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Near Surface 2008 - 14th EAGE European Meeting of Environmental and Engineering Geophysics
- Conference date: 15 Sep 2008 - 17 Sep 2008
- Location: Kraków, Poland
- ISBN: 978-90-73781-56-6
- Published: 17 September 2008
41 - 60 of 130 results
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Underground DC-geoelectrical and Seismic Surveys to Investigate Weakness Zones in Salt Rock Formations
Authors C. Schuetze, A. Just, C. Ruecker, H. Zoellner and T. SchichtThe results of a research project concerning the safety assessment of underground waste disposal sites using non-destructive subsurface geophysical surveys within salt rock are presented here. The geophysical techniques were methodically adapted to detect possible weakness areas, like fault zones, disturbed rock zones and fractures with brines. The recent results concern DC-geoelectrical and seismic investigations within disused potash mines in Central Germany where brine reservoirs were supposed in the fractured anhydrite layers. The geoelectrical investigations served to determine areas with higher water content, the seismic surveys were useful to image layer boundaries of the geological units. The combined interpretation of the methods leads to more reliable information on the occurrence of potential weakness areas within the salt rock.
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Comparison of Profiling Results of Attenuation and Velocity of Refracted P-wave in Coal-seam
Authors Z. Szreder, Z. Pilecki and J. KlosinskiIn the paper the problem of effectiveness of seismic profiling of attenuation and velocity of refracted P-wave in coal-seam along mining excavation in conditions of coal-seam edge impact has been presented. For practical use of seismic attenuation profiling, special measurement and interpretation methodology has been prepared. The measure of calculated attenuation is the value of attenuation coefficient based on determination of amplitude of refracted P-wave. In the paper examples of attenuation coefficient and velocity of refracted wave changes in the zones of exploitation seam edge in one of the Polish coal mines have been described. The usefulness of attenuation coefficient for such analysis has been underlined due to its greater sensitivity for changes of the state of stress and deformation in coal-seam comparing to changes of refracted P-wave velocity. It is shown that attenuation can be an interesting parameter complementary to refracted wave velocity in coal-seam, especially in high stress conditions.
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Intensity Scale of Mining Seismic Events – GSIGZW
Authors G. Mutke, J. Dubinski, A. Baranski and A. LurkaIn Polish hard coal mines seismic events occur very often and reach value of magnitude up to 5,0. In the epicentre areas strong mining tremors cause slight damaging effect in buildings. The new criteria of empirical assessing influence of mining tremors on the surface are presented. The so far applied scales, mainly borrowed from the earthquake science or worked out for paraseismic vibrations, have not delivered an authoritative assessment of consequences of vibrations caused by mining tremors. For the purposes of assessing the influence a conception was adopted, that is based on the parameters of ground velocity amplitude, and vibration duration of velocity. As a result of two-year’s science work a new empirical intensity scale of mining seismic events, GSIGZW for assessing the impact of mining tremors on buildings has been worked out. It was elaborated by correlating observed consequences with recorded parameters of vibration velocity and time duration of ground motions. A very good fit are observed between the vibration intensity estimated by means of the GSIGZW scale and the macroscopic observations of their consequences at the Coal Company’s collieries – Poland. The scale GSIGZW is successful used in Polish hard coal mines.
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Dynamics of Rupture Process of Selected Seismic Events at Rudna, Poland Copper Mine
Authors W. Debski and B. DomanskiUnderstanding the physics of the rupture processes of the mining induced seismic tremors has two important aspects. The first one is purely scientific. The induced seismicity provides the bridge between well controlled laboratory experiments on rock samples and natural earthquakes. It concerns both the size of the induced tremors as well as the measurement conditions. On the other hand, the analysis of the rupture processes of induced events is very important for an improving the safety of the mining as it is a key factor for the accurate estimation of the seismic hazard. In this contribution we present the preliminary results of an analysis of the dynamic stress drops for selected events at Rudna, (Poland) copper mine.
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Embankment Dam Seepage Evaluation from Resistivity Monitoring Data
Authors T. Dahlin, P. Sjödahl and S. JohanssonMethods for monitoring seepage are important for dam safety of embankment dams. Increased seepage may be associated with internal erosion in the dam, and internal erosion is one of the main reasons for dam failures. Internal erosion progresses inside the dam, and is difficult to detect by conventional methods. Therefore, there is a need for new or improved methods. The resistivity method is a non-destructive method that may accomplish this task. A method for evaluating the seepage from resistivity monitoring data is theoretically described and tested for four selected areas in the foundation of the Sädva dam. Seasonal resistivity variations are apparent in the reservoir as well as inside the dam. The four selected areas represent areas with low, via intermediate to high variations in the seasonal resistivity variation. The areas are compared qualitatively and thereby permeable zones within the dam may be identified. Quantitative assessment of the seepage flow is also carried out as an initial test of the described method. It is concluded that the experiences from the Sädva dam are valuable for the application of the resistivity method on embankment dams. The presented method is a promising first step for quantitative assessment of seepage.
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Geophysical Investigation of Earth-fissures by Means of ERT
Authors P. Tsourlos and G. VargemezisEarth fissures tend to be an issue of increasing concern, especially at the margins of sedimentary basins at semi-arid areas, since they cause damage to houses, commercial buildings, or infrastructure. In this work we present case studies involving relatively high resolution ERT measurements carried out at areas of earth fissures at the margins of sedimentary basins in Greece. From the results presented in this work, it is obvious that the application of the technique of electric tomography provides important information on the structure of subsoil in the investigated regions and is capable to locate regions in which earth fissures are likely to take place.
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Detection, Localization and Backfill Assessment of Old Mining Shafts in the Upper Silesia Coal Basin with Geophysical Me
By A.M KotyrbaThe old shafts can create serious hazards for safe use of post mining lands. They complicate engineering conditions and need special geotechnical solutions to be applied when have to serve as structures bedrock. The paper describes experiences from application of various geophysical methods for old shafts detection and characterization. It concerns mostly gravity surveys that are compared with supplementary resistivity and GPR surveys, conducted on areas of abandoned coal and ore mines in the Upper Silesia Coal Basin (UCSB - Poland.). As an introduction to applications several geophysical models of post mining subsurface structures are described and discussed.
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Tunnel Seismic Investigations – 3D Imaging
Authors J. Tzavaras, K. Groß, S. Buske and S.A. ShapiroThe project OnSITE (Online Seismic Imaging for Tunnel Excavation in hard rock) aims at developing an integrated approach for seismic imaging around the tunnel and prediction ahead of the tunnel face during construction work. We present the recent results of our subproject which is concerned with the determination of the spatial locations of faults, fractures and heterogeneities by advanced seismic imaging techniques. So far we have extended existing 2D imaging techniques to 3D. We have implemented 3D versions of Kirchhoff prestack depth migration(KPSDM), Fresnel-Volume-Migration (FVM) and Reflection-Image-Spectroscopy (RIS). The application of the mentioned imaging techniques to data from the Gotthard base tunnel show significant improvements compared to standard (KPSDM) processing. The 3D RIS approach suppresses scattering effects in the low frequency band and increases resolution in the high frequency band so that some of the geological structures are much better visible. The 3D FVM technique uses slowness and polarization based estimates of the emergence angles at the receivers and restricts the imaging to the region around the actual reflection or diffraction point. We observe less spatial ambiguity and a higher resolution of most structures in the stacked section as well as in common receiver gathers.
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Geophysical Anatomy of the Hollin Hill Landslide, North Yorkshire, UK
Authors J.E. Chambers, A.L. Weller, D.A. Gunn, O. Kuras, P.B. Wilkinson, P.I. Meldrum, R.D. Ogilvy, G.O. Jenkins, A.D. Gibson, S.J. Ford and S.J. PriceGeophysical methods are playing an increasingly important role in the investigation and monitoring of landslides; such methods are proving to be particularly effective for revealing the 3D structure, failures surfaces, and the hydrogeological regimes associated with rock and earth slides. In this paper we present the results of a geoelectrical reconnaissance survey of the Hollin Hill landslide, UK. This work was undertaken in advance of the installation of a permanent geophysical and geotechnical monitoring system, and was designed to assess the suitability of resistivity (resistivity mapping and 2D/3D ERT) and self-potential methods (profiling and mapping) for investigating and monitoring this site. In particular, we were concerned to assess the electrical property contrasts and the magnitude of SP response across the study area. The surveys revealed that there was a good resistivity contrast between the slipped material and sandstone bedrock, which allowed us to use resistivity mapping data and ERT models to define the geometry of the landslide. An SP signature consistent with the movement of groundwater through the landslide was observed at the site, and was used to identify seepage patterns associated with the slipped material.
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Application of GPR Scanning for Landslide Investigations in Polish Carpathians
More LessLandslides in recent years became a serious problem and were causing economic losses in Poland. They are formed on steep Carpathian slopes of flysch sediments. Built from many thin layers of marine sedimentation, soil-rock type deposits were difficult for in-situ and laboratory tests. It required effective techniques of investigations. Traditional drillings were very important but time consuming, costly and not always gave answer for the entire question in mass movement investigations. Some types of geotechnical tests were proper for soils some other only for rocks. Therefore good quality core drillings always should be connected with other types of field measurements and monitoring techniques chosen with respect for the landslide type and its internal structure. Ground penetration radar GPR measurements were found to be a one of very useful methods in conjunction with other geotechnical engineering tests. Using GPR surveys landslide depths were recognized at 1-20m below the natural terrain level. Over 10 km of GPR measurements was performed on 24 landslides inside the project for Polish Roads Authorities, financed by European Investment Bank. In the paper conclusion from using GPR, together with diamond impregnated core drillings, ground movement measurements, groundwater monitoring and geotechnical laboratory tests are described.
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Mapping Quick-clay Sites for Geohazard Assessment – The Finneidfjord Case Study, Norway
Authors I. Lecomte, M. Bano, S.E. Hamran, E. Dalsegg and K.M. NielsenOn June 20th, 1996, a submarine land failure in a fjord near the village of Finneidfjord (Northern Norway) developed into a retrogressive quick-clay slide encroaching 100-150 m inland, resulting in the loss of life and significant material damage. Reports in the aftermath of the slide concluded that build up of excess pore pressure may have been the main reason for the slide, though other causes are invoked too. Several field campaigns in the fjord since 1997 consisted of sediment coring, VHR seismic surveys, and long term in-situ instrumentation. To complete offshore data with land data, several geophysical techniques were tested onshore in July 2007. Seismic, GPR and resistivity (method of choice in quick clay) were tried at two sites (one intact and one close to the 1996 slide scar), and all three techniques proved to be useful for a better definition of the underground. Despite clay-prone sites, a 50 MHz GPR antenna was used with success on one site because of the unknown presence of a thick layer of morainic material. Though standard refraction seismic profiles were acquired for P-wave tomography, surface-wave processing tests on the same data gave promising results.
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Improving the Seismic Hazard Evaluation of the Lisbon and Lower Tagus Valley Area
Authors J.P. Carvalho, C. Pinto, M. Costa, S. Heleno, M. Silva, T. Rabeh, G. Cooksley and F. CarrilhoThe Lisbon and surrounding area of the Lower Tagus Valley has experienced in the past the effects of several moderate sized earthquakes that caused significant damage and destruction. They have been attributed to local sources, though in some cases the source remains to be located. The lack of outcrops in the flat lying Quaternary terrains, the low slip-rates of the area in connection with sedimentation and erosion rates that erase surface ruptures are among the causes of a poor association between faults and seismicty, which has opened way to geophysical studies. Seismic, potential-field and seismicity data have been recently used to improve the seismic hazard evaluation of the area. In this work we complement these studies with DTM and PSInSAR data with the purpose of obtaining an accurate evaluation of the seismic hazard of the study area. The correlation of improved epicentre locations with major fault zones located from the above mentioned data shows that we have progressed in the understanding of the earthquake sources in the region. Some structures show no apparent relationship with present-day seismicity but some are known to be active into the Quaternary. Further geophysical and geological studies are required to understand the causes.
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Retrieving Surface Wave Dispersion Curves from Cross-spread Seismic Acquisition
Authors D. Boiero, P. Bergamo and L.V. SoccoThree-dimensional (3D) seismic surveys are always more often used both in oil prospection and in near surface problems to handle complex geological structures. At the same time surface wave methods are often coupled to other seismic techniques (2D seismic reflection or refraction) where we can use seismic data to retrieve dispersion curve along the seismic line. In this work we prove the possibility of retrieving dispersion curves from cross-spread 3D seismic acquisition scheme. Several tests based on synthetic and real data show that the dispersion curves estimated from cross-spread seismic acquisition scheme are in agreement with the dispersion curves estimated through the traditional methods. Furthermore, through a 3D synthetic model, we show that the proposed processing approach can be used to retrieve 3D subsoil models, also for inaccessible areas.
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Experimental Design for Crosshole Electrical Resistivity Tomography Data Sets
Authors I. Coscia, L. Marescot, H. Maurer, S. Greenhalgh and N. LindeWe plan to employ crosshole electrical resistivity tomography for monitoring fast hydrological processes that involve complex interactions between a river that frequently floods and the adjacent groundwater. To obtain as much information as possible over relatively short periods, we need to optimise the electrode configurations that will be used to acquire the resistivity data. For this purpose, we have adapted an experimental design procedure first introduced for the planning of surface electrical resistivity surveys. Our new experimental design algorithm seeks electrode configurations for which the linear dependencies are low, such that each electrode configuration provides information that is largely independent of information supplied by all other electrode configurations. The resultant optimised electrode configurations yield overall resolution values and inter-borehole coverage that are superior to those supplied by a random selection approach.
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Complex Resistivity (CR) Behavior of Building Material – First Results of Field Scale Measurements
Authors S.F. Kruschwitz, C. Trela, J. Wöstmann and E. NiederleithingerMoisture ingress is one of the major damaging factors for masonry buildings. As complex resistivity (CR) is sensitive to textural properties as well as to the pore fluid chemistry of wet porous media, its non-destructive application provides helpful information for conservators. In a comprehensive laboratory study it could be shown that CR might even be able to distinguish between salt content and saturation degree in only one measurement. The combined use of electrical and electromagnetical measurement techniques in a field-scale flooding experiment has shown some unexpected differences. Possible reasons are discussed and it is shown that bringing together the information contents of both methods leads to a clearer picture.
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Mapping the Geothermal Potential of the Shallow Underground – A Geophysical Approach
By R. KirschThe use of near surface geothermal energy (borehole heat exchangers and heat pump) for heating can save energy and reduce CO2-reduction if the borehole heat exchangers are properly designed. The required length of borehole heat exchangers depends on the thermal conductivity of the underground. An approach for an assessment of thermal conductivity by geophysical techniques (resistivity and NMR) is discussed in this paper.
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The Application of Tilt Derivatives to EM Conductivity Data
By D. BeamishIn the processing of geophysical potential fields, a wide range of spatial derivatives are available to enhance the information contained in the basic data. Here the ability of the tilt and tilt derivatives to provide enhanced mapping of conductivity data is considered. Tilt and its associated functions are formed by taking combinations of vertical and horizontal derivatives of the data set. A theoretical forward modelling study is carried out to assess the performance of tilt derivatives in relation to the detection and definition of concealed conductivity structure. Case studies of the practical application of the procedures to survey data are performed. The case studies derive from large scale airborne EM data sets but the methods have a general applicability to a wide range of geophysical conductivity and resistivity data. The tilt functions embody Automatic Gain Control that normalise the detection and definition of both weak and strong conductivity gradients across an appropriate subsurface depth range. The use of high order spatial derivatives inevitably results in a degree of noise amplification that is survey and technique specific. Filtering methods for the reduction of undesired, usually high wavenumber, artefacts are available and are shown to be effective.
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Spectral Balancing GPR Data Using Time-variant Bandwidth in t-f Domain
Authors N. Economou and A. VafidisA deterministic method to increase vertical resolution of GPR data is proposed, based on spectral balancing in t-f domain. Taking advantage of the variation of time and frequency resolution of S-transform, GPR signals can be balanced and de-noised after the selection of a time-variant bandwidth. The algorithm is fast, since it involves one FT and two IFTs for each trace. The proposed methodology was applied on a synthetic trace and real GPR data from a sandbox experiment, revealing reflections, which were not clearly visible after conventional processing. Additionally, weak reflections present in the spectrally balanced GPR section, are attributed to the interface between the water - oil mixture zone and the water zone.
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Float TEM – Inloop Transient Electromagnetic Measurements on a Lake
Authors B. Tezkan, L. Mollidor, R. Bergers and J. LöhkenWe developed a floating TEM setup with a transmitter size of 18 x 18m2. Due to its modular design it can be handled by two operators and is easy to transport. As lacustrine sediments in maar lakes provide paleoclimatic proxy data, an extensive TEM survey at Lake Holzmaar (Eifel, Germany) was carried out to investigate the sediment thickness. The data collected can be explained well by means of three dimensional Finite Element Modelling.
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Elastic Parameters of Rocks from Well Logging Even in Near Surface Sediments
Authors J.A. Jarzyna, M.J. Bala and A. CichyResults of the computer program FalaFWS for processing and interpretation of acoustic full waveforms in deep and shallow rock formations are presented. The goal of the paper is to show a possibility of obtaining correct values of elastic properties of shallow formations on the basis of acoustic waveforms recorded with standard device. Results of measurements with a device constructed for deep wells and results of data interpretation using computer program written for that device provide an interpreter with correct values of dynamic elastic parameters in shallow, poorly consolidated rocks. Field examples are given to confirm the presented analysis.
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