bluuebunny/crossref_metadata_2025 huggingface dataset:
THERMAL INFRA‐RED TECHNIQUE APPLIED TO MODERN INVESTIGATION*
Authors: THOMAS J. , PEDEUX J. P. , ARNAUD C.
Published: April 2006

Abstract

During the last few years a substantial improvement has been made in the development of the thermal infra‐red scanner so that 1.5 milli‐radian resolution is now commonly obtained. Direct transfer of information on 70 mm film through fiber glass transcoder allows immediate and refined interpretation.

Although the collected data represent the image of thermal anomalies within a pellicular section of the earth's crust, it is proved that because of “per ascensum” phenomena, deep buried sources induce surface thermal changes. The difficulty lies in showing an absolute relationship between these deep phenomena and thermal surface occurrences.

A careful examination of several cases related to hydrology, karstic geology, civil engineering, pollution, hot springs should help the geophysicist by providing him a new tool for shallow investigations. Thermographics with interpretation are shown to support this statement.
INTERPRETATION OF MAGNETIC ANOMALIES USING SPECTRAL ESTIMATION TECHNIQUES*
Authors: CASSANO E. , ROCCA F.
Published: April 2006

Abstract

The depth of causative bodies may be derived from the power spectrum of their magnetic anomalies. After a short review of the theoretical basis of the method, several examples of its application to synthetic cases are shown. Disturbing effects due to improper choice of the sampling interval and to anomalies only partially contained in the examined segment of the profile are studied.

The spectral method is then applied to real cases; the tapering of the anomalies, the application of non‐linear filters and the effects of anomaly superpositions are investigated.

In conclusion, an appraisal of the method and of its possible practical impact has been given.
HOMOMORPHIC FILTERING — THEORY AND PRACTICE*
Authors: BUTTKUS B.
Published: April 2006

Abstract

The application of homomorphic filtering in marine seismic reflection work is investigated with the aims to achieve the estimation of the basic wavelet, the wavelet deconvolution and the elimination of multiples. Each of these deconvolution problems can be subdivided into two parts: The first problem is the detection of those parts in the cepstrum which ought to be suppressed in processing. The second part includes the actual filtering process and the problem of minimizing the random noise which generally is enhanced during the homomorphic procedure.

The application of homomorphic filters to synthetic seismograms and air‐gun measurements shows the possibilities for the practical application of the method as well as the critical parameters which determine the quality of the results. These parameters are:

the signal‐to‐noise ratio (SNR) of the input data

the window width and the cepstrum components for the separation of the individual parts

the time invariance of the signal in the trace.

In the presence of random noise the power cepstrum is most efficient for the detection of wavelet arrival times. For wavelet estimation, overlapping signals can be detected with the power cepstrum up to a SNR of three. In comparison with this, the detection of long period multiples is much more complicated. While the exact determination of the water reverberation arrival times can be realized with the power cepstrum up to a multiples‐to‐primaries ratio of three to five, the detection of the internal multiples is generally not possible, since for these multiples this threshold value of detectibility and arrival time determination is generally not realized.

For wavelet estimation, comb filtering of the complex cepstrum is most valuable. The wavelet estimation gives no problems up to a SNR of ten. Even in the presence of larger noise a reasonable estimation can be obtained up to a SNR of five by filtering the phase spectrum during the computation of the complex cepstrum. In contrast to this, the successful application of the method for the multiple reduction is confined to a SNR of ten, since the filtering of the phase spectrum for noise reduction cannot be applied. Even if the threshold results are empirical, they show the limits fór the successful application of the method.
CONTRIBUTION A L'ETUDE DE L'EQUIVALENCE EN PROSPECTION ELECTRIQUE (COURANT CONTINU ET MAGNETOTELLURIQUE)*
Authors: ROCROI J. P.
Published: April 2006

Abstract

In all electrical methods (EM, MT, DC), a theoretical one‐to‐one relation links the apparent resistivity diagram at a station with the local distribution of the resistivities in a tabular earth. Unfortunately, the actual field diagrams derive from a few measurements of limited accuracy and the one‐to‐one relation vanishes. Calculating the distribution of the earth resistivities from the field diagrams is thus an undetermined problem, which experience has shown to be partly controlled by approximate laws of “equivalence”. The use of these rough rules can produce only a very restricted number of the resistivity distributions that correspond to calculated diagrams which do not differ from a given field curve by more than a tolerable discrepancy. On the other hand, the full set of such “equivalent” solutions is given automatically by a computer program. Tests made on field examples prove that a few geological data generally reduce the wide range of undetermination.
RESULTS OF GRAVITY SURVEY OVER RANIGANJ COALFIELD, INDIA*
Authors: VERMA R. K. , MAJUMDAR R. , GHOSH DEBABRATA , GHOSH ASHISH , GUPTA N. C.
Published: April 2006

Abstract

Results of a gravity survey conducted over Raniganj coalfield, one of the Gondwana basins of Damodar Valley in north‐eastern part of India, are presented. The gravity field was separated into regional and residual components. The residual Bouguer anomaly map shows that the coalfield is characterized by a gravity low of about—32 mGal associated with Gondwana sediments. The deepest part of basin is found to be located near Asansole (23° 40’N, 86° 55’E), where the maximum thickness of sediments is estimated to be about 1.3 miles (2.08 km). The faults along the northern as well as the southern boundaries are found to be normal. The Gondwana sediments appear to continue eastward beneath alluvium and laterite of Bengal basin as far as 87° 25’E.
THE INDUCED POLARIZATION RESPONSE OF A THIN HIGHLY‐CONDUCTIVE ORE BODY*
Authors: FISHER M. E. , HURLEY D. G.
Published: April 2006

Abstract

Consider a lamina of ore of thickness 2t whose electrical resistivity p2 is much smaller than the resistivity p1 of the surrounding host rock. The induced polarization response of such an ore body is investigated under the assumption that it arises from the variation of p2 with the frequency of measurement.

Let p2l and p2h be the resistivities of the ore‐body for the low and high frequencies of measurement and L a length of the order of the distance between the transmitting electrodes. A theory is developed under the assumptions that each of the quantities t/L, p2l/p1, p2h/p1, Lp2l/2tp1, and Lp2h/tp1 is small. The main conclusion is that the frequency effect parameter P is given approximately by P=cL(p2l − p2h)/2tp1, where the constant c is independent of t, p2l, p2h, and p1. Thus for a family of similar ore bodies having differing values of t, P will be the larger the smaller t.

Detailed results are given for a semi‐infinite submerged dipping dyke and the two dimensional Wenner array.
FAST AUTOMATIC PROCESSING OF RESISTIVITY SOUNDINGS*
Authors: BICHARA M. , LAKSHMANAN J.
Published: April 2006

Abstract

The difficulty to use master curves as well as classical techniques for the determination of layer distribution (ei, ρi) from a resistivity sounding arises when the presumed number of layers exceeds five or six.

The principle of the method proposed here is based on the identification of the resistivity transform. This principle was recently underlined by many authors. The resistivity transform can be easily derived from the experimental data by the application of Ghosh's linear filter, and another method for deriving the filter coefficientes is suggested.

For a given theoretical resistivity transform corresponding to a given distribution of layers (thicknesses and resistivities) various criteria that measure the difference between this theoretical resistivity transform and an experimental one derived by the application of Ghosh's filter are given. A discussion of these criteria from a physical as well as a mathematical point of view follows.

The proposed method is then exposed; it is based on a gradient method. The type of gradient method used is defined and justified physically as well as with numerical examples of identified master curves. The practical use for the method and experimental confrontation of identified field curves with drill holes are given. The cost as well as memory occupation and time of execution of the program on CDC 7600 computer is estimated.
MINI‐SOSIE FOR LAND SEISMOLOGY*
Authors: BARBIER M. G. , BONDON P. , MELLINGER R. , VIALLIX J. R.
Published: April 2006

Abstract

Mini‐sosie consists in using a vibration‐rammer as seismic source and changing the striking rate by varying the engine speed, resulting in a random impulse transmission. The recording instruments are made up of two seismic traces, two constant gain amplifiers and a two‐channel sosie processor which performs the decoding in real time by using the actual transmission times supplied by a captor located on top of the vibration‐rammer's plate. An idea of the possible penetration is given by the recording of a velocity survey. Other results obtained in seismic reflection and refraction are given.
A FAST FOURIER TRANSFORM METHOD FOR RAPID COMPUTATION OF GRAVITY AND MAGNETIC ANOMALIES DUE TO ARBITRARY BODIES*
Authors: BHATTACHARYYA B. K. , NAVOLIO M. E.
Published: April 2006

Abstract

The spectrum of a magnetic or a gravity anomaly due to a body of a given shape with either homogeneous magnetization or uniform density distribution can be expressed as a product of the Fourier transforms of the source geometry and the Green's function. The transform of the source geometry for any irregularly‐shaped body can be accurately determined by representing the body as closely as possible by a number of prismatic bodies. The Green's function is not dependent upon the source geometry. So the analytical expression for its transform remains the same for all causative bodies. It is, therefore, not difficult to obtain the spectrum of an anomaly by multiplying the transform of the source geometry by that of the Green's function. Then the inverse of this spectrum, which yields the anomaly in the space domain, is calculated by using the Fast Fourier Transform algorithm. Many examples show the reliability and accuracy of the method for calculating potential field anomalies.
LONG PERIOD STATICS DETERMINATION BY INVERSE FILTERING*
Authors: KIRKHAM D. J. , POGGIAGLIOLMI E.
Published: April 2006

Abstract

The relative time shift of CDP reflections, caused by long period statics, is treated as the result of a filtering process. The shape of the filter is that of a comb having the magnitude and spacing of its teeth determined by the CDP spread geometry. Convolution of a near surface anomaly with a comb filter representing the CDP spread geometry produces the same time fluctuations at CDP reflections (CDP statics) as the stacked traces across the anomaly. Conversely, the near surface time anomaly is given by the convolution of the CDP statics with the inverse of the comb filter. Provided that CDP statics can be separated from noise, dip, and residual normal moveout, it is pcissible to determine long period statics with a relative wavelength of between half a spreadlength and five spreadlengths.

The object of this paper is to present the theory and practical applications of the method. Several examples based on synthetic and real data will also be discussed.
ON TRACING SEISMIC RAYS WITH SPECIFIED END POINTS IN LAYERS OF CONSTANT VELOCITY AND PLANE INTERFACES*
Authors: CHANDER R.
Published: April 2006

Abstract

A polygonal ray path connects the seismic source and detector positions when the intervening medium consists solely of constant velocity layers with plane interfaces which may have arbitrary orientation. The coordinates of the ray vertices satisfy a system of coupled equations resulting from the requirement that Fermat's principle be satisfied along the ray path. Solving the system of equations is equivalent to tracing the ray numerically. A notable feature of this approach is that a ray which is critically refracted over a segment of its path requires no special handling.
CHARACTERISTICS OF AUDIO AND SUB‐AUDIO TELLURIC SIGNALS*
Authors: TELFORD W. M.
Published: April 2006

Abstract

Telluric current measurements in the audio and sub‐audio frequency range, made in various parts of Canada and South America over the past four years, indicate that the signal amplitude is relatively uniform over 6–8 midday hours (LMT) except in Chile and that the signal anisotropy is reasonably constant in azimuth.
RESOLVING ANISOTROPY IN LAYERED MEDIA BY JOINT INVERSION*
Authors: JUPP D. L. B. , VOZOFF K.
Published: April 2006

Abstract

A finite number of layers must normally be used to represent the electrical properties of a horizontally‐layered region. It is well known that these representative layers must include anisotropy.

Applying the concept of joint inversion to DC resistivity and magnetotelluric (electromagnetic) data from a structure consisting of many fine layers, we show how the resistivities in the horizontal and vertical directions can be separately determined in each layer. The results are related to the contrasts existing in the interbeds which comprise the composite layers.

The method has applications in both engineering and exploration.
USE OF REMOTE SENSING FROM SPACE PLATFORMS FOR REGIONAL GEOLOGIC EVALUATION AND FOR PLANNING GROUND EXPLORATION*
Authors: CASSINIS R.
Published: April 2006

Abstract

The advantages and limitations of remote sensing exploration from space platforms are outlined with special reference to the geologic objectives.

The enhancement techniques of the multispectral imagery and their effects are illustrated in order to improve the interpretation of geologic linears and the discrimination of soils and rocks.

Three cases of application are shown, dealing with different geologic regions.

The ability of remote sensing from space to be employed in both regional and local problems is shown.

The planning of exploration by airborne and ground geophysical methods can be substantially helped after the results of remote sensing, and large economic gains can be reached.
RESISTIVITY SOUNDING ON A MULTI‐LAYERED EARTH WITH TRANSITIONAL LAYERS. PART I: THEORY*
Authors: PATELLA D.
Published: April 2006

Abstract

The electrical potential generated by a point source of current on the ground surface is studied for a multi‐layered earth formed by layers alternatively characterized by a constant conductivity value and by conductivity varying linearly with depth. The problem is accounted for by solving a Laplace's differential equation for the uniform layers and a Poisson's differential equation for the transitional layers. Then, by a simple algorithm and by the introduction of a suitable kernel function, the general expression of the apparent resistivity for a Schlumberger array placed on the surface is obtained. Moreover some details are given for the solution of particular cases as 1) the presence of a infinitely resistive basement, 2) the absence of any one or more uniform layers, and 3) the absence of any one or more transitional layers. The new theory proves to be rather general, as it includes that for uniform layers with sharp boundaries as a particular case. Some mathematical properties of the kernel function are studied in view of the application of a direct system of quantitative interpretation. Two steps are considered for the solution of the direct problem: (i) The determination of the kernel function from the field measurements of the apparent resistivity. Owing to the identical mathematical formalism of the old with this new resistivity theory, the procedures there developed for the execution of the first step are here as well applicable without any change. Thus, some graphical and numerical procedures, already published, are recalled. (ii) The determination of the layer distribution from the kernel function. A recurrent procedure is proposed and studied in detail. This recurrent procedure follows the principle of the reduction to a lower boundary plane, as originally suggested by Koefoed for the old geoelectrical theory. Here the method differs mainly for the presence of reduction coefficients, which must be calculated each time when passing to a reduced earth section.
A NOTE ON MAGNETIZED SPHERES*
Authors: RAO B. S. R. , RAO T. K. S. PRAKASA , MURTHY A. S. KRISHNA
Published: April 2006

Abstract

The interpretation of total field anomalies becomes somewhat complicated, especially when an arbitrarily magnetized spherical ore mass happens to be the causative body. Even though some attempts have been made to analyze total field anomaly maps, they are often too complicated and their underlying assumptions in respect of permanent and induced components of magnetism are far from realistic. In this note, an attempt has been made to show that vertical magnetic anomalies are capable of yielding interpretation with ease and precision as far as magnetized spheres are concerned. An empirical method has been outlined for computing the magnetization inclination in the plane of the profile using the measured distances between principal maximum, principal minimum, and zero anomaly positions on a magnetic anomaly profile.
REFLECTIONS AND REFRACTIONS FROM CURVED INTERFACES: MODEL STUDY *
Authors: GUPTA S. K.
Published: April 2006

Abstract

Reflections and refractions from curved interfaces were studied on two dimensional scale models. Time of arrival, amplitude and character of reflected, converted, and refracted waves were mainly used for this study. Some reflected refractions, refracted reflections and diffractions were also considered. It was possible to separate PS and SP waves and to study their amplitude and character separately. From the amplitude study of refracted arrivals it was concluded that the refracted ray path penetrates into the high velocity layer rather than propagating along the interface. Although most of the results are interesting from the theoretical point of view, a few applications to exploration problems are suggested.
SOME APPLICATIONS OF IP‐TECHNIQUE FOR DIFFERENT GEOPHYSICAL PROSPECTING PURPOSES *
Authors: MALMQVIST L.
Published: April 2006

Abstract

The usefulness of IP‐technique for different geophysical purposes is discussed on the basis of field examples. IP and resistivity results are not always correlated, and the IP‐information may be unique in prospecting for very low grade sulphide mineralizations. The IP‐technique seems to be useful sometimes in prospecting for disseminated Ni‐Cu‐ mineralizations. A massive sulphide mineralization could be localized using IP.

The disturbances from different kinds of geological objects other than prospecting targets generally are smaller in IP‐work than in resistivity work. It was possible to discriminate between apparent resistivity anomalies caused by shear zones and by sulphide mineralizations by means of IP‐measurements. The influence of magnetite on IP‐ measurements is briefly discussed. The relation between ground magnetic measurements ΔZ and the IP‐parameter is in many areas weak and does not seriously influence the interpretation of the IP‐measurements. A high correlation between ΔZ and IP‐measurements has been found on a titaniferous iron ore. This ore body gives strong IP‐anomalies indicating that it is a good IP‐target. Finally, the application of small moving arrays in very detailed IP‐measurements is found useful for detailed mapping of a mineralized zone under a thin overburden and for determination of the dip of mineralized zones.
GEOELEKTRISCHE SONDIERUNGEN IN GRADIENTMEDIEN UND ÄQUIVALENTEN SCHICHTSYSTEMEN *
Authors: RÖSLER R. , SCHALLAR M.
Published: April 2006

Abstract

Analytical solutions exist for the potential of a Point Source in media with depth dependent conductivity of the form σ(z) =σ0(1 +αz)n.

Of particular importance is the case of the linear gradient (n= 1). More general distributions of conductivity with depth can be approximated by equivalent sequences of homogeneous layers. Comparison between such approximations and the analytical solution for media with linear gradient of conductivity indicates that already a coarse step function yields a reasonably good approximation.
RESISTIVITY SOUNDING ON A MULTI‐LAYERED EARTH WITH TRANSITIONAL LAYERS. PART II: THEORETICAL AND FIELD EXAMPLES *
Authors: PATELLA D.
Published: April 2006

Abstract

This final part of our study of the resistivity sounding method in the presence of transitional layers deals with the direct application of the theoretical developments, previously reported, to both theoretical and field examples. The former are used to explain in more detail all steps of the direct procedure of interpreting resistivity measurements, when transitional layers with different dispositions are present in the assumed earth section. An alternate sequence of uniform and transitional layers is at first considered, then the case of a random sequence of these layers, and finally a sequence of only transitional layers. Then we give some logical considerations about the best fields of application of the new interpretation theory, with particular reference to hydrogeological, geological‐ structural, and mining exploration problems. Representative field examples are finally presented and discussed in detail for each of the exploration fields above listed. The comparison of the geophysical models obtained with the old interpretative scheme and the new system shows the greater resolving power of the new theory, provided that preliminary geological considerations, and where existing–borehole evidence justify the use of the new approach.
CALCULATION OF VELOCITY FROM SEISMIC REFLECTION AMPLITUDE *
Authors: BOISSE S.
Published: April 2006

Abstract

It is not possible to determine accurate geological velocities from seismic velocity analysis for thin layers or complex structural features, especially under an unconformity. Instead, we can approach the problem of interval velocity with seismic amplitudes analysis and compute the reflection coefficient along the unconformity surface.

An error estimation has been made on a model to test the possibility of such a method and to choose the best parameters to be used. The method has been applied on an actual case: the computed interval velocities show good correlation with the values obtained by a sonic log.
QUASI‐STATIC ELECTROMAGNETIC FIELDS OF A HORIZONTAL ELECTRICAL DIPOLE ON THE SURFACE OF A POLARIZABLE HALF‐SPACE *
Authors: RATHOR B. S.
Published: April 2006

Abstract

The expressions for quasi‐static electromagnetic fields of a horizontal electrical dipole placed on the surface of a polarizable half‐space have been derived for low and high values of induced polarization parameter and presented along with numerical results. It has been observed that the polarity of the mutual impedance function is negative for low values and positive for high values of the induced polarization parameter in the entire time domain, whereas the induced voltage function is positive for low values of induced polarization parameter and becomes negative for high values. In the case of low values of induced polarization parameter the transient electromagnetic field in the beginning increases with time, later on it starts to decay with time. The present study shows that the decay rate of electromagnetic field is highly dependent upon the induced polarization parameter. In the light of the present study the conductivity of the polarizable medium may be determined more accurately.
INVERSION OF GRAVITY PROFILES BY POLYNOMIAL METHOD *
Authors: BALDI P. , UNGUENDOLI M.
Published: April 2006

Abstract

The inversion of a gravity profile associated with a twodimensional distribution of mass with constant difference in density is dealt with, in an initial approximation, by using a polynomial of appropriate degree. The method can be applied successfully, for example, to sedimentary basins.

Some examples confirm the applicability of the method, which can be readily programmed on a computer.
CALCULATION OF SYNTHETIC REFLECTION SEISMOGRAMS IN THE FREQUENCY DOMAIN *
Authors: NIELSEN P. H.
Published: April 2006

Abstract

Calculation of reflection seismograms in the frequency domain makes it possible to treat absorption correctly, i.e. makes it possible to include dispersion (= causality) and frequency dependent reflection coefficients.

In the paper it is shown how such a calculation can be done in a reasonably efficient manner.
THE PHASE PROPERTY OF A FINITE REALIZATION OF RANDOM NOISE AND ITS INFLUENCE ON DECONVOLUTION *
Authors: DE VOOGD N.
Published: April 2006

Abstract

A finite realization of a discrete random noise process may be considered as a one‐sided energy signal. Its phase property can then be described by means of the center position. The samples of such a realization are the components of a random signal vector and the center position is therefore a random variable. A statistical analysis shows that the expected value of the center position equals half the time duration of the realization. This implies that the Z‐transform of the realization may be expected to have an equal number of poles and zeros inside and outside the unit circle. The standard deviation from the expected value of the center position is shown to depend on the time duration of the realization and on the autocorrelation of the process. It follows that, for processes that can be described by the convolution of a white series and a disturbance wavelet, the center position is independent of the phase property of the wavelet. A conclusion based on these results is that the homomorphic technique of wavelet estimation through cepstrum stacking must give questionable outcomes. Another conclusion is that the super‐position of a realization of random noise on a minimum phase wavelet will in general give a mixed phase resulting signal. It is pointed out that schemes for the derivation of deconvolution filters do not take account of this phenomenon.
THE THIN‐LAYER PROBLEM IN GEOELECTRICAL PROSPECTING *
Authors: MUNDRY E.
Published: April 2006

Abstract

For a thin highly‐conducting layer with given longitudinal conductance the recurrence formulae for an n‐fold horizontally stratified subsoil are established for d.c. resistivity and magnetotelluric soundings. Similarly, a thin low conductivity layer with given transverse resistance is treated in the d.c. case and a non‐conducting intermediate bed in magnetotellurics. Model curves for a thin high‐ or low‐conductivity intermediate layer in the three‐layer case have been carried out, which may serve as an extension of the well‐known three‐layer diagrams for a Schlumberger configuration. The corresponding model curves in magnetotellurics are given.

By numerical comparison of these curves with real three‐layer curves some diagrams have been developed to show the allowed thicknesses of the intermediate layer in the Schlumberger case and in the case of magnetotelluric sounding.
ESSAI D'UNE APPLICATION DE LA TRANSFORMATION DE KARHUNEN‐LOÈVE AU TRAITEMENT SISMIQUE *
Authors: HEMON CH. , MACE D.
Published: April 2006

Abstract

Multispectral recordings used for remote sensing are not without analogy with seismic records from CDP field set‐ups. These seismic data may be regarded as “photographs’ of deep regions of the earth taken from various angles.

The Karhunen‐Loève (K.L.) transformation is commonly used for multispectral data processing, where it helps emphasize some features of remote sensing information. The same method may be applied to seismic data processing. Signal‐to‐noise ratio is improved on synthetic or field examples when K.L. transformation is applied instead of conventional CDP stacking. Residual statics seem to be diminished by a significant factor.
COMPUTATIONS OF SYNTHETIC SEISMOGRAMS FOR COAL SEAMS WITH THE REFLECTIVITY METHOD *
Authors: FERTIG J. , MÜLLER G.
Published: April 2006

Abstract

The reflectivity method for computing synthetic seismograms can be applied to seismic prospecting problems with special focus on coal‐mining problems. The method allows the calculation of reflected waves for point‐source excitation and non‐vertical incidence. It automatically includes all possible conversions of wave types and all inner multiple reflections. Synthetic horizontal‐ and vertical‐component seismogram sections are given for a simple two‐seam model and for a realistic seam sequence which is represented by 48 layers; the source‐receiver distances range from 100 m to 1000 m. These seismograms show prominent PS reflections already at moderate source‐receiver distances. These waves complicate the vertical‐component records by producing arrivals of similar strength as the PP reflections. From this it is concluded that PS reflections in strongly layered media can cause problems in routine CDP stacking. On the horizontal‐component records the PS reflections are dominant. Because of the lower velocities of S waves the time resolution of PS reflections is better than that of PP reflections. This suggests that horizontal‐component recording may be useful in the investigation of subsurface regions with strong velocity contrasts, even with conventional energy sources producing mainly P waves.
STEEP DIP FINITE‐DIFFERENCE MIGRATION*
Authors: BERKHOUT A. J.
Published: April 2006

Abstract

A method is presented to derive approximate versions of the wave equation which allow finite‐difference migration for very steep dips (> 50°). It is shown that for conventional finite‐difference schemes, in addition to the dip limitation, the maximum acceptable frequency should be specified. A finite‐difference migration technique is proposed in the frequency domain. It is derived that finite‐difference wave field extrapolation in the frequency domain consists of a space‐variant convolution procedure for each frequency component, the space‐variance being defined by the lateral variation in the velocity.

Finally it is shown that with finite‐difference migration, particle velocity data can be easily obtained from pressure data.
GEOPHYSICAL ANOMALY INTERPRETATION OF POTENTIAL FIELDS BY MEANS OF SINGULAR POINTS METHOD AND FILTERING*
Authors: CIANCIARA B. , MARCAK H.
Published: April 2006

Abstract

The calculation of potential field anomalies on different levels below the measuring level permits to localize the singular points related to the sources of anomalies.

It is possible to achieve considerable improvement of the resolution of this method

filtering of analytical downward continuation,

the use of the magnitude of the gravitational vector,

calculation of physe changes.

The numerical examples confirm these assumptions.
A SIMPLE APPROACH TO HIGH RESOLUTION SEISMIC PROFILING FOR COAL*
Authors: ZIOLKOWSKI A. , LERWILL W. E.
Published: April 2006

Abstract

Seismic exploration techniques which have been developed for oil prospecting contribute a valuable means for surveying coal measures. Since the object is to detect minor faults within the first 1500 m, rather than structural features at great depth, the new technique requires much higher resolution in the early part of the traditional seismic cross‐section.

Higher resolution means broader bandwidth, which must be obtained by extending the high frequency end of the spectrum. This is achieved (a) by scaling down the explosive charge size and using single geophones instead of groups, and (b) by reducing the sampling interval in space and time. Noise which does not scale down includes static anomalies and ground‐roll. The consideration of statics, ground‐roll, and the high‐cut filtering effect of the near surface layers forces the use of deep shot holes and, where possible, deep detectors. This approach is confirmed by experiments and has been implemented on a regular basis in production.

It is demonstrated that the present technique will clearly resolve faults with a vertical throw of about 5 m at 800 m depth.
CUBIC SPLINE APPROXIMATION OF INACCURATE RMS‐VELOCITY DATA*
Authors: WARD R. W. , REINING J. B.
Published: April 2006

Abstract

The reliable determination of the root‐mean‐square seismic velocity from multiple coverage seismic reflection data requires coherent horizontal reflections equally spaced in time. Observational error in the rms‐velocity data produces significantly greater error in the instantaneous or interval velocity.

A cubic spline approximation technique developed by Powell (1967) is designed to minimize the rapid velocity variation due to observational error and retain the significant variation in the rms‐velocity data. The approximation algorithm requires the difference between the observed and approximated rms‐velocity to be statistically random, and seeks to follow the “real” trends in the rms‐velocity measurements and reject observational error. Provided the trends of the rms‐velocity are reproduced, the instantaneous velocity derived from the spline approximation to rms‐velocity data with significant scatter is more reliable than the interval velocity determined from the inaccurate rms‐velocity values using the Dix (1955) approximation. This interval velocity is also a more reliable indicator of variations of lithology.

The utility of the spline approximation of rms‐velocity is illustrated for a special common depth point (CDP) expanding reflection spread test recorded in Hardeman County, Texas by the Consortium for Continental Reflection Profiling (COCORP). In this wave test reflections are observed from several CDPs which are closely spaced. It is desired to combine the inaccurate observations from a collection of nearby CDPs. The approximation algorithm for the rms‐velocity determination is applied to both the rms‐velocity data for the individual CDPs and the collection of rms‐velocity data for eight nearby CDPs.
THE SUPPRESSION OF SURFACE MULTIPLES ON SEISMIC RECORDS*
Authors: KENNETT B. L. N.
Published: April 2006

Abstract

A new approach is presented for the suppression of multiples reflected at the surface of a horizontally layered fluid or elastic medium, recorded at non‐zero offsets from the source. The scheme used is to extract the effect of the free surface in the frequency‐wavenumber domain and then to replace this surface by a non‐reflecting boundary. The multiple suppression operator requires a detailed knowledge of the source time function and the elastic properties of the medium between the source and the surface.

For a stratified fluid or a liquid layer overlying a stratified elastic medium, complete multiple suppression can be achieved with noise free data. If only the vertical component is available for an elastic medium an approximate approach may be used which removes most of the multiple energy. Good results may be achieved with this multiple suppression scheme in the presence of noise. The method is designed to be used before records are stacked in a CDP gather.
SOME RELATIONS BETWEEN POTENTIAL FIELDS AND THE STRENGTH AND CENTER OF THEIR SOURCES*
Authors: ANDERSEN F. H. , PEDERSEN L. B.
Published: April 2006

Abstract

From gravity it is well known how to determine the excess mass and the horizontal center of mass of the disturbing body. We show that a magnetic body—under rather weak assumptions—possesses excess magnetization and centers of magnetization (both horizontal and vertical), which can be uniquely determined from measurements. It also follows that the vertical center of mass can be uniquely determined from the vertical derivative of the gravity field.
MORE ON THE LATEROLOG* DEVICE**
Authors: MORAN J. H. , CHEMALI R. E.
Published: April 2006

Abstract

Basic Laterolog devices employ a measure‐current focusing technique to provide well logs of formation resistivity that feature sharp vertical definition combined with a depth of investigation much improved over those of normals of comparable spacings.

To develop the concept of measure‐current focusing, a disk‐electrode arrangement analogous to a guard‐ring capacitor is considered first, leading finally to consideration of a real sonde in a cylindrical borehole. In the latter, auxiliary currents are adjusted to maintain substantially at zero the vertical potential gradients above and below the central measure‐current electrode; this has the effect of focusing the measure‐current beam.

However, prediction of sonde responses on the basis of current patterns can in some cases be misleading. Indeed, for a given Laterolog array, one may use a (reciprocalmode) current pattern radically different from the one defined by the basic (direct‐mode) measure‐current focusing scheme and still obtain the same resistivity measurement. This feature is illustrated for Laterolog 3 by use of transfer impedances, and demonstrated for certain more general cases using the reciprocity theorem.

Comparisons of Laterolog responses across typical thin beds, both non‐invaded and invaded, with those of normal devices of a comparable range of spacings illustrate the improved vertical resolution obtained with Laterolog devices. The examples also show the different magnitudes of the auxiliary currents (thenceforth designated “bucking”‐ or “focusing” currents) used in the direct and reciprocal modes and illustrate how these currents must continuously vary in order to maintain the focused condition as the sonde moves through the bed.

Finally, briefly considering possible applications of Laterolog‐type arrays in surface prospecting, it is shown that a one‐dimensional array laid out on the surface does not provide the same degree of measure‐current focusing as is obtained in a borehole. Some improvement is obtained with a combination of two crossed linear arrays. Much more is obtained using a circular array.
SCALE MODEL ELECTROMAGNETIC RESPONSE TO INLINE AND BROADSIDE SYSTEMS AT SKEW TRAVERSES OF A DIPPING HALF PLANE EMBEDDED IN A CONDUCTING HOST ROCK*
Authors: GUPTA O.P. , JOSHI M.S. , NEGI J.G.
Published: April 2006

Abstract

Laboratory scale model experiments have been performed to obtain the electromagnetic response of a finitely conducting half plane embedded in resistive/conductive surrounding and excited by an oscillating magnetic dipole. Inphase and quadrature profiles are presented for two horizontal coplanar transmitter‐receiver systems (inline and broadside) for normal and skew traverses and for different dips of the conductor. It is observed that the broadside system is more diagnostic in delineating the strike and dip of the conductor and is more sensitive to the conducting host rock. The broadside profile over a vertical or dipping half plane is characterized, when traversing perpendicular to strike, by two positive peaks flanking a zero response when the coils are over the top edge of the conductor. For skew traverses a negative peak replaces the zero response. An increasing asymmetry in the anomalies is caused by changing the dip of the conductor from the vertical in both the systems, but it is more pronounced for the broadside system. The quadrature response in the broadside system changes in a characteristic way when the target is surrounded by a conducting host rock. The comparative results of the two systems may, therefore, be useful in the induction prospecting for ore deposits approximated by a half plane, especially in delineating the strike, dip, and effect of conductive host rock.
ON THE PROPERTIES OF THE RECIPROCAL GEOELECTRIC SECTION*
Authors: SEARA J.L. , CONAWAY J.G.
Published: April 2006

Abstract

The interpretation of vertical electrical sounding data can be facilitated by the application of the reciprocal geoelectric section. If an apparent resistivity field curve has a descending right end, the apparent resistivity curve of the reciprocal geoelectric section can be obtained by the application of linear filter theory; from this the total transverse resistance of the geoelectric section can be calculated without having to interpret the field curve. In addition, Orellana's auxiliary point method can now be extended to interpret three and four layer apparent resistivity curves of all types.

This paper summarizes the properties of the resistivity transform curve, the apparent resistivity curve, and the apparent resistivity curve of the reciprocal geoelectric section, with several new applications.
DIPOLE‐DIPOLE DEEP GEOELECTRIC SOUNDINGS OVER GEOLOGICAL STRUCTURES*
Authors: ALFANO L.
Published: April 2006

Abstract

Alfano L. 1980, Dipole‐Dipole Deep Geodectric Soundings over Geological Structures, Geophysical Prospecting 28, 283–296.

The dipole‐dipole array is used for deep vertical geoelectric soundings for practical reasons. However, the data obtained are often too scattered and the quality is lower than that of a Schlumberger sounding. The mathematical transform from these fields data to the corresponding Schlumberger ones is needed. It is demonstrated that for more general underground structures different from plane parallel stratifications, only the continuous polar dipole‐dipole array permits a general and reliable transform of this type. It follows that any other dipole‐dipole array, (for instance the azimuthal, equatorial, parallel, perpendicular, etc.), are useless over complex structures, or in the presence of irregularities on the ground surface.
MAPPING NON‐REFLECTING VELOCITY INTERFACES BY NORMAL MOVEOUT VELOCITIES OF UNDERLYING HORIZONS*
Authors: KREY TH.
Published: April 2006

Abstract

The normal moveout velocity of a reflecting bed is a function of the dips and curvatures of all overlying velocity interfaces. Now let the (N– 1)th velocity interface be a non‐ (or badly) reflecting bed, whereas the other interfaces, including the base of the Nth layer, reflect satisfactorily, and let the velocities UN– 1 and UN of the (N– 1)th and Nth layer, respectively, be known. Then the normal moveout velocity for the base of the Nth layer, if known in one direction at a certain part of the surface of the earth, provides a second order differential equation in the horizontal coordinates x and y for the depth ZN – 1(x, y) of the unknown interface.

The mathematics becomes rather simple in the case of two‐dimensional geological structures. For this case and N= 2 the differential equation mentioned can be solved by stepwise integration or by iteration. One of the many possible applications of the new concept is the determination of the structure of the base of an overthrusting sheet.
FIELD PROCESSING OF MAGNETIC DATA*
Authors: GREEN R.
Published: April 2006

Abstract

This paper deals with the practical problem of processing magnetic data in the field, and it shows how the parameters describing a geological contact can be obtained quickly and conveniently on the basis of five measurements. The complete interpretation can be performed in the field using a programmable calculator. For a small ground‐party the method greatly improves the quality of the field‐work and the interpretation of the magnetic data. The method has been applied to the data from a magnetic survey over the Mooki Fault (Gunnedah‐Manilla, N.S.W.), and the results are discussed as an illustration of the efficacity of the method as a field procedure.
ESTIMATION OF THE MINIMUM DENSITY CONTRAST OF A HOMOGENEOUS BODY AS AN AID TO THE INTERPRETATION OF GRAVITY ANOMALIES*
Authors: GOODACRE A.K.
Published: April 2006

Abstract

Goodacre A.K. 1980, Estimation of the Minimum Density Contrast of a Homogenous Body as an Aid to the Interpretation of Gravity Anomalies, Geophysical Prospecting 28, 408–414.

The minimum density contrast value for which a homogeneous body will accurately reproduce an observed gravity low can often be used to determine whether the causative body is a low‐density granite batholith or a sedimentary basin. If the minimum density contrast value is large, the anomaly source is probably a sedimentary basin; if it is small, the source may be either a sedimentary basin or a granite batholith. The minimum density contrast method is tested on the Cheshire Basin and the Weardale Granite.
APPARENT RESISTIVITY OF A MULTILAYERED EARTH WITH A LAYER HAVING EXPONENTIALITY VARYING CONDUCTIVITY*
Authors: BANERJEE B. , SENGUPTA B. J. , PAL B. P.
Published: April 2006

Abstract

If the conductivity of any one of the layers of a horizontally stratified earth varies exponentially with depth with or without a discontinuity at the interface, the corresponding expressions for apparent resistivity for Wenner‐ and Schlumberger‐sounding arrays can be formulated. The general case has been broadly divided into three categories for mathematical simplicity. All previous discussions of this problem can be regarded as particular cases of the present study.
A PARAMETRIC APPROACH TO THE COMPRESSION OF SEISMIC SIGNALS BY FREQUENCY TRANSFORMATION*
Authors: BERESFORD‐SMITH G. , MASON I. M.
Published: April 2006

Abstract

The compression of seismic signals which have propagated through a dispersive medium can be achieved by a frequency‐domain transformation. This transformation is formally related to the dispersion characteristic of the medium and is independent of phase and group velocities. By defining a suitable cost‐function to measure the degree of dispersion of a time‐ signal, an iterative technique can be employed to find that transformation which gives minimum dispersion.

In this paper, we assume that the inverse of the dispersion characteristic can be adequately approximated by a finite polynomial in the region of maximum signal energy density. The coefficients of this polynomial are the parameters of dispersion of the medium. These parameters can be estimated both in the presence of noise and in the case of signals made up of multiple arrivals.

The techniques developed in this paper are applied to seismic signals which have been recorded underground by a set of geophones designed to detect and map discontinuities in coal‐seams. Results of dispersion estimation and signal compression are discussed for data collected in the Blackshale seam, Pye Hill Colliery, near Derby, in the United Kingdom.
THE INDUCTIVE RESPONSE OF A HORIZONTAL CONDUCTING CYLINDER BURIED IN A UNIFORM EARTH FOR A UNIFORM INDUCING FIELD*
Authors: OGUNADE S.O. , DOSSO H.W.
Published: April 2006

Abstract

The inductive response of a conducting horizontal cylinder embedded in a uniform earth is studied using numerical results obtained for an analytical solution for the problem of a conducting cylinder buried in a homogeneous earth for the case of a uniform inducing field. A check of the validity of the numerical results is made by a comparison with analogue model measurements for a number of cases. Numerical results for a range of cylinder radii (a = 1–10 km), depths of burial (d= 0–4 km), conductivity contrasts (σ2= 10−2‐10 Sm−1), and source frequencies (f= 10−1‐10−4 Hz) of interest in the interpretation of magnetotelluric field measurements are presented. The results indicate that for a uniform inducing field the conductivity and depth of burial of a horizontal cylindrical inhomogeneity are best determined through a measurement of the amplitudes Hy, Hz and Ex and the phases φy and Ψx.
RESISTIVITY SOUNDING ON A MULTILAYERED EARTH CONTAINING TRANSITION LAYERS*
Authors: BANERJEE B. , SENGUPTA B.J. , PAL B.P.
Published: April 2006

Abstract

For curves over a horizontally stratified earth where any of the layers has a conductivity variation proportional to (1 +β·z)N, where β and N are arbitrary constants and z is the depth to the layer, expressions for apparent resistivity for Wenner and Schlumberger sounding are derived. No assumption has been made about the continuity of conductivity at the interface. It is shown that most of the previous investigations in this connection can be regarded as particular cases of the present study.
AN OPTIMIZED TECHNIQUE FOR DETERMINING STACKING VELOCITY FROM SEISMIC REFLECTION DATA*
Authors: KHATTRI K. , VIG P.K. , RAO N.D.J.
Published: April 2006

Abstract

A new method of estimating seismic stacking velocity from reflection seismograms is based on Fibonacci search technique and provides the highest rate of reduction of the interval of uncertainty of the stacking velocity. A review of the Fibonacci search strategy is presented, the application of the method is illustrated with synthetic and field examples.