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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
61 - 80 of 130 results
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Single- and Cross-well Flow Analysis for Flowpath Characterization in a Fractured Mudstone
Authors J. Williams, A. Anderson, P. Lacombe and C. JohnsonSingle- and cross-well flow analysis was used to characterize fracture zones and flowpaths in a mudstone within the Newark Basin of northeastern United States as the preliminary part of a bioaugmentation research study. Flow logs were analyzed from a shallow recovery well, a deep monitoring well scheduled for bioaugmentation injection, and three test wells installed along the dip direction to determine potential flowpaths between the recovery well and the monitoring well. Flow logs collected under quasi-steady-state ambient and single-well pumped conditions were analyzed to estimate fractured-zone transmissivity and hydraulic head. Flow logs collected under transient cross-well pumped conditions were analyzed to determine fracture-zone connections. Integrated analysis of the flow logs with gamma, image, and core logs indicates that most of the transmissive fracture zones occur in thin beds of laminated and carboniferous mudstone, which are cyclically interbedded with more massive mudstone units. Estimates of transmissivity and hydraulic head of the fracture zones based on single-well flow analysis were consistent with values from hydraulic tests and water levels measured in discrete intervals isolated with straddle packers. Fracture-zone connections determined from the cross-well flow analysis were consistent with the dip of the transmissive beds.
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Application of Surface Waves for the Geotechnical Characterisation of Dykes
Authors L. Karl, T. Fechner, S. François and G. DegrandeRecent flood events in central Europe accompanied by the failure of river dykes have shown a clear need in effective and reliable methods to survey and monitor the structure of earth-fill dams. Among the geophysical techniques the imaging of the electrical resistivity is used in most cases, occasionally ground penetrating radar is applied in the frame of the search for subsurface facilities, seismic methods are rarely used. This paper focuses on the multichannel analysis of surface waves method (MASW) to determine elastic soil properties and aims to extend its application field to dyke and dam structures. An elaborated testing campaign was conducted and provided the chance to collect experiences in the practical use. Test results obtained at one test site are selected and presented in comparison with the conclusions from borehole logs. A remarkable relation between the shear wave velocity and the consistency of the clay liner was found. Valuable additional information on the composition of dyke body and base could be obtained. Possible influences of the dyke's topography on the test results were studied by means of a numerical analysis which showed the principal applicability of standard processing procedures.
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Deep Resistivity Image of the Agri Valley, Southern Italy
Authors M. Balasco, A. Giocoli, V. Lapenna, E. Rizzo, G. Romano, A. Siniscalchi and M. VottaA deep geophysical electromagnetic investigation has been used to improve the geo-structural knowledge of Agri Valley, a large quaternary basin located in Southern Italy. In the longitudinal section, the basin is probable composed of three depocentral areas separated by two structural highs, bounded by NE-oriented faults investigated with several Deep Electrical Resistivity Tomography (DERT) by Colella et al., 2004. A destructive event occurred in 1857 (I=XI MCS) in the Agri Valley and at present, this area is characterized by large low-magnitude events but uncertainty there is about the location of the seismogenic sources. In order to solve some unexplained questions such as, for example, the depth of the bedrock below the quaternary deposits and geometrical characterization of the faults, a magnetotelluric profile transversally to the Agri river basin was carried out.
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Improved Monte Carlo Inversion of Resistivity Data
Authors C. Piatti, D. Boiero, A. Godio and L.V. SoccoInversion of 1D technique (VES and TDEM) by using Global Search Procedures (GSPs) as proved to be effective in evidencing local minima and equivalence problems, evaluating non-uniqueness in the solution, and estimating the values and uncertainties of the model parameters. The proposed approach is based on a Monte Carlo algorithm optimised through the application of the scale properties of the apparent resistivity curves. A statistical test selects a limited number of final models according to data uncertainties, model parameterisation and a chosen level of confidence.
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Self Organized Criticality Methods for Modeling Natural Dynamical Systems
More LessSelf –organized criticality (SOC) is one of deterministic chaos methods. The new concept makes it possible to reach qualitative solutions of complex systems behaviour. There are a few popular SOC models. One of them is cellular automata model. Cellular automaton is a dynamical system where space, time, and the states of the system are discrete. Space is represented by a number of identical cells arranged in a regular grid. Each cell can be in one of a finite set of states. The state may be represented by numeral or logical values. The state of every cell depends on the rules. The boundary conditions chosen depend on the nature of the system. This paper presents the phenomenon of self-organized criticality and simplified models for natural dynamic systems modeling. SOC models have important common features, such as single element influence on system’s unstable behaviour, which may help with modeling natural complex systems. One of the models, 2-dimensional cellular automata model, may be used for more precise simulations for better understanding and description of some complex systems and forces modeling them.
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Coherent Noise Attenuation in the GPR Data via the Karhunen-Loéve Transform
By M. RudzkiThis paper deals with application of the Karhunen-Loéve (KL) transform for system ringing attenuation in GPR data. The system ringing usually originates from strong shallow reflections or bad ground-antenna coupling, and appears as horizontal banding through a dataset. System ringing can be a serious obstacle in case of GPR surveys aimed at geological/hydrogeological mapping, where this type of coherent noise can coincide with geological horizons. The Karhunen-Loéve transform is investigated here as one of the filtration methods capable of attenuating the coherent noise. The KL transform has been used in the field of seismic data processing, mainly for dipping coherent noise attenuation and multiples suppression on CDP gathers, but is seldom used in GPR data processing. This paper presents a brief outline of the theoretical background, highlight the main features of the KL transform, and gives two examples of its application, followed by the comparison of the results with those obtained using other techniques. As it is shown, the KL transform can be an effective mean of suppressing the coherent noise, contained in GPR data.
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Reducing Ambiguities in the Measured Vertical Electrical Sounding Data by Using Artificial Neural Networks
Authors M.M. Abou Heleika and E. NiesnerThe methods were tested on synthetic VES data as well as on field data collected from the central part of Egypt. This work exhibits adaptability of ANN in smoothing measured apparent resistivity data involving a variety of curve types and quality. Good results are observed with the three layer type curves with very small network errors. At the same time, the network errors rise with higher order of layers as obtained in the case of five curve type. As the network is over-trained, the weights will try to adjust to the minor details of the training data set itself. Though the problem gets complex with increase in layers, it is found that a proper network design can solve it, provided a good representative database for the training. The special advantage offered by ANN for resistivity inversion is that once the network is trained, it can perform the smooth of any VES data set very rapidly. The result from a neural network can be used as a starting model for inversion to decrease the inversion time. The technique can also be developed for assisting with first hand information for the model initialization in other conventional inversion schemes.
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Bathymetry, Seabed Sediments and Aquifers Imaging with Constrained Inversion of Airborne EM Data
Authors A. Viezzoli, A.V. Christiansen, N. Foged and E. AukenA shallow (depth < 20 m) layer of water, fresh, brackish or saline, covers tens of thousands of km2 of sediments and bedrock along European coastlines, rivers, lakes, and lagoons. These geological units are extremely important, both environmentally and economically. Airborne electromagnetic (AEM) data has been lately used to obtain the bathymetry of shallow surface water. Some attempts have also been made to retrieve information about the sub-bottom. The limited research carried out so far calls for improvements and further developments, both hardware and in data processing and modelling. This manuscript aims at giving a contribution at data inversion level, by applying to different AEM datasets flown over water the constrained inversion methodology. In this technique, adjacent model parameters are regularized through lateral constraints that allow information to flow from soundings that contain more to those that contain less. We present results from constrained inversion (smooth and few layers) of a portion of SkyTEM survey flown over the North Sea. Bird height was included as an inversion parameter. Both the seabed and the freshwater coming from land and protruding into the sediment under the seabed are imaged. Other case studies from lakes and rivers will be presented at the conference
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Joint Inversion of Direct Current (DC) and Electromagnetic (EM) Measurements in Parallel Computing Environment
More LessThis extended abstract presents the results of solving the global optimization problem in association with joint inversion. Apparent conductivity data obtained from electromagnetic soundings at low induction numbers for horizontal magnetic dipoles (EMHD) and Schlumberger apparent resistivity data were inverted individually and jointly. Global optimization with Monte Carlo Multistart algorithm was used in the inversion of data. The ambiguities in the model parameters associated with the target layer(s) are then studied using individual and joint inversions. This paper also presents the results of parallelization of the global optimization algorithm and its efficiency tests hold in cluster of 21 computers.
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Vs Soil Profile Estimated from Inverse Analysis of Observed Rayleigh-wave Dispersion Characteristics
By K. TokeshiThe possible limitations and/or potentials of Vs soil profiles estimated from inverse analysis of observed Rayleigh-wave dispersion characteristics of microtremor records at 4 sites in Akita prefecture (Japan) are discussed. Available borehole records of these sites were used for comparison purposes. Seven vertical component microtremor records arranged in triangular array were measured at each site. The Rayleigh-wave dispersion characteristics were estimated after using the high resolution f-k spectral method. Random inverse analysis using the Rayleigh-wave dispersion characteristics was performed assuming a ground model of six layers overlying a half-space. Ten millions of random ground models were tested at each site. According to results, two conclusions could be given. First, the Vs soil profiles for S-wave velocities lower than the value of the fastest observed Rayleigh-wave velocity agreed well with borehole records. Second, the Vs soil profiles for S-wave velocities faster than the value of the fastest observed Rayleigh-wave velocity showed larger variations when comparing with borehole records. Due to the limitations of Rayleigh-waves to be propagated through these consolidated layers, S-wave velocity and thickness of deeper consolidated layers using observed passive Rayleigh-wave dispersion characteristics would be difficult to be estimated.
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Comprehensive Inversion of Magnetic Resonance Sounding – Water Content, Decay Times and Resistivity
Authors M. Braun, J. Kamm, M. Müller-Petke and U. YaramanciMagnetic Resonance Sounding (MRS, or Surface Nuclear Magnetic Resonance – SNMR) is used for direct groundwater exploration and for an improved aquifer characterization. Currently, it is the only geophysical method that is capable to directly determine the free water content and to estimate the pore sizes of the aquifer in the subsurface. However, MRS is basically an electromagnetic method. Therefore, it is sensitive to the resistivity of the subsurface. The water content is the main target of investigation, therefore first inversion routines in the past focussed on the water content. Later on, inversion routines determining water content and decay times became available. Very recently, MRS inversion for water content and resistivity has been realized. We present here a comprehensive inversion of MRS in terms of determining the three inversion parameters water content, decay time and resistivity within one single inversion routine. Within the iterative inversion scheme, the extrapolated initial values are determined on the basis of the physical effective decay times in the subsurface, that are estimated within the inversion scheme.
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Zonal Cooperative Inversion of Crosshole Tomographic Data
Authors S. Linder, H. Paasche, J. Tronicke and E. NiederleithingerIn many near-surface geophysical applications, it is now common practice to acquire multiple geophysical datasets. The cooperative inversion of the co-located geophysical data sets may result in an improved reliability of the tomographically reconstructed parameter distributions underlying the acquired data. Here, we apply a recently developed zonal cooperative inversion approach to crosshole georadar and P-wave traveltimes collected at a well-studied test side (Horstwalde, Germany). In this inversion approach fuzzy c-means cluster analysis links the regularized least squares inversion algorithms used to invert the two traveltime data sets. This results in a single zonal model of the subsurface, which outlines the major subsurface units and explains both data sets. At the Horstwalde test site a comparison of the zonal model to direct push cone penetration test data demonstrates that the inversion approach delineates the major subsurface lithology.
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Horizon and Discontinuity Tracking using Active Contours
Authors N. Drissi, J.M. Boucher and T. ChonavelThis paper presents a new approach of automatic extraction of seismic horizons and discontinuity in 2-D seismic images. This approach is based on active contours applied to amplitudes of seismic data combined with constraints using seismic attributes. This new approach uses an algorithm that detects strong seismic reflectors before dealing with discontinuities. This approach is applied to real data. It presents a new method that helps for automated structural interpretation.
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Interval Inversion of Borehole Geophysical Data for Surveying Multimineral Rocks
More LessIn the paper a new application of the interval inversion method is presented. In investigating multimineral rocks like carbonates and metamorfits the nonlinear well-logging inverse problem becomes an underdetermined or at the best a very narrow type of overdetermined problem. The problem can not be treated by conventional point by point inversion methods with no ambiguity or satisfactory accuracy many times. In order to determine the unknown petrophysical model composed of many parameters in a reliable and accurate way, it is essential using a joint inversion process. Interval inversion is a kind of joint inversion method developed by this team, which adopts a Very Fast Simulated Annealing algorithm in its optimization phase. Having used this method succesfully for the case of shaly sand environments, now the efficiency of the interval inversion method is proven also for the case of rocks with complex lithology. In the presentation carbonate and a metamorfic field examples are shown.
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Deep Lithosphere Thermal Modelling Against Surface Temperature Condition
Authors M. Wróblewska and A. PietaHeat flow data from the Poland characterizes with strong diversification between Polish Basin, East European Craton and Teisseyre-Tornquist Zone (TTZ), and Paleozoic Platform. The analysis of this data and numerical modeling of the crustal temperatures shows evidence of extensive crustal-mantle warming in the area between the Sudetes to the south and the Trans-European Suture Zone to the north. The change in heat flow in Polish Basin is 100% when compared with values for the EEC. The borehole thermal data in upper few hundred to a thousand meters show lower geothermal gradient that indicate the Pleistocene-Holocene paleo-climatic event in Poland. The retreating of the ice sheet cover (12-15 thousands years before present) from the Polish lowland probably affected the subsurface thermal regime decreasing the geothermal gradient in the upper part of the sedimentary rocks. In this paper we construct two dimensional numerical models of the crustal and upper mantle temperatures in the transitional zone between the craton (Baltica) and the areas south west of the TTZ in order to trace the impact of the long term temperature changes at the surface.
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Multi-channel Analysis of Surface Wave (MASW) Technique in Geotechnical Studies
Authors A.I. Kanli, L. Hermann, P. Tildy, Z. Pronay and A. PinarThe soil classification in UBC (NEHRP) and Euro codes is mainly based on the ground type and description of stratigraphic profile. In the determination of the ground type which has a direct relation with the stratigraphic profile of the investigated site, one of the 3 important parameters is used: the average shear wave velocity of the top 30 m of the soil (Vs, 30-m/s), or NSPT (blow counts/30 cm) or cu (kPa) values. Usually the Vs30 values are calculated from velocity profiles determined from borehole (down-hole or cross-hole) measurements. In that case it is necessary to drill holes down to at least 30 m depth. The SPT and CPT techniques also need appropriate, usually expensive equipments. Recently, the MASW technique (multichannel analysis of surface waves) is effectively used in the determination of Vs profiles. In this study, 1-D share-wave velocity profile obtained from a MASW profile is both correlated with the borehole data and with the result of the SPT data. A shear modulus distribution map is plotted for the geotechnical purpose.
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Project "The Preparation of a Complex of Geophysical Methods for Diagnosing of Defects of Structure after the Floods
Authors K. Spacek, D. Dostal, M. Tesar and S.V. IzyumovProject „The preparation of a complex of geophysical methods for diagnosing, monitoring and analyzing of defects of structure and road foundations that occurred in consequence of the floods“ is based on the exchange of experience of Czech and Russian specialists and its aim is to evaluate possibilities of individual geophysical methods in surveying of the after-flood damages in the constructions and roads. The project started in April 2006 and its termination is expected in December 2010. The methodology for individual tasks is continuously optimized, and new procedures are tested. If some of the object will be subject to the flood, there will be measurements immediately after the floods subside.
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Recognizing the Permafrost by Vertical Electrical Sounding
Authors A. Wysowska-Swiebodzinska, S. Bialek and M. KondrackaThe aim of measurements was determination of the permafrost in the Slovak Tatra mountains and recognation of shallow geological construction. Measurements were carried out in the Copper Valley which is a fragment of the Każmierska Valley. Very good conditions to collect the snow and to convert it into firn ice was created putting and forming the bottom of the Copper Valley. Examinations were carried out with vertical electrical sounding with the Schlumbergera array. There was made 10 electrical sounding in two profiles, distance between means sounding amounted to 25m. There were distinguished 4 to 5 layers. Layer being on average 9m depth was interpreted as permafrost stayed for 2 to 3m thicknesses.
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Relationships between Water Flow Rate and Geophysical Measurements in Alluvial Aquifer
Authors P. Senechal, G. Senechal, J.M. Martin and C. BordesOur study focuses on the potential helpful of surface geophysical data to constrain the water context within an alluvial aquifer. On a given area where 2 wells have been drilled, we have performed several geophysical acquisitions, including ground penetrating radar, resistivity, seismic refraction and magnetic resonance soundings. From these data, we estimate several parameters which are the water height in the deposits, the effective porosity, the water content, the permeability and the transmissivity of the alluvial deposits. Theses physical parameters allow us to characterize the alluvial deposits in order to constrain the estimation of the potential water flow. The lithology and the water flow rate being known from the wells, geophysical results obtained in a high water flow rate zone are compared to those obtained in a low water flow rate zone. Correlation appears from the water flow rate observed in both wells and the geophysical data obtained in the vicinity of these wells.
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Application of the Simplest Geophysical Method, the Pricking Probe Method to Map Bedrock Topography in a Karstic Area
More LessFormation of surface depressions is a significant geological hazard. Prediction of future sinkholes in buried karstic areas needs knowledge about the subsurface. In order to determine the varying topography of the karstifiable bedrock we carried out multielectrode measurements. Due to the hard field conditions, the bedrock depth could not be detected. The resistivity anomalies in some places had a seasonal variation (low-resistivity in springtime, high-resistivity in the end of summer); therefore we interpreted the springtime resistivity lows as indicators of locations with high water content, that is as high porosity, saturated with water. At the same time, when pushing the current- and potential electrodes into the ground, we discovered a regularity in the areal distribution of the soil's rock debris content. Therefore we carried out a systematic electrode-pricking experiment, and categorized the soil's "toughness" corresponding to soft penetration, scratching or blockage within the upper 30 cm. We have found a close relationship between the locations of resistivity- and the soil's toughness extremes. From some epikarstic features we think that high "pricking probe" values indicate smaller depths of the bedrock. The corresponding (springtime) resistivity minima may indirectly indicate more or less collapsed horsts of the carbonate rock.
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