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Near Surface Geoscience 2014 - 20th European Meeting of Environmental and Engineering Geophysics
- Conference date: September 14-18, 2014
- Location: Athens, Greece
- Published: 08 September 2014
141 - 160 of 185 results
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Realistic Modelling of High Frequency Ground Penetrating Radar for Near Surface Applications
Authors A. Giannopoulos and I. GiannakisSUMMARYA modelling framework for realistic ground penetrating radar simulation in complex environments is presented. This approach incorporates detailed models of ground penetrating radar transducers as well as realistic descriptions of the underlying media and targets. The simulation of air-coupled horn antennas is presented and their performance is evaluated and compared to results from ground coupled bowtie antenna designs. The application of the modelling process to an engineering problem in pavement evaluation is discussed.
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Benefits of Joint Magnetic and Electromagnetic Surveying with Boom-mounted Helicopter Systems
Authors W.E. Doll, J. Norton, T.J. Gamey, D.T. Bell and J.S. HolladaySUMMARYBoom-mounted airborne magnetic and electromagnetic data sets provide complementary information regarding a site, whether the primary purpose of the investigation is to map and locate munitions or other buried metals, or to characterize shallow geologic features. Current boom-mounted systems are described along with distinctives of these systems for geologic mapping and metal detection. Observed falloff in sensitivity of both types of systems with respect to altitude is summarized. Several examples are provided that demonstrate the benefits of joint magnetic and electromagnetic surveys with boom-mounted systems.
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Mapping Small Conductive Objects by Vertical EM38 Acquistion
Authors J. Guillemoteau and J.T. TronickeSUMMARYIn this study, we propose to evaluate the potential of making measurements with a vertical EM38 device. We first show the related sensitivity that describes the 3D ground illumination. Then, we generate synthetic data computed by 3D spectral forward modelling. The analysis of the sensitivities as well as the synthetic data show that this configuration allows to image well small conductive targets but is strongly affected by the direction of acquisition. A first test of dual azimuth acquisition across a buried pipe is presented.
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Frequency-domain EM Response of a Conducting Sphere to a Magnetic Dipole Field Using Fast Continued Fraction Expansion
More LessSummaryThe electromagnetic response of a conductive sphere excited by an alternating magnetic field has been a traditionally important problem. In this study, for calculation of general solution in frequency domain of a conductive sphere in a magnetic dipole field, coordinates rotation and continued fraction expansion are applied. Coordinates rotation for transmitter and receiver location, respectively produces very fast and simple calculation process. The precise results are allowed for more wide range of response function with continued fraction expansion. This enhanced algorithm could be applied to examine the result of numerical modeling like FEM. It also can be quite helpful for in-situ application at fast speed on interpretation which can sweep large minefield and borehole 3D modelling.
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2.5D ERT Survey in Oslo Harbor - Medieval Heritage in an Urban Development Area
Authors A. Kydland Lysdahl, S. Bazin, C. Stokkeland, S. Ahrens, R. Helander, Å. Høiseter, J. Scheibz and A.A. PfaffhuberSummaryFour ERT profiles have been acquired in the Bjørvika area in Oslo in order to reveal resistivity anomalies that could correspond to archaeologically interesting timber objects. The data has been processed and analyzed with three different inversion softwares, and both two- and three-dimensional resistivity models have been generated. The different 2D profiles as well as the 3D models were in good agreement, and anomalies located by the ERT survey were excavated and proven to correspond to buried concrete structures. The pinpointing capabilities, correctness and resolution of the different inversion methods have been elucidated.
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Comparison between 3D Inversions of ERT and Total Magnetic Field Data on an Archaeological Site
Authors S. Piro, L. Sambuelli and A. AratoSummaryNon-destructive geophysical prospecting methods are increasingly used for the investigation of archaeological sites, where a detailed physical and geometrical reconstruction of structures is required prior to any excavation work. In this work the comparison between 3D inversions of ERT and vertical gradient of the total magnetic field (VGTMF) data, to delineate sharp discontinuities (boundary of cavities and fractures in the medium) in the Archaeological Test Site of Sabine Necropolis at Research Area of National Research Council of Rome (Montelibretti, Italy) are shown and discussed. While the VGTMF data inversion has been made minimizing an L-2 norm, the ERT data have been inverted minimizing an L-2 and an L-1 norm, obtaining different information and details. The results are then compared in the volume under the surveyed area: merits and shortcomings of the different techniques are pointed out and analyzed.
Both ERT and VGTMF locate the tomb; VGTMF overestimates its barycentre depth and gives a smeared volume; ERT L-1 inversion gives a fine picture of the chamber, delineates the corridor and underestimates the resistivities; ERT L-2 inversion gives a broad image of the chamber, does not delineate the corridor but gives more appropriate resistivities.
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Imaging of Ancient Water Management Infrastructures through 3-D Electrical Resistivity Tomography - The Case of Eleuthern
Authors N. Papadopoulos, C. Tsigonaki, M. Guy and A. SarrisSummaryWater resources and their efficient management though specialized hydraulic construction works comprise the basic guide in each human activity and the main criterion for the selection of a permanent residence. This work describes how geophysical methods can be used in order to map such hydraulic structures enlightening at the same time past and completely unexplored archaeological hypotheses. To this direction a high resolution surface 3D ERT survey was completed at the site of “Anemomylos” on the hill Pyrgi, the Acropolis of Eleutherna in Central Crete (Greece). The analysis and the 3D inversion of the data revealed the existence of a new structure that is either a cistern or a basin to the management of water. This lies between the aqueduct tunnel and the two existing cisterns verifying a past archaeological hypothesis.
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Near Surface Geophysical Archaeological Prospection at the Prehistoric Site of Akrotiri on Santorini/Thera
Authors I. Trinks, P. Tsourlos, K. Löcker, G. Vargemezis, G. Tsokas, A. Vlachopoulos, C. Doumas, M. Kucera, G. Verhoeven and W. NeubauerSummaryIn February 2014 high-resolution ground penetrating radar and earth resistance tomography measurements have for the first time been used successfully for the distinct mapping of buried archaeological structures in the vicinity of the Bronze Age archaeological site of Akrotiri on Santorini/Thera in Greece.
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Geophysical Investigation in the Temple of Poseidon at Cape Sounio, Attica, Greece
Authors G. Apostolopoulos, K. Leontarakis, C. Orfanos, G. Amolochitis and F. LoizosSummaryThe famous Temple of Poseidon at Cape Sounio in Attica, whose columns still stand today, was probably built in 440 BC. by Athenians after its first destruction by Persian troops during Xerxes I’s invasion of Greece in 480 BC. and his defeat in the naval Battle of Salamis. The later construction was during the ascendancy of Athenian statesman Pericles, who also rebuilt the Parthenon in Athens. An integrated geophysical investigation in the Temple with EM, GPR and ERT measurements and the appropriate field design, processing and interpretation, has detected horizontal features and vertical ones under the Temple with the later being either walls of the previous temple or constructions to hold loose material on which the existing Temple of Poseidon is. Sudden conductivity changes in EM, diffractions in GPR and lateral inhomogeneities in ERT sections through pole-dipole array and MOST technique indicate in the same position the vertical features.
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Imaging Shallow Structures in the North Sea with Tailored Shallow Water Multichannel Seismics and Subbottom Profiling
More LessSummaryLaterally heterogeneous and complex near-surface sediment structures in shallow water environments like the North Sea, where the Pleistocene sedimentation is influenced by alternating glacial, post-glacial and marine processes, require acoustic imaging methods and tools optimized for vertical resolution but also for complex geometric settings and a broad variety of sediment types. While sediment echosounders are indispensable tools to image the uppermost few metres of the sediment column and the soft infill of shallow depressions, they quickly come to their limits in terms of penetration, especially in the North Sea with the sand rich top deposits. The Bremen multichannel seismic system represents a special streamer design specifically developed to operate in shallow water conditions and to still provide undistorted signals at wide incidence angles. Combined with a high frequency seismic source this system allows detailed analysis of the upper few hundreds of metres North Sea sediment. To illustrate the achievable quality in this setting some typical examples of glacial and postglacial structures in the German North Sea are presented, where the different systems show their individual strengths.
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Comparative Seismic Source Study for Buried Palaeolandscape Investigations in the Southern North Sea
Authors O.J. Zurita Hurtado, T. Missiaen, M. De Clercq, W. Versteeg, P.P. Kruiver and M.P.E. De KleineSummaryThe southern North Sea has been an attractive region for human settlement throughout the late Quaternary. Unfortunately, to this date, little attention has been paid to the rich submerged archaeological potential in Belgium. Marine seismic techniques have been used for more than 20 years to investigate buried landscapes but in general the archaeological community often has to work with data acquired for other purposes, meaning they are not well adapted for archaeological studies. In this study, we aim to develop an efficient survey methodology to image buried palaeolandscapes for the purpose of archaeology, through the comparison of a wide range of high-resolution seismic source/receiver configurations. This should finally allow to accurately assess the geo-archaeological potential of the Quaternar
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Sub Bottom Profiling for Glacial Trenches in the German Bight
Authors U.J. Swoboda, R. Misiek and M. KneppenbergSummaryOn behalf of the German “Hamburg Port Authority” (HPA) the company DMT GmbH & Co. KG carried out seismic sub bottom profiling measurements in the German Bight. The survey area was on the lower river Elbe between the towns Cuxhaven and Brunsbuttel.
The seismic measurements were embedded in a project which studied the sustainable development of the lower Elbe region. The aim was to show the distribution and the volume of neogene soils. These soil materials are mainly placed in glacial trenches and so it was the main target of the seismic survey to find these trench structures.
The results showed high resolution seismograms with a penetration depth of 60 to 70 meters. The trenches and numerous sedimentation layers were found. Additional, typical characteristics for tidal sedimentation areas like fermentation gas effects were visible in the data sets.
The final geologic 3 D model showed the glacial trench system of the ancient river delta. With the differences between the top and the bottom of the soil material laying in the glacial trenches a volume calculation was done.
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Re-evaluating Shallow Geology in the Central North Sea
By F.A. BuckleySummarySeismic data from Quad 30 in the Central North Sea is revealing hitherto unreported aspects of the shallow sequence. In the south and west of the study area a stratigraphic unit outcropping at seabed (MLP4) forms a more or less continuous cover overlying a surface (SR4) characterised by a mega-scale glacial lineation. The MLP4 unit contains two main seismic facies, the lowermost of which comprises a bedded sequence which loses its identity towards the middle of the unit where the seismic texture becomes highly chaotic with few coherent reflections. Geotechnical boreholes show the chaotic facies to be a disordered assemblage of sands and slickensided clays. Towards the northeast the bedded facies within MLP4 disappears, the SR4 reflection loses its identity and the chaotic facies becomes more pronounced. In the furthest northeast the entire shallow sequence displays evidence of disruption and tectonisation down to a detachment surface at 90m – 140m below seabed. Base of the tectonised and un-tectonised sequences throughout the study area is taken as the erosian surface defined by the oldest generation of tunnel valleys recognised in the area. This surface is commonly dated to the Elsterian glaciation and marks the top of the Early-Middle Pleistocene Aberdeen Ground Fm.
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HiRes P-Cable 3D Data for Shallow Reservoir Mapping and Geohazard Predictions – Case Examples from the Barents Sea
Authors F.N. Eriksen, M. Assad, O.K. Eriksen, H.H. Stokke and S. PlankeSummaryShallow marine seismic imaging is of interest to the research and industrial communities to evaluate geohazards and for geotechnical considerations.
The P-Cable technology offers a 3D seismic acquisition technique based on densely spaced sources and receivers. It is a versatile, proven, efficient and cost effective method compared to conventional seismic exploration and site survey techniques. The acquired data have an enhanced horizontal (3–6 m) and vertical resolution (1–1.5) as compared to conventional seismic data. The data is also very useful for exploration of shallow hydrocarbon reservoirs and gas hydrates.
Four P-Cable surveys were acquired in the southwest Barents Sea in 2012. These cubes suggest the presence of shallow Jurassic reservoirs and potential geohazards associated with gas chimneys, shallow gas pockets, and pockmarks on the seafloor.
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Integrated Characterization of Deep-water Natural Hydrocarbon Seeps - First Insights
By S. UntersehSummaryThe occurrence of natural hydrocarbon (HC) at seabed or sub-seabed within the foundation zone represents a significant geohazards for any development in the deep offshore Angola. Indeed, the HC detected on geophysical datasets are commonly associated with Methane Derived Authigenic Carbonates (MDAC), asphalts nodules / seabed mounds and / or oil-clay mixtures, which may affect/ modify the soil geotechnical properties.
This study presents the preliminary results of an integrated geophysical and geotechnical approach, where a site characterized by multiple sub-seabed HC indicators (High Impedance Reflectors HIR) has been selected on high resolution CHIRP sub-bottom (SBP) profiles and has been ground truthed by Cone Penetration Testing (CPT) and continuous sampling boreholes.
The geophysical data discloses eight stacked HIRs, conformable to the stratigraphy and occasionnaly displaced by faults.
Two of the HIRs are characterized by high cone resistance value on the CPT data and are interpreted as representing MDAC levels.
The collected samples have logged using non-destructive techniques including multi-sensor core logging and X-ray imaging. As result, the sample logging detected MDAC or asphalt nodules, clay levels infiltrated with HC, micro-fissuring / fracturing induced by or associated to HC infiltration, several biturbation patterns and significant cracks and voids.
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Seafloor Expression of Subsea Morphology in Lower Congo Basin, an Integrated Study
Authors F. Zolezzi, M. Calarco and W.J. JohnsonSummaryHigh resolution data, ranging from geophysical, geological and geotechnical, acquired to evaluate the potential hazards and constraints to offshore operations might also provide new insights into the geological processes. We present a case study where an integrated geosciences study performed in a deepwater province of the Congo Basin lead to a better understanding of the post-depositional processes affecting the sedimentary column.
In particular we investigate the possible correlation between subsea structure (polygonal faults) and seafloor morphology (furrow-like features). The integrated interpretation revealed a complex development of the furrow-like features related to geological processes causing an anisotropic stress regime rather than erosion by deep water currents.
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New Data on Near-bottom Sediments Structure and Geohazards in the Black Sea Deep-water Zone
Authors A. Roslyakov, M. Tokarev, S. Kleshchin, A. Pirogova and Y. TerekhinaSummaryNew high-resolution seismo-acoustic data collected from the abyssal plain and from the foot of the continental slope with uninhabited autonomous underwater vehicle (AUV) allowed the identification of regional sedimentary processes formed its present morphological and structural image. The geological interpretation of the new data shows recent activity of the gravity, lithodynamic, erosion and neo-tectonic processes in deep water areas of the Black sea. All of these processes are of significant importance in formation of upper part of the section and are a major geologic hazards for different submarine installations.
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Geophysics As a Tool for Pipeline Design in Challenging Terrain
By L. WoodsSummaryPipeline regulators are increasingly demanding more information from pipeline operators about ground conditions along proposed new pipeline routes. Pipelines are frequently routed through challenging and sensitive terrain. The two examples presented herein include watercourse crossings in mountainous terrain and alignments underlain by discontinuous permafrost. These areas require geotechnical investigations for pipeline design requirements; however, non-intrusive geophysics is a powerful and cost-effective tool that can be used to refine extensive drilling programs.
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Geophysical Methods As an Aid to Planning, Monitoring, and Abandoning Tailings Facilities in the Alberta Oil Sands
Authors P.D. Bauman, D. Parker, L. Pankratow and R. ShindukeSummaryThe oil sands tailings ponds of Northern Alberta have become the centerpiece of environmental opposition to unconventional hydrocarbon development in Western Canada. Significant efforts are being made to moderate the impact of oil sands tailings and tailings impoundments. Both surface and borehole geophysical techniques have a wide range of cost-effective applications to all stages of oil sands tailings management.
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Seabed Characterization - Developing Fit for Purpose Methodologies
Authors D. Dove, R. Cooper, R.M. Lark, S. Green, B.P. Marchant, K. Crombie, H.A. Stewart, A.G. Stevenson and M. DiesingSummaryWe briefly describe three methods of seabed characterization which are ‘fit for purpose’, in that each approach is well suited to distinct objectives e.g. characterizing glacial geomorphology and shallow glacial geology vs. rapid prediction of seabed sediment distribution via geostatistics. The methods vary from manual ‘expert’ interpretation to increasingly automated and mathematically based models, each with their own attributes and limitations. We would note however that increasing automation and mathematical sophistication does not necessarily equate to improve map outputs, or reduce the time required to produce them. Judgements must be made to select methodologies which are most appropriate to the variables mapped, and according to the extent and presentation scale of final maps.
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