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Near Surface Geoscience 2016 - 22nd European Meeting of Environmental and Engineering Geophysics
- Conference date: September 4-8, 2016
- Location: Barcelona, Spain
- Published: 04 September 2016
41 - 60 of 189 results
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Mapping Alteration Zones over Botija Deposit, Using Reinterpretation of TDEM Data Flown for Geotechnical Purposes
Authors A. Viezzoli, V. Kaminski, A. Menghini and M. HopeCurrent study describes a case of reinterpretation of legacy TDEM geotechnical data for mining purposes. This reinterpretation allowed to extract new valuable information about alteration in Botija Cu porphyry deposit (Panama) and shine light on such phenomena as airborne IP effect and Cole-Cole modelling of airborne TDEM data.
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Application of Joint Inversion of Seismic and Gravity Data for Geological Characterization of Near Surface Zone
Authors A. Cygal, J. Pilch, M. Stefaniuk and T. MackowskiA comprehensive research on developing P-wave near-surface velocity models conducted during classic seismic data processing enabled not only a calculations of reliable values of static corrections, but also obtaining a detailed geological characterization of the shallow deposits and structures. Such a solution was possible to obtain by application of joint inversion of seismic refraction and gravity data and aimed to deal with complex geological and hydrogeological conditions of the Polish Lowlands. The presence of large thickness of glacial and post-glacial deposits typical for this region became an essential challenge for the presented experimental seismic study. This Quaternary formation comprises problematic for seismic acquisition unconsolidated material: gravel, sand and clay, which are additionally characterized by remarkable lateral and vertical lithological heterogeneity. In order to improve the quality of near-surface interpretation, it was inevitable to support the traditional interpretation methods, mainly seismic refraction tomography, with incorporation of the other, independent geophysical data. High-quality seismic data together with gravity anomaly gave an opportunity for the wider application of the joint inversion method to near-surface imaging for groundwater aquifers and mineral deposits prospection.
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Localization of Underwater Objects Using DC Resistivity Method with Two Detection Line
More LessSeveral methods were introduced as a technique to detect underwater objects such as submarines. Acoustic methods were generally exploited for underwater objects detection. However, they are prone to be disturbed by acoustically noisy marine conditions. To solve this problem, a new method adopting the geophysical DC resistivity method is introduced. Detection feasibility of underwater objects using this method was verified through numerical modeling and physical scale modeling. When we use a detection line, a peak point of responses indicates an object position along a detection line, however, the position along the perpendicular direction is not verified. However, fast localization of the target object is required since the final goal is real-time tracking of underwater object. In this study, a localization method for moving underwater objects is introduced using two detection lines and localization algorithm is developed with response library. A feasibility of detection and localization using the algorithm is confirmed through the experiments using physical scale modeling data.
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pyDFERM - Towards a Versatile and Efficient Environment for ERT Monitoring Data Management and Processing
Authors O. Kaufmann and A. WatletWe developed a Data Format for Electrical Resistivity Monitoring alongside a Python package (pyDFERM) as a novel approach for managing long-term ERT monitoring experiments. Large datasets produced in such experiments are indeed quickly difficult to handle with conventional data storing techniques. In parallel, long-term experiments are subject to changes in experimental conditions that are not always easy to report. Our approach covers 4 aspects that aim at improving the management and processing of ERT monitoring measurements. These can be listed as (1) checking and logging data acquisition job status, (2) structuring, documenting and storing incoming data, (3) efficiently retrieving and processing subsets of stored data, (4) structuring, documenting and storing processed results. Current developments show the added value of the project for subsurface imaging and data management in long-term ERT monitoring.
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Optimizing Geoelectrical Arrays for Special Geoelectrical Monitoring Instruments
Authors P. Tsourlos, B. Jochum, R. Supper, D. Ottowitz and J.H. KimIn this work we adopted an array optimization scheme for a special geoelectrical monitoring instrument for which no standard geoelectrical arrays exists. Optimized measurements are selected on the basis of their Jacobian matrix values. Application is demonstrated though model and real examples from a landslide site in Austria. Synthetic and real tests demonstrated that though measurement optimization it is possible to reduce the number of collected data without reducing the overall geoelectrical imaging quality. This is a very important for reducing both the power consumption as well the time-lapse data processing time.
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Modelling of Seismic Amplitude Anomalies Observed During Sub-surface Gas Injection Monitoring
Authors H. Perroud, P. Pezard, J. Lofi, N. Denchik and H. AbdoulghafourSeismic amplitude anomalies have been observed at the Maguelone site in the course of sub-surface gas injection experiments. To allow the interpretation of the seismic monitoring in terms of physical parameter changes, various modelling attempts were conducted that all share the elastic wave theory principles. We show in this presentation that we cannot reproduce the experimental results with this theory, thus some form of anelastic energy dissipation would be required.
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Time-lapse Electrical Resistivity Monitoring of Subsurface CO2 Storage at the Maguelone Experimental Site (France)
Authors N. Denchik, P. Pezard, H. Perroud, J. Lofi, H. Abdoulghafour, D. Neyens and G. HenryCO2 geological storage remains a recent research field and many questions are still open, particularly for saline formations, which are expected to provide over time a larger storage capacity than depleted hydrocarbon reservoirs. The Maguelone shallow experimental site for shallow CO2 injection (Mediterranean coastline, Gulf of Lions, France) has been developed to study in an integrated manner surface and in-situ (downhole) monitoring methods. The presence of two small reservoirs with impermeable boundaries (R1: 13-16 m and R2: 8-9 m) provides an opportunity to study a saline formation for gas geological storage both in the field and in a laboratory context. During the shallow injection experiment (~48 m3 of CO2 was injected over ~2 hours on December 4, 2014), traces of the CO2 plume were detected by time-lapse downhole and surface electrical resistivity monitoring techniques, although some of the injected CO2 appeared to leak along the new injection hole, which should be corrected in the future with additional cementing around the new holes.
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Monitoring Transport of Contaminants During Snowmelt Infiltration with Invasive and Non-invasive Techniques
Authors E. Bloem, H.K. French and A. BinleyThe impact of agriculture, industry, airport activities on soil and water quality is strongly influenced by soil heterogeneity. At Oslo airport large amounts of de-icing chemicals are used for removal of snow and ice. The objective is to quantify how the different processes occurring during snowmelt infiltration of meltwater contaminated with de-icing chemicals affects the geophysical signals. The study describes two field experiments were tensiometers, suction cups, and multi- compartment sampler (MCS) techniques have been combined with non-invasive time-lapse electrical resistivity measurements (ERT). The MCS combines variable-suction with multi-compartment aspects to measure spatial and temporal distribution of water flow and solute transport. The tracer experiments were performed at the research station at Oslo airport. The low resistivity values at the top of the ERT profiles on day 6 and 12 are explained by rapid increase of water saturation (Day 6), derived from tensiometer data, and infiltration of tracer (Day 12), derived from suction cup data. The low resistivity is also explained with MCS by saturation conditions at day 3 and increased electrical conductivity at day 12. By combining ERT, tensiometers, water sampling via suction cups or MCS, we can observe the contributions from water content and solute concentration to ERT.
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Seasonal Monitoring of Soil Water Content and Infiltration Using Soil Temperature Measurements
Authors A. Tabbagh, R. Guérin, B. Cheviron, H. Henine and M. BechkitWe use high precision Pt 100 sensors and apply numerical models of convective and conductive heat transfer to temperature experimental data recorded versus depth and time along a vertical soil profile. After having determined the thermal diffusivity and the convective flux rate it is possible to calculate the water content and the Darcy’s velocity using empirical soil properties models. The results obtained at Boissy-le Châtel site between April 16, 2009 and March 8 2010 are presented here. The ten day period results are reliable in accordance with local rain and potential evapotranspiration data.
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The Use of Surface Geophysics to Determine the Aquifer Characteristics in the Folldal Mining Site, Norway
Authors S. Puig, C. Duque, T. Pabst and P. AagaardOver two centuries of mining activity in Folldal area (Norway), now an industrial cultural heritage site, led to large amounts of uncovered waste materials. The exposure and subsequent oxidation of these materials produces acid mine drainage, which is discharging into the River Folla. Integration of surface geophysical and hydrogeological field methods was necessary to further obtain hydrogeochemical numerical models to assess the fate of the acidic groundwater, its contribution to the river and predict the effect of remediation. Seismic refraction and electrical resistivity tomography (ERT) were essential tools to characterize the aquifer geometry, locate the water table and obtain an overview of the topsoil sedimentological changes without altering the historical site. From the integration of the methods, the aquifer was characterized as a one single sedimentary layer aquifer of 30-40 m depth and areas with different hydraulic conductivity were defined, which permitted to obtain accurate groundwater flow.
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Analysis of the Water Content Variation in Different Timber Species Using the Nondestructive GPR Technique
Authors R. Martínez-Sala, I. Rodríguez-Abad and J. Mené-AparicioDeveloping a nondestructive system is crucial to inspect water contents in timber structures because the amount of water, beyond a certain point, can compromise the structure strength. With this in mind, the present work is aimed at analyzing the capability of ground penetrating radar technique (GPR), with a 2 GHz antenna, to detect water content variations in timber. To do that, GPR measurements were conducted on timber samples at two water content states: at hygroscopic equilibrium (HE) and after 72 hours of complete immersion in water. Given the anisotropic nature of timber, the data acquisition was performed in two directions respect to the grain, parallel and perpendicular. The obtained results highlighted that GPR can be a very suitable technique to monitor water content in timber structures that are in service, since it was confirmed that propagation velocities decreased as the water content increased for all samples and acquisition displays (parallel or perpendicular to the grain). Moreover, the dielectric anisotropy is more evident when the samples had been immersed in water than when they were at their HE.
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Electrical Resistivity Monitoring of Saline Tracer Fingering at Pore Scale under Partially Saturated Conditions
Authors D. Jougnot, J. Jiménez-Martínez, Y. Méheust, T. Le Borgne and N. LindeTime-lapse electrical resistivity tomography is a widely used geophysical method to remotely monitor water saturation and the migration of contaminant plumes. The effects of heterogeneous solute concentrations below the resolution limits of the tomogram are commonly ignored. We have adapted an experimental set-up to study the effects of sub-resolution solute heterogeneities on the effective bulk electrical resistivity. We used a 2D analogous porous medium consisting of a Hele-Shaw cell. We monitored simultaneously the bulk electrical resistivity and the spatial distribution of the water/air phases and the saline solute concentration field in the water phase using a fluorescent tracer injected together with the saline solute and a high-resolution camera. We performed saline tracer tests under full and partial water saturations. The bulk electrical conductivity measured at the scale of the medium were confronted to electrical conductivity computed numerically from the measured spatial distributions of the fluid phases and the salinity field. We find that the air distribution, saline tracer fingering, and mixing phenomena all result in large changes in the measured and simulated bulk resistivities by creating preferential flow paths or barriers for electric current at the pore scale.
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3D Resistivity and Induced Polarization for Leachate Plume Identification at a Challenging Field Site
Authors P.K. Maurya, A.V. Christiansen, G. Fiandaca and E. AukenIn the present study, we have used 3D ERT for detailed mapping of a polluted site at a challenging river site in the southern part of the Denmark. The survey layout involves several crossings of the meander of a river where a leachate plume from an old chemical factory site is expected to reach the river. Both resistivity and time domain induced polarization data were acquired, and full 3D inversion was performed for the resistivity data and 2D inversion of the IP data. Two sets of 3D data were acquired; one at a larger scale covering total area 410x90m2 and one at small scale covering 126x42m2, which enabled both details in the shallow part while covering a large area. 3D DC data were inverted using the inversion package BERT and 2D DC-IP data were inverted using AarhusInv. 3D DC inversion models show the presence of low resistivity anomaly at the northern bank of the stream interpreted as a contaminant plume. The contaminant plume is also seen in a deeper aquifer, which is separated by a low permeable clay layer to the upper aquifer. We could not discriminate the clay-lithology from the contamination using only resistivity model however, including the 2D inversions of the IP data we clearly separate the clay layer from the contaminated aquifer.
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Geoelectrical Characterization of Hydrological Processes in a Buried Braided River System
Authors A. Guinea, S. Hollins, K. Meredith, S. Hankin and D.I. CendónThe Macquarie Marshes (NSW, Australia) cover approximately 200 square km of the Macquarie River flood-plains. The marshes are one of the largest remaining inland semi-permanent wetlands in south-eastern Australia. Diversity of fauna and flora has decreased in the wetlands while the flood-drought cycles controlling these ecosystems have been affected by recent human activity. An Electrical Resistivity Tomography survey has been carried out to provide insight into the surface water/groundwater interactions occurring at the north-western part of the marshes and to identify potential recharge areas of the aquifer systems. In the resistivity sections three main units can be identified: 1. A top unit of low-resistivity (1 to 6 ohm.m) with about 5 meter thick on average. 2. A middle unit of higher electrical resistivity (6 to 20 ohm.m) that continues to a depth of approximately 20 metres and is discontinuous laterally. 3. A bottom unit below a depth of 20 to 25 metres with resistivity decreasing to values similar to those of the top unit. The resistivity results has allowed to identify clay dominated and sand dominated materials. The groundwater is recharged from surface water following sandy windows in the clay created by modern channels on the surface of the marshes.
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Potential for Reconstruction of the Subsurface Salinity Distribution Using the Frequency Domain Electromagnetic Method
Authors S. Delefortrie, T. Saey, P. De Smedt and M. Van MeirvenneWe explore the usefulness of FDEM conductivity mapping for hydrogeological investigations by surveying farming land overlying a salt plume. Specifically the potential for reconstructing the salinity distribution of the subsurface is researched. To this end, calibration of the collected FDEM data and accuracy of the inverted responses are looked into. In addition, ancillary data were collected to validate the results.
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Seismic Imaging of Esker Sediments within the Satakunta Sandstone Depression in Köyliö, SW Finland
Authors E. Ahokangas, G. Maries, J. Mäkinen, A. Pasanen and A. MalehmirThe Satakunta sandstone depression infilled by the Pori-Koski interlobate esker sediments hosts a major high-quality groundwater reservoir in Köyliö, SW Finland. These up to 100 m thick sediments were delineated for the first time down to bedrock level by high-resolution reflection seismic method using a newly developed landstreamer consisting of 80-3C MEMs (micro electro mechanical) broadband sensors together with 50 wireless recorders connected to 10 Hz geophones to obtain greater depth penetrations. The 5-day survey resulted in about 5 km long seismic data (2-4 m receiver and shot spacing) and two profiles. Indications of crystalline basement are lacking in the tomography sections, implying that the (fractured) Rapakivi granite area extends further southeast than expected. The sandstone contact position was also ca. 500 m further to the east than expected. The sandstone depression and infilling esker sediments and the bedrock level were shown with good accuracy in both tomographic model and the reflection section. The hydraulically conductive esker core does not follow the sandstone contact and is underlain by older sediments. This case study illustrates the capability of high-resolution seismic surveys with the parameters used in this study for hydrogeological investigations and in particular in thick glacial sediments.
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Fault Zone Imaging with Seismic Refraction Tomography
Authors S. Ostrowski, B. Rybak-Ostrowska and M. LasockiThe authors applied seismic refraction tomography (SRT) for imaging geometry, surrounding medium and internal details of fault zones. The applicability of the SRT technique to structural analysis of fault zones is demonstrated. Typical effects of fault zone occurrence on seismic velocity field distribution is described and discussed. Three examples of fault zones from southern Poland are presented, illustrating the description. A phenomenon of seismic velocity increase in some fault zones is introduced and is ascribed to presence of residual stress in recently active fault zones.
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Monitoring of “Contaminant” Flow Using Time-lapse Optimized 3D ERT in a Supervised Experimental Test Site
Authors K. Simyrdanis, P. Tsourlos, N.G. Papadopoulos and S. KirkouMonitoring of subsurface contaminants is crucial for environmental purposes. Electrical resistivity tomography has been extensively used the last years for spatial-temporal mapping and monitoring of various contaminants. In order to explore different aspects of survey planning regarding the employment of ERT in monitoring conductive contaminants, a supervised field test site was considered thus simulating more realistically the actual field conditions. A 3x2x2.5 m ditch was dug in the subsurface and equipped with an apparatus made of plastic pipes resembling four vertical and two horizontal boreholes, each one carrying 12 electrodes. The ditch was carefully backfilled with the same clay soil extracted by the ditch. A step-like sandy target was placed between the boreholes to control the contaminant flow and a saline tracer was injected on the top of the sandy target. The mapping and monitoring of the contaminant flow was made through optimized focussed ERT protocols compiled with the Jacobian matrix approach. The contaminant flow is represented using 2D and 3D inverted images, through space and time. Time-lapse 4D inversion presents with considerable accuracy the contaminant’s movement through the different time phases signifying the effectiveness of the borehole setting and the employed measuring protocol.
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An Assessment on the Recent Seismicity in the North Anatolian Fault Zone, Turkey
More LessA statistical assessment of recent seismicity in the North Anatolian Fault Zone, Turkey, is made by using seismotectonic b-value and precursory seismic quiescence Z-value. The catalogue including 28,420 earthquakes between 1970 and 2016 is used. Using the Reasenberg declustering process and the earthquakes with MD≥2.7, 51.4% of the events are removed and so, 13,815 events are used for a quantitative evaluation of seismic quiescence in the NAFZ in the beginning of 2016. Completeness magnitude is estimated as 2.7. Resulting values show that significant anomalies are observed in both b- and Z-values in some parts of the NAFZ. The larger b-values are calculated in Silivri, Black Sea, Izmit and Düzce whereas the smaller b-values are estimated in the western, the eastern and the middle parts of the NAFZ, covering Gulf of Saros, Gelibolu (Çanakkale), Ismetpaşa segment, Bingöl, Erzincan, Amasya and Çankırı. Several quiescence regions in and around Tekirdağ, Gulf of Saros, İstanbul, Marmara and Black Sea, İzmit, Düzce fault, Mudurnu, Çankırı, Amasya are observed. Consequently, the same regions including Gulf of Saros, Çankırı and Amasya where the smallest b-values and the largest Z-values are obtained may give important evidences to reveal the future earthquake potential in the North Anatolian Fault Zone.
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Airborne TEM Measurements Used As Reconnaissance Tool for Mapping Areas with Quick Clay in Sweden
Authors L. Persson, M. Bastani, H. Löfroth and C.A. SmithAn airborne transient electromagnetic (ATEM) survey was carried out over four test areas to evaluate the method for mapping potential quick clay areas in Sweden. The first results from an area located in southwestern Sweden are presented here. Previous geotechnical investigations confirm the presence of both quick clays and un-leached marine clays in the area. Based on the results from the ATEM survey, additional geotechnical investigations (including CPTU-R) and ERT measurements were also carried out. Comparison between ATEM results and the geotechnical investigations show that, over low resistivity areas (around 1 Ohmm) the clay is generally low sensitive, while in areas with resistivities higher than 5 Ohmm, high sensitive quick clay is identified. The resistivities obtained from the ATEM survey also correlates well with the results from ERT and CPTU-R measurements. The results show that the ATEM method can be used as an effective tool in mapping potential quick clay zones. Geotechnical sampling is always needed for comparison and confirmation of results from ATEM measurements.
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