poisson's ratio has been established.The average relationships between longitudinal velocities and the corresponding elastic moduli proved to be:The values from each site differ from the average values with about ± 2 GPa for Edyn and about ± 1 GPa for μ and k.It was confirmed that in igneous and metamorphic rocks longitudinal velocities ≤ 4000 m/s generally indicate rock masses where heavier tunnel support will be needed. This velocity limit corresponds to an average fracture frequency of about 10 cracks per meter and a RQD value of about 65 %. The prediction of the tunnel reinforcements needed at a particular site will, however, be improved if the general velocity level of the more competent rock is considered.
ADAPTIVE LONG‐PERIOD MULTIPLE ATTENUATION*
Authors: BRANDSÆTER H. , URSIN B. 
Published: April 2006

AbstractA least squares estimation procedure is used to estimate the pulse‐shape, amplitude function, and arrival time of multiple reflected signals. The estimates of the multiple reflections are subtracted from the data which are subsequently processed by standard methods. The estimation algorithm is applied continuously along the seismic line for each shot point or common datum point. In some cases it is advantageous to apply a pulse‐shaping filter prior to using the estimation algorithm.The effectiveness of the technique is demonstrated by studying common shot point gathers, velocity analyses, and stacked sections derived from field data.
CONSTRAINED INVERSION OF POTENTIAL FIELD DATA*
Authors: PEDERSEN L. B. 
Published: April 2006

AbstractFor constrained inversion of potential field data within the framework of generalized inversion an analysis of data error variances leads to confidence limits for the model parameters. For that purpose Pseudo‐hyper‐ellipsoids can be used to describe the nonlinear behaviour of the given inverse problem, and upper and lower bounds can be added to those parameters of which some independent knowledge is available. A gravity example is treated to show the application of the method.
AN EFFICIENT METHOD OF OPERATING THE AIR‐GUN*
Authors: SAFAR M.H. 
Published: April 2006

AbstractA new technique is developed for generating a short seismic pulse from the bubble pulses which are radiated by an air‐gun. The new technique, which is useful in well velocity surveys and vertical seismic profiling, can be implemented by firing a single air‐gun several times at the same depth but with different chamber pressures.A record obtained by this procedure from a well‐geophone clamped at a depth of 2450 m gave a maximum peak‐to‐peak amplitude within the first 100 ms of the effective seismic pulse at least ten times any later peak‐to‐peak amplitude.
FACTOR ANALYSIS FOR INTERPRETING PETROPHYSICAL DATA ON RORO ULTRAMAFICS, SINGHBHUM DISTRICT, INDIA*
Authors: RAO B. NARASIMHA , PAL P.C. 
Published: April 2006

AbstractThe physical properties of the serpentinized pyroxenitic and saxonitic rocks from stratiform ultramafic complexes of Roro, Singhbhum distrct, India, are examined using principal factor (R‐mode) analysis technique. The variations and inter‐relations of these properties reflect the compound effects of two processes—(a) degree of serpentinization, and (b) mineralogical and other changes attendant to serpentinization. Factor analysis is thus shown to be an effective tool for petrophysical inferences.
PARTIAL COHERENCE MATCHING OF SYNTHETIC SEISMOGRAMS WITH SEISMIC TRACES*
Authors: WHITE R.E. 
Published: April 2006

AbstractA crucial step in the use of synthetic seismograms is the estimation of the filtering needed to convert the synthetic reflection spike sequence into a clearly recognizable approximation of a given seismic trace. In the past the filtering has been effected by a single wavelet, usually found by trial and error, and evaluated by eye. Matching can be made more precise than this by using spectral estimation procedures to determine the contribution of primaries and other reflection components to the seismic trace. The wavelet or wavelets that give the least squares best fit to the trace can be found, the errors of fit estimated, and statistics developed for testing whether a valid match can be made.If the composition of the seismogram is assumed to be known (e.g. that it consists solely of primaries and internal multiples) the frequency response of the best fit wavelet is simply the ratio of the cross spectrum between the synthetic spike sequence and the seismic trace to the power spectrum of the synthetic spike sequence, and the statistics of the match are related to the ordinary coherence function. Usually the composition cannot be assumed to be known (e.g. multiples of unknown relative amplitude may be present), and the synthetic sequence has to be split into components that contribute in different ways to the seismic trace. The matching problem is then to determine what filters should be applied to these components, regarded as inputs to a multichannel filter, in order to best fit the seismic trace, regarded as a noisy output. Partial coherence analysis is intended for just this problem. It provides fundamental statistics for the match, and it cannot be properly applied without interpreting these statistics.A useful and concise statistic is the ratio of the power in the total filtered synthetic trace to the power in the errors of fit. This measures the overall goodness‐of‐fit of the least squares match. It corresponds to a coherent (signal) to incoherent (noise) power ratio. Two limits can be set on it: an upper one equal to the signal‐to‐noise ratio estimated from the seismic data themselves, and a lower one defined from the distribution of the goodness‐of‐fit ratios yielded by matching with random noise of the same bandwidth and duration as the seismic trace segment. A match can be considered completely successful if its goodness‐of‐fit reaches the upper limit; it is rejected if the goodness‐of‐fit falls below the lower one.
ESTIMATION OF THE SIGNAL‐TO‐NOISE RATIO OF SEISMIC DATA WITH AN APPLICATION TO STACKING*
Authors: RIETSCH E. 
Published: April 2006

AbstractThe amplitude of the signal and the energy of the noise on each of at least three traces can be estimated provided that the signal has the same form (but not necessarily the same amplitude) on these traces and that the noise on any trace is correlated with neither the signal nor the noise on any other trace. This estimation of signal amplitude and noise energy can be achieved by a rather simple algorithm. The accuracy of the estimate depends, of course, on the degree to which the assumption that signal and noise on the different traces are mutually uncorrelated is actually met. The accuracy tends to improve with increasing number of traces.
VERTICAL SEISMIC PROFILES: THEIR APPLICATIONS IN EXPLORATION GEOPHYSICS*
Authors: KENNETT P. , IRESON R.L. , CONN P.J. 
Published: April 2006

AbstractDuring the past four or five years, Vertical Seismic Profiles have been run in a large number of wells and in a variety of geological provinces with the object of assisting the seismic data processor and improving the geological interpretation.The special properties of the Vertical Seismic Profile, which allows the separation of the upward and downward travelling components of the recorded waveform, provides a means of studying the acoustic response of the earth in detail. Deconvolution of the data in particular gives a clearer understanding of the mechanics of multiple reflections and the way in which they may obscure primary reflections in the vicinity of the well.The primary reflection response of the earth can be observed with greater resolution than conventional seismic data permits, making correlation with lithology more precise, and allowing a good estimate of the reflection coefficient series to be determined. Inversion of the seismic traces to produce an acoustic impedance log leads to better definition of the sedimentary sequence and is of particular interest in predicting lithologic variations ahead of the drilling bit.In addition, Vertical Seismic Profile data can be used to assess parameters in areas such as deconvolution and signal band width for the evaluation of conventional seismic data.
THE LAW OF PARALLELISM IN REFRACTION SHOOTING*
Authors: SJÖGREN B. 
Published: April 2006

AbstractThe half‐intercept‐time for in‐line reversed profiles is highly adaptable to multi‐layer cases, but the deep evidence of the intercept time on the depths and the velocities at the shotpoint and detector position poses a problem. The law of parallelism provides a reliable and simple means to solve this problem. The interpretation procedure implies that from a travel‐time curve the refractor segment is projected back to the shotpoint parallel to a refractor curve from an offset shot. The intercept time thus obtained refers only to the geological conditions in the immediate vicinity of the shotpoint, and varying conditions outside this region are automatically climinated. The assumptions involved in the interpretation technique are confined to the region where, in relation to the shotpoint, the rays leave and strike the refractor surface.The use of the “ABC method” to establish true intercept times at the shotpoint is also discussed briefly as well as the applicability of the method to eliminate or minimize arrival time disturbances in order to improve velocity determinations.
GRAVITY INTERPRETATION USING THE HANKEL TRANSFORM*
Authors: PATELLA D. 
Published: April 2006

AbstractThe Hankel transform theorem can be applied to the inversion of gravity data for the buried sphere, the horizontal cylinder, and the vertical rod. This new approach leads to exact solutions of the transforms for the assumed bodies. A comparison with the classical procedure by Fourier transform reveals that for the sphere and the vertical rod, the Hankel transform is preferable.
MODEL STUDIES ON SOME ASPECTS OF RESISTIVITY AND MEMBRANE POLARIZATION BEHAVIOUR OVER A LAYERED EARTH*
Authors: ROY K.K. , ELLIOTT H.M. 
Published: April 2006

AbstractElectrolytic model tank experiments to study resistivity and time domain induced polarization (IP) response over layered earth models were initiated primarily to facilitate the understanding of field results. Alternate layers of clay and sand (or clay‐coated sand) with, in some cases, a surficial layer of water were assembled in the tank and resistivity and IP measurements made for a range of electrode spacings using the Wenner configuration. Graphite and silver‐silver chloride electrodes were used as current and potential electrodes respectively.Clay‐coated (3% by weight) sand was found to generate stronger polarization than either clay or sand alone. Apparent chargeability ma was observed to be positive for a nonpolarizable surface layer. For a polarizable surface layer, the sign of IP was controlled by the polarizability, the thickness of the second layer, and the spacing of the electrode spreads. The apparent chargeability ma can theoretically change sign from positive to negative and vice versa with a gradual increase in electrode spacing, and such negative IP effects were obtained in a few observations. A simultaneous decrease in IP and an increase in resistivity, which is a qualitative diagnostic feature for the occurrence of clean freshwater sand aquifers, could also be generated in the model tank experiment.Combined resistivity and IP soundings were carried out near Fredericton Junction and Tracy, New Brunswick, Canada. Field curves are presented along with the model curves for qualitative comparison and understanding of IP behaviour over a layered earth. Twenty‐five out of twenty‐seven soundings show only positive apparent chargeabilities, whereas two show chargeability sign changes (positive/negative/positive). The model study gives reason to believe that surface soils and Quaternary gravel boulder deposits near Fredericton Junction are relatively non‐polarizable.As an auxiliary experiment, sand and clay were taken in different proportions by weight and mixed thoroughly with water in a cement mixer. The mixtures were then compressed with a suitable die and plunger under 3.6 Pa pressure to prepare cylindrical samples of height 18 cm and diameter 15.5 cm. IP measurements were done on the flat faces using the Wenner configuration with a= 2 cm. Chargeability was found to be negative for 100 and 90% clay mixtures. It reached a positive maximum for an 80% clay‐20% sand mixture and then decreased gradually with increasing sand and decreasing clay content.
RESISTIVITY PROFILING WITH DIFFERENT ELECTRODE ARRAYS OVER A GRAPHITE DEPOSIT*
Authors: BRASS G. , FLATHE H. , SCHULZ R. 
Published: April 2006

AbstractMotivated by several papers by Indian colleagues suggesting that a single‐pole array is the most favorable one for locating electrically conductive targets in the underground, detailed measurements were carried out with different electrode arrays over a well‐known graphite deposit near Pfaffenreuth, Germany. The following arrays were used: (1) Wenner array; (2) single‐pole array; (3) half‐Wenner array; (4) half‐Schlumberger array. Each of the arrays established the location of the main graphite deposit. The half‐Schlumberger array turned out to be the most reliable one since it showed details which were only very poorly indicated by the other arrays or not at all.Mathematical modeling of three‐dimensional bodies simulating the geological situation for this deposit were carried out. These results show an unexpectedly good correlation with the measured effects.
FOCUSSED ELECTRICAL RESISTIVITY ARRAYS: SOME THEORETICAL AND PRACTICAL EXPERIMENTS*
Authors: JACKSON P.D. 
Published: April 2006

AbstractThe “Laterolog 7′’and the “Microlaterolog’ have been studied theoretically for the case of a conducting halfspace containing a single overburden, using a technique based on the method of images. The results have shown these focussed arrays to be more sensitive to the lower medium (i.e., having greater depth of investigation) than unfocussed ones of the same dimensions, when the “correct’ geometric factor is used. The geometric factor of a focussed electrode array is somewhat involved, and is explained with reference to an ideal focussed array; such an array would pass a measuring current of constant intensity into a fixed geometrical shape of conducting material, irrespective of any layering or any other heterogenities that may be present, using auxiliary current sources of variable magnitude. This concept of a constant amount of current flowing in a beam of fixed geometry and current density, is the basis of focussed arrays, and it is shown that the geometric factor, used to calculate the apparent resistivity, is the one derived when considering the homogeneous case. The value of the constant measuring current, alone, is used to convert the measured potential difference into a resistance, the ratio between this value and the combined intensities of the auxiliary current sources, for the homogeneous case, being incorporated into the geometric factor.Surprisingly good agreement was found between the theoretical models and practical experiments using a focussing seabed resistivity probe which is a substantial modification of the “Microlaterolog”. Both show similar deviations from the ideal case which are explained in terms of refraction at the overburden interface. All experiments indicated that focussed arrays have a greater depth of investigation than similar unfocussed ones for a single overburden, whether it be resistive or conductive.
QUASI‐ANALYTIC CONVOLUTION SOLUTION OF THE ELECTROMAGNETIC FIELD*
Authors: ERCAN A. 
Published: April 2006

AbstractThe objective of this study is to generate the separation‐distance‐domain (r‐domain) transformation of the theoretically calculated wave number domain (m‐domain) electromagnetic induction field component Bz(m, ω) of a stratified medium and to search for interpretive information which has been absent in the previously achieved numerical solutions of the problem.The r‐domain kernel R̃(r, ω) function defining the induction field appears to adequately reflect the layering and electrical properties of the medium if it is expressed as a function of the frequency if the source‐receiver separation r is small with respect to the thickness of the first layer. However, exact values of the conductivity cannot be distinguished from those of the neighboring values unless a resistive basement layer is present. This feature is the result of the truncation in series representation of the kernel function R̃(m, ω). However, this truncation is regarded as significant in the case of a conductive first layer. In m‐domain static‐zone studies, a conductive first layer slightly influences its r‐domain correspondent.Although the computational cost of obtaining the kernel B(r, ω) by evaluation of the convolution in a cylindrical coordinate system is high, this semi‐analytic solution is still superior to those based on the asymptotic assumptions.
THE OFFSET SYSTEM OF ELECTRICAL RESISTIVITY SOUNDING AND ITS USE WITH A MULTICORE CABLE*†
Authors: BARKER R.D. 
Published: April 2006

AbstractOne of the most troublesome problems in resistivity sounding is caused by the spurious effects of near‐surface lateral resistivity variations. It has been found that the effects can be strongly reduced by measuring earth resistances at two electrode array positions such that in one position the lateral effect is a positive contribution to the total measured signal and in the other the contribution is negative. The subsequent combination of the two measurements virtually eliminates the lateral effect.The same technique can also result in a significant reduction in the total number of necessary electrode positions. Consequently the method can be used with a multicore cable system. In this way, in addition to improving the accuracy of the measured results, time and manpower are considerably reduced.Details of the method, examples and comparisons with traditional sounding techniques are given.