bluuebunny/crossref_metadata_2025 huggingface dataset:
ON THE MINIMIZATION OF THE DISTORTION CAUSED BY THE GEOPHONE‐GROUND COUPLING *
Authors: SAFAR M. H.
Published: April 2006

Abstract

It is well known that the application of the “bright spot’ technique has been more successful in marine prospecting than in land prospecting. This is due partly to the problem of distortion of the seismic signal caused by the geophone‐ground coupling, especially when carrying out high resolution, shallow seismic surveys in swampy terrain.

The effect of geophone‐ground coupling on the response of a single geophone to the incident compressional waves has been treated by several authors. However, they have always neglected the influence of mutual interaction between an array of geophones on the response of each geophone forming the array. We show that mutual interaction, which results from the re‐radiation of the incident compressional waves by the geophones forming the array, can have considerable effect on the response of each geophone.

The effect of the geophone‐ground coupling on the response of a seismic channel is considered in the absence and presence of mutual interaction between a group of geophones for the case when the shear wave velocity of the soil varies by a factor of three.
DEPTH ESTIMATION FROM RESIDUAL BOUGUER ANOMALIES: A PROCEDURE BASED ON THE BACKUS‐GILBERT MINIMUM DISTANCE CRITERION *
Authors: CHANDER R.
Published: April 2006

Abstract

The minimum distance criterion of Backus and Gilbert is used to determine the depths of line masses approximating the subsurface two dimensional distribution of density differences responsible for the observed residual Bouguer anomaly values. The quantity minimized is the sum of the squared differences between the starting trial depths and the desired final depths of line masses. The search for the desired depths is limited to preset depth ranges.
TRANSFORMATION OF DIPOLE SOUNDINGS OBTAINED ALONG A CROOKED LINE *
Authors: THOMAS L. , KOELLE A.
Published: April 2006

Abstract

Data collected in a dipole‐dipole sounding along a crooked line can be transformed to form an approximately equivalent Schlumberger sounding, using a simple matrix inversion technique. The equivalent curve can be interpreted using rapid interpretation methods.
A BLIND ZONE SOLUTION TO THE PROBLEM OF HIDDEN LAYERS WITHIN A SEQUENCE OF HORIZONTAL OR DIPPING REFRACTORS *
Authors: MERRICK N. P. , ODINS J. A. , GREENHALGH S. A.
Published: April 2006

Abstract

In seismic refraction surveys, in particular those using first arrival recording techniques, the hidden layer problem occurs where energy from a refractor of higher velocity arrives at the surface before energy from an overlying refractor. The maximum thickness of the hidden layer is referred to as the blind zone.

Hypothetically, every recorded refractor has an associated blind zone which may or may not contain a hidden layer. For an assumed earth model of plane constant‐velocity layers and stepwise increase of velocity with depth, the effect of a blind zone on an interpreted depth section may be evaluated by defining an intercept time for a blind zone of assumed or known velocity and by using standard time‐term equations for layer thicknesses and depths.

The treatment covers an arbitrary number of blind zones embedded within a multilayer sequence of horizontal or dipping refractors. Model calculations affirm the benefits of this approach compared with previous methods which, in general, have been restricted to the case of two horizontal layers with one intermediate blind zone.
THE USE OF FILTERED BESSEL FUNCTIONS IN DIRECT INTERPRETATION OF GEOELECTRICAL SOUNDINGS *
Authors: BERNABINI M. , CARDARELLI E.
Published: April 2006

Abstract

We start from the Hankel transform of Stefanescu's integral written in the convolutionintegral form suggested by Ghosh (1971). In this way it is possible to obtain the kernel function by the linear electric filter theory. Ghosh worked out the sets of filter coefficients in frequency domain and showed the very low content of high frequencies of apparent resistivity curves.

Vertical soundings in the field measure a series of apparent resistivity values at a constant increment Δx of the logarithm of electrode spacing. Without loss of information we obtain the filter coefficient series by digital convolution of the Bessel function of exponential argument with sine function of the appropriate argument. With a series of forty‐one values we obtain the kernel functions from the resistivity curves to an accuracy of better than 0.5%. With the digital method it is possible to calculate easily the filter coefficients for any electrode arrangement and any cut‐off frequency.
SEISMIC SIGNAL DETECTION AND PARAMETER ESTIMATION*
Authors: URSIN B.
Published: April 2006

Abstract

In the mathematical theory of seismic signal detection and parameter estimation given, the seismic measurements are assumed to consist of a sum of signals corrupted by additive Gaussian white noise uncorrelated to the signals. Each signal is assumed to consist of a signal pulse multiplied by a space‐dependent amplitude function and with a space‐dependent arrival time. The signal pulse, amplitude, and arrival time are estimated by the method of maximum likelihood.

For this signal‐and‐noise model, the maximum likelihood method is equivalent to the method of least squares which will be shown to correspond to using the signal energy as coherency measure. The semblance coefficient is equal to the signal energy divided by the measurement energy. For this signal model we get a more general form of the semblance coefficient which reduces to the usual expression in the case of a constant signal amplitude function.

The signal pulse, amplitude, and arrival time can be estimated by a simple iterative algorithm. The effectiveness of the algorithm on seismic field data is demonstrated.
ON WIENER FILTER AND MAXIMUM ENTROPY METHOD FOR MULTICHANNEL COMPLEX SYSTEMS*
Authors: NEGI J. G. , DIMRI V. P.
Published: April 2006

Abstract

The Wiener filtering scheme is obtained for a multichannel complex system utilizing the “block‐Toeplitz” property of autocorrelation matrix. A numerical example is given to elucidate the application of the filter design. The study also outlines Burg's maximum entropy method to include the multi‐channel complex realm.
SEISMIC DISCRIMINANTS OF STRATIGRAPHY DERIVED FROM MONTE CARLO SIMULATION OF SEDIMENTARY FORMATIONS*
Authors: KHATTRI K. , SINVHAL A. , AWASTHI A. K.
Published: April 2006

Abstract

The impulse response of models of subsurface formations are statistically analyzed for abstracting seismic parameters which could be characteristic of the stratigraphy and lithology of the formations. Two types of formations have been considered, consisting either of sand‐shale sequences or of coal‐shale sequences. Models of the formations are generated using the Monte Carlo method. It is found that three features in the power spectrum of the impulse response, namely the frequency fe at which the spectrum can be divided into a zone of high energy from a zone of low energy, the lowest frequency fp where there is a significant energy peak, and the frequency fm at which there is a maximum energy, can be used statistically to distinguish between the formations consisting of sand‐shale sequences and the formations made up of coal‐shale sequences. Three additional parameters A2/A1, A2/A0, and A1/A0, where A denotes the autocorrelation function of the impulse response and the subscripts denote the lags, are also statistically significant discriminators between the sand‐shale formations and the coal‐shale formations. The discrimination between the two subgroups of each model consisting of more (or less) than fifty percent of one lithology is also feasible, although there are fewer discriminants available.
GEOLOGICAL INFORMATION FROM FLUCTUATING EARTH‐CURRENTS*
Authors: HOOGERVORST G. H. T. C.
Published: April 2006

Abstract

Investigation of fluctuating earth‐currents has led to a simple method of eliminating the noise superimposed on the signal in geoelectrical resistivity surveys. The similarity of the potential fluctuations, simultaneously measured at different locations, is used to calculate the direction and magnitude of the potential gradient. Contour maps of equipotential lines were made, both from disjointed gradient measurements using a numerical approximation method and from a network of measured potential differences. These contour maps were compared with potential fields calculated for simple homogeneous models. A good fit was obtained with the field of a conducting plate. When this is subtracted from the measured field, the result is a map that shows anomalies that can be correlated with geological structures.
MIGRATION IN TERMS OF SPATIAL DECONVOLUTION*
Authors: BERKHOUT A. J. , PALTHE D. W. VAN WULFFTEN
Published: April 2006

Abstract

The relationship between two finite‐difference schemes (15° and 40°) and the Kirchhoff summation approach is discussed by using closed form solutions of Claerbout's approximate versions of the wave equation. Forward extrapolation is presented as a spatial convolution procedure for each frequency component. It is shown that downward extrapolation can be considered as a wavelet deconvolution procedure, the spatial wavelet being given by the wave theory. Using this concept, a three‐dimensional model for seismic data is proposed.

The advantages of downward extrapolation in the space‐frequency domain are discussed.

Finally, it is derived that spatial sampling imposes an upper limit on the aperture and a lower limit on the extrapolation step.
IN SITU SEISMIC MEASUREMENTS OF CRACK ANISOTROPY IN THE CARBONIFEROUS LIMESTONE OF NORTHWEST ENGLAND*
Authors: BAMFORD D. , NUNN K. R.
Published: April 2006

Abstract

Seismic velocity anisotropy is predicted for cracked rocks containing either a naturally‐occurring or an artificially‐induced preferred orientation of cracks. Methods developed for the study of velocity anisotropy in the uppermost mantle have been applied to the in situ measurement of P‐wave velocity anisotropy in fractured Carboniferous Limestone in Northwest England. At three different sites, first‐arrival travel‐time data has been obtained using conventional refraction equipment and a weight‐drop source. Velocity anisotropy of 15–29% is identified with directions of maximum and minimum velocities that can be broadly related to previously mapped orientations of joints.
BICUBIC SPLINE INTERPOLATION: A QUANTITATIVE TEST OF ACCURACY AND EFFICIENCY*
Authors: RASMUSSEN K. L. , SHARMA P. V.
Published: April 2006

Abstract

Two different methods for the construction of an approximation to bicubic splines for interpolating irregularly spaced two‐dimensional data are described. These are referred to as the least squares line (LSL) and linear segment (LINSEG) construction procedures.

A quantitative test is devised for investigating the absolute accuracy and efficiency of the two spline interpolation procedures. The test involves (i) laying of artificial flight lines on the analytically known field of a model, (ii) interpolation of field values along the flight lines and their subtraction from the original field values to compute the residuals. This test is applied on fields due to four models (three prism models and one dyke model) placed at different depths below the flight lines, and for each case the error estimates (the mean error, the maximum error and the standard deviation) are tabulated.

An analysis of the error estimates shows in all cases the LSL interpolation to be more accurate than the LINSEG, although the latter is about 50% faster in computer time. The relative accuracy and efficiency of the LSL interpolation is also tested against a recent method based on harmonization procedure, which shows the latter to be more precise, though much slower in speed.
TOWARDS UNIFICATION OF GEOPHYSICAL PROBLEMS FOR HORIZONTALLY STRATIFIED MEDIA*
Authors: SZARANIEC E.
Published: April 2006

Abstract

Theorems and relations describing a system of horizontal layers are considered as the elements of a meta‐system having a layered structure. This implies a layered structure of a solution of geophysical problems for horizontally stratified medium.

Wave equation, Laplace's equation, and Maxwell's equations are the special cases of a more general differential equation. By separation of variables the basic equation for layered structures is obtained.

A multi‐layer medium may result from accumulation of successive layers. The descending or ascending accumulation is possible, depending whether the successive layers are inserted at the top or at the bottom of the medium. The discretization of a basic equation provides two sets of formulas for descending or ascending accumulation, respectively.

The relationship between the mathematical expressions of the seismic transfer function and the magnetotelluric input impedance is derived. The deduction leads to the possibility of converting the magnetotelluric observations into an equivalent synthetic seismogram.
DEFINITION AND APPLICATION OF THE FREQUENCY ‐EFFECT TRANSFORM FUNCTION TO THE INTERPRETATION OF IP SOUNDINGS*
Authors: PATELLA D.
Published: April 2006

Abstract

This paper deals with a new method of quantitative interpretation of induced polarization soundings in the frequency‐domain. From the general expression of the apparent frequency‐effect for soundings carried out on a multi‐layered earth the application of Hankel's inversion theorem allows to introduce a new function, called here the “frequency‐effect transform”. The new interpretation method consists of two steps: 1) the inversion of field data to obtain the frequency‐effect transform graph and 2) the analysis of this graph to derive the layering parameters. The first step is performed by means of a slightly revised version of a simple numerical procedure, previously suggested by the author for the inversion of d.c. resistivity sounding data. The second step is carried out by a complete curve‐matching procedure, applied directly on the transform graph. This implies suitable master curves, whose preparation doesn't meet all the mathematical difficulties which are present when preparing master curves of the apparent frequency‐effect function.
THE POSSIBILITIES OF GEOPHYSICAL METHODS APPLIED FOR INVESTIGATING THE IMPACT OF MAN ON THE GEOLOGICAL MEDIUM*
Authors: Ogilvy A. A. , Bogoslovsky V. A.
Published: April 2006

Abstract

Geophysical methods can be applied to investigate the harmful effect of man's activities on the environment: the study of specific electrical resistivities and natural electric fields of filtrational origin makes it possible to control the penetration of exogenic pollutants into soil as well as desalinization and secondary salinization of soils; electrometric and seismometric methods allow to observe the groundwater level near water reservoirs thus evaluating the harmful effect of backing up natural groundwater flow; contrasting properties of bedrocks and rocks in a landslide body permit application of seismic and electrical prospecting methods. Observation of the changes in specific electrical resistivities with time on the slopes of quarries is an effective method of assessing slope stability and predicting landslide hazard.

Mining activities, groundwater pumping, and oil extraction are the main causes of endogenic pollution of geological medium; surface and borehole geophysical methods make it possible to assess vertical and horizontal displacements of the interfaces between salty and fresh subterranean waters resulting from an extensive exploitation of water supply sources; activation of geodynamic processes associated with mining activities is determined from the data of ‘regime’ electrometric, seismometric, gravimetric, and inclinometric observations. Geophysical methods are applied widely for studying the intensification of physico‐geological processes under the impact of man. A specific object of electrometric investigations is degradation of permafrost and intensification of karst processes in soluble rocks.

The principal advantage of geophysical investigations lies in the possibility of creating high spatial and temporal density of observations permitting an extensive employment of statistical methods in the assessment of the impact of man on the geological medium.
PROSPECTING FOR SUBSURFACE WATER IN THE CENTRAL VOLCANIC HIGHLAND OF ARMENIA BY GEOPHYSICAL METHODS*
Authors: MINASIAN R. S.
Published: April 2006

Abstract

Work carried out in several volcanic areas in Armenia has led to a combination of geophysical methods for hydrogeological problems. Prospecting of interlava and sublava water flows is done by electrical profiling and vertical electrical sounding. When mapping the relief of sublava water‐resisting rocks, the electrical sounding (ES) method is widely used. This is based on the evaluation of lava resistivity. The method discussed allows to determine the most probable value of this parameter, by using statistical methods.
MODEL TANK EXPERIMENTS ON RESOLUTION OF RESISTIVITY ANOMALIES OBTAINED OVER BURIED CONDUCTING DYKES — INLINE AND BROADSIDE PROFILING*
Authors: APPARAO A.
Published: April 2006

Abstract

Model tank inline resistivity profiles with Wenner and two‐electrode systems obtained over two vertical, parallel, infinitely conducting dykes submerged in water show that the two‐electrode resistivity anomalies resolve better than the four‐electrodes Wenner. anomalies. In contrast, the broadside resistivity anomalies obtained with a Wenner configuration resolve much better than those obtained with two‐electrode configuration over an identical ground structure.
PROCESSING AND APPLICATIONS IN MICROGRAVITY SURVEYS*
Authors: BLÍžKOVSKÝ M.
Published: April 2006

Abstract

An economic and precise processing system for microgravity surveys is presented. Three computer processing modes covering areal ground and underground measurements, measurements in vertical shafts, and measurements of vertical gravity gradients with a 3 m high tower are dealt with.

Diagrams for manual calculation of gravity effects of prismatic walls, vertical shafts, and horizontal galleries, as well as programs for calculation of accurate terrain corrections and corrections for gravity effects of bodies with complicated ground‐plan are proposed.

The method of processing microgravity data is two to three times quicker than any traditional way, with maximum accuracy preserved in resulting gravity micro‐anomalies. Applications from the field of mining geophysics and archaeology are included.
THE CORRELATION REFRACTION METHOD AS APPLIED TO WEATHERED ZONE STUDIES IN A GRANITE TERRAIN*
Authors: RAO NAIK S. BANDU , KUMAR G. NANDA , RAGHAVA M.S. VIJAYA
Published: April 2006

Abstract

The combined observation of first and later arrivals in shallow seismic refraction surveys, particularly on hard rock terrains, is discussed. Details of experimental weathered‐zone investigations by the correlation refraction method in a granite terrain (i.e. field procedure, seismograms obtained, plotting of the data, and identification of the waves are presented). Complete travel time data and interpreted subsurface sections of a few test refraction surveys are included. In one instance the interpreted results of normal and converted refracted wave data have been tested by drilling at three points along a 220 m long profile.
GENERALIZED KUNETZ‐TYPE EQUATIONS*
Authors: MENDEL J. M.
Published: April 2006

Abstract

A Kunetz equation is often used as the starting point in the development of solutions for the inversion of one‐dimensional, noise free, normal incident seismograms, for which |ro|= 1. In this paper we demonstrate a need for a Kunetz‐type equation in which filtered signals can be used, so that noise effects can be reduced. We then show that an infinite number of Kunetz‐type equations exist for the lossless wave equation in layered media. Finally, we show that it is indeed valid to formulate and solve the inverse problem using filtered signals.
INTERACTION EFFECTS IN MARINE SEISMIC SOURCE ARRAYS*
Authors: SINCLAIR J.E. , BHATTACHARYA G.
Published: April 2006

Abstract

Past design of marine source arrays has been based on one or more of the following principles:

simultaneous operation of multiple identical sources to increase radiated signal strength by simple addition;

superposition of wavelets of different fundamental frequency to achieve a total pulse of desired, front‐loaded form (e.g. mixed volume air‐gun arrays);

horizontal spacing of units or groups to achieve spatial filtering effects.

The phenomenon of interaction between sources, affecting the loading experienced by each, has usually been ignored, or else avoided by wide spacing of units. However, interactions can significantly affect the efficiency and frequency response, in a way that can be favourable.

Calculations are presented for sources emitting continuous or long duration signals, showing the energy efficiency as a function of frequency for arrays in a variety of configurations. Interaction effects are significant for inter‐source spacings smaller than or comparable with the wavelength—not, as is often stated, up to a distance related to the radii of the sources. The results show that potential exists for tailoring the frequency response of a source system, according to the application, by simple spatial rearrangement of units.

Similar effects occur with interacting impulsive sources, but it is shown that different criteria apply for the optimum arrangements of units.
MIGRATION IN THE PRESENCE OF NOISE*
Authors: BERKHOUT A.J. , VAN WULFFTEN PALTHE D.W.
Published: April 2006

Abstract

It is shown that the so‐called Kirchhoff‐summation operator is of a very wide‐band nature and even contains an evanescent part. As a consequence, discretization may cause serious aliasing errors, particularly for small extrapolation steps. It is proposed to use in all practical cases band‐limited versions of the summation operator, the spatial cut‐off frequency being determined by the spatial Fourier spectrum of the coherent noise.
ON THE RESPONSE OF MARINE SEISMIC STREAMER SYSTEMS*
Authors: SAFAR M.H. , HOSKEN J.W.J.
Published: April 2006

Abstract

The response of transformer‐coupled and transformerless marine seismic streamers feeding seismic amplifiers with and without input transformer is analysed with the aid of equivalent circuits. Examples are calculated showing how improvements in the performance of two practical transformer‐coupled streamers, namely the increase in bandwidth and sensitivity and the decrease in the dependence on cable length, can be achieved when some of the streamers parameters are properly chosen.

Transformerless streamer systems driving either a voltage amplifier or a “charge” amplifier are shown to be inherently superior to those with coupling transformers, save possibly in respect of their sensitivity to cross‐feed.
INVERSION OF SURFACE AND BOREHOLE ELECTROMAGNETIC DATA FOR TWO‐DIMENSIONAL ELECTRICAL CONDUCTIVITY MODELS*
Authors: ORISTAGLIO M.L. , WORTHINGTON M.H.
Published: April 2006

Abstract

A method for inverting electromagnetic fields induced by a line source in an earth of two‐dimensional conductivity structure is developed. Certain unique features of the finite element method are used to construct an efficient algorithm for the accurate calculation of the Jacobian matrix of partial derivatives, and the resulting linearized equations are solved using the damped least squares method.

Case studies of theoretical data generated from a simple model of interest in geophysical prospecting show that, in general, it is impossible to obtain, from surface data alone, accurate estimates of the conductivity of structures buried deeper than 0.2 skin depths under a conducting overburden. The addition of borehole data to the surface data is found to increase the resolving power of the electromagnetic method dramatically. In particular, the borehole data appear to stabilize the inverse when only a poor initial estimate of the likely structure is given.
EQUIVALENCE IN ELECTROMAGNETIC (FREQUENCY) SOUNDING*
Authors: VERMA R.K.
Published: April 2006

Abstract

An analysis of the equivalence phenomenon, analogous to that encountered in resistivity sounding, has been made for electromagnetic (frequency) sounding with the following systems: horizontal coplanar coils, perpendicular coils, vertical coplanar coils, and vertical coaxial coils. Cases analyzed are three‐layer H and K type resistivity distributions. The theoretical responses for the EM sounding systems have been computed by the digital linear filter method using short filters. An analysis has been made of the resolution by the four EM systems considered f the equivalence effect. It is concluded that from the equivalence point of view electromagnetic (frequency) sounding has relatively better resolution compared to resistivity sounding for the H type three‐layer cases. For the K type three‐layer cases electromagnetic (frequency) sounding provides a serious problem in resolution similar to that encountered in resistivity sounding. Empirical relationships have been established for the H and K type cases respectively in order to numerically quantify the equivalence involved in electromagnetic (frequency) sounding.
WAVELET DECONVOLUTION USING A SOURCE SCALING LAW*
Authors: ZIOLKOWSKI A.M. , LERWILL W.E. , MARCH D.W. , PEARDON L.G.
Published: April 2006

Abstract

We present a new method for the extraction and removal of the source wavelet from the reflection seismogram. In contrast to all other methods currently in use, this one does not demand that there be any mathematically convenient relationship between the phase spectrum of the source wavelet and the phase spectrum of the earth impulse response. Instead, it requires a fundamental change in the field technique such that two different seismograms are now generated from each source‐receiver pair: the source and receiver locations stay the same, but the source used to generate one seismogram is a scaled version of the source used to generate the other. A scaling law provides the relationship between the two source signatures and permits the earth impulse response to be extracted from the seismograms without any of the usual assumptions about phase.

We derive the scaling law for point sources in an homogeneous isotropic medium. Next, we describe a method for the solution of the set of three simultaneous equations and test it rigorously using a variety of synthetic data and two types of synthetic source waveform: damped sine waves and non‐minimum‐phase air gun waveforms. Finally we demonstrate that this method is stable in the presence of noise.
CORRELATION METHODS OF TRANSFORMATION AND INTERPRETATION OF GEOPHYSICAL ANOMALIES*
Authors: SHRAIBMAN V.I. , ZHDANOV M.S. , VITVITSKY O.V.
Published: April 2006

Abstract

The methods of anomaly transformations considered are based on a system of combined analysis of the geophysical field and a priori) information on the structure of a geological object. The methods involve calculation of a transformative polynomial (describing geophysical noise) which makes it possible to separate the residual field component related to the geological characteristic under study in a correlatively optimal way.

The structure of the transformative polynomial is determined by the nature of the geophysical noise that is eliminated by the field transformation. Various correlation methods of anomaly transformations arise, depending on the structure of the transformative polynomial chosen.

By way of example, the correlation method employed for separating the geophysical anomalies is shown to be highly effective in investigating the local geological structure.
GEOELECTRIC MODELS IN ENGINEERING GEOPHYSICS*
Authors: OGILVY A.A. , BOGOSLOVSKY V.A. , KUZMINA E.N.
Published: April 2006

Abstract

Man'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

Abstract

The 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

Abstract

Laboratory 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

Abstract

The 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

Abstract

Six 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

Abstract

The 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

Abstract

Dipole‐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

Abstract

For 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

Abstract

Optimum 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

Abstract

The 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.
A TIME‐DOMAIN APPROACH TO THE NORMAL‐INCIDENCE INVERSE PROBLEM*
Authors: MENDEL Jerry M.
Published: April 2006

Abstract

This tutorial paper presents a time‐domain derivation of the Normal equations which are associated with the normal‐incidence inverse problem. Connections are made between our time‐domain derivation and the more familiar z‐transform transfer function derivation.
TECHNIQUE DE MESURE ET D'INTERPRETATION MINIMISANT LES ERREURS DE MESURES EN MICROGRAVIMETRIE*
Authors: BICHARA M. , ERLING J.C. , LAKSHMANAN J.
Published: April 2006

Resume

Les 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

Abstract

A 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

Abstract

The 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

Abstract

In 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

Abstract

Vertical 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

Abstract

A 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

Abstract

A 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

Abstract

A 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

Abstract

An 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

Abstract

Application 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

Abstract

Time‐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.