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53rd EAEG Meeting
- Conference date: 26 May 1991 - 30 May 1991
- Location: Florence, Italy
- ISBN: 978-90-73781-03-0
- Published: 28 May 1991
221 - 240 of 315 results
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A high-density 3-component reflection-refraction survey across an exposed lower crust in Southern Italy
Authors E. Lüschen, M. Romanelli, J. Feddersen, R. Nicolich and L. CernoboriThe outcropping crystalline basement of the Serre Mountains in Calabria (Southern Italy) presents a tilted block containing a nearly complete section of the continentallower crust (granulites, metabasites). This has been regarded as key area to study the structure, composition and evolution of the Hercynian lower crust in a multidisciplinary approach. Petrological, petrophysical and structural data are available from surface mapping and laboratory experiments at varying P-T conditions on rock samples. Using these data as direct input for modelling techniques, the seismic in-situ characteristics, e.g. the reflectivity and the P- and S-wavevelocities can be interpreted. Since direct observations of the actual lower crust are not possible, this calibration of a fossil lower crust is expected to provide a better understanding of deep seismic results.
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Shot gathers amplitude and frequency processing and fast prestack depth migration. Application to ECORS deep reflection seismic data
Authors A. Bitri, D. Rappin and J. M. MarthelotStacked sections of ECORS deep reflection seismic profiles are characterized by: - an important variability in the lateral continuity of the reflections, - the presence of transparent zones, - the occurrence of highly dipping reflections, - the often strong and complex reflectivity of the lower crost. The CDP stacking procedure may not be well adapted because: - the quality of the shot gathers is quite variable, - the reflection events are assumed to have continuous hyperbolic moveout, - the lateral smearing of the CDP on dipping reflectors is large since the spreads used are long, - normal moveout is a dip selective procedure.
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The application of shear waves to studying the upper part of section with view to detecting the karst zones
Authors T. I. Oblogina and D. A. KouchenevThe shear SR-waves were used for studying the upper part of the geological section in the Moscow region. The field observations were carried out by the refraction and reflection surveys.
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Algebraic reconstruction for 3D seismic quality control
More LessDerived from medical applications, algebraic reconstruction techniques (ART) were first implemented by geophysicists for crosswell tomography (Bois et al, 1972 ; Bishop et al, 1985 ; Paulson et al, 1985; lvansson, 1985). 2-D refraction cases were recently studied (krajewski et al, 1989 ; Ruhl and Luschen, 1989), using a particular ART variant known as Simultaneous Iterative Reconstruction Technique (or SIRT), whereby each model bin slowness is modified when all raypaths pertaining to that bin have been taken into account .
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Two case histories of diffraction tomography applied in engineering geophysics
More LessThis paper presents the application of diffraction tomography to real data in engineering geophysics. In the past many papers developed the theory of diffraction tomography and discussed possible applications (Devaney and Beylkin, 1984; Wu and Toksöz, 1987). This new inversion technique is based on the acoustic wave equation. It tries to reconstruct the velocity perturbation against a constant background (constant density assumed) from a scattered, diffracted wavefield. In contrast to traveltime tomography where only picked times of some phases are inverted diffraction tomography uses the full wavefield.
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Deep and shallow aquifer modelling from gravity and reflection seismic data in Southwestern Denmark
Authors S. Thomsen, H. Lyke-Andersen, B. H. Jacobsen and R. FribordGravimetry is efficient and cost effective as a means for revealing the horizontal geometry of shaIlow as weIl as deep aquifers. Depth resolution of this method however is poor.
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Integration of mineral exploration data using fuzzy set theory
Authors W. M. Moon and P. AnThe traditional geophysical information processing theory is founded on Boolean logic and in Euclidean space. However, accurate assessment of given sets of multiple layer exploration data requires that one must define preciseness of one's knowledge as precisely as possible. Fuzzy logic provides a theoretical means of quantifying imprecise information, which was first utilized as early as 1965 and has been extensively applied since in engineering and related sciences. Fuzzy set theory is tested and applied to integrate geophysical, geological and remote sensing data sets in this research.
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A combined square array resistivity and magnetic survey in the archaelogical site of Noville, Coruna, Spain
Authors M. J. S. Matias and F. E. R. AlmeidaGeophysical exploration techniques have been adapted to archaeological exploration successfully. The use of Exploration Geophysics in Archeology has proved to be a fast and economical tooI in excavation planning of archaeological sites.
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Bedrock fractures as seismic reflectors
By O. OkkoThis paper presents the interpretation of reflections from same very shallow fracture zones located at the depth of less than 250m and recorded in soundings carried out on bedrock outcrops and in boreholes. The resolution of the seismic reflection method is compared to the corresponding acoustic logs and other geophysical and geological investigations.
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Conventional and modern seismic investigations for elastic properties determination in gneiss-schist. A case history
Authors J. Louis, T. Papadopoulos, G. Drakatos and P. PantzartzisRefraction seismics and modern tomographic surveys were employed at Platanovrissi damsite on Nestos river in Northern Greece in an effort to investigate the dynamic elastic properties and rockmass condition of gneiss-schist which outcorps in the area and it is prone for a hydroelectric dam construction.
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3-component colored 'attribute seismograms'
Authors H. Steentoft and S. WendeAn integrated system for recording, processing and interpretation of seismic data has been developed in order to increase the resolution in near - surface measurements and to perform first analysis during the field measurements. An extensive 3 - component - processing software - package was installed on a 68000 CPU micro - computer for completion of this processing system.
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Test park for environmental geophysical measurements
More LessIn the last decade the role of geophysics has been increasing in prospecting and prevention of environmental damages in Hungary. The reason is that geophysical methods are the most effective, quick and economical tools and what is similarly important, they can be used without causing damages to the environment. Inspite of these favourable features these methods have not spread in the expected degree, because theory for application of geophysical methods in environmental protection has not developed sufficiently and application has not been proved with practical measurements.
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Geoel: An IBM PC algorithm for the automatic processing and graphic presentation of geoelectric data
Authors G. -A. Tselentis and G. DelisThis paper addresses the problem of automatic processing and interpretation of geoelectric data with personal computers. The main algorithm is divided into two processing stages. During the first processing stage, the field curve is aproximated by a group of layers which are determined automatically by the program in such a way that the resulting theoreticaI curve describes as close as possible the field curve. This operation is performed in the resistivity - space domain and the optimum number of layers needed to describe the resistivity distribution versus depth is determined from the algorithm.
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Model curves for vertical electrical sounding over 2D structures
Authors J. Pous and P. QueraltVertical electrical sounding is one of the most used electrical methods in Geophysical Prospecting and its application is restricted to those problems according to structures that do not differ strongly from stratified media. Even in these situations the simplicity of a near one dimensional earth approach is sometimes not reached and some important lateral resistivity variations may appear.
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Borehole-to-surface D.C. resistivity and time domain electromagnetics monitoring of contaminant plumes. A model study
Authors A. Zerilli and B. A. JamesContamination of ground water and soils is one of today's most pressing problem. It has its origin in a number of causes, such as improperly buried wastes, poor effluent disposal and improper use of agricultural and industrial chemicals and spillages. The waste migrate along paths determined by subsurface soil types, stratigraphy and presence of faults, shear zones and fracture zones.
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Transient airborne EM applied to geological mapping
By A. P. AnnanGEOTEM is a high performance time domain airborne EM (AEM) system developed for mineral exploration and geological mapping applications. The historical focus for transient AEM has been on direct detection of massive sulfide type targets or other mineralized zones which have intrinsically high electrical conductivity. A bi-product of airborne EM surveys, particularly transient airborne EM surveys, has been a wealth of data which has considerable potential for mapping geology but which has seen limited use. With the advent of high quality digital GEOTEM data, new applications are being addressed.
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Ground penetration radar survey design criteria
Authors A. P. Annan and S. W. CoswayGround penetrating radar (GPR) is now becoming a weIl accepted geophysical technique. Basic criteria for the design and execution of surveys as weIl as the processing of data subsequent to these surveys have yet to be established in any satisfactory form. Experience from many sites over the past 15 years have provided many useful guidelines for survey design and data presentation. In this paper, criteria which are helpful to the new user in this field are presented.
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The TRH procedure for transient soundings. Practical results and some new ideas
By K. L. KakasOn the Oostende meeting of EAEG in 1986, a simple depth inversion of transient (time-domain EM) soundings was suggested by the author for the CIL (coincident loop) layout. This procecure (called TRH, because the transformation goes from the time to depth via resistivity) has been proved serviceable for preliminary interpretation of sounding curves, and combined with master curves and/or interactive curve fitting, the results seem to be stables and geologically acceptable.
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Magnetic interpretation using the 3D analytic signal
Authors W. R. Roest, M. Pilkington and J. VerhoefWith the availability of large digital datasets of magnetic data (e.g. Committee for the Magnetic Anomaly Map of North America, 1988) the need for automated techniques for the analysis of magnetic anomalies is growing. Several methods have been developed that have been successful in predicting source characteristics, using certain assumptions.
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Apparent density mapping from gravity data using the walsh transform
Authors P. B. Keating and M. PilkingtonThe purpose of apparent density mapping is the identification of uniform density areas that can be related to geological units. Apparent density maps are usually calculated by linear filtering in the Fourier domain (Gupta and Grant, 1985). The Earth model is then a set of right rectangular blocks extending to depth d, below which significant contributions to the residual gravity anomaly do not arise.
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