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54th EAEG Meeting
- Conference date: 01 Jun 1992 - 05 Jun 1992
- Location: Paris, France
- ISBN: 978-90-73781-04-7
- Published: 01 June 1992
361 - 380 of 405 results
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Multivariate statistical analyses of geophysical multi-method prospecting data as applied to geologic mapping
By D. G. EberleThe simultaneous evaluation of multi-method geophysical observations - most profitable in geologic mapping and known as integrated or complex interpretation - has been usually performed manually. This man-made synopsis is laborious. Its result strongly depends on the skill and experience of the geophysicist. To obtain more objective and efficient results it was necessary to develop an automatic and quantitative procedure. It is based upon multivariate analysis methods which offer a promising approach to the integrated interpretation, as LANNE (1986) demonstrated. Our paper is thought to promote the use of multivariate analysis methods in applied geophysics.
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Time domain EM measurements with grounded cable
Authors O. B. Lile, J. S. Ronning and B. QianA time domain electromagnetic instrument has been constructed by the Geological Survey of Norway. The instrument records the horizontal and vertical magnetic field simultanously in 8 channels. One of the channels has a time window in the pulse-on period, from minus 0 .02 to 0.00 milliseconds.
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Two-dimensional magnetotelluric modelling: a case study from the Northeastern boundary of the Danube-Raba Lowland in Hungary
More LessThe two studied, 34 and 52 km long parallel profiles are located over a gradually deepening sedimentary basin (Fig. 1). Northward these profiles terminale near the Rába Line which separates the East Alpian tectonic unit from that of the Transdanubian Central Range and the profiles are nearly perpendicular to its strike direction. Magnetotelluric profiles measured earlier over the latter tectonic unit have revealed a conductive zone within the crust.
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Separation of the fields and transformations in the space domain in VLF resistivity prospecting
Authors R. Guerin, P. Andrieux and A. TabbaghInterpretation of VLF-resistivity mails has often proven to be difficult due to the interaction of anomalies of different origins and different depths. We propose new techniques, aimed at separating the effects of different sources and thus improving the quality of the final interpretation.
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Inversion of HEM data for resistivity and susceptibility
By P. WalkerAn algorithm has been developed for processing helicopter electromagetic (HEM) data for mapping both conductivity and permeability variations in the earth. The motivation behind its development was to correct HEM resistivity maps for the presence of magnetite in a gold prospect in northern Norway, and to use those corrections to produce susceptibility maps from the electromagnetic data. Gold in this area is known to be associated with breaks in graphitic conductors which are often associated with oxidation of graphitic schist and magnetite in the adjacent metadiabase.
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On the importance of determining electrical anisotropy in hydrogeological investigations
More LessMeasurements with electric and electromagnetic methods on the Earths surface have a limited capability of resolving the conductivity structure of the ground. Thin layers that are not individually resolved will cause an apparent anisotropy - macro anosotropy - of an interpreted layer.
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Combined traveltime inversion of shallow seismic data: data acquisition and inversion
More LessNear offset traces are usually not recorded during normal seismic data acquisition. If the near offsets are nevertheless recorded, shallow reflection can not be identified due to a combination of groundroll and shot generated noise. This shallow window can provide useful information about the velocity distribution in the near-surface necessary for further processing. In this paper a method for data acquisition and processing of shallow seismic data to obtain macro velocity models to a depth of approximately 500m is described.
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Perfecting the migrated-based travel-time reformulation of the 2D seismic inversion problem
Authors F. Clement and G. ChaventIn this work, we present two steps toward the implementation of the Migrated-Based Travel-Time (MBTT) reformulation for the determination of 2D background velocities: we first indicate how to define the propagator/reflector unknowns required in MBTT; then we give a very simple a priori guess of the new reflector unknowns
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Comparison of gradient and Quasi-Newtonian inversion
Authors G. Lambarde and E. ForguesThe power of Seismic inversion Algorithms has groven particularly rapidly during the last ten years. However as the problem is highly nonlinear for the relation between the velocity field and the seismic record the most works dealt with the recovery of the linear part of the model (the short wave lengths of the velocity). Also this study revealed to be difficult. The first reason is the cost of the forward modelleng essential in all inversion processen. The second one came from the huge dimensions of the problem. In fact for complex applications it is no more possible to compute the explicit solution (involving the inversion of a big square matrix: the hessian) and iterative algorithms have to be implemented.
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Complex convolution decomposition (CCD) - The new approach to seismic dynamic analysis
Authors G. M. Mitrofanov and A. G. MadatovThe approach apples to the processing of the reflection seismograms. It combines several methods used in the seismic data processing. They are spectro-statistical method (S. Goldin, G. Mitrofanov) or surface consistent corrections (M. Taner, G. Cambois), ray-method of seismic waves propagation (B. Gelchínsky, A. Alekseev, V.Babich) and AVO-analysis (W. Ostrander) on frequency.
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Complex convolution decomposition (CCD) and new possibilities at detail investigation of attenuation
Authors V. P. Kovaljev, A. G. Madatov and G. M. MitrofanovThis paper represents some applications of CCD technique at the investigations of transmission losses into macro model and multiple-scattering reflection mechanism into local model of medium.
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Fast and effective method of waveform inversion
Authors I. Kondratjev, Y. Kiselev, A. Mikhaltsev and A. PolovovAs it is well known, the seismic inverse problem has non-unique solution. To overcome the non-uniqueness and to find the true solution among many suitable solutions it is necessary to take into account a priory information. Moreover the larger the volume of a priory information is used, the higher resolving power and accuracy of seismic inversion methods are achieved.
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Complimentary features of geophysical methods and computational aspects of joint data inversion
By A. AnatolySometimes seismic processing, when used separately, will not yield a correct silution of a seismostratigraphic problem due to the lack of information and instability of the computational procedures. The joint data inversion implementing a few methods (seismic and gravity, for example) can result in a correct solution.
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Direct Bayesian algorithm for the soft inversion of seismic data
More LessOne of the key problems in Reservoir Characterization relates to the reliable description and visualization of reservoir heterogeneities with respect to properties such as porosity, permeability, thickness, lithofacies types, fracture/fault orientations, sand body geometry, etc. The inherent non-uniqueness associated with this problem has prompted considerable interest in the development and application of stochastic (ie. probabilistic) imaging techniques.
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Fuzzy velocity inversion
By Y. YaoA new velocity inversion technique which can incorporate different kinds of a priori information is developed. Using fuzzy set theory makes it possible to model partially defined, imprecise, subjective information as well as all-defined, precisé, objective information. Fuzzy constraint sets in parameter space and data space are constructed and used to etage fuzzification of tost function. Final solutions are computed by using simulated annealing.
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Ground probing radar characterization of the settlements produced by building loads over soft sediments
Authors A. Casas, J. M. Carmona, A. Permanyer, V. Pinto, L. Rivero and A. ValencianoA reconnaissance program of geophysical surveying was conducted during 1990 to evaluate the application of ground probing radar for characterization of subsurface foundation disturbances associated with historical buildings. The study combines geophysical surveys and historic-archaeological investigations. The results obtained are then compared with standard geological engineering evaluation tests.
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Arctic '91: seismic investigations in the central arctic ocean
Authors W. Jokat, V. Buravsev, Y. Kristoffersen and G. Uenzelmann-NebenIn summer 1991 the two ice breaking research vessels ODEN and POLARSTERN were able to carry out extensive geoscientific research programs in this inaccessible region. In total 1500 km of multichannel seismic data could be collected in the Arctic basins. For acquisition a 300m streamer (12 channels) and a 24 ltr airgun array were used.
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Sea bottom geophones for seismic surveying
Authors I. Magnus, J. K. Hovde, K. -A. Berteussen and P. KristiansenIn a previous presentation (Kolbjernsen et al, 1991) it was shown that sea bottom geophones give excellent results when monitoring the effect of accidentally injected gas. This demonstrated that such instnuments could be used with great advantage when passively listening to activity in the underground.
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Seismic acquisition with a slant cable: Sigsbee Scarp Area, Gulf of Mexico
Authors S. K. Sahai and J. B. SintonExploring for hydrocarbons in areas of complex salt tectonics in the marine environment is a difficult problem. In some cases, potential oil and gas reservoirs lie beneath massive salt bodies. Imaging the subsalt features with traditional seismic methods is not very successful because of the attenuation of high frequencies in salt. Low frequencies fair better for deeper penetration in the ground, but their amplitude is very small. However, the low frequency amplitude increases as the depth of the hydrophones increases. This is due to the influence of the ghosting operator in such a way that the ghosting notch occurs at lower frequencies. In order to preserve the high frequency information as well as boost the low frequencies, the slant cable technology has been used in the oil industry, albeit in a limited way. The idea involves towing a cable that has a series of hydrophones at various depths in the water. The depth of the hydrophones linearly increases with offset. Current technology limits receiver depth to about 50 m .
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Applications of real-time 3D processing
Authors P. Haskey and D. KitcherA continuing problem in the application of 3D seismic techniques is the delay of several months which is still normal between the conclusion of the data acquisition and the availability of 3D migrated data for interpretation. Advances in the power of processing hardware are largely offset by the increasing size of the average 3D survey. The delay is frequently compounded by the increasing complexity of the processing required of the navigation data, considerable time and effort being generally expended on the problem of streamer positioning.
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