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56th EAEG Meeting
- Conference date: 06 Jun 1994 - 10 Jun 1994
- Location: Vienna, Austria
- ISBN: 978-90-73781-05-4
- Published: 10 June 1994
21 - 40 of 537 results
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Characterising seismic time series using the discrete wavelet transform
More LessWe discuss an approach to summarising the features of seismic time series using the discrete wavelet transform (DWT). The aim is to provide several informative "attributes" which characterise lateral changes in the seismic traces. These attributes can be mapped for visual interpretation (Fig. 3) and also used to group together or to separate traces in regions from a survey, by application of statistical clustering techniques. Such clusters can inform extrapolation of observed characteristics from wells, or point to regions for more detailed examination.
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Wavelet transform (WT) in geophysical signal processing - An application to velocity analysis
Authors G. Olmo, L. Lo Presti and U. SpagnoliIn geophysics the reflected signals are often processed using stationary signal approximation witkin a timespace window. The Wavelet Transform (WT) represents a powerful analysis tool for nonstationary signals (e.g., Rioul and Vetterli, 1991); in this context the reflection seismology represents a promising field of application.
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Wavelet estimation via fourth-order cumulants
More LessA recent paper by Lazear (1993) holds out the possibility of directly measuring wavelet phase from seismic data, with no restrictive assumptions on the nature of the phase spectrum. His approach is "4th-order cumulant matching", in which an initial guess for the wavelet is iteratively updated until its 4th-order statistics match those of the data. A relatively large number of traces, several hundred at least, are needed to obtain reliable results, so the process does not readily lend itself to a trace-by-trace or even a shot-by-shot deconvolution. Even so, if reliable wavelet estimates can be obtained in typical circumstances this would be a considerable breakthorough, cutting across a number of existing uncertainties and difficulties in this area. In this paper I investigate the accuracy and the limitations of the 4th-order cumulant approach to wavelet estimation. I propose a procedure that can be used to assess the reliability of the derived wavelets, and I investigate the preprocessing necessary to improve their reliability. I demonstrate the technique as part of a quality control procedure that tracks the seismic wavelet through the different stages of a processing sequence.
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Successful estimation of Q from surface seismic data - A case study
Authors R. Dasgupta and R. A. ClarkAttempts have been made to estimate seismic quality factor, Q. of different rocks in the laboratory as well as from different forms of seismic data and the efforts have met with varied degree of success. The computation of Q from VSPs and check-shot surveys is quite successful (Ganley and Kanesewich,1980. Jannsen et al.1985 ; Stainsby and Worthington, 1986; Tonn,1991) whereas there exists no reported evidence of its successful estimation from surface seismic data. The main reason this is attributed to the multiplicity of the ray-paths associated with surface seismic data, where every sample represents a different ray-path. Apart from this, even for a CMP, path lengths and the reflectivity/transmissivity vary from one trace to another. Dasgupta and Clark (1993) proposed a method of computing Q from surface seismic data which solves the problems arising due to multiplicity of the ray-paths, and tested the technique using model data. In this paper, the method is reviewed and results of computing Q from surface seismic data from the central part of the southern UK North Sea are discussed. The method is further validated by comparison of the surface seismic results to estimates from VSPs both adjacent to the seismic line and in similar lithologies elsewhere in the North Sea.
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Spectral induced polarization studies of a Ni-Cu ore deposit
Authors H. Soininen and H. VanhalaLaboratory and field spectral IP results are presented from the Keivitsa Ni-Cu deposit in northern Finland. The deposit is related to basic-ultrabasic intrusive rocks (a layered basic intrusion), and has been estimated to contain more than 1000 Mt of low grade sulphide ore. Low sulphide content, high Cu/Ni ratio, and enrichment in platinum group elements are other characteristic features.
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Rapid least-squares inversion of apparent resistivity pseudosections
Authors M. H. Loke and R. D. BarkerA fast iterative inversion technique for the interpretation of data from resistivity imaging surveys using a microcomputer has been developed. This technique is based on the smoothness-constrained least-squares method and it produces a two-dimensional subsurface model directly from the apparent resistivity pseudosection. The inversion method is completely automatic and it does not even require the user to supply a starting model. In the initial iteration, a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically. For subsequent iterations, a quasi-Newton method (Broyden, 1965) is used to estimate the partial derivatives. By avoiding the direct calculation of the partial derivatives, the computer time and memory space required by the finite-difference method to calculate the apparent resistivity values can be reduced by about eight and ten times respectively. The time taken to solve the system of normal equations for the least-squares method is also reduced by using matrix updating techniques associated with the quasi-Newton method (Golub and van Loan, 1989). Overall, this quasi-Newton inversion technique is about eight times faster than the conventional Gauss-Newton least-squares method.
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Modelling self potential anomalies from electronic conductors
By O. B. LileThe theory on the mechanism of SP anomalies over electronic conductors which Sato and Mooney published in 1960 has, until now, not been seriously challenged in its basic principles. The SP anomalies are explained by the shortcircuiting of the high redox potential in the pore electrolyte at the surface and the low redox potential deeper down. The conductor itself is inert and functions only to transport electrons from the low redox to the high redox environment. The redox potential is controlled by the oxygen activity. Close to the surface the pore water will regularly be supplied with rain water rich in oxygen. Especially in the porous and permeable overburden the pores will often be flushed by water coming from the surface. Beneath the grundwater table there is a lateral flow of groundewater in the permeable ocerburden with little exchange of water with the underlying bedrock. While the overburden may have a porosity of 30%, the porosity of a metamorfic bedrock may be 1-5%. On the basis of this discussion, a profile of the redox potential distribution in the ground can be drawn.
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SP Monitoring during the hydraulic fracturing using the TG-2 well
Authors N. Kawakami and S. TakasugiAs a part of the "Technology for Increasing Geothermal Energy Recovery" project being undertaken by the New Energy and Industrial Technology Development, Organization. (NEDO), a hydraulic fracturing test was carried out at the TG-2 well in Yunomori area, Iwate prefecture, in November 1992.
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A Study on nonlinear spectral IP phenomenon
By P. AlikajThe Spectral Induced Polarization (SIP) method according to the Cole - Cole model proved to be an interesting tool in metallic mineral exploration, particularly in texture discrimination. It opened a new scope in scientific studies and practical exploration on both the Frequency and Time Domains. However, while the mathematical treatment of this method was highly developed, the same thing did not happen in the explanation of its physical (electrochemical) basis. Such was the goal of the study presented in this paper, which led a new treatment called Nonlinear Spectral Induced Polarization (NSIP).
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Airborne electromagnetic anomalies related to low-conductivity 3D bodies
Authors M. Peltoniemi, R. Bars and G. A. NewmanResponses of a multifrequency, multicoil AEM system were modeled numerically for poor, 3D electrical conductors embedded in a resistive bedrock and overlain by an overburden of poor to moderate conductivity. Results were computed for horizontal coplanar coil configuration with coil separation L = 6.45 m and two frequencies, 7837 Hz and 51250 Hz. The EM3D code (based on Newman et al. 1989) used in the modeling is a set of programs, which takes into consideration both the induction currents, and the galvanic currents in the host rock and overburden. The separate programs are necessary to facilitate the solving of models with high or low conductivity contrasts and different primary-field sources.
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Multidimensional interpretation of TDEM data collected for mineral exploration in Israel
Authors L. Hellwig, M. Goldman and A. HoerdtDuring a feasibility study survey in 1987 thirteen central loop time-domain electromagnetic soundings were carried out over the sediments in Makhtesh Ramon, Israel. The aim of these measurements was to trace the subsurface extension of known quartz-syenite intrusions.
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Negative response of coincident loop above layered polarizable ground
Authors H. M. El-Kaliouby, S. A. Hussain, E. A. Eldiwany and E. A. HashishTransient Electromagnetic (TEM) response of Coincident loop above dispersive conductive layered ground shows an evidence of Induced Polarization (IP) effect which appears in what is termed as Negative-Response (NR) phenomenon. This phenomenon may be used as a simple guide for the detection of under-ground polarizable targets (Lee 1981 and Smith and West 1988a).
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Seismic processing on single- and multi-offset ground penetrating radar
Authors M. Grasmueck and H. HorstmeyerA comparison study of single- and multi-offset ground -penetrating radar (GPR) has been conducted across a crystalline terrane in central Switzerland. Electromagnetic waves can travel relatively long paths in crystalline rock, thus providing an optimum media for multi-offset GPR surveys with long transmission ranges.
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Resonance based target recognition for ground penetrating radar
Authors T. Campbell and J. M. TealbyThe ability to detect voids with Ground Penetrating Radar (GPR) has been recognised as one of its strengths [Campbell et al., 1993]. This is of importance in civil engineering, building assessment, and archaeology. The dielectric difference between an air void and its soil/ground surround (dielectric half space) is sufficient to enable comparatively easy detection.
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3D Processing of GPR data
By M. FritscheWith the application of GPR becoming more and more established in environmental engineering tasks, there is an increasing need for 3D data acquisition and processing capabilities. Making use of the full information present in data volumes that have been acquired along parallel profiles, a 3D diffraction stack will deliver better results in terms of signal-to-clutter ratio and positioning accuracy of buried objects. The most important factors, governing the output quality are the aperture width used for the stack, inline and crossline sampling intervals and possibly soil attenuation.
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Application of ground penetrating radar to geotechnical problems
Authors R. Fruhwirth and R. MuellerEspecially in the field of Geotechnics and environmental research there is an increasing demand for a method, which is applicable for the analysis of the subsurface and materials embedded therein in a flexible and rapid way and without too big a technical or financial effort. Among various geophysical surface and well logging methods the Ground Penetrating Radar (GPR) has turned out to be the one, that meets most of the previous requirements.
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Ground Penetrating Radar data interpretation in the Radon space
Authors P. A. Vercruijsse, M. Vermaas, J. W. A. W. Schoolmeesters and M. CsonkaIn recent years Ground-penetrating Radar (GPR) techniques have gained interest for the characterization of shallow subsurface properties. The areas of application of GPR in shallow subsurface characterization are numerous: e.g. mapping ice thickness, water depth, bedrock depth, soil stratigraphy, and groundwater depth (Davis and Annan, 1989) . Fisher, McMechan and Annan (1992) argued that multichannel recording and standard seismic processing can be used to improve the quality of GPR data.
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Eccentricity-migration for the imaging of pipes in radar reflection data
Authors C. Stolte, D. Ristow and K. -P. NickHyperbolas are a widely observed feature in reflection data aquired with ground probing radar. Zero-offset migration of these hyperbolas rarely improves the subsurface image. Often energy is smeared out and weak reflections disappear. The reasons are perturbations in the local geology influencing the velocity field, uncertainties introduced by uneven movement of the antennas, the bistatic character of the antenna as well as the geometry of the buried objects. In this work the target geometry is incorporated into migration to enhance the imaging of pipes and tables.
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Monitoring of a water well field by georadar
More LessGeoradar has been successful in detecting sudden steps in the water table which are created by thin, steeply inclined clay layers in push moraines in the Netherlands (Van Overmeeren, 1993). An example is shown in the georadar section of Figure 1, where an abrupt offset of 30 ns in the observed water-table reflector. (Fig. 1a) has recently been confirmed to be a groundwater step of considerable size (1.7 m) by test drilling (Fig. 1b). The jump in the reflector was traced along a number of parallel lines, where a further series of 9 horeholes confirmed the presente of important steps in the water table and proved the georadar predictions on depths and offsets to be remarkably close to reality.
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Georadar surveys in ice-pushed moraine areas in The Netherlands - Processing and interpretation
Authors B. C. Scheffers and M. CsonkaGeoradar becomes more and more common in hydrogeological and environmental studies as a cheap continuous profiling tool. In sediment filled basins with low conductivity and deep water table the maximum penetration achievable is approximately 40-50 m. Georadar, therefore, can be applied as a general geological reconnaissance tool. This paper will discuss the application of georadar for mapping the structural geological setting in a region of glacial deposits and icepushed moraines. Processing is carried out with seismic processing software. Interpretation is performed using all information available.
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