bluuebunny/crossref_metadata_2025_split huggingface dataset:
INVERSION OF SEISMOGRAMS AND PSEUDO VELOCITY LOGS*
Authors: LAVERGNE M. , WILLM C. 
Published: April 2006

AbstractPseudo 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

AbstractSeismic 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

AbstractThe 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

AbstractConsider 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractOtt 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

AbstractAn 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

AbstractThe 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

AbstractA 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

AbstractIt 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

AbstractFour 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

AbstractStratigraphic 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

AbstractMost 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.
ON THE MINIMIZATION OF THE DISTORTION CAUSED BY THE GEOPHONE‐GROUND COUPLING *
Authors: SAFAR M. H. 
Published: April 2006

AbstractIt is well known that the application of the “bright spot’ technique has been more successful in marine prospecting than in land prospecting. This is due partly to the problem of distortion of the seismic signal caused by the geophone‐ground coupling, especially when carrying out high resolution, shallow seismic surveys in swampy terrain.The effect of geophone‐ground coupling on the response of a single geophone to the incident compressional waves has been treated by several authors. However, they have always neglected the influence of mutual interaction between an array of geophones on the response of each geophone forming the array. We show that mutual interaction, which results from the re‐radiation of the incident compressional waves by the geophones forming the array, can have considerable effect on the response of each geophone.The effect of the geophone‐ground coupling on the response of a seismic channel is considered in the absence and presence of mutual interaction between a group of geophones for the case when the shear wave velocity of the soil varies by a factor of three.
DEPTH ESTIMATION FROM RESIDUAL BOUGUER ANOMALIES: A PROCEDURE BASED ON THE BACKUS‐GILBERT MINIMUM DISTANCE CRITERION *
Authors: CHANDER R. 
Published: April 2006

AbstractThe minimum distance criterion of Backus and Gilbert is used to determine the depths of line masses approximating the subsurface two dimensional distribution of density differences responsible for the observed residual Bouguer anomaly values. The quantity minimized is the sum of the squared differences between the starting trial depths and the desired final depths of line masses. The search for the desired depths is limited to preset depth ranges.
A BLIND ZONE SOLUTION TO THE PROBLEM OF HIDDEN LAYERS WITHIN A SEQUENCE OF HORIZONTAL OR DIPPING REFRACTORS *
Authors: MERRICK N. P. , ODINS J. A. , GREENHALGH S. A. 
Published: April 2006

AbstractIn seismic refraction surveys, in particular those using first arrival recording techniques, the hidden layer problem occurs where energy from a refractor of higher velocity arrives at the surface before energy from an overlying refractor. The maximum thickness of the hidden layer is referred to as the blind zone.Hypothetically, every recorded refractor has an associated blind zone which may or may not contain a hidden layer. For an assumed earth model of plane constant‐velocity layers and stepwise increase of velocity with depth, the effect of a blind zone on an interpreted depth section may be evaluated by defining an intercept time for a blind zone of assumed or known velocity and by using standard time‐term equations for layer thicknesses and depths.The treatment covers an arbitrary number of blind zones embedded within a multilayer sequence of horizontal or dipping refractors. Model calculations affirm the benefits of this approach compared with previous methods which, in general, have been restricted to the case of two horizontal layers with one intermediate blind zone.
THE USE OF FILTERED BESSEL FUNCTIONS IN DIRECT INTERPRETATION OF GEOELECTRICAL SOUNDINGS *
Authors: BERNABINI M. , CARDARELLI E. 
Published: April 2006

AbstractWe start from the Hankel transform of Stefanescu's integral written in the convolutionintegral form suggested by Ghosh (1971). In this way it is possible to obtain the kernel function by the linear electric filter theory. Ghosh worked out the sets of filter coefficients in frequency domain and showed the very low content of high frequencies of apparent resistivity curves.Vertical soundings in the field measure a series of apparent resistivity values at a constant increment Δx of the logarithm of electrode spacing. Without loss of information we obtain the filter coefficient series by digital convolution of the Bessel function of exponential argument with sine function of the appropriate argument. With a series of forty‐one values we obtain the kernel functions from the resistivity curves to an accuracy of better than 0.5%. With the digital method it is possible to calculate easily the filter coefficients for any electrode arrangement and any cut‐off frequency.