bluuebunny/crossref_metadata_2025_split huggingface dataset:
SEISMIC SIGNAL DETECTION AND PARAMETER ESTIMATION*
Authors: URSIN B. 
Published: April 2006

AbstractIn the mathematical theory of seismic signal detection and parameter estimation given, the seismic measurements are assumed to consist of a sum of signals corrupted by additive Gaussian white noise uncorrelated to the signals. Each signal is assumed to consist of a signal pulse multiplied by a space‐dependent amplitude function and with a space‐dependent arrival time. The signal pulse, amplitude, and arrival time are estimated by the method of maximum likelihood.For this signal‐and‐noise model, the maximum likelihood method is equivalent to the method of least squares which will be shown to correspond to using the signal energy as coherency measure. The semblance coefficient is equal to the signal energy divided by the measurement energy. For this signal model we get a more general form of the semblance coefficient which reduces to the usual expression in the case of a constant signal amplitude function.The signal pulse, amplitude, and arrival time can be estimated by a simple iterative algorithm. The effectiveness of the algorithm on seismic field data is demonstrated.
ON WIENER FILTER AND MAXIMUM ENTROPY METHOD FOR MULTICHANNEL COMPLEX SYSTEMS*
Authors: NEGI J. G. , DIMRI V. P. 
Published: April 2006

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

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

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

AbstractThe relationship between two finite‐difference schemes (15° and 40°) and the Kirchhoff summation approach is discussed by using closed form solutions of Claerbout's approximate versions of the wave equation. Forward extrapolation is presented as a spatial convolution procedure for each frequency component. It is shown that downward extrapolation can be considered as a wavelet deconvolution procedure, the spatial wavelet being given by the wave theory. Using this concept, a three‐dimensional model for seismic data is proposed.The advantages of downward extrapolation in the space‐frequency domain are discussed.Finally, it is derived that spatial sampling imposes an upper limit on the aperture and a lower limit on the extrapolation step.
IN SITU SEISMIC MEASUREMENTS OF CRACK ANISOTROPY IN THE CARBONIFEROUS LIMESTONE OF NORTHWEST ENGLAND*
Authors: BAMFORD D. , NUNN K. R. 
Published: April 2006

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

AbstractTwo different methods for the construction of an approximation to bicubic splines for interpolating irregularly spaced two‐dimensional data are described. These are referred to as the least squares line (LSL) and linear segment (LINSEG) construction procedures.A quantitative test is devised for investigating the absolute accuracy and efficiency of the two spline interpolation procedures. The test involves (i) laying of artificial flight lines on the analytically known field of a model, (ii) interpolation of field values along the flight lines and their subtraction from the original field values to compute the residuals. This test is applied on fields due to four models (three prism models and one dyke model) placed at different depths below the flight lines, and for each case the error estimates (the mean error, the maximum error and the standard deviation) are tabulated.An analysis of the error estimates shows in all cases the LSL interpolation to be more accurate than the LINSEG, although the latter is about 50% faster in computer time. The relative accuracy and efficiency of the LSL interpolation is also tested against a recent method based on harmonization procedure, which shows the latter to be more precise, though much slower in speed.
TOWARDS UNIFICATION OF GEOPHYSICAL PROBLEMS FOR HORIZONTALLY STRATIFIED MEDIA*
Authors: SZARANIEC E. 
Published: April 2006

AbstractTheorems and relations describing a system of horizontal layers are considered as the elements of a meta‐system having a layered structure. This implies a layered structure of a solution of geophysical problems for horizontally stratified medium.Wave equation, Laplace's equation, and Maxwell's equations are the special cases of a more general differential equation. By separation of variables the basic equation for layered structures is obtained.A multi‐layer medium may result from accumulation of successive layers. The descending or ascending accumulation is possible, depending whether the successive layers are inserted at the top or at the bottom of the medium. The discretization of a basic equation provides two sets of formulas for descending or ascending accumulation, respectively.The relationship between the mathematical expressions of the seismic transfer function and the magnetotelluric input impedance is derived. The deduction leads to the possibility of converting the magnetotelluric observations into an equivalent synthetic seismogram.
DEFINITION AND APPLICATION OF THE FREQUENCY ‐EFFECT TRANSFORM FUNCTION TO THE INTERPRETATION OF IP SOUNDINGS*
Authors: PATELLA D. 
Published: April 2006

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

AbstractGeophysical methods can be applied to investigate the harmful effect of man's activities on the environment: the study of specific electrical resistivities and natural electric fields of filtrational origin makes it possible to control the penetration of exogenic pollutants into soil as well as desalinization and secondary salinization of soils; electrometric and seismometric methods allow to observe the groundwater level near water reservoirs thus evaluating the harmful effect of backing up natural groundwater flow; contrasting properties of bedrocks and rocks in a landslide body permit application of seismic and electrical prospecting methods. Observation of the changes in specific electrical resistivities with time on the slopes of quarries is an effective method of assessing slope stability and predicting landslide hazard.Mining activities, groundwater pumping, and oil extraction are the main causes of endogenic pollution of geological medium; surface and borehole geophysical methods make it possible to assess vertical and horizontal displacements of the interfaces between salty and fresh subterranean waters resulting from an extensive exploitation of water supply sources; activation of geodynamic processes associated with mining activities is determined from the data of ‘regime’ electrometric, seismometric, gravimetric, and inclinometric observations. Geophysical methods are applied widely for studying the intensification of physico‐geological processes under the impact of man. A specific object of electrometric investigations is degradation of permafrost and intensification of karst processes in soluble rocks.The principal advantage of geophysical investigations lies in the possibility of creating high spatial and temporal density of observations permitting an extensive employment of statistical methods in the assessment of the impact of man on the geological medium.
PROSPECTING FOR SUBSURFACE WATER IN THE CENTRAL VOLCANIC HIGHLAND OF ARMENIA BY GEOPHYSICAL METHODS*
Authors: MINASIAN R. S. 
Published: April 2006

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

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

AbstractAn economic and precise processing system for microgravity surveys is presented. Three computer processing modes covering areal ground and underground measurements, measurements in vertical shafts, and measurements of vertical gravity gradients with a 3 m high tower are dealt with.Diagrams for manual calculation of gravity effects of prismatic walls, vertical shafts, and horizontal galleries, as well as programs for calculation of accurate terrain corrections and corrections for gravity effects of bodies with complicated ground‐plan are proposed.The method of processing microgravity data is two to three times quicker than any traditional way, with maximum accuracy preserved in resulting gravity micro‐anomalies. Applications from the field of mining geophysics and archaeology are included.
THE CORRELATION REFRACTION METHOD AS APPLIED TO WEATHERED ZONE STUDIES IN A GRANITE TERRAIN*
Authors: RAO NAIK S. BANDU , KUMAR G. NANDA , RAGHAVA M.S. VIJAYA 
Published: April 2006

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

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

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

simultaneous operation of multiple identical sources to increase radiated signal strength by simple addition;
superposition of wavelets of different fundamental frequency to achieve a total pulse of desired, front‐loaded form (e.g. mixed volume air‐gun arrays);
horizontal spacing of units or groups to achieve spatial filtering effects.

The phenomenon of interaction between sources, affecting the loading experienced by each, has usually been ignored, or else avoided by wide spacing of units. However, interactions can significantly affect the efficiency and frequency response, in a way that can be favourable.Calculations are presented for sources emitting continuous or long duration signals, showing the energy efficiency as a function of frequency for arrays in a variety of configurations. Interaction effects are significant for inter‐source spacings smaller than or comparable with the wavelength—not, as is often stated, up to a distance related to the radii of the sources. The results show that potential exists for tailoring the frequency response of a source system, according to the application, by simple spatial rearrangement of units.Similar effects occur with interacting impulsive sources, but it is shown that different criteria apply for the optimum arrangements of units.
MIGRATION IN THE PRESENCE OF NOISE*
Authors: BERKHOUT A.J. , VAN WULFFTEN PALTHE D.W. 
Published: April 2006

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

AbstractThe response of transformer‐coupled and transformerless marine seismic streamers feeding seismic amplifiers with and without input transformer is analysed with the aid of equivalent circuits. Examples are calculated showing how improvements in the performance of two practical transformer‐coupled streamers, namely the increase in bandwidth and sensitivity and the decrease in the dependence on cable length, can be achieved when some of the streamers parameters are properly chosen.Transformerless streamer systems driving either a voltage amplifier or a “charge” amplifier are shown to be inherently superior to those with coupling transformers, save possibly in respect of their sensitivity to cross‐feed.
INVERSION OF SURFACE AND BOREHOLE ELECTROMAGNETIC DATA FOR TWO‐DIMENSIONAL ELECTRICAL CONDUCTIVITY MODELS*
Authors: ORISTAGLIO M.L. , WORTHINGTON M.H. 
Published: April 2006

AbstractA method for inverting electromagnetic fields induced by a line source in an earth of two‐dimensional conductivity structure is developed. Certain unique features of the finite element method are used to construct an efficient algorithm for the accurate calculation of the Jacobian matrix of partial derivatives, and the resulting linearized equations are solved using the damped least squares method.Case studies of theoretical data generated from a simple model of interest in geophysical prospecting show that, in general, it is impossible to obtain, from surface data alone, accurate estimates of the conductivity of structures buried deeper than 0.2 skin depths under a conducting overburden. The addition of borehole data to the surface data is found to increase the resolving power of the electromagnetic method dramatically. In particular, the borehole data appear to stabilize the inverse when only a poor initial estimate of the likely structure is given.
EQUIVALENCE IN ELECTROMAGNETIC (FREQUENCY) SOUNDING*
Authors: VERMA R.K. 
Published: April 2006

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

AbstractWe present a new method for the extraction and removal of the source wavelet from the reflection seismogram. In contrast to all other methods currently in use, this one does not demand that there be any mathematically convenient relationship between the phase spectrum of the source wavelet and the phase spectrum of the earth impulse response. Instead, it requires a fundamental change in the field technique such that two different seismograms are now generated from each source‐receiver pair: the source and receiver locations stay the same, but the source used to generate one seismogram is a scaled version of the source used to generate the other. A scaling law provides the relationship between the two source signatures and permits the earth impulse response to be extracted from the seismograms without any of the usual assumptions about phase.We derive the scaling law for point sources in an homogeneous isotropic medium. Next, we describe a method for the solution of the set of three simultaneous equations and test it rigorously using a variety of synthetic data and two types of synthetic source waveform: damped sine waves and non‐minimum‐phase air gun waveforms. Finally we demonstrate that this method is stable in the presence of noise.
CORRELATION METHODS OF TRANSFORMATION AND INTERPRETATION OF GEOPHYSICAL ANOMALIES*
Authors: SHRAIBMAN V.I. , ZHDANOV M.S. , VITVITSKY O.V. 
Published: April 2006

AbstractThe methods of anomaly transformations considered are based on a system of combined analysis of the geophysical field and a priori) information on the structure of a geological object. The methods involve calculation of a transformative polynomial (describing geophysical noise) which makes it possible to separate the residual field component related to the geological characteristic under study in a correlatively optimal way.The structure of the transformative polynomial is determined by the nature of the geophysical noise that is eliminated by the field transformation. Various correlation methods of anomaly transformations arise, depending on the structure of the transformative polynomial chosen.By way of example, the correlation method employed for separating the geophysical anomalies is shown to be highly effective in investigating the local geological structure.