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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
21 - 40 of 189 results
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Seismic Investigation for the Characterization of a Gravity Concrete Dam
Authors P. Capizzi, R. Martorana, C. Pirrera and A. D'AlessandroMonitoring of large-scale infrastructures plays an important role for public safety and prevention. The control of the safety assessment of a dam is largely dependent on knowledge of the mechanical parameters of the actual construction, as well as its geological substratum. The application of geophysical methods can considerably contribute to the examination indicating the less consolidated material and the degradation of mechanical parameters. A seismic tomographic approach has been used in a typical gravity concrete dam without reinforcement to detect mechanical properties of the body of the dam and its geological setting. Three seismic travel time tomographies in the dam body as well as S-wave velocity values obtained by a down hole testify that the dam is composed of high quality concrete. Small variations on the P-wave velocities seem to be the effect of moisture and infiltration. In addition seismic surveys in the surrounding grounds of the dam confirmed the expected properties of the foundation terrain.
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Identification of Landslides Processes on the Slope Areas near Gas Pipeline Bovanenkovo-Ukhta Permafrost by GPR
By V. NoskevichIdentification of landslides processes on the slope areas near gas pipeline Bovanenkovo-Ukhta permafrost by the method of georadiolocation (GPR). SUMMARY The article presents the results of profiling radar scanning along the gas pipeline in sloping areas in the permafrost zone. The technique of GPR survey at two sites and describes setting choices of GPR emitting and receiving antennas, as well as methods of data processing. Criteria for the selection in the GPR cross-sections shifting blocks weakly bound soils, and set the curve slip line of these blocks, which is a boundary between the melt and frozen grounds.
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Tunnel Assessment with Borehole Radar
Authors V. Perez Gracia, O. Caselles, J. Clapes and J.A. CanasThe collapse of a tunnel and the damage in a second tunnel during the construction works, forced to the assessment of the ground in the front tunnel of the second structure, in order to avoid additional problems. The first evaluation was carried out with a borehole radar, because the structure was in a populated zone of a dense city. The uncertainty associated to the near surface studies is, in this case, greater because the unshielded antennas produce a rotational ambiguity. The imprecision in the location of the targets was reduced using seven non-parallel boreholes. The results shows the anomalies that could be associated to faults and also an irregular area of the B-scans that could be related to heterogeneous materials and the existence of a large number of voids.
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Using the Resistivity Method for Leakage Detection at Sant Llorenç de Montgai Embankment (Lleida, NE Spain)
More LessThe infiltration through the core of foundation of embankment dams is a main concern for maintenance and safety. The mechanism of infiltration induces internal erosion which can be progressive and can disturb the stability and the durability of the structures. Internal erosion occurs when water flows through a cavity, crack, and/or other continuous void within the embankment. Geophysical survey at Sant Llorenç de Montgai embankment has evinced the effectiveness of the ERT technique in assessing the state of the dam embankment. In particular, the method has revealed areas with high electrical resistivity values related with mortar injection. In the other side, we have registered areas with very low electrical resistivity values correlated with areas with possible abnormal seepage.
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Study of Integrated Geophysical and Geological Research Methods on Mapping Weakness Structures in Bedrock at Urban Areas
Authors T.K.T. Huotari-Halkosaari, M.H. Wennerstöm and I.A.S. SuppalaThis abstract present one example site from a short project where the idea was to develop integrated geophysical and geological research methods for the urban studies for detecting fracturing and mapping weakness structures in the bedrock. The sample case is located in the route of planned west metro line in the City of Espoo. The area is called Hannusjärvi. The geophysical methods included old airborne interpretations as well as different ground geophysical test measurements together with geological interpretations from existing data and interpretations. Bedrock drilling data for this project was distributed by the West Metro Project. The old interpretations of weakness zones were produced in two earlier projects using aerogeophysical data and topographic models combined with structural geological analysis. The use of different ground geophysical methods was considered according to methodological and geological features. Magnetic, gravimetric, ground penetrating radar, electrical resistivity tomography and electromagnetic methods were utilized in test with new geological mapping. The combined geological and geophysical interpretation gave promising results and new information about the possible fractures and weakness zones in the vicinity of the new metro line. The ongoing excavation of the metro tunnel gives data to verify the geophysical and structural geological interpretations made in this project.
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Investigation with Seismic Methods of the Sedimentary Cover of an Astrobleme at Outskirts of Sao Paulo City, Brazil
Authors R.L. Prado, I. Ullah and I.C.E. FenollThe paper shows the results obtained from seismic reflection and HVRS/MASW (horizontal and vertical ratio spectrum and multichannel analysis of surface waves) data acquired in a circular structure whose formation is attributed to a meteorite impact. The structure, known as Colonia crater, is partially located in urban area at São Paulo outskirts. The aspects presented here are related to data processing and interpretation.
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Landfill Geophysical Imaging - Babica Landfill Case Study
Authors R. Putiška, D. Kušnirák, I. Dostál, V. Vybíral, R. Pašteka and J. PapčoOne of major environmental challenges in Slovakia is to deal with numerous contaminated sites polluted by improper waste management in the past. We present a case study from Babica landfill located in western part of Slovakia near the village Bošany. The landfill was established in 1970, in a very inappropriate environment of abandoned meander. Waste composition of the Babica landfill is mainly formed by waste from the leather and footwear production. Broad spectrum of geophysical methods were applied on several profiles in order to describe the spatial limitation of landfill materials and to monitor the spread of contamination from the landfill in the surrounding environment. Combination of several geoelectrical methods (EMI, ERT, VES and SP) allows us to define the resistivity model of the area, where the contaminated area was clearly outlined by low resistivity values. Moreover VES measurements were sorted in four elementary classes defined by the shape of the VES curve, which allows us to create schematic model of the area. Self-Potential method proved the active connection of the abandoned meander with the river. Additionally, soil vapour method survey revealed three outbreaks of methane gas generation that are connected to the area near the old meander.
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Comparison of Fracture Models for Seismic Wave Propagation in a Medium with Multiple Parallel Fractures
Authors E. Parastatidis, M.W. Hildyard, G.W. Stuart and D.A. AngusRock fractures create a secondary porosity giving new fluid paths due to the increased permeability. Seismic waveforms can provide useful information on the fracture network of a rock as a result of wave interaction with the fractures. This study is targeted at improving the understanding of wave propagation modelling in fractured media. For this purpose we use numerical modelling to model wave propagation through multiple parallel fractures based on an experiment with ‘simulated’ fractures in a steel block from (Pyrak-Nolte et al. 1990). Three models (Transversely Isotropic, Heterogeneous Transversely Isotropic and explicit fracture representation), each one using a different solution to the wave propagation in fractured medium, are developed in order to compare the similarities and differences. We use a P- and S-wave source which we have inverted from the experiment to study propagation in two different orientations perpendicular and parallel, to the fractures.
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Geoelectrical Monitoring at the Reclaimed Landfill of Derveni, Thessaloniki (Greece)
Authors F. Kapeti, G.N. Vargemezis, P. Tsourlos, N. Kazakis, A. Tatsi and A. VoumvourakiInfiltration of rainwater is of major importance for old waste disposal sites where production of leakage is taking place even after reclamation. In this work we present an ERT monitoring case study in a reclaimed Derveni Landfill. Previous studies in the area showed that important amount of water flows within the waste volume or by lateral groundwater flow or by direct infiltration of rainwater. Maag permeability measurements showed differential behavior of the top soil. Thus, geophysical monitoring of resistivity changes during injection of known conductivity water in high resolution 2D and 3D tomographies has been applied in two selected sites according permeability distribution map. 4D inversion of 2D and 3D data sets showed the flow paths of the injected salty water within the top soil up to the depth of almost one meter. At the same time increase of the resistivity has been observed deeper than one meter that cannot be easily explained. A possible explanation, except the case of disturbed current flow which could lead to artefacts, could be the biogas flow that is interrupted by the water cap of the injection. Both explanation are to be examined as a next step to the integration of the geoelectrical monitoring.
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Comparison between the Measurement of SP and Resistivity Method to Detect Wastewater in the North and South Bantar Geban
Authors B. Prasetyo and M.T. AlfiansyahThe problem of waste day by day more noticeably for many people. Garbage heap from households in DKI Jakarta is the cause pollution and health problems, so the rest of the household garbage heap is collected and transported to Final Disposal (TPA) Bantar Gebang, Bekasi which far from residential areas in order to keep the environment clean. Now, in fact the problem is not only on the surface like the smell of garbage wafted until the hundreds of meters, but also below the surface. Many residents are complained that several wells have bad odor, and allegedly a result of polluted by leachate water. The garbage are mounting (open dumping) without a thick layer of skin geotextile and channel leachate container, so that oozes down the surface. Based on the study, leachate water conductivity higher than groundwater which means the resistivity value was low. Utilization of SP and resistivity method is used to review and determine the distribution of the leachate below the ground surface which already oozes to the well of residential areas. Keywords: resistivity, conductivity, SP, leachate water, waste
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Microtremor for Evaluating the Effect of Shallow Sediments on Earthquake Ground Motion at Quseir City, Red Sea, Egypt
More LessRecording microtremor data is increasingly used in determining the site effect on earthquake ground motion especially in regions of moderate to low earthquake activity. In this study we used microtremor data to evaluate the effect of shallow sedimentary layers on earthquake ground motion in Quseir city which is located in the Red Sea coast, Egypt. The increasing in urbanization and land use planning, and the constructions of tourist resorts in Quseir city are the motivation of this work. The microtremor data was recorded by single seismic stations and by array of seismic stations at number of sites at Quseir city. The single stations microtremor data was analyzed based on the horizontal-to-vertical (H/V) spectral ratio technique in order to get the fundamental site frequency (f0) and its associated amplitude of ground motion (A0). The raw data of array was analyzed by using the SPatial AutoCorrelation (SPAC) technique to infer the shear-wave velocity structure beneath Quseir city. The results demonstrate that the value of f0 is ranging between 0.56Hz and 2.5Hz. The retrieved shear-wave velocity profile is characterized by significant interfaces at depths 20m, 50m, and 80m corresponding to velocities 170, 240, and 365 m/s respectively. The resulted f0 values were used in the calculation of bedrock depth at the measured sites. The parameters obtained in this study show a good agreement with the geological setting of Quseir city.
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History of Geophysical Work for Potash Salt Investigation in the Catalonian Potash Basin - ICL Iberia Súria & Sallent
Seismic surveys have been used for potash prospection in the Catalonian Potash Basin since the early 1970’s. More recently, 3D high-resolution seismic surveys have proved to be a powerful tool for potash mine evaluation and planning when professionally designed by geophysicists in collaboration with mining companies. Interpretation by mining geologists for mining engineers is key to achieving an improved geological understanding of the mine. In this case study in-depth seismic interpretation made it possible to obtain a structural geology model as well as produce isobath and isopach maps. The resources were evaluated after a drilling campaign and a calculation of on-site resources was made using geostatistical methods in compliance with International Standard Codes for Reporting of Exploration Results, Mineral Resources and Ore Reserves (JORC Code).
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Near Field Modeling of the Explosion Waveforms and the Key Contributing Factors
Authors M. Saeidnezhad, A. Sadidkhouy and S. KeshavarzipourtaftiFor modeling the blast wave, first its Green function must be solved. Therefore, we use the Green function solution of explosive source by Herman (1979). Study area, was located around the gas pipes in high-speed rail project Qom – Isfahan, with the longitude of the 50.5 to 51 degrees north and the latitude of the 33.5 to 34.5 degrees east. In this study, was used the number of four-digit seismograph machine type CMG-6TD. Sort seismograph machines around the blast site in such a way that the three-component seismic energy radiation patterns of blast were recorded in the vertical, radial and transverse. A condition that has a component (the radial component) was placed in the site of the explosion; also the distance between two consecutive samples was determined at a digitize of 10 milliseconds.
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Case Study of Seismic Surveying and Data Processing for Small-scale Carbon Capture and Storage in the Pohang Basin
More LessCarbon capture and storage (CCS) can be manipulated in subsurface sediment, which is a porous and permeable interval, after geological characterisation. We conducted multichannel seismic surveying to image the subsurface for geological interpretation of the Pohang Basin, Korea. The length of the streamer could not stretch to a far offset, due to the limited area of Pohang Harbour. The 24-channel streamer allowed six folds, which provided a low signal-to-noise ratio for conventional seismic data. Investigation of the seismic processing enhanced the quality of the stack section, which showed a reflector at the 800-ms TWT time domain. Geological interpretation using the seismic investigation mapped the thickness of the sedimentary unit for feasible CO2 injection.
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Mapping the Thickness of Gyttja by Using the Pull-down Effect on Shallow Reflection Seismic Data
Authors E. Nørmark, H. Sabra, H. Lykke-Andersen, K.J. Andresen and O.R. ClausenA reflection seismic survey has been carried out in Vejle fjord in Denmark in order to map the thickness of organic rich gyttja sediments. The reflection seismic data was severely contaminated by multiples and suffered from high absorption in the near surface sediments. Consequently, a direct and reliable interpretation of gyttja in the entire survey area could not be accomplished. Alternatively, the interpretation has been based on the pull-down effect on reflections which in the present case is the only way to achieve a coherent estimate on sediment thicknesses. Borehole information has been used to estimate the velocity in the gyttja layer.
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Combination of Active and Passive Seismic Methods for Subsoil Characterization of Seismic Stations
Authors A. Macau, B. Benjumea, S. Figueras, R. Puig, A. Gabàs, F. Bellmunt and A. RocaWithin the framework of Alertes-RIM (Regional and on-site earthquake early warning system for the Ibero-Maghrebian region) project twenty five seismic stations located in this region have been characterized. The aim of this work is the application of a methodology based on combination of active and passive seismic techniques in order to study potential soil effects at these stations. During the first step of this study, seismic noise recordings are extracted from seismic stations in order to apply the H/V spectral ratio technique and classify sites as rock or soft soil. Once identified seismic stations installed on soft soil the second stage is done. This phase consists on carrying out the fieldwork in the location of seismic stations. Surface wave analysis (MASW) and linear seismic noise array analysis are performed to get the shear-wave velocity model of soil column. Seismic refraction tomography (SRT) provides a 2D P-wave velocity model to identify bedrock geometry and soil parameters. The H/V spectral ratio is used in different places along the seismic profiles in order to obtain soil fundamental frequencies and compare these values with the fundamental frequency obtained from seismic stations recordings. The proposed methodology ensures a good characterization of seismic station subsoil.
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Shallow Seismic Reflection Survey by Using Accelerated Weight Drop as Seismic Source
Authors A. Alfian, M.R. Sule and A. PriyonoOnshore reflection seismic surveying for shallow objectives is a challenging task in Indonesia. The use of AWD (accelerated weight drop) as seismic source for an eco-friendly onshore shallow seismic survey is tested. The experiment was conducted around Jepon-1 well in Central Java, Indonesia which is a candidate for CO2-injection. This experiment is as initial investigation before baseline seismic survey is carried out around mid-2016. The CO2-injection itself will be started end-2017. This site was chosen as the first carbon capture and storage (CCS) pilot project in Southeast Asian region. The purpose of this survey is only to study the effectiveness of the AWD source for shallow seismic survey. Moreover, this survey is intended only to test the performance of AWD (ESS-200) seismic source and determine the optimum survey parameters for subsequent seismic baseline survey for monitoring CO2 injection in wells Jepon-1 and its vicinity. We found that the deepest reflections that could be imaged is only 650 m below the surface. To complete the data acquisition of 500m, it took only two operation days with a total cost of about USD 2,000. Thus, the use of AWD needs much less investment than similar surveys that use dynamite or mini-vibroseis as source.
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New Airborne Methods and Procedures for the Exploration of Mineral Resources - An Overview of BGR Activities
Authors U. Meyer, B. Siemon, M. Becken, R. Stolz, U. Noell, M. Frei, P. Buchholz, A. Steuer, S. Costabel, T. Martin, M. Ibs-von Seht and C. NittingerOne of the major tasks of the Federal Institute for Geosciences and Natural Resources (BGR – Bundesanstalt für Geowissenschaften und Rohstoffe) is to contribute to a sustainable future supply for Germany with minerals for industrial use. Part of the BGR’s strategy is to develop innovative ways of mineral exploration. The presented study focusses on airborne technologies, being applied and developed in ongoing projects. The methods used can be classified in established methods and newly evolving systems. The repertoire of established methods includes airborne electromagnetics, magnetics, radiometry and hyperspectral imaging. Systems based on latest technologies are full tensor magnetic gradient (FTMG) systems and audio-frequency magnetics (AFMAG) systems. Since a single airborne system usually cannot reveal the whole complexity of mineral bearing structures, new combinations of survey systems are being tested and new techniques are under development. The projects used to demonstrate and develop new systems, combinations and designs are E3 (Ore exploration in the Ore Mountains of Saxony, Germany), HYPGEO (New procedures for exploration of mineral raw materials using hyperspectral and geophysical sensing systems) and DESMEX (Deep Electromagnetic Sounding for Mineral Exploration). HYPGEO is being introduced as a new conceptual project combining different sensing systems and resources of BGR and partners.
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Test Airborne EM Surveys at a Black-shale Type Uranium Deposit in Korea
Authors M.J. Yi, J.H. Kim, N.H. Sung, M.H. Han, K. Motschka, R. Supper, A. Ahl and A. Johmorilogy in Korean geologic environment, test airborne geophysical surveys were conducted over a known uranium deposit using two AEM systems; GSA’s frequency domain loop-loop EM system and time domain EM system with grounded electrical source (GREATEM system). The main geologic feature of the test site is the phyllite formation with uranium mineralization in a graphitic zone and AEM surveys by two systems successfully delineated the graphitic conductors in this site. Considering the field condition with tough topographic variation, GREATEM system seems to have better performance in terms of data acquisition and depth of investigation, while GSA’ system provides better resolution for shallow subsurface structures, which is due to underlying EM principles used in the two systems. By this comparative study, we could convince that AEM technology is a very effective tool to the exploration of mineralized zone in Korean geologic environment.
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Archaeological and Resources Assessment of Sand and Gravel Deposits Using 3D ERT and Automated Interface Detection
Authors S.S. Uhlemann, J.E. Chambers, P.B. Wilkinson, M. Kirkham and M. BeamishRiver terrace deposits form one of the major sources for Palaeolithic artefacts and are of economic importance for the groundwater and aggregates industry. Their depositional history and thus structure can be highly complex. We present automated interface detection techniques applied to 3D geoelectrical data in order to guide archaeological prospecting and mining activities. Three different interface detection techniques were applied, which were based on resistivity iso-surfaces defined from clustering techniques and comparison to intrusive investigation, and on the steepest gradient in resistivity depth sections. Their results were compared to intrusive investigations. All three methods successfully imaged an incised channel underlying 3 – 8 m of sand and gravel deposits. The results showed good agreement with bedrock depths obtained from boreholes. The extracted bedrock topography was used to define archaeological trenching locations, within which Palaeolithic artefacts were recovered. The remaining sand and gravel resource of this extraction phase was estimated to be more than 1 350 000 m3.
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