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Near Surface 2006 - 12th EAGE European Meeting of Environmental and Engineering Geophysics
- Conference date: 04 Sep 2006 - 06 Sep 2006
- Location: Helsinki, Finland
- ISBN: 978-90-73781-62-7
- Published: 04 September 2006
81 - 100 of 142 results
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Large Scale Geophysical Landslide-Genetic Models for the Adriatic Apennine-Ridge Slopes
More LessApennine geodynamic and geophysical evidences suggest models generating landslides affecting numerous Italian Regions, namely Emilia-Romagna, Marche, Umbria, Abruzzi, Molise and also Campania and Basilicata. These Adriatic Foredeep landslide models use concepts of Visco-Elasticity and Catastrophe Theory, recently including original contributions, i.e. Quasi-Sufficient Catastrophe Condition and Hopeless System. These models should be up-to-dated by processing field survey data and realtime Remote Sensing imageries, so using them like expert instruments helping civil protection organisations to alert people and protect natural and built environment.
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Integrated Approach for Exploration of Geothermal Energy in Sri Lanka
Authors H. M. R. Premasiri, U. G. A. Puswewala and S. WeerawarnakulaOver 70 percent of the island's total energy consumption was satisfied by firewood, agricultural residues, and animal waste, mostly for household use. Coal or petroleum deposits have not been discovered in the country yet, and the only other indigenous energy source was hydropower. Though Sri Lanka does not fall within very active tectonic zone in the earth , as nature’s wonderful gift, several hot water springs occur in the island (Map 2). However, no adequate steps have been taken to develop these thermal resources for use as energy resources.
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Some Geophysical and Geomechanical Remarks on Recognition Sinkhole Processes in Post-Mining Areas
Authors Z. Pilecki and H. MarcakA geomechanical process leading to sinkhole appearance in post-mining areas has been analysed. Changes of rock mass physical properties can be expected in the vicinity of inhomogeneities moving up towards the surface. Some geophysical measurements can be used for locating the risk site. The examples presented prove the effectiveness of the geophysical methods used to identify a sinkhole formation process in geological conditions of post-mining areas in Poland. Finally, some basic remarks on limitations of the geophysical methods have been underlined as well as the direction for further research work.
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Influence of Black Schists to Metal and Sulphur Content of Peat
Authors J. M. Lerssi and K. VirtanenThe purpose of this study was to find out the influence of black schists to metal and sulphur content of peat. Geophysical ground measurements, logging and peat sampling were done over the chosen profiles in selected peatlands. Element concentrations of peat samples were analysed in laboratory.
Exact positions of black schists were mapped using airborne data and ground EM-multi-frequency measurements. Resistivity logging probe was used to map the variation of resistivity by depth in peat. Different species and the stage of decomposition of peat and elevated metal concentrations can be observed from some logging results.
The influence of black schist is clearly observed in some high element concentrations compared to normal concentrations, in spite of quaternary layer between the peat and black schist. Some element concentrations are roughly twice as big as the normal ones. In some single samples very high concentrations were observed. Element concentrations clearly above normal level were: Barium, cobalt, chromium, iron, manganese, nickel, lead, sulphur, titanium, vanadium and zinc.
Most of the elements are concentrated near the black schist formations. Some of the elements have drifted several hundred meters and concentrated evenly in high contents over the whole bottom layer of the peat basin.
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Application of Shallow Seismic during Groundwater Filtration Investigations in the Vicinity of an Electric Power Station
Authors V. P. Lisin, I. A. Sanfirov, B. A. Bourdjukov, K. Celminsh and V. A. GrinjokDifferent aspects of shallow seismic methodology features in order to evaluate the condition of a protective dam and for an upgrade of the drainage system of the Plavinas HEPS on the Daugava River are considered. Within the framework of unified field technique, data was obtained for investigating soils, morainic deposits and buried karst manifestations on the bedrock surface in the foundations of hydraulic engineering structures using different kinds of seismic waves. Based on the obtained data, optimal locations of hydrogeological and testing boreholes were determined at the probable sites of increased filtration zones within the regional confined groundwater horizon.
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Diagnostic of Reinforced Concrete Constructions on Base GPR Technology
Authors V. V. Glazounov, N. N. Efimova, A. I. Kulikov and C. M. DanilievPractical capabilities of Ground Penetrating Radar (GPR) method in engineering diagnostics of defects arising and developing in time under operating loads in bulky reinforced concrete constructions are considered. GPR method makes it possible to detect and locate defects in concrete and metal structural components. As an illustration of vast GPR method capabilities, the results of many years’ investigation of underwater Kanonersky road tunnel in St-Petersburg are adduced. Beginning from 1998, GPR method was successfully used for qualitative estimation of the state of pavement at the tunnel foundation both before and after repair work, the latter was the cementation. Merits of GPR method and its development prospects are described.
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Studies for the Dependence of the Geotechnical Ground Parameters on the Hydrogeological Conditions
Authors V. Ciszkowski, T. Moldoveanu and G. TicuThe modifications of the geotechnical parameters lead to the decrease of the bear capacity of the foundation ground and to the yield of the ground under the pressure of the foundation causing the degradation of the building.
For establishing the supplying sources and the flowing directions of the ground water it is required to examine the ground through geophysical studies.
The image of the map of the electric field indicates the zone where the excess of water that came from the loss out of the underground pipelines network is situated in the loess dust but it cannot show the source of these infiltrations.
The map with the isobaths at the surface of the phreatic water allows placing the sources that generate water infiltrations.
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High Resolution 3D Geoelectrical Imaging of Quaternary River Valley Deposits at a Brownfield Site, Midlands, UK
A case study is described in which 3D electrical resistivity tomography (ERT) is used to investigate a chlorinated hydrocarbon contaminated site. The geophysical survey formed a component of a wider site investigation programme that included intrusive geological, hydrogeological and geochemical sampling. The primary goal of the 3D ERT survey was to characterise the thickness and lithological variations within the superficial deposits covering the site, and to assist in identifying suitable targets for the intrusive sampling programme. Interpretation of the 3D resistivity model has been aided by data collected from borehole sampling and cone penetration tests (CPT).
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Determination of Water Wells Location Based on Geophysical Investigations - An Example in an Alluvial Plain
Authors P. S. Sénéchal, G. Sénéchal, D. Rousset and J. M. MartinIn order to determine the best location of well for pumping drinking water in an alluvial plain, different non destructive geophysical methods (Ground Penetrating Radar (GPR), electrical prospecting, seismic refraction) are tested on the studied site. The goal of this study is to determine non destructive geophysical protocol for the lithological and geometrical characterization of the alluvial deposits (6 to 10 meters thick) and the bedrock constituted of clays. We have evaluated the efficiency of geophysical methods on the same site. The preliminary results are presented here. The results obtained with each method depend essentially of the lithology inside alluvial deposits and thick of vegetal soil. The combination of GPR and electrical measurements appears to be the best solution to have geometrical informations with good resolution for the top of the bedrock and informations about the lithological variations inside the alluvial deposits.
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Aquifer Modeling Using Geostatistics to Include Regional, Qualitative Heterogeneity Information
Authors W. J. Trainor and J. K. CaersClimatic changes and extremities make Aquifer Storage and Recovery (ASR) an increasingly attractive and practical water management tool. Homogeneous models will be insufficient for predicting the recovery potential of a particular aquifer or for predicting problems with flow barriers. This study generates many heterogeneous models using geostatistics without traditional reservoir data (wells/seismic). These models are used in a sensitivity analysis to determine the most influential flow structures; this analysis can then be used to design an informative geophysical survey. Lastly, ASR activities are simulated to evaluate the local aquifer's potential for groundwater storage and recovery.
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Geophysical Studies to Detect a Favourable Location for a Thermal Water Well
Authors J. P. Carvalho, E. C. Ramalho, R. Gonçalves, F. Santos and J. Martins de CarvalhoSeveral geophysical surveys were carried out in order to determine the best location for a new production well for the spa of Caldas de Monção, in order to increase production of thermal waters due to an increasing demand of the facilities. After a dipole-dipole survey conducted in 2001 that reached a depth of investigation of about 40 m and 2 shallow wells, three seismic reflection profiles were acquired to locate deep rooted faults capable of groundwater transport to the surface. Vertical electrical soundings and the refraction interpretation of the first arrivals of the reflection data were also undertaken to complement the information. This paper presents the integrated interpretation of geophysical and geological data in order to achieve the above mentioned goal. After the interpretation and lateral correlation of the structures found in the geophysical profiles, two locations appear as the strongest candidates for a successful thermal water production well. This example shows the utility of geophysical methods in detecting favorable areas for water borehole drilling, reducing economical costs considerably.
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Groundwater Flow Model to Simulate Drawdown Due to Leakage into Planned Rock Caverns at the Centre of Helsinki
Authors T. Vaittinen, P. Raudasmaa, J. Korpi and K. MelanderA groundwater flow model was compiled to simulate drawdown due to groundwater leakage into planned rock caverns under the city area of Helsinki. Numerical model was applied to complete standard groundwater management plan.
The main features to be described in the model were hydrostratigraphic units forming a system of an unconfined and a confined aquifer, leakage of the groundwater into existing underground facilities, e.g. metro tunnels at the northern boundary, and the sea water intrusion depending on the sea level. Both aquifers carry out a risk from the point of view decreasing groundwater head, condition of wooden piles in the unconfined aquifer and subsidence of the clay layer above the confined aquifer.
Groundwater leakage to planned maintenance tunnel at two possible locations was simulated. As a steady-state result, leakage at Kluuvi crushed zone is not as critical as leakage at the western boundary of the model. Compensatory sea water can intrude along the crushed zone, but based on the present concept, there is no such hydraulic connection from the sea to the western boundary. Therefore at the western area recharge wells may be needed to maintain groundwater table and hydraulic head.
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Groundwater Modelling - A Geophysical Approach
Authors J. Vendelbo, J. S. Damgaard and N. A. EdsenA regional groundwater model covering a 375 km2 large Danish island is established on the basis of 1D interpretation of geophysical datasets including almost 3.000 electromagnetic TDEM soundings. The model is based on 13 layers with downward increasing thickness and initial model parameters were determined on a presumed statistical dependence between electric resistivity and hydraulic conductivity.
During the last decade, geophysical methods for groundwater purposes have been intensively developed and applied in Denmark as electric and electromagnetic methods measuring the subsurface resistivity distribution have shown most suitable for Danish conditions.
The modelling strategy is based on a relationship between geophysical models and the hydraulic properties of the geological sediments. The actual case has proven a relationship between the electrical resistivity and hydraulic conductivity, though for some sediment-/rock-types with some uncertainty. As expected, interpretation difficulties are connected with transferring the geophysical information (resistivity from 1D interpretation of TDEM-soundings) to hydrogeological information. However, by combining electrical resistivity with borehole information, a model that yields a good representation of the aquifer properties can be defined.
Conclusively, a significant advantage can be achieved by including geophysical surveys when setting up regional groundwater models.
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Geophysical and Hydraulic Properties in Rock
Authors B. E. Danielsen and T. DahlinAn extensive database with data from southern Sweden invites for a thorough investigation of the geophysical and hydraulic properties. In the first attempt to find a relation between geophysical and hydraulic properties the information from core drillings and CVES are used. The records from the drillings include lithology, weathering and hydraulic conductivity. From the inverted CVES profiles separate soundings are extracted at positions close to the core drillings.
The results from the investigation are not easy to interpret. Some drillings and resistivity soundings shows good correlation and some do not. The problem might be that the resistivity measurements have a too low resolution compared to the very detailed observations from the core sample. Another problem could be that the core drilling and resistivity sounding most likely are made at positions close to each other but not the exact same place.
As expected this type of investigation is too simple for a complex relationship as the one that might exist between geophysical and hydraulic properties. It shows the importance of further investigations of existing and new data.
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First Steps in Hydrogeophysical Characterisation of Buried Valley Aquifers
Authors H. M. Rumpel and H. WiederholdIn the scope of the BurVal project buried valleys are explored in the North Sea region. They developed as subglacial tunnel valleys during Quaternary times and are refilled with sediments afterwards. Depending on the distribution of permeable to non-permeable layers (sand and clay) they are important for future water supply. In order to address the intrinsic complexity of the buried valleys, high-resolution reflection seismic, vertical seismic profiles (VSP) and electromagnetic (EM) surveys are used amongst other geoscientific measurements for investigation. In the two German pilot areas, the Cuxhavener Rinne and the Ellerbeker Rinne, we can map the extension of a covering clay layer in the buried valley. It is visible in the EM surveys as good conductor. In combination with the seismic sections the relative position of the clay layer in the valley is further specified. Side deposits on the valley flanks influence the protective function of the clay along the valley rim. VSP measurements show the wide range of the seismic velocities in an unconsolidated and water-saturated environment. The collected data is integrated in a 3D structural model which enables the visualisation of the buried valley and will serve as basic model for future groundwater modelling.
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Mapping Limestone Aquifer by Electrical and Seismic Methods in the Zmajevac Area (Croatia)
Authors F. Šumanovac, Z. Pekaš and H. Majtanić;Exploratory area is located in the Pannonian basin, 95 km east of Zagreb, with a geological model atypical for basin conditions. The aquifer is a “package“ of limestones, clayey limestones and marls (for geological and petroleum exploration purposes named “Croatica layers”), characterized by secondary porosity and very slight increase in relation to the impermeable “package“ of the Sarmatian deposits, which are similar to turbid sediments. Due to a complex geological model, electrical and seizmic methods were applied, with 2-D electrical tomography being the main exploration method. The Croatica layers were successfully isolated and mapped, located at depths ranging from several to approximately 40 metres, as well as the fault zones with increased rock fragmentation. The forecasting model was confirmed by the exploratory borehole, set in one of the identified fault zones in the Croatica layers, and satisfactory quantities of ground water (about 5 l/s) were obtained by exploratory pumping.
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Spatially Constrained Inversion of Area Covering Datasets
Authors A. V. Christiansen, E. Auken, N. Foged and K. SørensenWe present a new inversion methodology for large area-covering datasets. Many new data acquisition systems are capable of covering large areas with densely sampled data sets. However, it is not possible to apply 2D or 3D inversion algorithms on a routine basis because of computational problems.
We propose a Spatially Constrained Inversion (SCI) inversion scheme using a local 1D model description ensuring fast computation times. Information on the geological variability is included as constraints between model parameters applied on an all-to-all basis. The 1D formulation means that the SCI works best on a sub-horizontal layered geology.
To ensure flexibility even for very large surveys we sub-divide the area in hexagons, which are independently inverted and afterwards stitched together. Continuity over hexagon edges is ensured by applying an overlap between neighbouring hexagons.
A field example demonstrates that the SCI enables better resolution of otherwise poorly resolved model parameters. Lineations observed in line-inversion are removed.
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Geophysical Investigation of a Mud-Volcano in the Northern Apennines
Authors A. Bratus, F. Accaino, U. Tinivella, S. Conti and D. FontanaIn the frame of a co-operation between the Earth Science Department of the University of Modena and Reggio Emilia and the OGS, a geophysical investigation, including geo-electrical profiles and a 3D seismic acquisition, was detected in Nirano (Italy, Northern Apennine) where mud volcanoes are present.
The aim of the investigation was to determine the geometries of the shallower structures, across a mud volcano (Fig. 1), using information obtained by tomographic inversion of first arrivals of 3D seismic data and resistivity models obtained by 2D ERT (Earth resistivity Tomography) data.
The joint information from different geophysical methods furnished a detailed map of the structures of the first 30 - 50 m in depth, and the final results are in agreement.
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Seismic Interferometry in Near-Surface Seismics - An Experiment
Authors D. S. Draganov and R. GhoseSeismic interferometry (SI) is the process of generating new seismic records from the cross-correlation of existing records. The interest to SI is growing, but mainly in hydrocarbon exploration and global seismology. The application of SI to shallow seismics could help to extract more information form the data and at the same time save efforts and time in the field.
We tested the SI method on a dataset from physical model with a VSP geometry. We could reconstruct direct arrival events and some reflections.
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Stress Dependence of Shear-Wave Velocity in Unconsolidated Sand: Implication for New Monitoring Possibilities
By R. GhoseWe have performed an experiment on an unconsolidated sand sample in a biaxial pressure chamber to observe the effect of horizontal stress on seismic shear-wave velocity. Multi-offset seismic reception was successfully implemented in the laboratory scale. From changes in shear-wave moveout velocity observed in a receiver array we could distinguish the effect of horizontal stress change. The approach appears to be realisable in field. This may lead to a new methodology for in-situ monitoring of horizontal stress change in soil. Further, we found a good match between the observed and the modelled shear-wave velocity change as a function of horizontal stress. This has potential to offer the magnitude of in-situ stress in soil, which has so far remained difficult to estimate in the field. Our observation also reinforces the possibility of implementing the model-based integration of seismic and CPT data, proposed earlier, for obtaining unique estimates of in-situ porosity and horizontal stress.
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