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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
321 - 340 of 405 results
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Joint interpretation of high frequency seismic and GPR sections
Authors E. Toros, E. Hegedus, L. Hermann, M. Pattantyus and Zs. PronayExperimental shallow seismic and ground penetrating radar measurements were performed in a tectonic zone of the Pannonian basin considered as one of the youngest. The aim of this project was to examine the usability of these methods, covering different depth interval, the history of movements along a recent fault system.
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Archaeological prospecting using GPR: some case histories
Authors A. Kathage, S. Lorra and H. SteentoftArchaeological prospection requires a fast, cheap and nondestructive survey - technique with high resolution. On the one hand, exploration with ground penetrating radar can fulfill most of the requirements, but on the other hand, the radargrams as the result of radar surveys are hard to interprete. Case histories help to increase our experience and knowledge how to extract information out of georadarsections.
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Pulse broadening of subsurface radar signals
Authors A. Siggins and G. TurnerGround penetrating radar is a technique that is noted for its potential for high spatial resolution. This compensates somewhat for the relatively modest ranges usually achieved in geological media. High resolution is achieved by generating radio frequency pulses in the VIS to UHF band with band-width to centre-frequency ratios approaching unity. Consequently, subsurface radar pulses in the time domain have pulse widths of the order of nanoseconde providing, in principle, goud definition of subsurface interfaces .
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G.P.R. Investigations in the 'Talg de Luzenac' open-air mine. Ariege, France
Authors M. Picollo, G. Niccolini, G. Spanghero and D. GrigoriouDuring the development of a research programme within the framework of the EEC Primary Raw Material Programme 1990-92, "Acquisition rapide de données structurales pour l'optimistion de l'ensemble foration-tin-changement dans les exploitations a ciel ouvert", a Ground Penetrating Radar survey was carried out inside the "Talc de Luzenac" open-air mine (Ariège-France). Many G.P.R. profiles was performed with a GSSI SIR System 10 with 100 and 500 MHz transducers.
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Complex conductivity of sandstones between 10-4 Hz and 10-6 Hz
Authors D. Ruffet, Y. Gueguen and M. DarotTransport properties of rocks, such as permeability or electrical conductivity are of great interest to the studies of reservoir engineering. Electrical conductivity is related to porosity and fluid saturation of the rock. Electrical conductivity is also a function of permeability, but the relationship between these two parameters is not universally predictable by a standard mathematical equation. The study of electrical properties provides information on pore geometry and pore surface area, because both the transport of free charge carriers in the pore space and polarization at the poregrain interfaces contribute to the total conductivity. This work focuses on complex conductivity because this parameter is related to the microgeometry of rocks, and possibly to the fractal nature of the internal surfaces, so that there is potentially an important source of information in the frequency dependence of electrical properties.
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Geophysical prospecting of Maar-type basaltic craters in Hungary
By C. TothAbout 4 million years ago a violent volcanic activity disturbed the calm Pannonian Take system filling up the Carpathian basin. In Hungary the repeated volcanic eruptions not only built up scenic basalt cones (Badacsony, Somló, Sághegy etc.), but-special tuff rings were produced as well. Later on, water filled these maar-type tuff rings and crater lakes came into being. In this closed and silent lakes the nutritive richness, coming from dissolution/decomposition of the volcanic material, yielded an extensive pullulating of algae. Decease and sedimenting of the organic mass produced the alginite, the alga rock. In most places the algaic deposits were covered by basaltic bentonites.
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Can scalar AMT be helpful to MT measurements?
More LessIn very recent years, the audiomagnetotelluric (AMT) method has come into increasing usage in projects with the magnetotelluric (MT) method. The first is a high frequency (>1 Hz) application of the MT that gives information about local structures at shallow depth. With the MT it is possible to study regional structures, whose effects are however often affected by the local ones .
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Conductivity - depth imaging of airborne EM data
By J. MacnaeConductivity Depth Imaging (CDI) for step response airborne electromagnetic (AEM) data was first described by Macnae et al (1990) . In this process, AEM data are transformed into a (smoothed) conductivity-depth section under an assumption that the physical properties (geology) are quasi-layered. While the CDI method of Macnae and Lamontagne (1987) is only applicable to step response data, other authors such as Eaton and Hohmann, (1989), Polzer (as described in West and Bailey, 1989) and Nekut(1987) have developed modifications suitable for impulse rather than step response data. Since then, a further mathematical development has allowed the CDI method to be applied to arbitrary waveform EM data in some limited cases; most notably the Geotem and Questem commercial airborne EM systems which use an approximately half-sinusoidal transmitter waveform with significant off-time.
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Magnetotelluric results from the Island of Mallorca
Authors J. Pous, P. Queralt and A. MarcuelloGeoscientists are becoming increasingly interested in the crustal structure of the Western Mediterranean Sea. Here, is located the island of Mallorca, part of the Alpine system linked with the Betic range. This island is formed by two Neogene imbricated thrust systems stacking Mesozoic rocks (Serra de Tramuntana along the NW coastline, and Serres de Llevant along the SE coastline) with a central part constituted by small post-orogenic basins.
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Calculation of gravity and magnetic anomalies of two- and three- dimensional sources having arbitrary geometry and density or susceptibility distribution
More LessThe gravity and magnetic anomaly of complicated two- or three- dimensional sources having arbitrary geometry and physical parameter distribution (density or susceptibility) can be calculated using a combination of analytical and numerical integration. We can, for example model intrusives or folded sedimentary beds altered by regional metamorphosis using sources whose upper and lower surf aces and the physical parameters are arbitrary functions of horizontal coordinates.
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The seismo-electrical effect - first ideas of recording and processing
By V. KrugSince the thirties we have been knowing the terminus seismoelectrical effect . At that time American, German and Russian scientists were studying this phenomenon . First useful field tests were carried out then by Marmer and Sparks (Geophysics 24 (1959)2, IS. 297-308). Since the seventies seismological research has drawn more attention to the effect. The current paper will present results gained from digital seismic surveys.
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Far zone that is not wave zone after all? electromagnetic sounding induced by grounded electric dipole over conductive layers covered by non-conductor
Authors J. Csorgei and S. SuleIn the field of the theoretical research of controlled source frequency sounding even in the sixties such a paper was published [1], that dealt with the electric component of the field induced by grounded electric dipole over a horizontally layered half-space included a non-conductive layer. The odd thing about the model computations was the unexpected difference in the far zone comparing with the magnetotelluric theoretical curves/wave-zone/ /Fig.1/. Both in apparent resistivity curven and phase curves interference phenomena can be seen that are characteristic features of the near and transitional zones.
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Physical modelling of frequency sounding and transient electromagnetic sounding
Authors A. N. Kuznetsov, A. A. Gromov, A. I. Ivanov and A. A. PudovkinFrequericy sounding (FS) and transient sounding (TS) are used to solve various geologic problems from ore prospecting and engineering survey in relatively near surface sections (FS), to oil and gas prospecting in large depths and Barth crost structure investigations (TS,TS-fixed source sounding). One of the major problems of the acquired data interpretation is taking account of model errors caused by non-horizontality of geologic interfaces studied as well as estimation of lateral effects of local and extended inhomogeneities of the medium on the sounding data.
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Outlook of IP anomal effect of a body settled in the electric field of an underground point current electrode
By A. FrasheriThe borehole underground IP survey present one of the main directions to increase the depth investigation of Electrical Prospecting for topper ore deposits search. The IP anomal effects are strongly increased when the current source is aproached the underground polarizable are bodies. Moreover, the outlook of spacial distribution and the intensity of this effect are quite different in comparison with cases when current arrays are settled into earth's surface.
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Measurement of sea ice thickness with airborne electromagnetic system
Authors M. Oksama, J. Multala and H. HautaniemiFor winter navigation in Finland it is economically important to know the ice conditions on the sea. First tests have been done with the fixed wing airborne electromagnetic system of Geological Survey of Finland to check its capacity to measure ice thickness quickly and economically.
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Airborne geophysical prospecting for groundwater in the metamorphic terrain of Eastern Botswana
Authors D. I. Koosimile, P. W. Zeil and S. D. BarrittIn late 1989, a GEOTEM™ survey for urineral exploration purposes was flown in eastern Botswana with flight lines spaced at 300m and oriented 165/345 degrees true north. The average flight altitude was 130m for aeromagnetics and 50m for EM. The areal coverage was about 6500km2. The data from this survey are used in this work to assess the groundwater potential of the area.
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Geophysical investigations for groundwater in the Pitsanyane basin, SE Botswana
Authors T. H. Ngwisanyi, R. J. Sporry and P. W. ZeilPitsanyane basin, located between the towns of Lobatse and Gaborone in SE Botswana, has been previously investigated for groundwater resources as a potential source for the supply of water to the two towns. The basin lies entirely in dolomites of the Transvaal Supergroup bounded to the west by impermeable rocks of the Ventersdorp Supergroup and to the east by cherty dolomite hills. The main aquifer horizons are fracture zones and karst solution cavities mostly associated with the fracturen in the dolomites. Until now, the geophysical methods used to site production and observation boreholes have mainly been geoelectrical soundings and resistivity profiling.
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Estimation of water retaining properties of rocks from seismic and resistivity data in North Greece
Authors J. Louis and V. KarastathisEstimating the water-retaining properties of rocks is a complicated problem which requires compound investigations. Few reservoirs can be considered watertight, while most of them require geotechnical investigations to a smaller or greater extent. The water loss paths are very complicated and often unexpected, while seepage may also exceed the permissble limits. The case study given by this paper illustrates the importance of the advanced interpretational techniques used, in examining the watertightness conditions of llarion reservoir on Aliakmon river.
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Determination of subface-wave dispersion characteristics in near-surface lateral inhomogeneous structures
Authors C. Schneider and L. DresenThe exploration of near-surface lateral inhomogeneous structures is an important talk for different applications. For example it is necessary to know the properties of the upper earth material to calculate static corrections in reflection seismics. Here the knowledge of the near-surface underground controls the quality of the image of the deeper structures. In other cases the near-surface underground directly is the target of exploration. Important examples are the search for waste sites and the investigation of the underground of waste deposits.
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The use of non-linear arrays in seismic applications
More LessIn standard seismic applications arrays of receivers are used to increase the signal to noise ratio of the recording. The directivity of the receiving system is also improved in a certain direction that can be chosen by appropriate phasing of the array elements. These arrays are so-called linear array. This means that only linear operations (like element weighting and addition) are applied in combining the outputs of the individual elements.
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