bluuebunny/crossref_metadata_2025_split huggingface dataset:
THE OLD AND THE NEW IN SEISMIC DECONVOLUTION AND WAVELET ESTIMATION*
Authors: LINES L. R. , ULRYCH T. J. 
Published: April 2006

AbstractVarious seismic deconvolution operators can be determined by estimating a seismic wavelet and subsequently designing an appropriate inverse filter which converts the wavelet to a spike. Seismic wavelets and deconvolution operators must be estimated in a time adaptive sense due to the nonstationarity of the seismic trace. The wavelet estimation methods considered in this paper either use the assumption of a minimum phase wavelet and a random impulse response, or the assumption that the wavelet cepstrum is readily separable from the cepstrum of the seismic trace. The former assumption is required in using the Hilbert transform and Wiener‐Levinson wavelet estimations, while the latter assumption is used in homomorphic deconvolution. These wavelet estimates can be used in the design of multichannel Wiener and Kalman deconvolution operators. Multichannel usage of homomorphic deconvolution can also be implemented through various types of cepstral stacking.The discussion of deconvolution filter design focuses on the problems of filter length, degree of prewhitening, and nonstationarity. In designing time adaptive deconvolution filters, the autocorrelation function can be used to monitor the nonstationarity of the seismic trace. The autocorrelation function, which is used in the computation of least squares inverse filters, can be estimated in an optimum fashion by using the maximum entropy method. Differences between minimum phase Wiener deconvolution and maximum entropy deconvolution become more pronounced for shorter data gates. As a result, the maximum entropy approach is preferred for time adaptive deconvolution.In this paper, the performance of various wavelet estimators and inverse filters is discussed using real and synthetic seismic data. Discussions of homomorphic deconvolution and maximum entropy prediction error filtering are merged with descriptions of conventional approaches to deconvolution.
INVESTIGATION OF THE SEISMIC RESPONSE OF CYCLICALLY LAYERED CARBONIFEROUS ROCK BY MEANS OF SYNTHETIC SEISMOGRAMS *
Authors: RÜTER H. , SCHEPERS R. 
Published: April 2006

AbstractSeismic exploration for coal as well as basic scientific research indicate the existence of unsolved problems. These problems arise partly because the requirements are different from those in exploration for gas and oil and are partly due to the geological situation. The medium to be investigated is composed of cyclically changing layers with extremely high velocity and density contrast. Furthermore, the structure of the carboniferous rock is highly fractured and folded. This leads to difficulties in interpreting the seismic response of carboniferous rock. To overcome these difficulties synthetic seismograms are a useful tool.Calculating synthetic seismograms the carboniferous rock has been modelled as a sequence of seams and rock. The following results have been obtained

A single seam gives rise to a distinct reflection signal even for a thickness of 1/50 of the wavelenght.
Individual reflections are not visible from a sequence of layers containing a great number of seams and interfaces. Due to constructive interference only a few high amplitudes appear. These high amplitudes are labelled “interference reflections”.
With increasing travel time the interference reflections are mainly composed of short lag multiples such that the primary reflections have no significant influence.
The sequence of seams acts on the reflected seismic signal as a high pass filter and on the transmitted signal as a low pass filter. The cut‐off frequencies are determined by the average seam thickness, and the steepness of the slopes increases with increasing number of seams.
The interference reflections can be used for determining the geological structure at least for the upper part of the sequence.
VELOCITY DETERMINATION AND ERROR ANALYSIS FOR THE SEISMIC REFRACTION METHOD*
Authors: DAMPNEY C.N.G. , WHITELEY R.J. 
Published: April 2006

AbstractA careful examination of the seismic refraction technique details the general assumptions and processes on which it is based. It is apparent that the normal interpretive process of determining velocity by hand fitting time breaks, while necessary to identify the refractors, is subject to imprecision.We describe a digital technique that calculates velocity and its precision from the time break measurements. The technique also facilitates examining for the possibility of systematic errors. Having observed the kind of imprecision that was apparent with velocity we extended our study to layer thicknesses (and thus depth) and found that the imprecision was significantly magnified.The technique and our claims for it are supported by an example of its application to a refraction survey in the Sturt Block, Western Australia.
LONG PERIOD SEA‐FLOOR MULTIPLES AND THEIR SUPPRESSION*
Authors: TANER M.T. 
Published: April 2006

AbstractMultiple sea‐floor reflections in deep water often are not effectively suppressed by either CDP stacking nor standard predictive deconvolution methods. These methods fail because the reflection coefficient varies markedly with angle of incidence and also because of the variation of arrival time with offset and because of dip. For a reasonablly flat sea‐floor, multiples of various orders and the primary sea‐floor reflection which have all been reflected at nearly the same angle lie along a straight line through the origin in time‐offset space. This line is called the “radial direction.” The multiples which lie along this line show a systematic relationship because they all experience the same water‐bottom reflection effect. In other words, multiples behave in a stationary manner along the radial directions on multi‐trace seismic records. A technique of multi‐channel predictive deconvolution, called “Radial Multiple Suppression,” utilizes this aspect to design Wiener operators for the prediciton and suppression of water bottom multiples.The effectiveness of the technique is demonstrated by the study of field records, autocorrelations, velocity analyses, and stacked sections before and after Radial Multiple Suppression processing.
GEOPHYSICAL DATA BASES: SYSTEM CONSIDERATIONS*
Authors: DILLAHUNTY R.C. , FASH J.L. , PARSLEY L.R. , TOWNSEND D.W. 
Published: April 2006

AbstractThe use of data file systems within the areas of geological well log and reservoir analysis is now accepted as a necessity in the storage and correlation of large volumes of diverse information.Multi‐channel and three‐dimensional seismic recording techniques of various types result in a situation where the amount of processing parameters and derived seismic properties of a trace are rapidly approaching the amount of the recorded data themselves. The requirement to access these statistics efficiently has introduced the problems of data management to the seismic processing community.Much software effort has been expended in the design of algorithms for cross reference and indexing of the statistics required in signal processing. These efforts, however, are generally in the direction of a localized solution to a specific requirement and tend to ignore the data base concepts well developed within the commercial data processing community.This paper examines the applicability of commercial data base concepts to the problems of data handling in the area of geophysical exploration, sets forth some basic definitions and organizational characteristics, and describes a system for the integration of several earth disciplines within a single data base from which parameters and mapped information may be derived and indexed for the purpose of processing and interpretation.
A FORWARD GENERATED SYNTHETIC SEISMOGRAM FOR EQUAL‐DELAY LAYERED MEDIA MODELS*
Authors: VETTER WILLIAM J. 
Published: April 2006

AbstractA forward solution for the reflection response of a parallel stratified lossless medium characterized by discrete reflection coefficients and unequal layer delays, for a normally incident pressure source signal, is presented. The notation, which details the reflection history of each wavelet in a response record, facilitates systematic enumeration of all terms in the reflection impulse response model, the determination of compact closed form expressions for amplitudes and delays of multiply reflected wavelets, and the aggregation of dynamic analog groups. An equal delay time constraint on layer thicknesses leads then to the reflection sequence or synthetic seismogram structure as an infinite sum of wavelets by their order of reflection.
ELECTROMAGNETIC PROSPECTING FOR GROUNDWATER IN PRECAMBRIAN TERRAINS IN THE REPUBLIC OF UPPER VOLTA*
Authors: PALACKY G.J. , RITSEMA I.L. , DE JONG S.J. 
Published: April 2006

AbstractThe “Autorité des amenegements des valées des Voltas (AVV)” is establishing new rural settlements in the Volta valleys. First, a survey of available water supplies is performed. Economic aquifers in Precambrian terrains are deep (15–50 m) and usually occur in fractured zones accompanying faults. Such zones can be identified on aerial photographs, but their precise location on the ground is virtually impossible by visual means. Because of the small size of the aquifers, a location error of 5 m can make the difference between a productive well and a dry hole.Traditionally, resistivity profiling has been used as the means of locating the fractured zones in the field. Our studies suggest that the task can be performed faster, cheaper and more accurately by VLF and EM methods. Because of the limited choice of transmitting stations reccivable in Upper Volta, the VLF method is not sufficiently sensitive to detect conductors with a strike between 45° and 105°. The results obtained with a multifrequency, horizontal‐loop EM (HLEM) system were satisfactory in all investigated areas. During the 1980 field season, 35 target areas were surveyed. Of the 24 holes drilled so far, 23 are productive.The weathered layer is a source of distinctive HLEM anomalies, which are characteristic of the underlying rocks. Therefore, different interpretational procedures had to be developed for granitic and volcano‐sedimentary areas. Despite the high background level of in‐phase and quadrature components, which varied with thickness and conductivity of the weathered layer, aquifers could be detected at a depth greater than 30 m. Attempts were made to interpret the HLEM results quantitatively using two models: a three‐layer medium and a valley discontinuity. The latter model is more realistic, but more scale modelling will have to be performed to permit development of viable interpretational procedures. Meanwhile, phasor diagrams based on drilling and resistivity sounding data can be used to estimate the aquifer depth.
SOME ASPECTS OF HANDLING VELOCITY INVERSION AND HIDDEN LAYER PROBLEMS IN SEISMIC REFRACTION WORK*
Authors: SCHMÖLLER R. 
Published: April 2006

AbstractThere are two types of masked layers in seismic refraction work: the velocity reversal (low‐velocity layer) and the hidden layer (insufficient velocity contrast or layer thickness). On the basis of an analytical formulation of the general case of a masked layer under an overburden of plane and parallel multiple refractors the two limiting cases are discussed: the solution resulting from an uncritical interpretation of the measured time‐distance curve and the blind zone solution. Between these two limiting cases there is a variety of possible masked layer solutions. These no‐blind zone solutions—as well as the blind zone solution itself—are formulated separately for the velocity inversion and the hidden layer case.For the evaluation of some no‐blind zone solution a diagram is presented which can be used for any case of multiple refractors in the overburden of the masked layer. However, it is only for the three‐ and the four‐layer case that a blind zone interpretation by use of diagrams is advisable. Such diagrams are presented together with the basic sets of formulae which contain as parameters only ratios of velocities and layer thicknesses. As the velocity of the masked layer is usually unknown the diagrams are principally constructed to show the dependence on the masked layer velocity. This is useful for estimation of the largest possible error.
EXPLORING THE INTERIOR OF SALT DOMES FROM BOREHOLES*
Authors: NICKEL H. , SENDER F. , THIERBACH R. , WEICHART H. 
Published: April 2006

AbstractPresently, salt deposits are used for storage of energy from liquid or gaseous carrier materials. Another application being considered is the storage of radioactive material. In order to avoid possible future environmental risk, extremely high security has to be guaranteed in advance for a long period. Therefore, a very precise exploration is absolutely necessary.Exploration methods already known—which are applicable during and after drilling of test holes—help in the recognition of structures in the salt only in the close vicinity of the holes. Radiowave electromagnetic methods developed for routine measurements in salt mines provide a penetration of some hundred meters. Appropriate well‐logging equipment has been designed here for measurements from surface boreholes.Discontinuities around one borehole in the salt can be detected through the electromagnetic reflection method. When measuring between two boreholes, additional reflecting zones can be detected, and attenuation of directly pathed waves can point out material with greater absorption properties between the holes.Additional attempts to use acoustic waves of nearly the same wavelength proved that it is possible to recognize the direction of signals arriving at the receiver and allow separation of P‐ and S‐waves.Instrumentation as well as recent results are reported.
WAVEFRONT DIVERGENCE, MULTIPLES, AND CONVERTED WAVES IN SYNTHETIC SEISMOGRAMS*
Authors: HRON F. , COVEY J. D. 
Published: April 2006

AbstractSynthetic seismograms can be very useful in aiding understanding of wave propagation through models of real media, verification of geologic models derived from interpretation of field seismic data, and understanding the nature and complexity of wave phenomena. If meaningful results are to be obtained from synthetic seismograms, the method of their computation must, in general, include three‐dimensional geometrical spreading of wavefronts associated with highly concentrated (i.e., point) sources. The method should also adequately represent the seismic response of solid‐layered media by including enough primaries, multiples, and converted phases to accurately approximate the total wavefield. In addition to these features, it is also very helpful, although not always essential, if the method of seismogram computation provides for explicit identification of wave type and ray path for each arrival. Various seismograms, computed via asymptotic ray theory and an automatic ray generation scheme, are presented for a highly simplified North Sea velocity structure. This is done to illustrate the importance of the above features and to demonstrate the inadequacy of the plane‐wave synthesis method of seismogram computation for point sources and the limitations of acoustic models of solid‐layered media.
DETECTABILITY OF AN INTERMEDIATE LAYER BY PERPENDICULAR AND VERTICAL COPLANAR ELECTROMAGNETIC SOUNDING SYSTEMS EMPLOYING DIFFERENT PRIMARY EXCITATIONS*
Authors: VERMA R. K. , MALLICK K. 
Published: April 2006

AbstractThe detectability of an intermediate layer in a three‐layer earth model in the time domain has been investigated. The calculations were made for the perpendicular loop (designated system II) and vertical‐coplanar (designated system III) electromagnetic (EM) sounding systems. The primary excitation employed is a train of half‐sinusoidal and square waveforms of alternating polarity. The time‐domain response has been determined by Fourier transformation of the matched complex mutual coupling ratios into the time domain and by linear digital filtering. Top and bottom layers have equal resistivity. EM responses have been computed for conductive and resistive intermediate layer with a wide range of thickness and for two values (500 m and 1000 m) of loop‐separation. For the detectability analyses, the root mean square (rms) difference between three‐layer and homogeneous‐earth responses is adapted. The threshold value for detectability is defined as an rms difference of 10% and the measurement error is arbitrarily assumed to be of the order of 3%. It is observed that the perpendicular‐loop system is better than the vertical‐coplanar system in detecting thin intermediate layers (either conductive or resistive). For a loop separation of 1000 m and half‐sinusoidal pulse excitation, the detectable thickness ratio (h2/h1) is 0.10 by system II for the conducting middle layers; for square pulse excitation the corresponding thickness ratios are 0.06 for system II and 0.12 for system III. For a loop separation of 1000 m and half‐sinusoidal pulse excitation in detecting the resistive intermediate layers, the corresponding thickness ratios are 0.9 for system II and 2.25 for system III; while for square pulse excitation the thickness ratios are 0.55 for system II and 1.55 for system III.Results in the frequency domain and time domain (for half‐sinusoidal and square pulsed field) have also been presented for systems II and III for detecting conducting layers by considering an earth model where p1≠ p3 and p3 > p1 (p is the resistivity). The loop separa‐ tion used is 1000 m. Direct comparisons between the frequency domain and time‐domain results clearly demonstrate the superiority of frequency‐domain systems for detecting con‐ ducting intermediate layers.
ON THE EQUALIZATION OF THE TRANSFORMERLESS SEISMIC STREAMER RESPONSE*
Authors: SAFAR M. H. 
Published: April 2006

AbstractThe use of very long streamers in marine seismic surveys makes the response offset dependent. Line equalization networks are used to balance this effect.In this paper the response of the transformerless streamer system driving a charge amplifier is analyzed. Examples are given for a seismic cable 2500 m long, showing that the delay and the reduction in amplitude of the streamer impulse response in the absence of leakage are of the order of 1 ms and 0.6 dB, respectively. This means that the line equalization network currently used with the transformerless streamer system is not needed. We have also demonstrated that the presence of leakage resistance across the hydrophone group render the sensitivity of the transformerless streamer system offset dependent.
FRACTURES AS CONDUCTING DYKES AND CORRESPONDING TWO‐DIMENSIONAL MODELS*
Authors: ÁDÁM A. 
Published: April 2006

AbstractA statistical treatment of MT data from the Pannonian Basin, Hungary, based on the distortion theory of the S‐effect suggests that the local increase in crustal conductivity is connected with deep fractures.Field model measurements have recently been carried out in a shallow, quasi two‐dimensional basin of well known tectonics using MT station distances of 1–3 km. The results of the investigation and numerical modelling of near surface distortions, support the idea that deep fractures (faults) contain the conducting formations. According to 2‐D model computations, several conducting dykes at considerable depths can cause anomalies which are indiscernible from an anomaly due to a conducting layer. The significance of these results is discussed from the point of view of geothermal energy exploitation.
LIMITS OF STRUCTURAL INVERSION OF SEISMIC HORIZONS*
Authors: BILGERI D. , CARLINI A. 
Published: April 2006

AbstractTime horizons can be depth‐migrated when interval velocities are known; on the other hand, the velocity distribution can be found when traveltimes and NMO velocities at zero offset are known (wavefront curvatures; Shah 1973).Using these concepts, exact recursive inversion formulae for the calculation of interval velocities are given. The assumption of rectilinear raypath propagation within each layer is made; interval velocities and curvatures of the interfaces between layers can be found if traveltimes together with their gradients and curvatures and very precise VNMO velocities at zero offset are known.However, the available stacking velocity is a numerical quantity which has no direct physical significance; its deviation from zero offset NMO velocity is examined in terms of horizon curvatures, cable length and lateral velocity inhomogeneities.A method has been derived to estimate the geological depth model by searching, iteratively, for the best solution that minimizes the difference between stacking velocities from the real data and from the structural model.Results show the limits and capabilities of the approach; perhaps, owing to the low resolution of conventional velocity analyses, a simplified version of the given formulae would be more robust.
INFLUENCE OF VELOCITY ERRORS ON THE FOCUSING ASPECTS OF MIGRATION*
Authors: DE VRIES D. , BERKHOUT A. J. 
Published: April 2006

AbstractIn migration procedures, the velocity profile of the subsurface is the most important input information. Since, in general, this information is only approximately known, errors in the migration output due to errors in the velocity input occur in all practical applications. In migration, velocity errors and depth errors can be interchanged. This interchange property is perfect in the paraxial approximation. From this result it follows that migration with incorrect velocities may still yield correctly migrated data if the imaging principle is modified. This attractive property can be used in the stripping version of migration (recursive migration).
GUIDED LOW‐FREQUENCY NOISE FROM AIRGUN SOURCES*
Authors: KENNETT B. L. N. , HARDING A. J. 
Published: April 2006

AbstractThe presence of the water layer in marine seismic prospecting provides an effective waveguide for acoustic energy trapped between the sea‐bed and the sea‐surface. This energy persists to large ranges and can be the dominant early feature on far‐offset traces. On airgun records, there is commonly a lower frequency set of arrivals following the water‐trapped waves. These arrivals are not as obvious with higher frequency watergun sources. By using a combination of intercept‐time/slowness (τ—p) mapping on observational data and theoretical modelling, we are able to identify the origin of the events. If a very rapid increase in a seismic wavespeed occurs beneath the sea‐bed sediments, a new waveguide is formed bounded by the sea surface and this transition zone. The low frequency waves are principally guided within this thicker waveguide. Numerical filtering in the τ—p domain followed by trace reconstruction is very effective in removing the low frequency noise.