bluuebunny/crossref_metadata_2025 huggingface dataset:
ADVANCED METHOD FOR SELF‐ADAPTIVE ESTIMATION OF RESIDUAL STATIC CORRECTIONS*
Authors: SÁGHY G. , ZELEI A.
Published: April 2006

Abstract

The estimation of residual static corrections is investigated as a linear system. For 1200% coverage shot one way offset weighting functions—or in other words, estimation error operators—are computed. Assuming zero time shift determination errors and zero RNMO it is seen that large residual corrections will distort the effectivity of the estimation.

With an iterative procedure which includes the repeated averaging according to depth point, shot point, and geophone point the effectivity of the method becomes more favourable. This can be learnt from the evaluation of estimation error operators computed by recursive formulae.

In practice, due to the time shift determination errors, the routine does not give improved results in the desired level. Errors can be reduced with a more reliable time shift determination routine.

For detecting and suppressing the unfavourable effect of time shift errors still remaining in the data a self‐adaptive method was developed. In this non linear routine the data are evaluated at all three averaging processes according to limit values and weighting factors computed from the data itself.

Field examples processed in different ways are presented.
NEW RESULTS IN RESISTIVITY WELL LOGGING*
Authors: ROY A.
Published: April 2006

Abstract

Two independent theoretical analyses show that, spacing for spacing, the two‐electrode normal device investigates deeper than the seven‐electrode focused Laterolog 7. The first analysis, published earlier, compares the radii of investigation of the different sondes from the portion of the ground that contributes maximum to, or fifty percent of, the measured signal. The second relates to the nature of the departure curves for the two sondes for an infinitely thick resistive formation pierced by a bore hole. With increasing spacing, the apparent resistivity for the normal device rises much faster and asymptotically approaches the true resistivity much earlier than that for Laterolog 7. These two analyses also prove that, in a Laterolog 7, the radius of investigation increases as O1O2 decreases relatively to A1A2. Since any complex point electrode system is equivalent to a superposition of elementary dipoles or two‐electrode devices, it follows that no resistivity sonde of discrete point electrodes can have a radius of investigation larger than that for the normal device of the same spacing. Laboratory measurements in a model tank confirm these theoretical results.

For thin highly resistive formations we find from theoretical and model studies that the normal device is markedly superior to Laterolog 7 as it gives apparent resistivity values much closer to the true. It has other advantages as well. Thus, our results on the comparative performances of the normal and Laterolog 7 devices are at variance with those published so far since the introduction of Laterolog 7 in 1951.

For reasons given in the text, the chief characteristic of Laterolog 7—namely, focusing the current from the central electrode in a thin horizontal sheet into the target formation—does not endow it with any special advantage. The main reason is that the measured potential in a Laterolog 7 is caused not only by the current focused into the target formation but also by the currents from the outer two electrodes which flow, due to the same focusing process, entirely through the adjacent formations and the mud column. Indeed, the contribution to the measured signal by the outer two power electrodes is considerably larger than that from the central.
DETECTION OF CAVES IN A KARST FORMATION BY MEANS OF ELECTROMAGNETIC WAVES*
Authors: KAŠPAR M. , PECEN J.
Published: April 2006

Abstract

The application of classical geophysical methods in locating karst caves did not yield always unambiguous results. It was our task to verify a new method that has not yet been tested. In investigating caves in a karst formation, electromagnetic waves in the band 2–10 MHz were applied.

The physical analysis of the problem is carried out, the measuring device used for the perradiation of the rocks between the boreholes is described, and the results of the measurements made in the karst area of East Slovakia (ČSSR) are shown. The verification from mines is included. The results mentioned are demonstrated in a space model. The work performed in the mines verified unambiguously the interpretation of the indications measured.

The results show the suitability of putting the electromagnetic method in question into the set of geophysical methods within the hydrogeological survey of karst areas.
COMPATIBILITE ENTRE LA COMPRESSION DE L'INFORMATION SISMIQUE ET SON TRAITEMENT*
Authors: BOIS P.
Published: April 2006

Abstract

Some time ago, we described and implemented two methods of seismic data compression. In the first method a seismic trace is considered as being the convolution of a distribution made up of the trace peak values with a Gaussian pseudo‐pulse. The second method is performed through a truncation of the sequential (Walsh, Paley or Haar) spectrum of each trace.

In this paper it is shown that neither method has adverse effects on quality when traces with their information compressed undergo conventional data processing, such as stacking and deconvolution.
PSEUDO‐DIAGRAPHIES DE VITESSE EN OFFSHORE PROFOND*
Authors: LAVERGNE M.
Published: April 2006

Abstract

Pseudo‐velocity‐logs are tentative determinations of subsurface velocity variations with depth, using both information of seismic amplitude and reflection curvature.

A rigorous theoretical method would consist in

deconvolving the seismic traces to remove the filtering effects of the ground and of the recording equipment

demultiplying the deconvolved traces by a complete desynthesization with convergence criteria

computing the velocities.

While this method works with synthetic examples, it is not generally applicable to field cases, one of the reasons being the poor reliability of desynthesization in the presence of noise.

The present method is a compromise between a rigorous and a practical process: the complete desynthesization is not performed; deconvolution and demultiplication are done by more classical techniques using real amplitudes; absolute velocities are determined to fit both the reflection coefficients and the rms velocities. It leads to pseudovelocity‐logs, accurate enough to show lithologic variations, smoothed enough to preserve the signal/noise ratio.

Examples are shown of Flexichoc profiles recorded in 2500 m (8000–9000 feet) deep areas of the Mediterranean Sea. Pseudo‐velocity‐logs show 1000 m (3000 feet) of a velocity‐increasing‐with‐depth Plio‐pleistocene marl formation, overlying Miocene evaporites. Intercalations of high and low‐velocity layers in the evaporites seem to indicate vertical facies variations.

The Pseudo‐velocity‐log, associated with other lithologic determination processes, should become a geological tool for deep offshore exploration.
ESSAIS D'AMELIORATION DU TRAITEMENT ET DE L'INTERPRETATION DES ENREGISTREMENTS MAGNETOTELLURIQUES*
Authors: ROCROI J. P. , ANDRIEUX P.
Published: April 2006

Abstract

The MT method has proved to be a useful tool for the resolution of some geophysical problems not well adapted to seismic prospecting. To meet the accuracy needed by such cases, the original field and processing techniques has to be somewhat improved.

The processing of the natural EM field (with two electrical and three magnetic components recorded) is made in the frequency domain, and the usual MT parameters are calculated. However, the dispersion of the results is given a great importance and the final plots (apparent resistivity vs. frequency, azimuths of the main directions vs. frequency, etc.) illustrate the distribution of the calculated values.

Average curves can then be selected and studied by means of the known master curves. However, if the earth can be assumed to consist of parallel layers, a computer program derives from the apparent resistivity diagram an automatic solution consisting of a great number of layers with the same ratio of thickness to square root of resistivity. This comprehensive solution is then simplified through an auxiliary diagram called the MT Dar Zarrouk curve and a set of geologically consistent solutions can be found.
A NEW APPROACH TO MAGNETIC PROFILE INTERPRETATION*
Authors: HJELT S. E.
Published: April 2006

Abstract

By using two components of anomalous magnetic fields and a formulation including complex numbers it is possible to calculate the position parameters of thick plates and both magnetization and position of thin plates directly from any two or three points of anomaly profiles. The formulae (interpretation operators) allow automatic topographic corrections to be made. The new two‐component operators give more reliable results than the conventional methods of interpretation. The variance of the parameter values obtained with subsequent points of an anomaly measures directly, the total error of interpretation.

The application of infinite thin plate operators to a long profile results in characteristic patterns, from which the estimation of the number of plates and their approximate position is possible.
KRIGEAGE APPLIED TO GEOPHYSICS THE ANSWER TO THE PROBLEM OF ESTIMATES AND CONTOURING*
Authors: HAAS A. G. , VIALLIX J. R.
Published: April 2006

Abstract

None of the processes of estimation currently available is fully acceptable to the geophysicist. Firstly, they all assume that the variable, be it seismic reflection time, rms velocities, Bouguer anomaly, etc.… is random, amenable to pure statistical considerations, and the processes all disregard the relationships which link the values of the variable in the different points of the domain under investigation. Secondly, they do not provide the geophysicist with any guideline for smoothing his data, as smoothing and estimation are considered two separate operations. Thirdly, they fail to offer a valid criterion of estimation and a measure of the estimation error.

The krigeage process overcomes the above mentioned difficulties. It synthesizes the structural or “geostatistical’ characteristics of the variable by using a function called the variogram (variances of the increases of the variable with respect to distance and direction). It smoothes the variable, when necessary, as a function of the “nugget effect’ (value at the origin of the experimental variogram). It yields an optimum estimation of the variable by minimizing the estimation error, and it computes a measure of the reliability of the estimation, the variance of krigeage.

The process is demonstrated herein with three examples of variograms on seismic and gravity data and an example of contouring of velocities, reflection times and depths of a productive layer in an oil field, with detection and correction of irregular data, smoothing of velocities, migration of depth points, and display of estimation error.
LABORATORY RESULTS IN RESISTIVITY LOGGING*
Authors: ROY A. , APPARAO A.
Published: April 2006

Abstract

This paper is an experimental extension of the theoretical investigations by Roy (1975) on the relative performances of the Laterolog 7, normal and some other sondes in logging of resistive formations. Only infinitely resistive formations have been simulated and placed in a tank containing tap water (true resistivity 27 Ωm) as electrolyte—representing both the mud column and the adjacent formations.

Two sets of laboratory results (Doll 1951, NN 1958, 1969), have been repeated and we find that, for both these sets, the performance of the normal device is by far the superior of the two. In addition, we have studied the effect of varying the spacings A1A2, O1O2 and AM of Laterolog 7, normal, and two new sondes—Laterolog 4 and modified unipole—for two bore hole diameters in each case. For formation thicknesses less than A1A2 or AM, the Laterolog 7 is unsuitable because its response is flat and close to the base‐line value. The normal device is more diagnostic, although, in such a case, it registers a trough or a resistivity low even against a resistive formation.

For bed thicknesses clearly greater than A1A2 or AM, the normal sonde is decidedly superior to Laterolog 7, since its anomalies are sharper and larger. When the formation thickness is equal to or only slightly larger than A1A2 or AM, Laterolog 7 is somewhat better as it records a readable positive deflection while the normal does not. However, one must remember that a single run of the conventional resistivity log includes two normals and a lateral at different spacings. Laterolog 4 and modified unipole can in many instances produce better logs than normal, other considerations apart.

The results are consistent with our own theoretical predictions and experience in surface resistivity profiling. They do not, however, agree with the prevalent concepts on Laterolog 7 vis‐a‐vis normal sonde.
ACCURATE DETERMINATION OF THE DIP ANGLE OF A GEOLOGICAL CONTACT USING THE GRAVITY METHOD*
Authors: GREEN R.
Published: April 2006

Abstract

From a gravity profile over a truncated horizontal plate, the horizontal derivative and, by means of the Hilbert Transform, the vertical derivative are obtained.

When the horizontal derivative is plotted against the vertical derivative, the axis of symmetry of the resulting curve is inclined at the angle of dip of the face of the truncated plate. The depths to the upper and lower surfaces of the plate can be obtained uniquely from the symmetrical figure. Because of the derivatives being used, the method avoids the difficulties which arise from other methods of interpretation which depend upon a knowledge of the position of the origin of the gravity field data. The entire procedure for interpretation can be accommodated on a programmable calculator. An illustrative example is given.
THE NANOLOG, A NEW WAY TO LOG THE RESISTIVITY OF THE SEA FLOOR*
Authors: BECKMANN H. , DEMIRAY G.
Published: April 2006

Abstract

A new device for resistivity logging has been developed with a doubly focussed system. It resembles a simplified double set of microlaterologs. The diagram of the log shows the formation resistivity factor of the sediments on the sea floor. The probe is trailed after the logging boat on a cable with at least two or four cores. The penetration of this log is better than 10 cm. The log is used for resistivity mapping, and it could be used for the exploration of heavy minerals and managese nodules.
CALIBRATION OF MARINE SEISMIC SOURCES USING A HYDROPHONE OF UNKNOWN SENSITIVITY*
Authors: SAFAR M. H.
Published: April 2006

Abstract

The absolute amplitude of the pressure pulse radiated by a marine seismic source is one of the prime criteria used in evaluating its performance. A technique for this measurement is proposed which is applicable to all sources which radiate a bubble pulse. The technique is described with reference to an air‐gun array in which the pulse radiated from a single gun is compared with that radiated by the full array. The advantage of the method is that absolute values of pressure are obtained without any need for a calibrated hydrophone. In theory this may seem a trivial advantage but in practice sensitivity factors for the hydrophone channel cannot always be relied upon. The proposed technique is illustrated by an example.
THE QUANTITATIVE ANALYSIS OF FREQUENCY‐DOMAIN INDUCED POLARIZATION SOUNDINGS OVER HORIZONTAL BEDS*
Authors: PATELLA D. , SCHIAVONE D.
Published: April 2006

Abstract

Following up our recent study of an indirect procedure for the practical determination of the maximum frequency‐effect, defined as fe = 1 − pρ∞/ρdc with ρ∞ the resistivity at infinite frequency, we show at first how, through the Laplace transform theory, ρ∞ can be related to stationary field vectors in the simple form of Ohm's law. Then applying the equation of continuity for stationary currents with a suitable set of boundary conditions, we derive the integral expression of the apparent resistivity at infinite frequency ρ∞,a in the case of a horizontally layered earth. Finally, from the definition of the maximum apparent frequency‐effect, analytical expressions of feα are obtained for both Schlumberger and dipole arrays placed on the surface of the multi‐layered earth section in the most general situation of vertical changes in induced polarization together with dc resistivity variations not at the same interfaces. Direct interpretation procedures are suggested for obtaining the layering parameters directly from the analysis of the sounding curves.
DIRECT APPLICATIONS OF THE DAR ZARROUK PARAMETERS IN GROUND WATER SURVEYS*
Authors: HENRIET J. P.
Published: April 2006

Abstract

The combination of layer resistivity and thickness in the so‐called Dar Zarrouk parameters S and T may be of direct use in aquifer protection studies and for the evaluation of hydrologic properties of aquifers.

The protective capacity of a clayey aquifer overburden is proportional to its longitudinal unit conductance S which, in terms of aquifer protection, gets a dimension of time (e.g. infiltration time). Aquifer storage in fissured reservoirs may be determined from differential conductance measurements (ΔS). Combination of the expression for ΔS with an empirical expression for electric conduction in fissured media yields a simple formula for water content per unit surface area. Both principles and possible developments are illustrated for a set of carboniferous limestone basins.
INSTABILITY OF FINITE DIFFERENCE SCHEMES DUE TO BOUNDARY CONDITIONS IN ELASTIC MEDIA*
Authors: ILAN A. , LOEWENTHAL D.
Published: April 2006

Abstract

The manner in which boundary conditions are approximated and introduced into finite difference schemes may have an important influence on the stability and accuracy of the results. The standard von Neumann condition for stability applies only for points which are not in the vicinity of the boundaries. This stability condition does not take into consideration the effects caused by introducing the boundary conditions to the scheme.

Working on elastic media with free stress boundary conditions we found that the boundary approximation gives rise to serious stability problems especially for regions with high Poisson's ratio. In order to detect these effects apriori and to analyse them, we have used a more elaborate procedure for checking the stability of the scheme which takes into consideration the boundary conditions. It is based on studying a locally spaced time propagating matrix which governs the time‐space behavior of a small region of the grid which includes free surface points.

By using this procedure a better insight into the nature of instability caused by the approximations to the boundary conditions was gained which led us to a new stable approximation for the free surface boundary conditions.
A STUDY OF THE SEISMIC SIGNATURES OF SEDIMENTATION MODELS USING SYNTHETIC SEISMOGRAMS*
Authors: KHATTRI K. , GIR R.
Published: April 2006

Abstract

In modern exploration for hydrocarbons there is a great emphasis on the location of stratigraphic traps and estimation of lithologic information like sand‐shale ratios from seismic data. In order to investigate the possibilities of success in this endeavour we have studied the synthetic seismograms for wave form and spectral characteristic for four basic sedimentation models: (I) interbedded sand‐shale model representing the sediments of generally fluviatile origin, (2) interbedded coal‐shale model representing deltaic deposits, (3) sedimentary models representing transgression and regression of shore lines, and (4) a basal sand model. The results have shown that for the first two models a change in the sand‐shale or coal‐shale ratio results in a characteristically different seismogram. The nature of the seismogram, however, is also strongly dependent on how the sand‐shale or coal shale layers are arranged to ultimately give the same number of total layers, thus implying the same coal‐shale or sand‐shale ratios. The transgression, regression, and basal sand models also produce characteristically different seismic signatures. The spectra of these seismograms show attendant characteristic changes. However, it seems that in the case of real data which are disturbed by noise and the effects of overlying layers these characteristic features may not always be distinguishable.
CDP RAY MODELING IN THE PRESENCE OF 3‐D PLANE ISOVELOCITY LAYERS OF VARYING DIP AND STRIKE*
Authors: HUBRAL P.
Published: April 2006

Abstract

Various Dix‐type formulae are derived, which are useful to approximate travel time functions that can be observed while modeling the common depth point (CDP) technique for 3‐D isovelocity layers of varying dip and strike. All formulae can be used to compute interval velocities and recover the depth model from surface measurements. They are established by making use of the concept of wavefront curvature. Many similarities with known formulae valid for the 2‐D plane isovelocity layer case exist.
AN ATTEMPT AT THE INVERSION OF REFLECTION DATA*
Authors: GJEVIK B. , NILSEN A. , Höyen J.
Published: April 2006

Abstract

The main problem in seismic prospecting is to infer from the observed reflection response the distribution of density and seismic velocity with depth. This process is generally called the inversion of the reflection data.

For plane waves propagating through plane parallel stratification, it can be shown that at any depth the ratio between the amplitude of the transmitted and reflected wave satisfies the Riccati equation. Based on this equation we have formulated an iterative inversion method, which is found to be suitable for numerical computations. We have applied this method on synthetic reflection data, and found that it provides a very fast and accurate inversion.
WHERE IS ZERO TIME?*
Authors: FARRELL J.
Published: April 2006

Abstract

Mis‐ties are all‐too‐common results of seismic surveys made at the same place but at different times with different equipment or by different organizations. Even after removal of positioning or polarity errors, reflection times often appear to differ by several tens of milliseconds. Zero time appears to fluctuate.

How can zero time differ on surveys with only minor differences in acquisition or processing? What can be done to identify the true zero time for each survey?

The first step toward establishing zero time is to record the source pulse. It is well‐known that the different sources currently used in reflection seismic prospecting (propane‐oxygen explosions, compressed‐air discharges, explosives, steam bubbles, mechanical implosions, vibrations, etc.) yield different pressure wavefronts as the input to the seismic reflection system. By recording this wavefront we capture the basic pulse shape and we establish the initial time delay.

The second step is to process the recorded source pulse as if it were reflection data to establish the additional time and shape changes introduced by data processing. Then, display the recorded and processed source pulse as an auxiliary variable at the ends of the seismic section. From this display the interpreter can systematically establish the time shifts appropriate to each picked event. He can determine also whether the pick should be a peak or a trough. He can see why surveys which appear to tie for shallow reflections appear to mis‐tie for deep reflections.

The display of the processed source pulse constitutes a major interpretation aid which, in a readily useable form, increases the information content of the basic seismic section.
SOME EXPERIMENTS ON TRANSVERSE WAVES*
Authors: SCARASCIA S. , COLOMBI B. , CASSINIS R.
Published: April 2006

Abstract

In‐situ seismic measurements on shear waves propagation both in soft formations (clays) and in hard formations (calcareous rocks), using several field techniques did not result in clear S arrivals.

Particular digital approaches were then used, based on spectral analysis of records, for the selection of the seismic events and the calculation of their propagation velocity.

The actual application of these numerical procedures are described and to some records obtained using the “crosshole” field technique show that the suggested procedures are a substantial contribution to the identification of transverse waves.
AUTOMATIC INTERPRETATION OF GRAVITY ANOMALIES ASSOCIATED WITH TWO‐DIMENSIONAL MASS DISTRIBUTIONS*
Authors: QURESHI I. R. , KUMAR A.
Published: April 2006

Abstract

Several new features are described which facilitate an automatic, more meaningful, and more accurate interpretation of gravity anomalies associated with approximately two‐dimensional mass distributions. These include a provision for fixed points on the bounds of a distribution, outward dipping boundaries, calculation of the gravity effect at individual elevations of stations, smoothing of models and end‐corrections for distributions of limited strike length. It is possible to obtain distributions about a median plane; these distributions are sensitive to shape and allow estimates of optimum depths and minimum density contrasts for the anomalous masses.
SOME REMARKS ON COMPUTING TRAVEL TIMES IN PLANE LAYERED MEDIA*
Authors: HUBRAL P.
Published: April 2006

Abstract

A satisfactory approximation to the travel time of a reflected wave is achieved by finding a ray, which originates in the source and emerges close enough to the receiver. The reason for this is, that the actual travel time function can be approximated in every emergence point of the wave by a time function which is entirely defined by seismic parameters along the ray connecting the source with the point of emergence.
GROUNDWATER EXPLORATION IN HARD‐ROCK TERRAIN—A CASE HISTORY*
Authors: SATPATHY B. N. , KANUNGO D. N.
Published: April 2006

Abstract

The utility of electrical resistivity and magnetic measurements to locate suitable wellsites in hard‐rock terrains intruded by dykes is illustrated. The example is taken from a highly hilly terrain of Karnataka State situated in the Western Ghat hills of Peninsular India. Electrical resistivity profiles and soundings, S.P., and total magnetic field measurements are discussed. Of the fifteen recommended sites, nine have been drilled, eight of which are reported to yield between 6–12 m3/hr (1500 to 3000 gals./hr), which is considered satisfactory in this region.
AN EXAMPLE OF THE APPLICATION OF THE RULES OF COMPOSITION IN RESISTIVITY INTERPRETATION*
Authors: MOHAMMED S. A. G. , HABBERJAM G. M.
Published: April 2006

Abstract

The application of approximate rules, whereby apparent resistivity space sections for two dimensional structures can be composited from spaces derived for elementary features is extended to a complex example drawn from a field survey over a fluorite mineral vein.

A quantitative solution for the observed resistivity space is presented and the computational sequence involved in matching the observed space is given in detail.

The interpreted results are examined in relation to the known geology, supplemented by the results of excavation, and to model tests conducted using a tank analogue.

The example also illustrates how successive compositions can be employed in estimating the form of resistivity space in a relatively complex situation.
ATTENUATION DES MULTIPLES EN SISMIQUE MARINE PAR ANTIMOYENNE*
Authors: LAMER A.
Published: April 2006

Abstract

A satisfactory attenuation of the multiples in marine seismic may be obtained by the application of the principle of “Antiaveraging”.

This principle in a first step consists in getting the model of the organized noise, which one tries to eliminate by using an averaging method, and in a second step to subtract that model from the initial information.

Obviously the elimination of the model should not simultaneously cause the elimination of useful signals.

The model may be obtained if the considered organized noise keeps a constant shape or if its time‐space deformation is known. Besides one has to assume the time‐distance curve of the organized noise can be determined. Thus noise arrivals may be detected on the records.

The “antiaveraging” is very often efficient when organized noises are stronger than signals or when a signal, once identified, exploited and then considered as an organized noise, can be attenuated in order to make the detection of the other signals easier.
INVERSION OF SEISMOGRAMS AND PSEUDO VELOCITY LOGS*
Authors: LAVERGNE M. , WILLM C.
Published: April 2006

Abstract

Pseudo velocity logs can be obtained by seismogram inversion, using true amplitude processing and detailed investigation of move‐out velocities. The precision of the results depends on the quality of the seismic data and on the possibility of deconvolving without increasing the noise. An investigation is made of the deformation of pseudo logs due to seismic signal variations and to imperfections of deconvolution.

Both marine and land examples are shown, in some cases with adjustment on well logs. When the dips are large, time sections must be migrated and pseudo velocity logs must be computed from migrated sections. Comparison of sonic logs with pseudo velocity logs obtained in the same area is usually good enough to obtain information on lithological parameter variations by adjustment of pseudo velocity logs on sonic logs. Even when no well is available, pseudo velocity logs can give some indications on the nature of sediments between seismic horizons.
WEIGHTED VERTICAL STACKING IN CRUSTAL SEISMIC REFLECTION STUDIES ON THE CANADIAN SHIELD*
Authors: BROWN R. J. , FRIESEN G. H. , HALL D. H. , STEPHENSON O. G.
Published: April 2006

Abstract

Seismic reflection methods are being developed at the University of Manitoba to aid in determining fine crustal structure in the Precambrian of Manitoba and northwestern Ontario. Present‐day environmental concern as well as mineshaft conditions necessitate the detonation of several smaller charges repeated, say, I times and followed by ‘vertical’ stacking. To obtain the familiar √I improvement in signal‐to‐noise (S:N) amplitude ratio applying the straight‐sum (SS) method, one assumes, among other things, that both S:N ratio and signal variance are the same on all traces. Dropping these assumptions, as we must for our data, it becomes necessary to apply weighting coefficients to optimize the S:N ratio of the stacked trace. We still assume the signal shapes to be the same for repeated shots, so for the jth trace on the record of the ith shot we model the time series as: tij=ai (sj+nij); where ai is a scaling factor. The proper weights wi are then shown to be proportional to σsi/σ2ni where σ2 is variance, or to γi/ai where γi is S:N power ratio.

Applying the weighted‐stack (WS) method gives S:N amplitude ratios which are, on average, 55% of the optimal ratios expected from WS theory compared with only 24% for the SS method. The 45% shortfall in WS performance is ascribed mainly to trace‐alignment (or time‐delay) errors. Varying noise levels on individual traces, slight dissimilarity of signal shape, and correlated noise may also contribute to a lesser extent (in decreasing order of significance). This WS method appears to strike a good practical balance between S:N improvement and processing efficiency.
THE ROTATING CURRENT DIPOLE METHOD ‐ A FIELD TEST*
Authors: HALL S. H. , DAVIS J.
Published: April 2006

Abstract

The outputs and neutral of a three phase generator are converted to six amplitude variable phases in a 3.5 kW 400 Hz transmitter. These outputs are applied to six groundimplanted electrodes, producing a horizontally rotating current dipole in the subsurface.

An investigation of the radiation pattern in the vertical magnetic field indicates, in symmetry and closure control, considerable advantages in this form of galvanic energization. These include optimization of inductive anomalies and the ability to interpret phase observations on a spatial basis in depth sounding and orebody location.
THE SPECTRAL FUNCTION OF A LAYERED SYSTEM AND THE DETERMINATION OF THE WAVEFORMS AT DEPTH*
Authors: ROBINSON E. A. , TREITEL S.
Published: April 2006

Abstract

Consider the mathematical model of a horizontally layered system subject to an initial downgoing source pulse in the upper layer and to the condition that no upgoing waveforms enter the layered system from below the deepest interface. The downgoing waveform (as measured from its first arrival) in each layer is necessarily minimum‐phase. The net downgoing energy in any layer, defined as the difference of the energy spectrum of the downgoing wave minus the energy spectrum of the upgoing wave, is itself in the form of an energy spectrum, that is, it is non‐negative for all frequencies. The z‐transform of the autocorrelation function corresponding to the net downgoing energy spectrum is called the net downgoing spectral function for the layer in question. The net downgoing spectral functions of any two layers A and B are related as follows: the product of the net downgoing spectral function of layer A times the overall transmission coefficient from A to B equals the product of the net downgoing spectral function of layer B times the overall transmission coefficient from B to A. The net downgoing spectral function for the upper layer is called simply the spectral function of the system. In the case of a marine seismogram, the autocorrelation function corresponding to the spectral function can be used to recursively generate prediction error operators of successively increasing lengths, and at the same time the reflection coefficients at successively increasing depths. This recursive method is mathematically equivalent to that used in solving the normal equations in the case of Toeplitz forms. The upgoing wave‐form in any given layer multiplied by the direct transmission coefficient from that layer to the surface is equal to the convolution of the corresponding prediction error operator with the surface seismogram. The downgoing waveform in this given layer multiplied by the direct transmission coefficient from that layer to the surface is equal to the convolution of the corresponding hindsight error operator (i.e., the time reverse of the prediction error operator) with the surface seismogram.
COMPARATIVE ANALYSIS OF TIME DOMAIN AND FREQUENCY DOMAIN IN THE INDUCED POLARIZATION PROSPECTING METHOD*
Authors: PATELLA D. , SCHIAVONE D.
Published: April 2006

Abstract

The polarization content of a medium, in both the time and frequency domains, can be described by parameters which differ in inherent physical meaning and their practical significance.

For real situations, general expressions for the apparent parameters, previously determined for both domains, exist for the general case of soundings on a horizontally multi‐layered earth.

The comparative analysis of these expressions, here restricted to the simple case of a two‐layered earth, shows that the theoretical sounding curves of the frequency‐domain are different from those of the time‐domain. In particular, for every resistivity or chargeability contrasts examined, the apparent frequency‐effect curve lies always over the corresponding apparent chargeability curve, but both curves reach the same asymptotical values for shortest and largest spacings.

The important conclusions which can be drawn from this result is that both techniques are suitable to investigate subsoil polarizability anomalies. However, from a practical point of view, it is more convenient to adopt the frequency‐domain technique when the polarizability increases with depth, while, on the contrary, the time‐domain technique is more efficacious when the polarizability decreases with depth.
ESTIMATION OF REFLECTOR PARAMETERS BY THE VIRTUAL IMAGE TECHNIQUE*
Authors: KÉMÁRKY I.
Published: April 2006

Abstract

The seismic interpretation process generally exploits three of the following independent basic assumptions:

Input quantities are obtained by simplification of measured data (travel time curves).

2. The geological model contains only a few parameters (for example, plane interfaces and constant interval velocities).

3. Approximate transformations may be applied.

The first two are related to the simplification of the phenomena and enhance their essential features. The transformation which establishes relations between simplified data and model is required to be unique, stable, and sufficiently accurate.

Practically, the travel time curves are almost exclusively regarded as hyperbolas. We also accept this approximation.

The paper presents a simple recursive algorithm for the evaluation of the depth and dip of plane reflectors and the interval velocities.

It is a simple fact, that there exists a unique relationship between three hyperbolic parameters and a homogeneous dipping layer. Accordingly, two layers can be replaced by a single layer and the parameters of the lower boundary can be estimated when the upper one is known, initiating virtual shotpoints and geophone points (virtual surface). So, the case of multilayered media can be reduced in sequential steps to the case of a single homogeneous layer using a stripping type procedure.

Some synthetic model examples are provided to demonstrate the abilities of the algorithm.
SEISMIC VELOCITY ESTIMATION*
Authors: URSIN BJØRN
Published: April 2006

Abstract

The accuracy of the two most common arrival time functions used in seismic velocity estimation is investigated. It is shown that the hyperbolic arrival time function is more accurate than the parabolic arrival time function for a horizontally layered elastic medium. An upper bound on the difference between the two arrival time functions is given.

A maximum‐likehood detector for estimating the arrival time of the signals is given. For the signal‐in‐noise model that is used the maximum‐likelihood detector is equivalent to a least‐squares detector which corresponds to using the signal energy as coherency measure. The semblance coefficient corresponds to a normalized least‐squares detector. The semblance coefficient is very similar to a filter performance measure that is used in least‐squares filter design.
A QUANTITATIVE EVALUATION OF OTT AND MEDER'S PREDICTION ERROR FILTER*
Authors: MENDEL J. M.
Published: April 2006

Abstract

Ott and Meder's prediction error filter can be rederived so that it correctly handles input noise vectors which are of smaller dimension than the state vector. The poor performance obtained by Ott and Meder for their example can be explained by means of the error covariance matrix for the prediction error filter.
LIMITING DEPTH OF DETECTION IN LINE ELECTRODE SYSTEMS*
Authors: ROY K. K. , RAO K. P.
Published: April 2006

Abstract

An infinitely resistive/conductive horizontal bed is assumed in an otherwise homogeneous and isotropic half space. Schlumberger, three electrode, and unipole profiles are computed at right angles to the strike of the bed. The Schwarz‐Christoffel method of conformal transformation and numerical methods of solving non‐linear differential equations are used to solve the boundary value problem. It is observed that (i) the three electrode system is the most sensitive gradient electrode configurations for electrical profiling, (ii) the apparent resistivities for Schlumberger, three electrode, and unipole methods become maximum when the depth of the bed is 0.06 L, 0.1 L, and 0.055 L for a resistive bed and minimum when depths are 0.085 L, 0.04 L‐0.02 L and indeterminate for conductive beds, respectively, (iii) the limiting depths of detection (defined in the text) by Schlumberger, three electrode, and unipole configurations are respectively 0.9 L, 6.6 L and 2.0 L for resistive beds and 0.58 L, 1.17 L and 1.5 L for conductive beds.

The electrode separation L is the distance between the two farthest active electrodes.
THE INFLUENCE OF OBLIQUELY DIPPING DISCONTINUITIES ON THE USE OF RAYLEIGH CHANNEL WAVES FOR THE IN‐SEAM SEISMIC REFLECTION METHOD *
Authors: FREYSTÄTTER S. , DRESEN L.
Published: April 2006

Abstract

The geological sequence rock‐coal‐rock represents a seismic low‐velocity channel. Channel waves generated in a coal seam and their reflections from discontinuities can be used for proving the minability of the seam. To investigate the process of reflection, two‐dimensional models of the sequence rock‐coal‐rock have been investigated by means of the ultrasonic transducer technique. Two‐dimensional models have the advantage that the wave field can be observed at an arbitrarily chosen point of the model plate. Thus, by means of these models the direct and the reflected Rayleigh channel wave can be observed along their path of propagation.

From the geophysical point of view the various types of discontinuities of a coal seam can be divided into two basic types: one is restricted to the seam, the other includes in addition a fractured zone in the adjoining rock.

The investigation of the symmetrical Rayleigh channel wave reflected by a discontinuity yields the following results:

For dip angles γ between approximately 90° and approximately 60° the reflectivity is virtually independent of the type of discontinuity. This does not hold for the limiting case of γ= 90° (vertical dip) for which the reflectivity increases with increasing influence of the fractured zone. For dip angles γ between approximately 60° and approximately 40° the reflectivity is still independent of the fractured zone but the shape of the reflected wave deteriorates with increasing influence of the fractured zone.

For dip angles γ below approximately 40° the reflected wave deteriorates such that the application of the in‐seam seismic reflection method will be difficult or even impossible.

The conversion of the direct wave of the symmetrical fundamental mode into a reflected wave of the antisymmetrical fundamental mode has been observed.
TRANSFORMATION OF TIME‐DISTANCE CURVES OF DIVING WAVES INTO A MULTILAYERED MODEL*
Authors: LASKI J. D.
Published: April 2006

Abstract

A method to compute the parameters of a multilayered medium with dipping interfaces is described. The input data are time‐distance curves of diving waves. The output data are the thickness of the layers, dips, and parameters characterizing the increase of velocity with depth. Three examples are presented.
VERTICAL FREQUENCY EFFECT SOUNDING IN INDUCED POLARIZATION AND GALVANIC RESISTIVITY METHODS *
Authors: KEÇELI A.
Published: April 2006

Abstract

It has been shown that for a polarizable layer as a transmission medium there is an indirect proportionality between the frequency effect (fe) in induced polarization (IP) and the wave number of the electrical induced field. Making use of this relationship for a two layered earth a polarization transform function has been obtained. Since the mathematical expression for the polarization transform function is the same as that of the resistivity transform function, it is possible to make direct interpretation for IP frequency effect field curves. Thus, AA or QQ type resistivity sequences can be interpreted from induced polarization response of a horizontally stratified earth without resistivity extrema.

A depth factor has been defined in order to obtain the true depth using the apparent depth. In this way, some electromagnetic effects between horizontal layers with different polarizabilities can partly be eliminated.
RADAR PROPAGATION IN ROCK SALT *
Authors: UNTERBERGER R. R.
Published: April 2006

Abstract

Four radar systems at three different frequencies are described which are useful in probing into salt for finding information of interest to miners. Ranges in salt to (a) the edge of a salt dome, (b) the top of the salt dome, (c) boreholes in salt, or (d) faults or hazards ahead of mining can be determined using one or more of these radar systems. Radar wave velocities in salt are determined by radar probing through pillars of known length, and then used to determine ranges in salt to timed radar reflections. Radar probing results are shown obtained in different salt mines probing upwards and downwards. Enclosed areas in the mine are the best radar station locations to probe into salt as air reverberation of radar energy is shortened.
A PREDICTION OF SEDIMENTARY ENVIRONMENT FROM MARINE SEISMIC DATA *
Authors: TUFEKČIĆ D.
Published: April 2006

Abstract

Stratigraphic models are usually oversimplified by petroleum geologists, and the result is that the principles which we use for interpreting geophysical data are also over‐simplified or even incorrect.

Based on the marine seismic data from the Adriatic Sea, an example of prediction of a rather complex sedimentation model of detrital sediments is shown. On the basis of the stratigraphic interpretation using seismic techniques only for this some very important characteristics are discussed:

— paleotopography of the valley and conditions which have given opportunity to map accurately the pre‐depositional surface,

— seismic signatures of the sedimentary section of the ancient valley in which we have recognized aluvial sequence and marine one.

The conclusion is that there is a real opportunity for exploration of stratigraphic traps in this part of the Mediterranean Basin.
A TRIGGERING DIGITAL SEISMOGRAPH UTILIZING MICRO‐PROCESSOR WITH MEMORY FOR PRESERVING FIRST‐MOTION INFORMATION *
Authors: ADAMS W. M.
Published: April 2006

Abstract

Most of the data recorded at seismological observatories are essentially noise, not signal. One way to achieve a higher information density is to trigger the seismograph, as in strong‐motion accelerographs. This approach loses the first motion—not important for earthquake‐engineering studies, but very important for studies of focal mechanism. To eliminate this defect, various cumbersome techniques have been used, such as closed‐loop tape‐recording.

Here we describe a seismograph that records only the signals and does not lose the first motion. Our procedure uses a microprocessor (MC6800) to monitor the energy level adaptively, uses a solid‐state memory like a large shift‐register, and has the microprocessor trigger recording from the solid‐state memory onto a tape cassette whenever a signal (as defined by energy level) is recognized by the microprocessor.

A field station consists of a crystal clock, seismometer, amplifier, analog‐to‐digital converter, Parallel Interface Adapter (PIA), MC6800 microprocessor, 8K solid‐state memory, Asynchronous Communications Interface Adapter (ACIA), cassette tape‐recorder, and battery. The duration of operation depends upon the frequency content of data, the sampling rate used, and the frequency of events. The design criteria used for the stations of the first field system are a 1 Hz to 10 Hz bandpass amplifier, 8‐bit digitization, 5 samples per cycle of highest frequency content, and quality tape cassettes. These requirements are appropriate for exploring for magma chambers in subduction zones—the motivation for developing this system. A playback facility uses the DEC LSI‐11 computer, which has an assembly language set very similar to that of the MC6800.

This equipment, or a slight modification thereof, would be suitable for recording strong‐motion earthquakes, for monitoring quarry blasts, or for any seismological effort in which the triggering criterion can be specified as an algorithm for programming into the microprocessor firmware. The resulting data are digital and only include significant signals, thus the data reduction facilities may properly concentrate on analysis and interpretation. Because the parameters of the system can be easily modified in firmware or software, the system is very flexible and can be considered the Universal Geophysical Recorder. An adaptation to recording transient EM phenomena is in progress. In this application, the source is controlled, but the use of the self‐triggering approach eliminates the need for a radio‐control system to activate the recorders, HIG Contribution no. 753.