bluuebunny/crossref_metadata_2025_split huggingface dataset:
GEOELECTRIC MODELS IN ENGINEERING GEOPHYSICS*
Authors: OGILVY A.A. , BOGOSLOVSKY V.A. , KUZMINA E.N. 
Published: April 2006

AbstractMan's engineering activities are concentrated on the uppermost part of the earth's crust which is called engineering‐geologic zone. This zone is characterized by a significant spatialtemporal variation of the physical properties status of rocks, and saturating waters. This variation determines the specificity of geophysical and, particularly, geoelectrical investigations.Planning of geoelectric investigations in the engineering‐geologic zone and their subsequent interpretation requires a priori) geologic‐geophysical information on the main peculiarities of the engineering‐geologic and hydrogeologic conditions in the region under investigation. This information serves as a basis for the creation of an initial geoelectric model of the section. Following field investigations the model is used in interpretation. Formalization of this a priori) model can be achieved by the solution of direct geoelectric problems. An additional geologic‐geophysical information realized in the model of the medium allows to diminish the effect of the “principle of equivalence” by introducing flexible limitations in the section's parameters. Further geophysical observations as well as the correlations between geophysical and engineering‐geologic parameters of the section permit the following step in the specification of the geolectric model and its approximation to the real medium. Next correction of this model is made upon accumulation of additional information. The solution of inverse problems with the utilization of computer programs permits specification of the model in the general iterational cycle of interpretation.
ELECTRICAL SOUNDING OF A HALF‐SPACE WITH A MONOTONIC CONTINUOUS VARIATION OF THE RESISTIVITY WITH DEPTH*
Authors: SATO H.K. , SAMPAIO E.S. 
Published: April 2006

AbstractThe interpretation of electrical sounding data for a subsurface with monotonic continuous variation of the resistivity with depth is becoming increasingly necessary. The contribution of this article is the derivation of the solution for the Wenner and the Schlumberger apparent resistivity functions for a resistivity varying as a real power of a linear positive function of the depth. The interpretation of sounding data in these cases can be used to estimate the variation of the porosity or the salt content of the pore water with depth.
ARMA PROCESSING OF ULTRASONIC DATA FOR ABSORPTION MEASUREMENTS
Authors: GUTOWSKI P.R. , FRISILLO A. L. 
Published: April 2006

AbstractLaboratory studies of absorption‐frequency behavior in rocks often use spectral ratios of digitally recorded ultrasonic signals which have been transmitted through a rock sample and a reference sample of very low absorption, respectively. It is proposed to treat the digitally recorded signals as an autoregressive‐moving average (ARMA) process which, using recursive filter concepts, can be represented as a ratio of two polynomials in the z‐transform variable z. The numerator polynomial contains only that part of the signal that is modified by anelastic effects, whereas the denominator contains the elastic effects of the physical apparatus such as reverberations. Examples are given which show that this separation of the recorded signal greatly facilitates the laboratory investigation of loss mechanisms and absorption‐frequency behavior based on spectral ratios.
EXPLORATION OF BURUNDI NICKELIFEROUS LATERITES BY ELECTRICAL METHODS*
Authors: PERIC M. 
Published: April 2006

AbstractThe laterites in Burundi, which are formed by weathering of ultrabasic rocks, show a complete profile with the following horizons: canga, the ferruginous crust capping, ferralite, consisting essentially of iron hydroxides, and saprolite, which contains a large quantity of hydrosilicate minerals. Nickel bearing minerals occur in the saprolite and the lower portion of ferralite.Resistivity well‐logging and resistivity sounding indicated that the electrical properties of rocks depend upon their composition: Canga and ferralite showed high resistivities of 6,500 Ωm and 800 Ωm, respectively. The resistivity of saprolite was found to be much lower, between 10 Ωm and 20 Ωm. The laterite is underlain by resistive peridotite. The chargeability of saprolite was found to be lower than that of the upper horizons and the bedrock.Electrolytic conductivity of laterite, which depends on the geometry of the deposit, was found to be low, because the laterite contains moisture and ground water, which are highly resistive. The relatively high conductivity of saprolite is caused by nickeliferous hydrosilicates, which exhibit the electrical properties of clay minerals, with an apparent maximum conductivity of 0.25 S/m. The conductivity of saprolite corresponds to a concentration between 30% and 50% of conductive silicate minerals distributed in the pore space of deposit. A nickel enrichment of up to 6% was estimated from the resistivity of the saprolite.Prospecting for laterites by electrical sounding showed that the development of laterite horizons in a nickel deposit correlates with the surface morphology of weathered ultrabasic massif. Thus the method can be used in preliminary exploration of such deposits.
RELATIONS OF IP DECAY‐CURVE STATISTICS AND GEOLOGY*
Authors: VOGELSANG D. 
Published: April 2006

AbstractSix thousand three hundred IP measurements made in central and southern Germany have been statistically evaluated. Shapes of IP decay curves obtained in the course of routine prospecting for sulfides were characterized in the following way: three chargeabilities were recorded during the 2 s current‐off time. By dividing the last by the first chargeability an “IP decay coefficient’ was calculated and statistically evaluated by means of histograms. When the histograms were compared with the statistics of apparent resistivity and chargeability, no relationship could be detected. Therefore, the histograms of M3/M1 values represent a characteristic property of distinct areas with certain geological features, mineral assemblage and tectonics. Weathering does not alter this geophysical “fingerprint”, which depends solely on geology.
SHOVER * SHEAR‐WAVE GENERATION BY VIBRATION ORTHOGONAL TO THE POLARIZATION **
Authors: EDELMANN H.A.K. 
Published: April 2006

AbstractThe radiation distribution of a single vibrator can be described using the formulas given by Miller and Pursey. From these the displacement characteristic for the radial component and also for horizontal component can be derived. This horizontal component is strengthened by adding another vibrator with opposite polarity near the first one. When this horizontal component is oriented perpendicular to the X‐Z plane (plane spanned by the direction of the spread and the vertical axes), an SH‐wave can be generated. Survey results indicate that this method works efficiently.
CONTOUR MAP PRESENTATION OF DIPOLE‐DIPOLE INDUCED POLARIZATION DATA*
Authors: FRASER D.C. 
Published: April 2006

AbstractDipole‐dipole induced polarization (IP) data are displayed typically as multi‐level profiles, or as contours on vertical sectional plots referred to as pseudo‐sections. The dipole‐dipole array tends to yield IP anomalies in which the most anomalous values are displaced laterally from the source body. The data patterns are fairly interpretable on pseudo‐sections or on multi‐level profiles but are sufficiently complex to discourage the contouring of the data in plan.A method was developed for the presentation of dipole‐dipole IP data on a contour map. The method consists of a simple averaging of data which can be performed manually if desired. It yields a single output value per station which reflects all levels of the pseudo‐section, and is suitable for contouring in plan. The advantage of the technique is that it provides a quantitative picture of IP anomalies in their background or regional setting.
NON‐LINEAR ESTIMATION OF REFLECTION COEFFICIENTS FROM SEISMIC DATA*
Authors: BILGERI D. , CARLINI A. 
Published: April 2006

AbstractFor years, reflection coefficients have been the main aim of traditional deconvolution methods for their significant informational content.A method to estimate seismic reflection coefficients has been derived by searching for their amplitude and their time positions without any other limitating assumption. The input data have to satisfy certain quality constraints like amplitude and almost zero phase noise—ghosts, reverberations, long period multiples, and diffracted waves should be rejected by traditional processing. The proposed algorithm minimizes a functional of the difference between the spectra of trace and reflectivity in the frequency domain. The estimation of reflection coefficients together with the consistent “wavelet’ is reached iteratively with a multidimensional Newton‐Raphson technique. The residual error trace shows the behavior of the process. Several advantages are then obtainable from these reflection coefficients, like conversion to interval velocities with an optimum calibration either to the well logs or to the velocity analysis curves. The procedure can be applied for detailed stratigraphic interpretations or to improve the resolution of a conventional velocity analysis.
OPTIMUM HYPERBOLIC MOVEOUT FILTERS WITH APPLICATIONS TO SEISMIC DATA*
Authors: ÖZDEMIR H. 
Published: April 2006

AbstractOptimum multichannel filters can be designed to process seismic events falling on hyperbolic moveout curves using the conventional least‐squares method. Contrary to the linear moveout filters, autocorrelation and crosscorrelation functions inherent in the normal equations have to be computed numerically. However, computation times of filter coefficients are comparable to linear moveout operators.For a given source‐receiver geometry and assuming straight ray‐path, relative moveout of a seismic reflection event is dependent on the two way arrival time and rms velocity. Consequently, to avoid overlapping of pass and reject moveout windows, hyperbolic moveout filters have to be designed over time gates rather than for the whole record lengths. Hyperbolic and hyperbolic‐linear moveout filters applied to synthetic and field seismic reflection traces show good signal‐to‐noise (S/N) ratio improvements. Results of some combined synthetic and field data examples are presented.
LOW‐FREQUENCY STANDARD HYDROPHONE * FOR CALIBRATING LINE HYDROPHONE ARRAYS (SEISMIC STREAMERS) AND MARINE SEISMIC SOURCES **
Authors: SAFAR M.H. , NEWMAN P. 
Published: April 2006

AbstractThe design of a standard hydrophone with a maximally flat (Butterworth) response in the frequency range 8.0 Hz‐1.0 kHz is described. The standard hydrophone has been developed primarily for calibrating line hydrophone arrays (seismic streamers) and marine seismic sources.The standard hydrophone has been used successfully during the past eight years for monitoring the output of a single air gun. It can be used for the calibration of a marine seismic streamer.
TECHNIQUE DE MESURE ET D'INTERPRETATION MINIMISANT LES ERREURS DE MESURES EN MICROGRAVIMETRIE*
Authors: BICHARA M. , ERLING J.C. , LAKSHMANAN J. 
Published: April 2006

ResumeLes différentes sources d'erreurs de la mesure gravimétrique sont examinées. Leur connaissance a une importance particulière dans les prospections de surface, dites “microgravimétriques”.Les auteurs démontrent, expériences à l'appui, que toutes précautions prises, la source la plus fréquente d'erreurs de mesure en microgravimétrie est une mauvaise estimation de la dérive.Les auteurs exposent alors un processus de mesure et d'interprétation dont le but est une meilleure estimation de la dérive. La justification théorique et expérimentale du processus est donnée. La méthode implique une prise de mesure suivant une répartition spatiale aléatoire ou semi‐aléatoire. Un cas réel est décrit.
COMPUTATION OF THE ELECTRIC POTENTIAL IN THREE‐DIMENSIONAL STRUCTURES*
Authors: SCRIBA H. 
Published: April 2006

AbstractA method has been developed for computation of the electrical DC potential of an arbitrary three‐dimensional resistivity structure using a finite difference method. The threedimensionality is necessary for interpretation of geoelectrical soundings with controlled point sources over a laterally inhomogeneous medium. Lateral inhomogeneities should be considered in resistivity soundings with large layouts. The results obtained with the described method permit a more realistic representation of geological features.The resolution of the method is determined by the number of elements in the resistivity network. The problem of core memory space has been resolved by using random access disc files. The results computed using a Fortran program are in good agreement with analytically obtained solutions.
ELECTROMAGNETIC FIELD OF SOURCES AT THE SURFACE OF A HOMOGENEOUS CONDUCTING HALFSPACE WITH HORIZONTAL ANISOTROPY: APPLICATION TO FISSURED MEDIA*
Authors: LE MASNE D. , VASSEUR G. 
Published: April 2006

AbstractThe electric and magnetic fields generated by horizontal electric and vertical magnetic dipoles lying on the surface of a conducting medium with horizontal anisotropy are investigated. Full expressions of their Fourier transforms are given, and the fields for a vertical magnetic dipole are calculated numerically. The radial and vertical magnetic components are found to be independent of the receiver‐transmitter direction, whereas the other magnetic and electric components strongly vary with this direction. These results give useful criteria for defining the direction and amplitude of anisotropy from ground data; a ground experiment on fissured limestone was found to confirm the expected variations of the various field components. It is believed that this electromagnetic method can be used in order to provide information about the direction and amplitude of electric anisotropy.
FILTER DESIGN FOR SUPPRESSION OF SURFACE MULTIPLES IN A NON‐NORMAL INCIDENCE SEISMOGRAM*
Authors: AMINZADEH F. , MENDEL J. M. 
Published: April 2006

AbstractIn this paper we design a non‐linear filter to suppress surface multiples in a non‐normal incidence plane wave seismogram of a horizontally‐layered elastic (or acoustic) earth model. Our filter is optimal in a least‐squares sense and is very efficient in suppressing surface multiples, especially for small incidence angles. The design is based on an extension of earlier work by Mendel on normal incidence Bremmer series decomposition to the case of non‐normal incidence, and relies heavily on work by Aminzadeh on a non‐normal incidence state space model.
CURVED RAYPATH INTERPRETATION OF SEISMIC REFRACTION DATA*
Authors: GREENHALGH S.A. , KING D.W. 
Published: April 2006

AbstractVertical velocity gradients can be readily accommodated in seismic refraction interpretations by using simple mathematical idealizations of curved raypaths entailed by certain analytic representations of these gradients. Computation procedures are formulated for velocity gradients in the overburden or an intermediate layer of a multilayer section. The former is demonstrated for an overburden velocity gradient manifest in published time‐distance data.
ON THE GENERATION OF P AND S WAVE ENERGY IN CRYSTALLINE ROCKS*
Authors: WRIGHT C. , JOHNSON P. 
Published: April 2006

AbstractA seismic source consisting of a 700 kg weight that could be dropped vertically or projected down a ramp inclined at 45° to the vertical was tested as a source of P, SV and SH waves within a crystalline rock body at Chalk River, Ontario. The seismic energy was recorded by arrays of both horizontal and vertical‐component geophones at distances between 30 and 600 m from the source, which was operated over glacial overburden varying in thickness from less than a meter to a few tens of meters. Seismic energy was more efficiently generated when the overburden thickness was at least several meters. The signals identified visually as S are generally true S, though some may be the converted wave PS. The SV amplitudes are generally larger than those of P, regardless of the type of shot, while the signal frequencies are roughly 60 Hz and 90 Hz, respectively. The horizontal‐component seismograms for the inclined shots showed no evidence of SH polarization, and the SH amplitudes were only rarely enhanced relative to P and SV amplitudes on changing from vertical to inclined shots. These unexpected results are attributed to the combined effect of the high velocity and density contrasts and the irregularity of the boundary between the glacial overburden and the rock body.
INTERPRETATION OF PULSE EM ANOMALIES OVER GANI CONDUCTORS, KURNOOL, INDIA*
Authors: PODDAR M. 
Published: April 2006

AbstractA survey using Crone pulse electromagnetic (PEM) equipment was conducted near the village of Gani in Andhra Pradesh, India. The anomalies obtained had a shape typical for an inclined sheet conductor. From the multichannel TEM response, the multifrequency Slingram response was calculated.A comparison of the Slingram response of the Gani conductors with the free‐air model response of a thin sheet conductor shows phase rotation and attenuation of the anomaly vector, thereby confirming the presence of a conductive overburden. Interpretation of the Gani results using free‐air phasor diagrams causes an overestimation of depth and conductance of the target conductor unless data obtained at a sufficiently low frequency are used for the interpretation. For areas like Gani this frequency can be as high as 336 Hz.
A SIMPLE FORM OF PRESENTATION OF MAGNETOTELLURIC DATA USING THE BOSTICK TRANSFORM*
Authors: GOLDBERG S. , ROTSTEIN Y. 
Published: April 2006

AbstractA new presentation for magnetotelluric data is proposed to be used together with the traditional representation. It is easily computed by applying the Bostick transform to all field data points. The result is an approximate depth‐resistivity diagram which contains an indication of the data quality as well as the homogeneity of the subsurface. This resistivity section should be used in the interpretation of surveys in which accuracy is either not of prime concern or cannot be achieved. Since this mode of presentation is easily understood it can be used to familiarize earth scientists with the use of the MT method in exploration.
PHASE UNWRAPPING, POSSIBILITIES AND LIMITATIONS*
Authors: POGGIAGLIOLMI E. , BERKHOUT A. J. , BOONE M. M. 
Published: April 2006

AbstractAn unwrapped phase curve from the principal values of the phase can be computed in a simple way. The validity of the unwrapping procedure is tested by exploiting the phase information in the signal's first moment. The significance of the unwrapped answer around notches in the amplitude spectrum is seriously degraded by noise.The proposed method and the validity test are illustrated with examples.
DIP‐MOVEOUT AND REFLECTOR POINT DISPERSAL*
Authors: DEREGOWSKI S. M. 
Published: April 2006

AbstractApplication of dip‐moveout attempts to correct pre‐stack data in such a way that they stack correctly, however far the reflector geometry departs from an ideal plane horizontal interface. Even for plane dipping reflectors under a constant velocity overburden a common mid‐point gather contains reflections distributed over a finite segment of the reflector. It is shown that under these conditions application of dip‐moveout moves dipping energy on common offset gathers in such a manner that common mid‐point gathers become true common depth point gathers.
AN APPROACH TO THE IDENTIFICATION OF FINE SEDIMENTS BY INDUCED POLARIZATION LABORATORY MEASUREMENTS*
Authors: ILICETO V. , SANTARATO G. , VERONESE S. 
Published: April 2006

AbstractTime‐domain‐induced polarization (IP) laboratory measurements were performed on about 200 fine sediment samples with varying water content. The results permitted an analysis of IP properties of clays, loams, silts, and sands.Particular emphasis has been given to the analysis of the chargeability m as a function of lithotype and the water content.By analyzing decay curves, a new parameter was identified. It is a statistically specific characteristic of the lithotype and is independent of the water content. Therefore, it provides a diagnostic parameter for lithotype identification. In association with the values of chargeability and electrical resistivity, this parameter permits a reliable evaluation of water content and yields useful information about the porosity and permeability of the lithotype.
SUBSURFACE GRAVITY MEASUREMENTS AND DENSITY MAPPING IN THE MAILARAM COPPER MINES, ANDHRA PRADESH, INDIA*
Authors: MURTY B. V. SATYANARAYANA , GHYASUDDIN M. , REDDY P. VENKAT 
Published: April 2006

AbstractGravity measurements were made in the Mailaram copper mines, Andhra Pradesh. The observations were distributed between the two shafts situated about 220 m apart and in the three levels up to a maximum depth of 100 m. Assuming a normal free‐air gradient, average densities for the three layers were determined as 2.631, 2.604, and 2.823 g cm‐3, respectively. Upon incorporating the weighted mean density values from measurements on samples, the free‐air gradients were found to be 0.315 mGal m‐1 for the second layer (i.e. between the first and second levels) and 0.2978 mGal m‐1 for the third layer (i.e. between the second and third levels). The density variation map obtained from the gravity data, the deduced anomalies, the weighted mean density values from measurements on rock samples, and the varying free‐air coefficients all suggest correspondence with the concentration of ore lodes.
A METHOD FOR THE DETERMINATION OF THE THERMAL CONDUCTIVITY OF SANDSTONES USING A VARIABLE STATE APPROACH*
Authors: STRACK K. M. , IBRAHIM A. W. , KELLER G. V. , STOYER C. H. 
Published: April 2006

AbstractCommon problems encountered during the determination of the thermal conductivities of tight sandstones are rock specimen‐to‐heat source contact and complicated sample preparation. An experimental technique using an electromagnetic heat source solves the direct contact problem between the heat source and the sample. Also, it simplifies the sample preparation and reduces the measurement time.A CO2 laser operating in a pulsed mode is used as a heat source with about 500 W output power. Thus, heat losses due to radiation and air convection are negligible. Unpolished penny‐sized samples of tight sandstones are irradiated on one side and the temperature is measured on the opposite side. The temperature is recorded with 12‐bit accuracy by a digital data acquisition system. Carbon black is used to give the samples a uniform absorption.The transient temperature data are acquired, processed, and interpreted with interactive computer programs. Transients for each sample can be stacked, to improve the signal‐to‐noise ratio, and normalized. The thermal conductivity is calculated from the rise portion of the transient using a ridge‐regression type generalized linear inversion scheme.As many as 20 samples per hour can be measured with this simple but expensive set‐up. In the long run, this means a reduction of laboratory expenses. In addition, the resolution of this method is superior to other variable‐state measurement methods due to the real time controlled data acquisition and the numerical interpretation.
NON‐NORMAL INCIDENCE STATE‐SPACE MODEL AND LINE SOURCE REFLECTION SYNTHETIC SEISMOGRAM*
Authors: AMINZADEH F. , MENDEL J. M. 
Published: April 2006

AbstractThis paper is directed at modeling layered media. We extend the plane‐wave normal‐incidence state‐space model developed by Mendel, Nahi and Chan in 1979, to the non‐normal incidence case. To do this we introduce a shifting principle, a zero‐offset wavefront, and zero‐offset travel times for different layers. We also develop an algorithm for obtaining a synthetic line source reflection seismogram. In this algorithm non‐normal incidence plane‐wave seismograms are summed over a range of incident angles. The algorithm is based on a modified version of Sommerfield's (1896) theorem. Simulations of acoustic and elastic media are included which illustrate the applicability of our plane‐wave and line source seismograms for both elastic and acoustic cases.