- Home
- Conferences
- Conference Proceedings
- Conferences
Near Surface Geoscience 2013 - 19th EAGE European Meeting of Environmental and Engineering Geophysics
- Conference date: 09 Sep 2013 - 11 Sep 2013
- Location: Bochum, Germany
- ISBN: 978-90-73834-38-5
- Published: 09 September 2013
1 - 20 of 116 results
-
-
3D Electrical Resistivity Tomography in Glacial Sediments’ Research
Authors A.M. Pavlova and V.A. ShevninThis article is about 3D electrical resistivity tomography (ERT) results in quaternary outwash and moraine sediments mapping and stratification. These investigations were conducted on Alexandrovka moraine plateau. We performed areal survey, using parallel 2D ERT profiles and following 3D inversion and as the result of our survey we obtained three-dimensional geoelectric model of the area. We studied and described technical and geophysical capabilities, efficiency and productivity of this technology. Moreover we estimated how parallel profiles' azimuth influenced investigation results, detected causes and proposed some methods of reducing this influence.
-
-
-
GPR Indicators of Identifying the Boundaries of Asphalt Concrete and Cement Concrete Layers
Authors R.A. Eremin and A.M. KulishnikovIn order to realize the reinforcement of the existing road pavement it is essential to know its internal structure. One of the important tasks is the localization of concrete slabs under asphalt concrete pavement. The GPR method is used successfully in solving these problems [1,2]. The paper reviews the results of GPR surveying for determining old cement concrete slabs location under asphalt concrete pavement on section of the Highway М-2 “Crimea” in the Moscow Region of the Russian Federation. For survey the GPR technical equipment was used (“Logis” Ltd, Ramenskoe), that is the antenna assembly with the central frequency radiation of 1700 MHz and the maximum sounding depth up to 0,8 m. The works were held in October 2012 on wet road surface under damp weather conditions.
-
-
-
Combined 1-D and 3-D Inversion of Helicopter-borne Electromagnetic Data
Authors A. Ullmann, B. Siemon, M. Scheunert, M. Afanasjew, R.U. Börner, K. Spitzer and M. MiensopustHelicopter-borne electromagnetic (HEM) surveys are an effective tool for investigating the spatial conductivity distribution in the subsurface, e.g. for groundwater or mineral exploration. As a standard procedure, the multi-frequency HEM data are inverted to resistivity-depth models using a 1-D inversion method. Since the footprint of the HEM system is rather small and smooth conductivity structures are close to 1-D settings this is a valid approach. However, conductivity structures with strong lateral variations (anomalies) are not reproducible by 1-D inversion and a multi-dimensional inversion is required. Our aim is to combine 1-D and 3-D inversion of HEM data. A 3-D inversion is only carried out for those parts of a HEM survey which are affected by an anomaly. For all other parts a 1-D inversion method is used. Thus, the knowledge where such anomalies occur in a HEM data set is crucial. We present a new method for identification, selection, and extraction of anomalies in HEM data sets. The identified anomalies are handed over to the 3-D inversion. The resulting 3-D inversion models are integrated in the quasi 1-D background. The technique is demonstrated on a synthetic HEM data set.
-
-
-
Feasibility Study of Multi-dimensional HEM Forward Modelling - Example of Cuxhaven Buried Valley
Authors M.P. Miensopust, B. Siemon and A. UllmannHelicopter-borne electromagnetic data sets are extensive in size and multi-dimensional modelling and inversion of the entire data set is in many cases impractical. On the other hand, the commonly used 1-D approaches might result in models with artefacts or distortion when higher dimensional structures are present. A complex procedure is required to enhance the resistivity models for such areas. One has to identify those areas either to investigate if artefacts are the potential cause of ambiguous structures in 1D-based sections/pseudo-3D models or to model and invert those using higher dimensional approaches. Multi-dimensional modelling and inversion codes vary considerably regarding their advantages but also their restrictions. The latter mainly result from structure related requirements but also from memory usage and computation time. Thorough testing of various codes is required to find the most applicable one for the specific data set. Small scale higher dimensional models obtained represent the local structure but might have shortcomings on the regional trend. Hence, merging those models with the overall model of the entire data set is a challenge. The focus of this paper is the feasibility study of multi-dimensional forward modelling programs based on the example of the Cuxhaven buried valley.
-
-
-
Aeromagnetics with an Unmanned Airship
Authors M. Petzke, P. Hofmeister, A. Hördt, K.H. Glaßmeier and H.U. AusterUnmanned aerial vehicles (UAVs) have a growing field of applications. Geomagnetic measurements in difficult terrain are one example where UAVs can be a useful tool. So far only a few case studies about ultra-light UAVs have been published. Most of them are based on the principle of rotary wings, e.g. helicopters or multicopters. The payload capacity of these systems is often limited to about 1 kg. Here, we introduce an alternative to the existing platforms: Our airship is able to carry a payload of about 3 kg and has a flight time of up to 60 minutes. Furthermore, we prove the feasibility of this system with the help of two field examples. These studies demonstrate the ability to detect magnetic anomalies and the challenges in operating an airship and interpreting the according data sets.
-
-
-
Sensitivity of Seismic Interferometry and Conventional Reflection Seismics at a Landfil to Processing and Survey Errors
Authors L.A. Konstantaki, D. Draganov, T.J. Heimovaara and R. GhoseUnderstanding how sensitive the seismic method is to errors that can occur during a seismic survey or during the processing of the seismic data is of high importance for any exploration geophysical project. Our aim is to image the subsurface of a landfill, which is typically a heterogeneous system due to the presence of numerous scatterers. Therefore, in our case precision is of very high importance. Because of this, we test and compare the sensitivity of seismic interferometry (SI) and conventional reflection seismics survey (CRSS) to errors produced due to time-lapse surveys, migration-velocity errors and muting. Using numerically modelled data, we show that SI provides better subsurface information than CRSS.
-
-
-
Semi-automatic Mobile Equipment Test for Detecting Holes in Geomembranes – the Prototypes Evolution
Authors R. Mota, L. Coimbra, M. Barroso, M. Matutino, M.G. Lopes, R. Dores and F. SilvaLandfills contain basal lining systems that include composite liners, among which a geomembrane (GM). The success of these systems depends mainly on the GM performance, which acts as the primary barrier to contaminants migration. GM performance is conditioned by the presence of holes, which represent preferential pathways for leachate migration. An equipment was developed to detect holes in geomembranes. It is based on the geophysical resistivity method and aims to overcome the main disadvantages of the existing methods for GM holes detection, mainly time spent to perform the tests and the associated high costs. Several prototypes were already developed and were tested at small scale in laboratory. The final version, which is the model for the equipment under construction, was already successfully tested at laboratory small scale pilot plant and in a large pilot plant at Laboratório Nacional de Engenharia Civil, I.P. (LNEC) campus. This paper presents the prototypes development and results so far obtained.
-
-
-
Investigation in Sinkhole Terrains Using Complex of Geophysical Methods – Case Study in the Karst Area, Slovakia
Authors R. Putiška, D. Kušnirák, I. Dostál, R. Pašteka and A. MojzešComplex of geophysical methods was used to investigate small karst area for purposes to make of detailed geological mapping survey, to confirm geological localization of known sinkholes and pits and find possible continuation of caves and voids below the surface. The electromagnetic (the Electromagnetic Conductivity method – CMD) and radiometric (the Gamma-Ray Spectrometry method) mapping was applied to determine the spatial distribution of hard carbonate rocks and weathered valley-filled sediments. Detailed high-definition magnetometry was realized on selected sites of the studied region with the aim to distinguish between real sinkholes and man-made lime-kilns (unearthed pits, where limestone was heated and transformed into lime), which have been built at the site during the history. The microgravity and the electrical resistivity tomography (ERT) methods were used to create high-resolution images of underground cave. The result of ERT and geological survey was used as an entry model for the gravity modelling. The most important results from ERT and microgravity are two interpreted low density (low resistivity) structures - these can be important from the point of view of karst structures investigation.
-
-
-
Geotechnical and Geophysical Properties of Soils in the Dead Sea Sinkhole Problem
Authors M.G. Ezersky and E. LivneGeotechnical and geophysical properties of Dead Sea (DS) sediments are of a great importance in the DS sinkhole problem. DS sinkholes are formed on the alluvial fans and mud flats. The first are composed of sandy-gravel sediments. Second ones are brine saturated lime carbonates. We reveal following features of the DS soil properties. Sandy-gravel sediments are presented by coarse sands, which are characterized by Vs = 300 – 650 m/s. Such increased shear wave values can be caused by increased the soil stiffness described in the literature. Brine saturated lime carbonates (DS mud) are characterized by low Vs values of 120 – 250 m/s. They do not exhibit cohesion. It is explained by mineralogical composition of the Dead Sea material, composed predominantly of calcite and not clay minerals, whereas other Israeli clays are comprised largely of montmorillonite (spectite) clay minerals. This feature allows considering of saturated lime carbonate as cohesionless soil like fine sands. Lime carbonates demonstrate also very low cation exchange capacity (CEC) that allows use of TEM resistivity method for determining of porosity of both sands and DS mud. Note also that significant difference of Vs in sands and lime carbonates allows mapping of different lithology along DS coastal areas.
-
-
-
Resistivity Modeling of Sinkholes Effects Caused by Karst and Suffosion
Authors V.A. Shevnin, P. Cuevas Castellanos, K.V. Krivosheya, A.M. Pavlova, A.A. Ryjov and A.A. BobachevSinkholes caused by two different processes of karst and suffosion have some similarity and both create damages in cities, settlements and single houses in rural areas. Not once the problem was set to give forecast of sinkholes before their output on the earth surface. The authors with the help of mathematical modeling of anomalous effect above vertical cylinder and similar models tried to estimate possibilities of resistivity methods for forecast of dangerous underground sinkholes before their collapse.
-
-
-
Detection and Mapping of a Palaeokarstic Network in a Quarry Work Using GPR
Authors C. Dubois, J. Deceuster, L. Dutilleul, B. Njinwoua, J. Poot, J. Tsongo and O. KaufmannA Ground Penetrating Radar (GPR) survey was conducted on the bench of a limestone quarry to detect and map a network of weathering. The investigated area is a rectangle of 16.60 m by 10.25m on the Carboniferous limestone from southern Belgium. Profiles are parallel and equally spaced of 25 cm from each other and the distance between each trace along a profile was 2 cm. The GPR survey was conducted using a 250 MHz antenna. After filtering, 2D-sections show very clearly weathered features to at least 10m in depth. A 3D model of the area was created to identify the branches of the weathered network. On time slices, these features are well located throughout the entire model and anthropic cuttings lines are recognized on their total height (~6m).
-
-
-
Localising Fractures by Geoelectric Null-arrays
More LessThe term “geoelectric null-array” is used for direct current electrode configurations yielding a potential difference of zero above a homogeneous half-space. This paper presents a comparative study of the behaviour of three null-arrays, midpoint null-array (MAN), Wenner-g null-array and Schlumberger null-array in response to a fracture. The main objective is to determine which array(s) best localise vertical structures. Forward modelling of the three null-arrays revealed that the Wenner-g and Schlumberger null-arrays localise vertical fractures the most accurately. The numerical analysis served as basis to interpret the field results too. Field test measurements were carried out above a quarry in Les Breuleux (Switzerland) with the three null arrays and many classical arrays. The results were cross-validated with quarry-wall geological mapping. In real field circumstances, the Wenner-g null-array showed to be the most efficient and accurate in localising fractures. This study shows that geoelectrical null-arrays are better than classical arrays for localisation of fractures.
-
-
-
A 3D GPR Time Slice Analysis of Paleo-reconstructions at Mound A, Ocmulgee National Monument
Authors D.P. Bigman and P.M. LanzaronePrehistoric societies from around the world constructed monumental mounded architecture or earthen pyramids for a variety of functions including the foundation for temples, leader’s residences, community stages, or cemeteries. Flat-topped earthen mounds often have complicated histories where the function, size, orientation, and summit architecture varied throughout time. This paper presents the results from a 500 MHz GPR survey conducted on the summit of Mound A, the largest prehistoric Native American mound at Ocmulgee National Monument located in central Georgia. Our study indicates that performing time-slice analyses of flat-topped mounds can effectively map successive construction stages and maintain sufficient resolution to identify summit architecture on earlier mound use episodes. The authors recorded four mound construction stages, the western expansion of the mound, and the shifting location and shape of summit architecture. Changes in summit architecture and mound size inform us of the shifting political landscape at Ocmulgee between approximately AD 900-1200.This study also resolved a discrepancy regarding the location of early archaeological excavation units from the 1930s. This may help archaeologists accurately provenience artifacts during future investigations.
-
-
-
Biogeochemical Controls on Magnetic Susceptibility Variations across a Hydrocarbon Contaminated Site
Authors E. Atekwana, F. Mewafy, G.A. Aal, E. Atekwana, C. Beaver, S. Rossbach, L. Slater, D. Ntarlagiannis, A. Revil and D. WerkemaBiogeophysical investigations over the last decade have provided evidence documenting that geophysical technique can be used to assess in-situ biogeochemical processes. In this study, we investigated a site contaminated by crude oil at Bemidji, Minnesota where intrinsic bioremediation is known to occur and iron is the dormant electron acceptor process.
-
-
-
Improving Resolution in Surface NMR by Transmitting Off-Resonance
Authors D. Grombacher, J.O. Walbrecker and R. KnightAn important development providing improved resolution in surface NMR images has been the advent of the inversion of complex NMR signals (Braun et al., 2005), instead of an amplitude only inversions. The signal phase is generally attributed only to conductivity effects, and a secondary geophysical survey is used to characterize the subsurface conductivity structure allowing the phase to be well constrained in the inversion. We propose a novel strategy for data acquisition motivated by similar reasoning as studies demonstrating improved resolution through inversion of a complex signal.
-
-
-
Long-term Monitoring at a Levee of Red River in Vietnam
More LessA long term monitoring has been performed at a levee of Red River in Vietnam. The monitoring system consists of a permanent electrode array for resistivity imaging and geotechnical tools including tensiometers, frequency domain reflectometry sensors and an observation well. The components were installed after a detailed inspection of the levee and foundation by drilling, sampling, and a geoelectrical survey. The levee monitoring system provided time series of the sensor data that were related to the variation of pore water pressure and water distribution. The data clearly indicate the influence of variations of the water level in the Red River during the monsoon season and also the drying process of the levee thereafter. Furthermore, it was possible to observe the upward and downward movement of the seepage line within the levee. A two-dimensional transient finite element modelling of the seepage and groundwater flow was performed using the database of a single flood season. The resulting hydraulic model was used for a stability analysis. It could be shown that the stability calculations taking into account the transient development of the seepage line enables a more favourable safety factor in the stability analysis in comparison with the conventional steady state approach.
-
-
-
Application of a Passive Surface Wave Method to Estimation of Deep S-wave Velocity Structure in San Francisco Bay Area
Authors K. Hayashi and D. UnderwoodWe performed two-station microtremor array measurements (2ST-MAM) at several sites in the South Bay of the San Francisco Bay Area. Two seismographs with three-component accelerometers were used for data acquisition. The two accelerometers were separated by 5 to 4125m and several different separations were used at each site. The total record length of microtremor data for each separation was about 10 to 60 minutes and measurements at one site took several hours. A spatial autocorrelation was used for calculating phase velocity and clear dispersion curves were obtained in frequency range from 0.2 to 10 Hz. A joint inversion of dispersion curves and H/V spectra was applied to observed data and S-wave velocity models to a depth of about 2km were obtained.
-
-
-
Comparison of 1D Conventional and 2D Full Waveform Inversion of Recorded Shallow Seismic Rayleigh Waves
Authors L. Groos, M. Schäfer, T. Forbriger and T. BohlenWe present a successful application of a 2D elastic full waveform inversion (FWI) to shallow seismic Rayleigh waves. With FWI we are able to reduce the data misfit significantly during the inversion and to find a subsurface model that explains the recorded seismograms well. The reconstructed S-wave velocity model is predominantly depth dependent which is expected for the site under investigation. We observe no significant 2D artefacts although a 1D structure is not enforced by regularization. The field data were acquired on a test site that we chose because of its almost 1D subsurface structure. This gives us the possibility to additionally derive a 1D model by a conventional method that we compare to the 2D model obtained by the FWI. The 1D inversion is done by an inversion of Fourier-Bessel expansion coefficients which requires constant phase velocities along the profile. We observe differences between the 1D and the 2D model although both models produce seismograms with a similar waveform fit of the field data. This shows the ambiguity of the inversion. The 2D model explains the field data slightly better in some details of the waveforms.
-
-
-
2D Full Waveform Inversion of Recorded Shallow Seismic Rayleigh Waves on a Significantly 2D Structure
Authors M. Schäfer, L. Groos, T. Forbriger and T. BohlenElastic full waveform inversion (FWI) of shallow seismic surface waves has the potential to infer lateral variation of the shallow subsurface which is important e.g. for geotechnical site characterization. First successful applications of a FWI to surface waves show the high potential of this method. In preparatory studies we have identified essential prerequisites for an inversion of field data: Viscoelastic damping and 3D to 2D correction filters. For the first time it is possible for us to apply FWI to shallow seismic field data. 2D full waveform inversion is reasonably applicable to field data acquired on 2D structures. We present a shallow seismic 2D survey on a transverse section of a vertical fault located on the southern rim of the Taunus (near Frankfurt on the Main, Hesse, Germany) which is a dominantly 2D feature of the subsurface. Next we apply the FWI to this shallow seismic field dataset. We are starting the inversion with strongly lowpass filtered data of 10 Hz. Within this frequency bandwidth we obtain reasonable inversion results. However, by adding higher frequencies the inversion is apparently trapped in a local minimum. We try to overcome this problem by preconditioning and smoothing.
-
-
-
Multiple Reflected Refraction Method in the Application of Near Surface Modeling
More LessIn this paper, we have derived and analyzed the kinematics law of the multiple reflected refractions, which are abundant in mountains, uplift of basin and piedmont tectonic belt, and then based on its time-distance curve formula, we discussed its application in the near surface structure modeling, which was analyzed and verified in Junggar Basin compared with other near surface structure modeling methods. The successful application in Junggar Basin indicates that the multiple reflected refraction method has an important significance for the near surface structure modeling when combined with other near-surface exploration methods in complex exploration area.
-