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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
41 - 60 of 153 results
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Combined GPR-FWD Survey to Detect Low Compaction Zones in a Harbour Area
By J. EndomSudden subsidence and occurence of voids and cavities in a harbour area lead to the developement of a new combination of two well known non destructive test methods - GPR and FWD - to identify areas of low compaction in a fast and cost effective way.
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Geophysical Survey of a Municipal Waste Landfill Using Electrical Resistivity and Induced Polarization Methods
By P. HolubAbandoned gravel pits have been often used as landfill area for the municipal and industrial waste. From 1971 to 1990 the ancient gravel pit En Colliare (north of the city of Lausanne, western Switzerland) was filled with slags of incineration, garbage from car shredding and municipal waste. The base of the landfill is in its central part close to groundwater table and landfill leachate polluted groundwater and the near river Venoge. Objective of this survey was to test the applicability of the geophysical method at this particular landfill site. Electrical resistivity and induced polarization 2D tomographic survey has been carried out to add quantitative data about the landfill content and its volume. In addition to the photogrammetric data, these results have served for the remediation project of the landfill. Since 2005 a new project has been prepared. The preparatory works have started in November 2008. Induced polarization (IP) method seemed to be more effective than electrical resistivity method due to variable lithological conditions and heterogeneous landfill content. Nevertheless, the combination of both methods proved to be valuable for the assessment of the landfill dimensions.
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Geophysical Assessment of Soil Volumes Polluted with Metal Elements from Long-term Waste Water Irrigation
Authors A. Tabbagh, J. Thiesson, R. Guerin, M. Dabas, M. Thiry and F. van OortAt WNW of Paris, a large area of coarse textured soil have been irrigated during one century (until 1999) with urban waste water so that large amount of soil organic matter (SOM), dissolved mineral compounds and metal pollutants accumulated in the surface horizons. One must now identify the volumes of polluted soils in order to favour as the stabilization or decontamination of these sites. Resistivity mapping and complementary magnetic properties measurements are used to assess the volume of polluted soil.
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A Hierarchic Approach for the Characterization of CO2 Permeable Pathways Using Geophysical and Geochemical Methods
Authors C. Schuetze, H. Lamert, U. Schneidewind, U. Werban and P. DietrichBefore large-scale underground CO2 storage can take place, it will be necessary to demonstrate that the processes are well understood, risks to the environment and population are low, and environmental disturbances are negligible. One of the main research questions is to understand the transport processes of CO2 from the reservoir through the earth’s crust to the surface. The locations of degassing areas are linked to faults acting as preferential pathways for the fluids. An important issue for the acceptance of the CO2 storage in geological formations is the availability of methods for the detection and monitoring of potential CO2 degassing. For an efficient and fast as well as cost effective assessment of different types of potential CO2 degassing different methods and technologies from chemistry, hydrogeology, geophysics and biology should be combined. The here presented study was carried out with the purpose to develop a sophisticated approach to investigate and to observe potential CO2 emanations in large areas with high resolution. For the secure monitoring of future geological CO2 storage sites an adapted concept for the investigations is crucially needed. The recent results obtained at natural CO2 degassing areas represent the successful application of the underlying basic hierarchical concept.
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Geophysical Assessment of Contamination from a Wastewater Treatment System in the Milltown Lake Catchment, Ireland
Authors S. Donohue, R. Flynn, V. McCarthy, A. Orr, P. Rafferty and K. GalvinResidential on-site wastewater treatment systems (OSWTS), where contaminated wastewater discharges to the subsurface, act as the dominant means of domestic wastewater disposal in rural Ireland; septic tanks constitute the most common technology employed. The objective of this study was to determine the effectiveness of a number of non-invasive geophysical techniques, employed in conjunction with hydrogeological data, for characterising the three dimensional extent of a contaminant plume generated by septic tank effluent discharging to glacial-till subsoils at a test site within the Milltown Lake Catchment, Co. Monaghan, Republic of Ireland. It was found that the integrated use of three geophysical techniques, electromagnetics, electrical resistivity tomography and seismic refraction with existing hydrogeological and water quality data, significantly improved our understanding of the contaminant plume and associated subsurface contaminant pathways. The geophysical results, when combined with hydrogeological data suggest that the majority of wastewater contamination originating from the septic tank is being transported through a fractured zone of bedrock, far quicker than originally expected.
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A High Sensitivity Impulse Neutron Method for Real-time Detection of Elements and Compounds in Soil and Subsoil Water
More LessThe PNN method was run as continuous monitoring under various conditions with different tasks like pollution control for organic and inorganic compounds. For many elements are established regressions for quantitative estimations. It does not matter under which conditions the PNN is performed, along the individual approach of the decay curve disturbing factors can be deleted and therefore always a representative result may be achieved. The PNN method is still undiscovered for a wide application to environmental problems. Technological adaptations may allow an continuous monitoring and even a neutron tomography on the whole polluting path water-soil-air.
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Airborne Geophysical Survey and Innovative Landslide Monitoring at Gschliefgraben, Austria
Authors R. Supper, I. Baron, A. Ita, E. Winkler, B. Jochum and K. MotchkaNew geophysical approaches for landslide investigation and monitoring were tested in the site of Gschliefgraben by the end of September 2009. Multiparameter airborne geophysics is a promising method for landslide investigation which could quickly determine the most susceptible areas to mass wasting (electromagnetics) and areas with active shallow mass movements (passive microwave); the content of radioactive elements could contribute to studying displacement or weathering degree. The introduced new techniques for mass movement monitoring and early warning (GEOMON4D and D.M.S. automated monitoring systems) proved, that such a combination of high-accuracy monitoring of displacement, ground-water level and ground temperature together with monitoring of the ground resistivity and self-potential temporal changes could definitely be an effective approach for early warning.
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Airborne EM Mapping of Rock Slides and Tunneling Hazards
Authors A.A. Pfaffhuber, E. Grimstad, U. Domaas, E. Auken, M. Halkjaer and N. FogedThe inner Aurland fjord and the adjacent Flåm valley (Western Norway) are subject to potential rock slides comprised of creeping rock- and debris masses. Based on indications that precipitation drives the sliding movements, the local municipality and regional hydroelectricity company are evaluating the option to drain the unstable area with a more than 10 km long drainage tunnel to a nearby hydropower reservoir. Both rockslides and tunnel corridor encounter phyllite, a low grade metamorphic rock type that is potentially reworked to clay in disturbed zones. Water saturated clay is a strong conductor and thus an ideal target for an electromagnetic (EM) survey. We conducted an airborne EM mapping survey to find indications for the sliding planes and to assess the tunnel corridor for potential tunnelling hazard areas. Spatially constrained inversion of the 250 line km data set reveals extended conductive zones that we interpret as sliding planes and/or gneiss / phyllite interface. Detailed follow up of initial results is planed with limited percussion drilling and ground resistivity surveys.
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Mudslide-bedrock Interaction at Super-Sauze (French Alps) by UAV-based Remote Sensing and Nanoseismic Monitoring
Authors M. Joswig, U. Niethammer, S. Rothmund and M. WalterThe Super-Sauze (French Alps) mudslide was observed by high-resolution aerial photography from UAV (unmanned Aerial Vecicle) and Nanoseismic Monitoring in 2008. Remote sensing could resolve mudslide movement, and different types of superficial fissure patterns. Nanoseismic Monitoring identified seismic event types of ‘rockfall’, ‘fracture’ and ‘scratch’. The spatial distribution of the 'fracture' epicenters and ‘scratch’ source areas indicate the generation of these events close to the 'in-situ' crests of bedrock topography, most of them hidden below the mudslide material today. Seismic source areas correlate to the spatial distribution of observed fissure patterns which diverse into extension and shear fissures of varying size, and to secondary scarps. The superficial fissure patterns reside at stable position despite the moving mudslide; their spatial distribution, dimension, shape and orientation relates directly to the in-situ crests and the lateral bedrock boundaries. Our hypothesis from joint analysis of both observation data is that ‘fracture’ impulses are induced by brittle failure of the uppermost, dried mud layer, while ‘scratch’ sequences are initiated by “scratching” and “grinding” of single rock particles within the mudslide against the hard rock in-situ crests.
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Tracking the Movements of Electrodes on an Active Landslide over Time Using Only Time-lapse Resistivity Data
Authors P.B. Wilkinson, J.E. Chambers, P.I. Meldrum, D.A. Gunn, O. Kuras and R.D. OgilvyThe movements of permanently installed monitoring electrodes on an active landslide will cause artefacts in the resulting resistivity images if their positions are not continuously updated and incorporated in the inversion. In this paper we investigate the effects of electrode movements on time-lapse resistivity tomography using a simple analytical model and real data. The correspondence between this model and the data is sufficiently good to be able to predict the electrode movements with reasonable accuracy. We show that the model can be used to invert the downslope displacements of the electrodes from their original baseline positions using only the time-lapse ratios of the apparent resistivity data. The example datasets are taken from an electrode array on an active lobe of a landslide. We show that the electrode positions can be recovered to an accuracy of 4% of the baseline electrode spacing, which is sufficient to correct the artefacts in the resistivity images. Using a time-lapse sequence of resistivity data, we demonstrate that this technique can be used to track the movement of the landslide over time to the same level of accuracy.
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The Use of Seismic Noise for Assessing the Potential Failure of an Overhanging Column
Authors C. Levy, L. Baillet and D. JongmansRock falls are difficult to predict events, owing to the suddenness of the phenomenon and to the little information available about the internal structure of the mass. In this paper, we apply the seismic noise recorded by autonomous monitoring systems for evaluating the degree of coupling of a prone-to-fall column to the rock massif. From numerical studies and in-situ seismic noise measurements, we show that natural frequencies of a rock column drop with the breakage of rock and increase with the presence of ice in winter. This frequency evolution can be followed until the column fall, using seismic noise measurements.
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Investigating a Creeping Hillslope by Layer-based Inversions of Seismic First Arrival Times
Authors M. Rumpf, U. Böniger and J. TronickeDetailed structural and geological models of the shallow subsurface are essential to understand the complex processes associated with creeping mountain or hill slopes. In this study, we present two seismic profiles collected across a creeping slope in the eastern Vorarlberg Alps (Austria). We use a layer-based inversion procedure known as the generalized linear inversion (GLI) method to invert the first break arrival times from both profiles. The resulting P-wave velocity models illustrate that, at this site, four layers are required to explain the traveltime data and to result in reasonable geological structures. These models can be easily interpreted using available borehole information. Our results demonstrate that the major relevant subsurface structures (e.g., depth to bedrock), which are believed to be critical in order to understand the mass movement at this site, can be sharply imaged by the used inversion strategy.
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Integrated Seismic 3D-processing for Tunneling
Authors D. Krüger, R. Groschup and T. DickmannFor tunnel constructions in difficult geologic conditions a reliable prediction system is necessary. Reflection seismic measurements from within a tunnel are a suitable tool to predict important engineering parameters of the rockmass to be excavated. To use this technique efficiently in the tunneling environment an integrated system of tunnel suited recording equipment and processing software is essential. In tunnel seismology data is often sparse and results have to be available in short time after a measurement campaign. Thus processing has to be integrated in a semi-automated approach effectively perfoming algorithms such as dip-filtering, inverse Q-filtering, 3D velocity analysis and 3D migration. We present these steps as they are implemented in the novel TSP (Tunnel Seismic Prediction) System.
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A New Petrophysical Model for Describing the Pressure-dependent Acoustic Velocity in Rocks
Authors J. Molnar and M. DobrokaThe pressure dependence of the velocity and absorption coefficient of seismic/acoustic waves in rock is an extensively explored rock physical problem. Based on simple physical assumptions, a new petrophysical model is developed, through which a relationship between velocity and pressure is set up and explained. The material parameters of the model are determined by using laboratory measurements data and linearized inversion method.
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Linear Spread Configuration in the MASW Method
Authors Ü. Dikmen, M.O. Arisoy and I. AkkayaIn this paper, we evaluate the effect of geophone configuration on dispersion image for linear spreads in the MASW method. To reveal the spectral resolution of dispersion images, MASW records were collected using nine different types of linear spread configuration, then dispersion image for each record were calculated using phase velocity analysis technique, and were compared to present preferable linear spread type for a MASW survey. The results show that, better dispersion image resolution and dispersion curve in the wide frequency range can be obtained by using an SL-type geophone configuration. Besides this, in a survey in which higher frequencies are more important, an SII-type configuration may be preferable. With the SII-type spread configuration, the fundamental mode can easily be distinguished from the higher modes.
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Site Characterization of São Sebastião Volcanic Crater Using Geophysical Tests
Authors I. Lopes, M. Mendes, G.P. Deidda, C. Strobbia and J.A. SantosThe Azores archipelago is located at the North America, Eurasia and Africa triple junction showing high seismicity and volcanism typical of an active plate boundary. Terceira Island has been affected by several damaging earthquakes and the 1980 January 1st earthquake (M=7,2) was the strongest in Azores during the last century. The São Sebastião volcanic crater, located at SE of Terceira Island, is characterized by an amplification of ground movements inside the crater with respect to the surroundings. Inside this volcanic crater, is located the village of São Sebastião that has shown an anomalous seismic behaviour in a more local expression during the past earthquakes. The local geology and geotechnical characteristics of the soil deposit play a strong role in the seismic ground shaking at the site. Some previous geophysical studies with information merely qualitative were not able to perform a rigorous and well-defined model of the crater. A recent survey added new information that allows a better comprehension of the damage distribution, since it indicates inside the crater a basaltic lava layer controls the seismic behaviour of that area, serving as a protection to the buildings in the SW region of the crater.
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3D Cross-hole Electrical Resistivity Tomography to Control the Injection of Expanding Resins: A Case History in Venice
Authors G. Morelli, F. Fischanger, D. Gualerzi, M. Occhi, G. Ranieri and G. SantaratoInjection of expanding polyurethane resins has recently become a widespread technique to improve the geotechnical characteristics of shallow soils for consolidation purposes. Although resins injection practice has revealed to be a satisfactory solution for the above mentioned problems, a continuous monitoring of the process is needed to achieve optimal results. In order to control the injection of expanding resins a field procedure has been developed, based on the use of three dimensional Electrical Resistivity Tomography. The choice of electrical resistivity, as a parameter for designing, monitoring and validating the homogenisation task, is based on the basic assumption that such a property is the most sensitive to water content. During the injection stage, repeated ERT acquisitions allow to control the process and to modify the injection program/parameters, whenever necessary. In this paper the procedure and its results are illustrated, through a case history in Venice (Italy), where environmental problems, due to the presence of salt water bearing soils, had to be taken into account. Therefore a specific, careful analysis of arrays of electrodes and selection of the main parameters affecting ERT resolution had to be performed in advance.
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Multi-method High Resolution Geophysical & Geotechnical Quick Clay Mapping
Authors A.A. Pfaffhuber, M. Bastani, S. Cornée, M. Rømoen, S. Donohue, T.E. Helle, M. Long, P. O'Connor and L. PerssonQuick clay is highly sensitive, marine clay with an unstable mineral structure due to post glacial heaving and consequent leaching of saline pore fluids by surface- and groundwater. Extended quick clay layers pose a serious geo-hazard in Scandinavia and North America and need to be delineated in detail. Geophysical methods, especially resistivity methods, have been tested for small scale quick clay mapping at a research site close to Oslo, Norway. By scrutinizing results from Electric Resistivity Tomography (ERT) and Controlled Source Radiomagnetotellurics (CSRMT) and integrating them to geotechnical borehole data with the help of a resistivity logging tool (RCPT) we confirm the value of this integrated study for quick clay hazard zonation. ERT is an ideal tool to interpolate limited borehole results and thus to provide a more cost efficient and detailed result than with boreholes alone. Our resistivity data from ERT, RCPT and lab measurements are consistent and appear isotropic.
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Imaging of the Shallow Alpine Fault Zone (New Zealand) Using 2D and Pseudo 3D Seismic Reflection Data
Authors A.E. Kaiser, H. Horstmeyer, A.G. Green, F. Campbell, R.M. Langridge and A.F. McClymontThe Alpine Fault Zone in New Zealand's South Island is part of the boundary between the Australian and Pacific tectonic plates. We use ultra-high-resolution 2D and high-resolution pseudo-3D seismic reflection imaging to investigate the structure of the fault and adjacent subsurface in a northern part of the Island. Employing acquisition schemes that minimise field effort while yielding high-resolution data together with fine-tuned processing strategies, we derive high-quality images of the shallow subsurface down to about 200 m depth. Gravels with a maximum thickness of ~50 m are seen on the two sides of the fault. On the hangwall side, these gravels overlie up to ~90 m of glaciolacustrine sediments.The basement underneath is interpreted to be an erosional surface that has been folded and faulted. The principal strand of the Alpine Fault Zone is shown to have a dip of 75° - 80° from the surface to the basement at ~60 m depth. The dip at greater depths is not well constrained, but is likely to range from 50° - 80°. The ~25 m apparent vertical offset of the basement yields an average dip-slip rate of 2.0 ± 1 mm/yr.
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Reflection Seismic Surveying Across the Alpine Fault Immediately North of the Intersection with the Hope Fault
Authors S.F.A. Carpentier, A.G. Green, H. Horstmeyer, A.E. Kaiser, F. Hurter, R.M. Langridge and M. FinnemoreThe Alpine Fault in New Zealand is one of only a few active transform fault boundaries worldwide that offsets continental terrains. Although paleoseismological data suggest that large earthquakes have struck the Fault in the past, it has been quiescent for at least the past 200 years. We have acquired five high-resolution seismic reflection profiles across the Alpine Fault a little to the north of its intersection with the Hope Fault. Slip-rates on the Alpine Fault appear to decrease by ~50% in crossing the Hope Fault from south to north, and at our study site the faulting is distinguished by step-overs and/or multiple strands. Accordingly, the goals of our seismic investigation are to define the structure of the Alpine Fault in the top few hundred metres of the subsurface with emphasis on defining its step-over or multi-strand character at the study site. Our seismic images contain evidence for significant changes in geometry across one major fault strand and an astonishingly abrupt transition from a highly reflective region to a non-reflective region across another major strand.
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