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9th EAGE/EEGS Meeting
- Conference date: 31 Aug 2003 - 04 Sep 2003
- Location: Prague, Czech Republic
- ISBN: 978-94-6282-116-3
- Published: 01 September 2003
21 - 40 of 180 results
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Resistivity monitoring for leakage detection at Hällby embankment dam
Authors P. Sjödahl, T. Dahlin and S. JohanssonIntemal erosion is one of the major reasons for embankment dam failures. Resistivity monitoring may have the possibility of detecting internal erosion processes and anomalous seepage at an early stage before the safety of the dam is at stake. This is done by analysing and comparing the seasonal resistivity variation schemes in the reservoir and inside the dam body. The technique is essentially non-destructive, which is particularly important when working with embankment dams where drilling and other penetrating investigations are normally avoided.
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Multi-electrode measurements at Thai Binh dikes (Vietnam)
Authors T. Canh, N. Trong Vu and A. WellerAbout 7000 km river dikes and sea dikes have been built in the northem provinces of Vietnam. Annually, Vietnamese govemment and people have spent a lot of money for maintenance and protection of the dike system against flooding. Nevertheless, breaks of the dikes still happen, which have serious consequences. The instability of dikes results from defects, termite nests, seepage effects, or distorted dike foundation. The origin of these effects is usually hidden in the dike's body or foundation. It is not directly visible. Methods of dike monitoring are necessary to assess the stability and the state of the dike.
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Geophysical applications to geotechnical projects in Australia and China
By B. WhiteleyCivil engineers use geophysics for site characterisation to reduce geotechnical risks associated with construction by improving the accuracy of geotechnical models and to provide design parameters. Unlike exploration geophysics where successful outcomes, i.e. new discoveries are improbable, geotechnical engineers always expect successful outcomes with geophysical interpretations accurately representing the subsurface.
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Geothermal planning maps based on geophysical measurements
Authors R. Kirsch, D. Eberle, B. Röttger, B. Siemon and W. VossThe use of near surface geothermal energy is not based on the temperature increase with increasing depth, but on the fact that under normal conditions no seasonal temperature differences are present at depths exceeding 10 m. Below that depth temperatures are 10 - 12°C all over the year. So subsurface temperatures are cooler in summer and warmer in the winter than surface temperature. This can be used for cooling purposes in the summer, and, using a heat pump, for heating in the winter (Fig. 1).
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Application of the 2-D resistivity tomography, electromagnetic profiling method and soil thermometry for a remedy of the existing road endangered by the slope instability shallow caves and other inhomogeneities in the karst area
More LessThe geophysical survey was carried out in Moravian Karst - the well-known national park of the Czech Republic that extends to the northeast from Brno city. This not very large but wonderful landscape is characterized by very high stage of karstification on one side and by intensive human activity from early age till these days on the other side. (There are many caves, sinkholes, rocky gorges and abysses as well as prehistoric stations, several castles, villages and remains of old industrial activities.)
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Dispersion diagram analysis for underground cavitie : A finite difference approach
Authors C. Gelis, D. Leparoux, J. Virieux, A. Bitri and S. OpertoIdentifiing physical phenomena induced by underground cavities on seismic surface waves will improve void detection methods involving surface seismic waves. Recent works (Leparoux et al., 2000) based on numerical analysis in elastic media with 2nd order finite differences method (Virieux, 1986) and experimental validation show the capability of Rayleigh waves to detect underground cavities, as well as other works (Shtivelman (2000)). Nevertheless, these results show the necessity of accurate numerical modelling taking into account weathered structures and different shapes of cavity. A new finite difference spatial stencil has been proposed by Saenger et al. (2000) for reducing numerical dispersion. After describing this numerical method applied to surface waves analysis, we present seismograms and dispersion diagrams for different cavity typlogies and shot gathers.
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Experimentation at a test site for detecting voids and buried objects with seismic methods
Authors D. Leparoux, G. Grandjean, O. Abraham and P. CoteThe presence of man-made and natural buried objects - and particularly voids - in the subsurface is a recurring problem in civil engineering and landscape management. For the past few years, and in conjunction with other classical methods, we have been testing the potential of seismic methods for detecting underground voids based on the techniques of P-wave reflection (Grandjean et al., 2002) and surface-wave diffraction (Leparoux et al., 2000).
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2D Resistivity imaging at the Alba Iulia citadel, Romania
Authors R. Lachapelle and C. Suteu2D Electrical resistivity imaging has been successfully used as a subsurface investigation tool in engineering and environmental investigations. We present the results of a 2-D resistivity imaging survey over a buried tunnel.
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Microgravity detection of the chambers caused by a battery breast coal mining
By V. BlechaThe area of study is located in the Northem Bohemia in the immediate vicinity of the Most town. The region is a traditional territory of brown coal mining. Horizontal and subhorizontal coal seams in the Tertiary sedimentary basin are surrounded by clays and claystones.
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High-resolution seismic reflection data reveal major fault zone in Lake Geneva, Switzerland
Authors F. Marillier, D. Dupuy, C. Proietti and M. ScheidhauerAlong the northern rim of the Swiss Alps, a major thrust fault zone separetes Plateau Molasse to the northwest fiom Subalpine Molasse to the southeast. This feature runs across the city of Lausanne and extends into Lake Geneva. Although fit is not observed on the southern shore of Lake Geneva probably because fit lies under a thick Quaternary cover, configuration of the AIpine units in this area suggests that the hult zone crosses the lake. To find out the location of the fault zone across the lake and to investigate its configuration, we acquired several high-resolution multi-channel seismic reflection profiles. The high quality of the seismic images obtained indicate that the fault zone includes a series of individual fault that can be accurately located.
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Seismic characteristics of shallow fault zones
Authors V. Shtivelman and S. MarcoDetecting and mapping fault zones in the shallow subsurface is an important problem in various applications, such as engineering site characterization, seismic risk assessment, archeology and others. The commonly used method for this purpose is the high resolution reflection seismics.
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Detecting fault of M = 7.6 Chi-Chi, Taiwan earthquake of 21 September 1999 using geophysical methods
By R. SunThe devastating M = 7.6 Chi-Chi, Taiwan Earthquake of 21 September 1999 caused about 2500 deaths and roughly US$12 billion in property loss. It is triggered by the rupture of the N-15°-E-striking, 120-km-long Chelongpu Fault, which is a direct result of the Philippine Sea Plate-Eurasia Plate collision, in central Taiwan.
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Mapping karst features using a 2-D resistivity survey
Authors Z. Z. T. Harith and A. DevendranThe presence of pinnacles, and underground cave / cavern are common phenomena in limestone area. The occurrence of ground subsidence and sinkholes are always associated with this karsts area. The area of known existence of buried karsts topography should be considered as an unsafe or unstable area. In order to have a suitable design, details investigation of the subsurface is needed. Conventionally it is done using a closed spacing soil investigation (drilling) method, of which is very costly. An altemative investigation method proposed here is the Resistivity Imaging Technique. This is one of many types of geophysical investigation technique, which can be used to investigate the subsurface. On this site, it was proposed to use a 2-D Resistivity Imaging technique.
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Optimizing the 2D laterally constrained inversion (2D-LCI) using a Quasi-Newton method and 1D derivatives
Authors A. V. Christiansen and E. Auken2D laterally constrained inversion (2D-LCI) is a new approach to interpretation of continuous resistivity data. The 2D-LCI enables a layered 2D inversion with sharp layer boundaries as compared to traditional smooth inversion types. However, the full 2D solution is quite time consuming when calculating the derivatives in the Jacobian matrix. To reduce the computation times we suggest using 1D derivatives, Broyden's update formula (Quasi- Newton) or combinations of Broyden's update formula and 1D derivatives together with the full 2D solution. The reduction in computation time is between 7 and 30 times dependent on the combination of approximations.
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3D resistivity finite element modelling using mesh-independent electrode location
Authors L. Marescot, S. P. Lopes, S. Rigobert, R. Lagabrielle and D. ChapellierThe finite element method (FEM) has been used by several authors in the context of direct current (DC) forward modelling to calculate the response of surveys on complex earth structures (e.g. Coggon, 1971; Pridmore et al., 1981; Sasaki, 1994). In practice, geophysicists often wish to use the same electrode sequence for the simulation of different surveys.
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Optimizing the information content of DC resistivity data
Authors H. Maurer, P. Stummer and A. G. GreenIn an attempt to exploit better the capabilities of multi-electrode acquisition systems, we have developed an experimental design procedure to identifi suites of electrode configurations that provide maximum subsurface information. The experimental design algorithm is based on a goodness function that ranks the sensitivity of every possible electrode configuration to changes in the subsurface parameters. To examine the potential and limitations of the new algorithm, we performed a synthetic experiment and compared the resolution power of the optimized data sets with those of Wenner and dipole-dipole configurations. The results indicate that the optimized configurations lead to substantially better inversion results than the standard data arrays.
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Phase difference analysis for surface wave methods
Authors C. Strobbia and S. FotiSurface wave propagation can be analysed using a variety of signal processing techniques, most of which are based on spectral analysis. Transient data are decomposed into their monochromatic components: at each frequency the phase information can be used to compute the phase velocity, while the amplitude can be used to estimate the material attenuation. SW methods use the dispersive properties of Raleigh waves to infer the shear wave velocity profile at a site. Similarly the material attenuation can be used to estimate the dissipative properties of the deposit.
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Study on surface wave resolution
Authors L. V. Socco and C. L. StrobbiaIn order to evaluate the effectiveness of a survey method and to supply information for survey planning it is very useful to estimate the spatial resolution related to investigation depth that can be achieved by the survey in different conditions.
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Laterally consistent, correct elimination of the source signature in shallow, high-resolution seismic reflection surveys: possibility and benefits
By R. GhoseFor safe and efficient design and construction of structures, as well as for environmental and hydrogeological reasons, lateral variations in the shallow subsurface are important targets of investigation. A lack of knowledge of the lateral continuity or discontinuity of shallow soil layers or of lateral change in the physical nature of a layer has caused serious accidents in the past. Significant increase in the construction cost and unacceptable delays are also common. There are occasions when localized discontinuities in the clay cap layer have caused contamination of pure water at greater depths.
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