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Near Surface 2010 - 16th EAGE European Meeting of Environmental and Engineering Geophysics
- Conference date: 06 Sep 2010 - 08 Sep 2010
- Location: Zurich, Switzerland
- ISBN: 978-90-73781-88-7
- Published: 06 September 2010
101 - 120 of 153 results
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Method for Comprehensive Computing of Water Flows Geodynamics in the Dead Sea Basin
Authors L.V. Eppelbaum, Y.S. Yakubov and M. EzerskyThe Dead Sea (DS) is a lowest place at the Earth with a unique physical-chemical water composition. The most important physical factor of this basin is the vertical gradient of water density: from 1150 kg/m3 at the DS surface up to 1430 kg/m3 at the depth of 310-330 m. The new mathematical solution obtained for stratified, rotating and compressible liquid (with utilization of gravity, density, temperature and acoustic data) permits to create a solvable system of differential equations and utilize it for development of exact physical/mathematical/geological model of the DS basin.
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Spectral Induced Polarization Measurements on Sand-clay Mixtures in Dependence of Water Saturation
Authors K. Breede, O. Esser, J.A. Huisman, E. Zimmermann and A. KemnaSpectral induced polarization (SIP) measurements are promising for the in-situ determination of soil hydraulic properties. Here, we investigate the influence of water saturation on SIP measurements. Combined electrical and hydraulic measurements were conducted on sand and sand-clay mixtures using a multi-step outflow setup to desaturate the samples with several pressure steps. Our experimental results show that the ohmic conduction decreases with decreasing water content in accordance with Archie’s Law. For the sand-clay mixtures, the phase angle as well as the chargeability increases down to a critical water content and then decreases again in accordance with the short-narrow-pore model. In this model, the chargeability first increases with decreasing water content because the variation in the effective pore radii and the variation in the ion transparency becomes larger. When the saturation decreases further, the chargeability decreases due to a reduction of the thickness of grain-contact water rings resulting in a decrease of effective pore diameters and ion transparency. It is also observed that the phase peak shifts to higher frequencies, i.e. smaller relaxation times, when the saturation decreases, suggesting that electrical relaxation is controlled by the saturated part of the pore space.
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Spectral Induced Polarization: Laboratory Measurements on Saturated Sandy Quartz Samples of Varied Pore Characteristics
Authors K. Koch, A. Kemna and K. HolligerUnderstanding the influence of pore space characteristics on the hydraulic conductivity and spectral induced polarization (SIP) response is critical for establishing relationships between the electrical and hydrological properties of surficial sedimentary deposits. Here, we present the results of laboratory SIP measurements on saturated quartz samples with granulometric characteristics ranging from fine sand to fine gravel. We alter the pore characteristics using three principal methods: (i) variation of the grain sizes, (ii) changing the degree of compaction, and (iii) changing the level of sorting. We then examine how these changes affect both the SIP response and the hydraulic conductivity. In general, the results indicate a clear connection between the applied changes in pore characteristics and the SIP response. In particular, we observe a systematic correlation between the hydraulic conductivity and the relaxation time of the Cole-Cole model describing the observed SIP effect for the whole range of considered grain sizes.
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Studies on the Origin of the IP-effect with Gel-filled Sandstone Samples
More LessThe origin of the induced polarization in the pore space of sediments is not completely understood. There are two groups of theories, which are either based on the grains, or on the structure of the pore space. We have carried out complex electrical conductivity measurements on gel-filled sandstone samples with different gel concentrations and fluid salinities. The idea is to reduce the ion mobility in the pore space, allowing to test hypotheses resulting from the different theories. The electrical conductivity of pure gel increases with gel concentration, indicating an increase in ion density. Thus, adding gel to a saline fluid reduces ion mobility, but does not completely destroy it. The conductivity spectra from the gel-filled sandstone samples are distinctly different from water-filled samples. The phase shifts decrease, the spectrum is flattened, and the maximum moves towards higher frequencies. We conclude that the geometry of the pore space, and the mobilities in the large pores, are important factors for the generation of the IP-effect. The reduction of the IP-effect by a reduction of mobilities is consistent with a quantitative theory which is based on the pore space geometry.
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Detecting Perched Water Bodies Using Surface Seismic Time-lapse Travel-time Tomography
Authors G.S. Baker, D.P. Gaines, S.S. Hubbard, D. Watson and S. BrooksSeismic timelapse methods have typically been constrained to large-scale geologic investigations associated with petroleum exploration and exploitation; however, there is growing interest in using geophysical methods for monitoring near-surface phenomena such as fluid flow in fractured or karstic geologic media, hydraulic infiltration, and near-surface anthropogenic manipulations during environmental remediation. To demonstrate additional utility of surface seismic time-lapse travel-time tomography for near-surface investigations, we monitored a site through time with the objective of attributing increases in seismic P-wave velocity with development of a perched water body in the vadose zone. Our study was conducted at the Oak Ridge National Laboratory, USA, during a multi-disciplinary investigation on the fate and transport of contaminants. Seismic data are processed using a wavepath eikonal traveltime tomography approach, and a modified trend analysis technique is applied to remove the regional velocity component. The final ‘residual’ velocity anomaly images are compared to the wellbore hydrologic data and error analysis, and used to interpret the presence or absence of a perched water body. Our study suggests that velocity estimates, obtained from surface seismic traveltime methods, are effective for indicating spatial and temporal distribution of near-surface perched water bodies.
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New Three-component Landstreamer System Developed for Groundwater and Engineering Applications
Authors K. Martinez, C. Ploug, A. Pugin and J.A. MendozaA new landstreamer system has been developed that provides high resolution imaging from near surface to medium depths. The system is comprised of a combination three-component array to acquire SH data for near surface and a single component array to acquire typical P-wave data at depth. The first application of the system is being carried out for a groundwater mapping project where detailed knowledge of the near surface geological complexity is desired. The landstreamer is also suitable for engineering applications and in difficult to survey urban environments.
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Migration and Instantaneous Phase Combination to Detect Hidden Culverts Characteristics in GPR Data
Authors B. Yousefi, S. Esmaeili and S. JazayeriGround Penetrating Radar (GPR) is a nondestructive testing method used to test the quality of roads, pavements, bridges and buildings. GPR uses high frequency electromagnetic waves at the Microwave or Radio Frequency range to investigate the subsurface. It is used to measure features such as pavement layer thickness, moisture content, horizontal cracks, and voids. The electromagnetic waves reflected from the interfaces in the subsurface are used to analyze the structure of the area under scan. This paper presents two processing methods in hide culverts detection in roads structure that complete each other successfully. At first, we applied Migration method to remove hyperbolas and then by instantaneous phase method, we determined the top depths of culverts on a GPR data that has been collected from a culvert with known characteristics. The results corresponded to visible parameters truly. Then these methods applied on a hide culvert data on a road in Fars providence, Iran. The results satisfied with existed documents of this culvert's construction. The results of the study will be presented in the paper.
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An Infrared Survey on a Concrete Bridge Deck
More LessAn infrared survey was carried out on a concrete bridge deck using a mobile IR-acquisition unit. The survey covered one lane of the bridge and was repeated once per hour during 20 hours. Results show only minor temperature differences between on bridge and off bridge and no influence of structural elements such as girders.
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Some Geophysical Characteristics of the Burning Products in Archaeological and Geological Studies
Authors S.E. Itkis, B.E. Khesin and E.A. VapnikFor the revealing and characterization of archaeological remains that were caused by the burning processes we studied magnetization and corresponding magnetic anomalies over such archaeological features as ovens, kilns and hearths in Israel. Our magnetic and gravity studies of sedimentary rocks subjected to combustion metamorphism were performed in Israel and Jordan. Comparison of obtained data shows general correlation between increase of magnetization and burning temperature, although magnetization decreases due to alteration of burnt matter as well. Magnetic heterogeneity is reflected by ground magnetic anomalies. High-temperature combustion rocks in the Hatrurim basin, Israel show increased density relatively to that of low-temperature rocks. Such density features are displayed in the pattern of residual gravity anomalies.
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Geophysical Researches on Excavations of the Bronze Age Fortified Settlement in Southern Ural Mountains
Authors P.S. Martyshko, V.V. Noskewich, N.V. Fedorova and L.A. MuravievGeophysical researches were carried out on archeological excavations of one of the numerous bronze age fortified settlements discovered in Southern Ural Mountains in 60 - 90th years of XX century. The purpose of the present work was the research of the settlement fragment by non-destroying methods for revealing and mapping separate objects - the remains of dwellings, constructions of economic value, furnaces, economic pits and fortified constructions. This information was required for carrying out more purposeful excavation by archeologists. As the most effective and economic, researches were carried out with magnetometry methods by means of two proton gradiometers and one cesium gradiometer on preliminary spaced network of 0,5х0,5m. For the account of the Earth magnetic field variations the variation station was used. Before survey, clearing of an investigated site from metal debris was performed by metal locator. As a result of survey the map of an anomaly magnetic field was acquired, where the wall with a ditch, remains of walls of separate dwelling, the furnace and economic pits were allocated. After interpretation of anomalies received from a wall its position and a configuration were established.
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Application of Electrical Resistivity Tomography to Detect Archaeological Structures at Tell Al Marj (Homs, Syria)
Authors M. Himi, A. Armendáriz, E. Iriarte, L. Teira, J. Urquijo, J. Ibáñez, M. Haïdar-Boustani, M. Al-Maqdissi, A. Guinea and A. CasasElectrical resistivity tomography has been applied at two different zones in Tell Marj archaeological site (Syria). In both, the electrodes were placed to a distance of 50 cm within each line, being of 1 m the distance between lines. The test in the west zone was carried out in an area where Roman pottery fragments outcrops in the surface. Resistivity measurements were taken from in 11 lines, on a total surface of 235 m2. The test in the east zone was conducted in an area with Neolithic remains (pottery and silex tools). The sampled surface was of 329 m2 (15 lines). In the west zone of Tell Marj, place where in surface they appear abundant fragments of Roman pottery, the inverted resistivity cross-section indicates clearly the presence of two layers: An upper resistive layer 1.5 m thick ness of 1.5 m and below very low resistivity values are observed. The results obtained from 3D resistivity tomography were imaged in two different ways. One corresponds to a general image of the pad diagram, where it is possible to observe the zones of higher electrical resistivity than define an orthogonal architectonic framework. The presence of walls, corridors and stays among 3 and 5 meters of side is observed.
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Examples of Resistivity Tomography for Cultural Heritage Management
Authors V. Compare, M. Cozzolino, E. Di Giovanni and P. MaurielloThe geophysical prospections we present were realized inside the King Ferdinando IV Borbone’ Royal Residence of San Leucio (Caserta, Italy) and in the Archaeological Park of Aeclanum (Mirabella Eclano, Italy).
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Analysis and Representation of 3D GPR Data Acquired across Archaeological Sites
Authors M.T. Jie-A-Looi, M. Hertrich, P. Nagy and A.G. GreenThree-dimensional (3D) ground penetrating radar (GPR) surveying is becoming an increasingly valuable tool in archaeological prospecting. To extract structural details from 3D GPR data usually requires interpretation of multiple vertical cross-sections and/or multiple horizontal slices. Such multiple representations are difficult to incorporate in integrated GIS-based analyses. Using a new 3D GPR data set acquired across the buried remains of a Roman villa complex in Switzerland, we demonstrate the benefits of two new attributes for GIS-based interpretations: (i) the cumulative reflectivities over time intervals containing all significant reflections, and (ii) the times of the amplitude-envelope maxima. When combined, these attributes yield most of the critical summary information in the form of only one or two colour-coded maps.
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Using Ground Penetrating Radar and Induced Polarisation to Detect a Wooden Track Way
Authors A. Weller, A. Fettig, A. Bauerochse and M. EidnerThe detection of wooden relicts embedded in peat is a challenge for geophysics because the contrasts in the relevant physical properties between wood and peat are rather weak. A small section of track way was excavated at a location in the meliorated peatland of Uchter Moor (Germany). Close to the excavation site, a geophysical survey including Ground Penetrating Radar (GPR) and Spectral Induced Polarisation (SIP) was performed to check whether the wooden track way can be identified by geophysical methods. The wooden track way consisting of wooden planks with a length of 2 m and a diameter of 0.2 m is expected at a depth of about 0.9 m. The radar sections measured at different frequencies do not provide a clear evidence of the wooden target. Only additional 3D processing of six parallel profiles by calculating the amplitude of the envelope and visualisation of time slices reveals an extended structure that coincides with the existing track way. The application of SIP is related to the moderate polarisation effects caused by cell membranes of wooden material. The imaginary part of complex electrical resistivity resulting from an inversion of the 12 Hz data provides a clear image of the track way.
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Complex Resistivity Tomography and Spectral Induced Polarization Analysis on Laboratory Device for Soil Characterization
Authors E. Cardarelli and G. De DonnoElectrical Impedance Tomography (EIT) and Spectral Induced Polarization (SIP) are large used techniques for environmental application. The aim of this work is to understand the polarization signatures related to uncontaminated soils using typical subsoil models on laboratory targets and to build a new versatile algorithm suitable for this situations, for a future better estimation of contaminated samples. To this end a new experimental device was build up and SIP measurements were acquired on this new configuration, within 1mHz – 12 kHz frequency range. A couple of frequencies was chosen among the entire frequency range depending on sample configuration, and for each frequency value an inversion of complex resistivity data was carried out through a new algorithm developed in EIDORS environment. SIP measurements have highlighted the spectral response of water, sand and clay, in terms of polarization signatures on the phase spectra, while 2D and 3D complex resistivity inversions have shown the good resolution achieved by the EIDORS algorithm and the importance of the device configuration.
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Application of DC Resistivity and TDEM to the Study of Water Ingress in a Mined Region of South Africa
Authors V. Hallbauer-Zadorozhnaya, E. Chirenje and P. NyabezeThis study investigates the identification of zones of possible ingress of water, taking place above shallow undermining. Water ingress here is associated with the location of buried mine shafts. Here, we evaluate their water bearing probability based on their electrical conductivity signature. Two geophysical methods were used: DC resistivity and time domain electromagnetic sounding (TDEM). Resistivity data were collected using a Syscal-Pro multi-electrode system utilizing 35 electrodes at 10m spacing. For TDEM we used two instruments: TEM-FAST48 and Tsikl-5, with a surface area of the receiver loop equal to 625 m2. In this area TEM-FAST48 allows us to investigate to a depth of 120-150 m, with Tsikl-5 to more than 300 m. 95% of the signals collected by both instruments were distorted by an electro osmosis IP effect. We inverted the TDEM data, resulting in the resistivity, thicknesses of layers, polarizability, and the time constant of decay, of each part of the cross-section. It was shown that the depth of investigation of DC resistivity method is limited at this area, and resolution is low. In contrast, the TDEM surveys revealed a distinct conductive unit which we attribute to an area of high water ingress in this mined region of Johannesburg.
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Ability of the Direct Wave Amplitude of Ground-penetrating Radar for Assessing the Moisture Content Variation of Timber
Authors I. Rodríguez-Abad, R. Martínez-Sala, F. García-García and R. Capuz- LladróThe moisture content (MC) has a significant influence in wood’s physicochemical properties and therefore in most types of wood pathologies. The MC variation leads to modifications of its electromagnetic properties and to specific effects upon waves’ characteristics. Given the advantages of the direct electromagnetic wave (DW) observation, the aim of this work is to asses the ability of this wave to provide access to timber MC characterization. For this purpose, GPR measurements were carried out on timber joists (1.6 GHz central frequency). The dielectric behaviour of wood varies according to the direction of the fiber. Therefore, it is necessary to distinguish between differences attributable to the wood anisotropy and those due to variations in MC. With this aim, prior to the MC analysis, assays were carried out in different directions regarding the fiber. The results of this study show very satisfactory correlations between DW amplitudes and MC in all fiber directions. These results showed, in agreement with theory, that a decrease of MC results in an increase of the DW amplitude. These results demonstrates the GPR efficiency and the innovative application of this technique as a non-destructive evaluation tool for the rapid sounding of timber structures.
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Bedrock Detection from an Integrated Procedure of Refraction Analysis and Tomographic Inversion of the First Arrivals
Authors G. Boehm, R. Francese and M. GiorgiThe aim of this work was to create an automatic procedure to define the near surface structures in the case of seismic acquisition of large quantity of data. The study area is located in North-Eastern Italy, in the Dolomites near the city of Belluno; in particular the target of this study was the definition of the depth and shape of the bedrock horizon. The seismic data used for this analysis are part of a seismic survey acquired in the surface area of Costalta comprising a dozen of 2D lines, sub-parallel to each other in the SW-NE direction, within a rectangular area of 800x600 m (Figure 1). The sources used were the miniVib and the mini-gun. We developed an integrated procedure involving the conventional refraction analysis and joint tomography of the direct (diving) and refracted arrivals (head waves).
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Full Wave Form Time-domain IP Data Acquisition
More LessWe present and discuss some examples of full wave form resistivity-IP data recorded at one site in Sweden and one in Malaysia. The examples show that highly detailed recordings can be made, and that various types of noise can be clearly distinguished. With such detailed information about the character of the signal and noise it is relatively easy to develop algorithms that can remove the noise without biasing the extracted data. Tests using a pure square wave as measuring signal show that information relating to the chargeability of the ground are as clearly visible as in traditional time-domain IP-data, and it should thus lend itself well to extraction of the spectral IP information. An advantage of using square wave for time-domain SIP over frequency domain SIP is that data acquisition can be much faster, furthermore it would be more time efficient than a traditional time-domain IP signal. The results also show that the transmitted current wave form is almost ideal, whereas recorded output voltage varies to a significant extent. This may be due to, for example electro-chemical processes, and a constant voltage transmitter would not have produced current wave forms with such regular shape.
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1D Laterally Constrained Inversion of Towed-array Capacitive Resistivity Imaging Data
Authors O. Kuras, A.V. Christiansen, D. Beamish and R.D. OgilvyTowed-array Capacitive Resistivity Imaging has proved to be a viable, convenient and effective technique for acquiring multi-channel high-resolution Electrical Resistivity Tomography data with dense lateral coverage on engineered surfaces. As resistance data measured with capacitive coupling under quasi-static conditions are equivalent to conventional galvanic data, popular ERT interpretation schemes such as least-squares smoothness-constrained resistivity inversion are fully applicable to CRI data. However, for certain specialised applications, much simpler earth models (e.g. 1D with moderate lateral variations) may be sufficient to adequately reflect the subsurface structure under investigation and a significant amount of a-priori information may exist that can be used to constrain the inverse models. One way to exploit these simplifications is to employ piecewise 1D Laterally Constrained Inversion, which divides the subsurface into a series of 1D earth models connected laterally by model constraints that control the similarity between adjacent models and the propagation of subsurface information along a given interpretational profile. In this study we demonstrate the feasibility of applying 1D-LCI to towed-array CRI data and show the utility of this approach for the analysis of datasets acquired to assess road subgrade condition.
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