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Near Surface Geoscience 2015 - 21st European Meeting of Environmental and Engineering Geophysics
- Conference date: September 6-10, 2015
- Location: Turin, Italy
- Published: 06 September 2015
101 - 120 of 164 results
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CRS Stack Using Global Simultaneous Multi-parameter Optimization - A Spatial Velocity Analysis for Near-surface Data
Authors Z. Heilmann, G. Satta and G.P. DeiddaSummaryCRS stacking employs a spatial three-parameter stacking operator that extents in offset and midpoint directions. Since this operator covers several CMP gathers, a large number of traces contribute to every single stacking process, thus generating a large improvement in signal-to-noise ratio. However, the standard implementations use the spatial operator only for stacking and not for the global stacking parameter search. Instead, they rely on a sequence of three one-dimensional searches which decreases the computational effort compared to the simultaneous three-parameter search by two orders of magnitude, but does not always deliver optimal results. Particularly for near-surface data, characterized by low signal-to-noise ratio and modest CMP fold, the efficiency gain is not crucial. Considering the huge computing power available today, we propose a new pragmatic search strategy using a spatial two-parameter diffraction operator for the global search, followed by a local optimization using the full CRS operator with the diffraction parameters as initial guess. For shallow shear-wave data, we show that while the computational cost of this hybrid approach reduces by an order of magnitude the results are still very close to those obtained by the full global three-parameter search and far superior to those obtained by three cascaded one-parameter searches.
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Refined Experimental Studies for Improving the Reduced-scale Physical Modeling of Seismic Subsurface Measurement
Authors D. Pageot, D. Leparoux, O. Durand, M. Le Feuvre, P. Côte and Y. CapdevilleSummaryThe potential of experimental seismic modeling at reduced scale is explored since several years because it provides an intermediate step between numerical tests and geophysical campaigns on field sites. The MUSC system is designed as a reliable tool, able to produce multi-sources and multi-receivers experimental seismic data suitable for high-resolution imaging techniques like Full Waveform Inversion. However, experimental seismic modeling has limitations such as finite dimensions models used instead of realistic half-space models and three-dimensional seismic data generated by the point-source whereas most of wave propagation and imaging algorithms make use of two-dimensional forward modeling for numerical cost reasons. The main objective of the presented study is thus to improve the experimental seismic modeling to generate reproducible, realistic and suitable data which will be distributed in the scientific community. In this scope, we have: 1) refined the comparison between numerical and experimental data by generating experimental two-dimensional line-sources, 2) assessed the reproducibility of the source emitted in a model by the piezzo-electric transducer and 3) reduced efficiently the boundary reflections with the help of an adapted new geometry of the edges which absorbs a large band of the incident waves spectrum.
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Seismic Tomography to Investigate Geologic Structures underneath Highway Bridges
Authors U.J. Swoboda, B. Kleinwechter and D. OrlowskySummaryIn Germany approx. 2500 bridges have to be inspected for the need of renovation. The knowledge about the underlying geological formations is partially very poor, especially for older bridge buildings. By the use of geophysical methods additional information can be achieved to minimize the risks and the renovation costs. This presentation is focussed on seismic tomography investigations in connection with traffic construction projects.
Generally the tomographic method uses the information of the curved propagation of refracted waves (refraction tomography) or it is applied between two boreholes (crosshole tomography). All results are calculated by an SIRT inversion approach and show the distribution of seismic velocities along a cut or a plane between the boreholes. The seismic velocities are correlated with material properties like density, shear strength and compressibility. Low velocity zones are indications to weak areas or cavities.
The potential of these non destructive tomography methods are shown in this presentation by several projects. The method was applied in the planning phase for new bridge constructions as well as in the construction phase of a bridge foundation in a karst area.
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Predicting Continuous Distributions of Sparse Data under Full Consideration of Tomographic Reconstruction Ambiguity
Authors A. Asadi, P. Dietrich and H. PaascheSummaryWe present a novel methodology to probabilistically predict spatial distributions of sparsely measured borehole logging data constrained by multiple geophysical crosshole tomograms. In doing so, we fully account for the ambiguity of the tomographic model reconstruction procedure by taking advantage of a recently developed fully non-linear inversion approach. We use Artificial Neural Networks to link the results of the non-linear inversion with sparse information of tip resistance logging data. Additionally, we achieve information during the training phase of the ANN about the compliancy of tomographic models found by the inversion with the available logging data, which may help to identify those tomographic models that may reconstruct the subsurface more realistically.
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Borehole Constrained Inversion of Geophysical Data Based on Fuzzy Clustering
Authors A. Romero and L. GallardoSummaryA recent increase on the need of combined use of multiple types of geophysical data has lead an intensive research on joint interpretation strategies. In the present work we explore a generalized methodology for joint inversion based on fuzzy c-means clustering, which, unlike structural or petrophysical joint inversion, does not require a priori property functionals. In our scheme, we build an objective function which includes at the same time the individual objective functions for geophysical sets of data and fuzzy clustering. We then test it using velocity borehole data and magnetic anomaly data to obtain velocity and magnetization models with well-defined zones for couples of parameters. The results show that cluster and property parameters can be estimated jointly and yield relevant models of the subsurface.
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Benefits and Potential Applications of 3D Borehole Radar
Authors B. Kleinwechter, C. Hartmann, S. Uchtmann and D. OrlowskySummaryThe direction sensitive 3D borehole radar system provides a three dimensional capture of complex subsurface structures. By default, ground penetrating radar (GPR) surveys out of boreholes are undirected and therefore require additional information for spatial interpretation. In contrast, with the 3D borehole radar a reliable spatial model can be gained from a single drill hole.
The DMT GmbH & Co. KG (DMT) has developed two radar systems for different tasks. Since 2002 over 60 vertical deep drillings have been investigated. The engineering radar system is suitable for any engineering applications in horizontal, vertical or inclined boreholes.
The operation in low conductive, non-magnetic media is essential for the success of a radar measurement. A high penetration depth of several hundreds of meters up to kilometers can be reached in dry rock salt. Under good conditions also limestone, crystalline solid rocks and dry sands are suitable for investigations with the method.
This measuring system is successfully implemented for geological surveys, for the preliminary reconnaissance of tunnels and mine buildings, the investigation of underground buildings and the detection of voids in karst areas. The directional borehole radar system itself will be introduced. Applications of the method in rock salt and in limestone are shown.
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A Very Broad Band Borehole Seismic Sensor in the Po Alluvial Basin near Ferrara (Italy) - Installation and Data Analysis
By D. PesaresiSummaryWe describe here details of the Ferrara VBB borehole seismic station installation and details of seismic site characterization with surface/borehole comparisons in terms of seismic noise, site amplification and resonance frequencies.
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Vertical Seismic Profiling Technique in Shallow Waters Using of P- and SH-waves
Authors M.R. Sadurtdinov, A.M. Tsarev, A.G. Skvortcov and M.S. SudakovaSummaryThere are a large number of works devoted to seismic logging. However, optimal techniques of such surveys in the shallow water areas using not only P- but also SH-waves do not exist.
The lack of SH-waves sources is one of the main problems for such work. Using only P- waves in seismic logging doesn’t always give a positive result, especially in cased bore holes.
In The Institute of Earth Cryosphere it was developed a technique of vertical seismic profiling in shallow waters using P- and SH-waves. It is based on the use of special equipment for p- and sh- waves simultaneous excitation and detection and on original methodological techniques. This technique is useful for borehole seismic surveys in shallow waters from ice and in open water.
The technique was successfully tested at sea and river for solving scientific and industrial problems.
It was shown that casing does not adversely affect on registration of SH-waves at a satisfactory well condition. On the contrary the presence of casing makes it almost impossible to register p-waves because of tube waves.
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New Results from a Project of Urban Geophysics. GPR Surveys of Palatino’s Archaeological Area (Roma, Italy)
Authors S. Piro, D. Goodman and D. ZamunerSummaryThe N-E foot of Palatino Hill and Coliseum Valley (Rome) are characterised by a sequence of complex buildings, related to the Roman period between the late Republican and Severo’s age (200 AD). To enhance the knowledge of this area a scientific collaboration between Sapienza University at Roma (Department of Archaeology) and the Institute of Technologies Applied to Cultural Heritage (ITABC-CNR), was initiated in 2001 and it is still a very active joint research program today. In this site a series of GPR surveys employing different frequencies were carried out between 2001 and 2011. Acquisition was made using a high-resolution approach in which parallel profiles were recorded very closely across the site. Signal processing, image processing, and visualization techniques have been used in conjunction with data modelling, elaboration, and interpretation of the recorded subsurface amplitudes. All GPR results have been verified through the direct archaeological controls. These archaeological excavations made by the team of Prof. Clementina Panella (Sapienza University of Roma) during the last few years after the geophysical surveys, have confirmed the structures individuated with the GPR method.
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Geophysics - An Essential Tool for Modern Archaeology. A Case from Monte Prama (Sardinia, Italy)
Authors G. Ranieri, A. Trogu, F. Loddo, L. Piroddi and R. ZuccaSummaryOne of the most important archaeological sites of the western Mediterranean is located in the Sinis peninsula (Sardinia, Italy). A necropolis with monumental sculptures from the early Iron Age characterizes the archaeological area of “Monte Prama”. Above the graves (8th/9th century BC) a large paved area was built, likely for funeral games, where statues, baetylus and nuraghe models were put. In 2013 thanks to a joint project between the Universities of Sassari and Cagliari and the Archaeological Superintendence of Cagliari and Oristano starts a new geophysical and archaeological research. The area was full investigated by 15 channel GPR and partially by other geophysical methods. Results show the widespread presence of anomalies some well aligned to the excavated necropolis and some other distributed along regular patterns. It is doubtless that the archaeological area is more extent than assumed after the previous archaeological survey. Geophysics is confirmed to be essential tools in the archaeological prospection, mainly when it is necessary investigate over large areas. Particularly multi-channel GPR open new scenarios thanks to its characteristics of high spatial resolution, precise positioning of anomalies and fast acquisition speed.
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Multidisciplinary Non-invasive Approach for the Reassembling of two Fragmented Roman Statues
Authors N. Amapane, A. Bovero, D. Castelli, C. Comina, D. Elia, M.B. Failla, V. Galizzi, L. Ghedin, G. Giraudo, A. Laccarino Idelson, L. Porcu, M. Nervo and G. PantòSummaryThis paper reports a case study on the analyses performed for reassembling two fragmented statues coming from the Archaeological Museum in Turin and belonging to the Savoy collection. A scientific and multidisciplinary approach to conservation is nowadays strongly required. This new approach consists in the dynamic integration of different scientific and digital analyses to determine in detail all phases of the work, with the purpose of minimizing the intervention to what is strictly necessary. For this purpose a precise knowledge of the type of material and conditions of the fragments, of the location and coupling of the ancient pins, and of the overall stability of the reassembled statues is required. Due to the uniqueness of the investigated masterpieces the use of non-invasive techniques is mandatory in order to preserve the materials. Several non-invasive or micro-invasive analyses on the statues’ fragments were thus performed and are hereafter reported: laser scanning and close-range photogrammetry, X-ray radiography and ultrasonic measurements, petrographic analyses. The final step of the work will be the preparation of models of the two statues with the Finite Element Method (FEM) for strain localization and stability analyses in order to quantitatively evaluate the feasibility of different restoration options.
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Physical-archaeological Modeling of Iron Age Casemate Walls
Authors S.E. Itkis and T.B. SokolovaSummaryThe magnetic method which based on the contrast in magnetic properties between a target objects (archaeological remains) and the host medium (surrounding soil) improved itself as a high efficiency tool in a number of archaeological sites in northern regions of Israel. Detailed magnetic prospecting was applied in Tel ‘En Gev in order to estimate archaeological importance of areas out of excavated parts. The site is located in close vicinity of kibbutz ‘En Gev living areas. Due to this reason desired magnetic signal was strongly affected by different artificial disturbances: electrical power lines, generators, water pipes, reinforced concrete plates, stakes, small iron trash on the surface or in the soil. This complicates magnetic data interpretation. To clear up the sources of the magnetic anomalies and evaluate the size and depth of anticipated archaeological features we applied forward modeling. Based on preliminary information obtained in excavated parts of the site, and numerous measurements of magnetic properties, were constructed physical-archaeological models (PAMs) of casemate walls were constructed. Then using forward modeling we obtained magnetic images of buried remains. This allows us to reveal magnetic anomalies produced by remains in complicated conditions of the survey.
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High Resolution Seismic Imaging in Alpine Environment by Common Reflection Surface Method
Authors S. Maraio, P.P.G. Bruno and V. PicottiSummaryIn alpine environment, alluvial fan architecture can reveal important information about the landscape geomorphic evolution and the climate change. The information about alluvial fan morphology and sedimentology can be obtained by a high-resolution geophysical approach. In this work, we acquired and processed a ~4 km long high-resolution seismic reflection profile across a representative transect of Val Venosta, over the Gadria fan, Eastern Alps, Italy, using non-conventional acquisition and processing approaches. We tested Dense-wide aperture arrays (DWA) and Common Reflection Surface stack (CRS) in a complex environment, in order to obtain seismic data with a quality and resolution adequate to: 1) study the internal reflective configuration of the fan; 2) image both the pattern of the bedrock below the valley and thickness of the sediment accumulation above it; 3) evaluate the geometrical relationships between the Gadria Fan and the Adige River sediments. By the analysis of our results, we can deduce that DWA seismic data in combination with high-resolution CDP/CRS processing can provide complimentary and low-cost information to aid the study of alluvial fans in alpine environments.
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Very High-resolution Seismic Imaging in Complex Environments - A Comparison among CRS, CMP and PSDM
By P.P. BrunoSummaryThe common-reflection surface stack technique was used, together with conventional common-midpoint and pre-stack depth migration to process a high-resolution seismic reflection line acquired in the dismissed industrial plant of ILVA. This brownfield site, now undergoing remediation, is located within the Bagnoli district of the city of Naples, near the southeastern border of Campi Flegrei caldera. The common-reflection surface stack, followed by post-stack depth migration, produced a seismic image more suited for a subsurface interpretation. Results reveal that the Common-Reflection-Surface stack can be a fast and cost-effective alternative to pre-stack depth migration in settings where structural complexity and high levels of ambient noise make it challenging to obtain a reliable background velocity model; therefore allowing high-resolution reflection seismology to be successfully employed in those environments.
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Successful CMP and VSP Acquisition Using an Accelerated Weight Drop System in a Mature Basin
Authors M.A. Barsottelli-Botelho, M.A. Schinelli and R. GuerraSummaryThe use of vibrators for onshore borehole seismic acquisition is uncommon in Brazil, mostly because of the presence of rough topography and a dense cover vegetation over most Brazilian basins. On the other hand, dynamite as a source involves much logistics and time to obtain the permission by the relevant authorities. Due to these reasons, air guns installed in pits, specially built for those operations, can be used on most onshore VSP acquisitions. A research program proposes a set of experiments to evaluate the accelerated weight drop system as a complementary seismic source for onshore acquisition. The system has been used with success to acquire high-resolution VSP data at a production well in Miranga field, Northeast Brazil, where Schlumberger has installed twelve receivers for monitoring purposes. The AWD source allows to survey CMP seismic data with more high frequency content (80 Hz) and is appropriate to work on environmental protected area.
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Performance Assessment of Novel Electrode Materials for Long-term ERT Monitoring
Authors O. Kuras, P.B. Wilkinson, P.I. Meldrum, R.T. Swift, S.S. Uhlemann, J.E. Chambers, F.C. Walsh, J.A. Wharton and N. AthertonSummaryWe present results of a laboratory study of novel electrical resistivity tomography (ERT) sensor materials, whose performance has been assessed in terms of suitability for long-term geoelectrical monitoring. The study has addressed concerns over the longevity of buried ERT sensors required to support nuclear decommissioning at the Sellafield Site in the UK.
Electrodes made from three candidate materials and installed in a bentonite grout were subjected to accelerated measurements and electrochemical analyses were carried out on both pristine and used electrodes after extraction from the laboratory tanks.
Electrical contact resistance showed significantly different behaviour for stainless steels compared with platinised titanium. Pt-Ti sensors displayed outstanding properties and their stability under operational conditions was remarkable. Their susceptibility to ERT noise, which was expected to be worse due to their higher nobility, was only marginally greater than that of stainless steels.
No tangible advantage in terms of electrical performance was found for using higher-grade varieties of stainless steel over a conventional 316L-based design. Crucially, both steel types were affected by the growth of carbonate scales when buried in bentonite. This fundamental process may well be (at least partially) responsible for the frequently encountered increase in contact resistance of stainless-steel electrodes over time.
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Observed Linear and Non-linear IP Effects - A Summary of Joint Italy-South Africa Bilateral Projects 2007–2014
Authors V. Zadorozhnaya, N. Abu Zeid, S. Bignardi, L. Maré, R. Mantsa and G. SantaratoSummaryAmong the several types of induced polarization effects, electro-osmosis and membrane polarization by constrictivity of pores my result in non-linear behaviour, i.e. chargeability is not constant with supplied dc current. A new model, based on the second Fick’s equation succeeded in predicting, on laboratory samples, this behaviour. In fact, The non-linear behaviour was shown to correlate well with Pore Size Distribution (PSD) of laboratory tested samples whose PSD distribution was measured experimentally using a mercury injection capillary pressure test method. The model predicts also the non-linearity of the electrical resistivity for sufficiently high current densities. In this paper, we show that non-linear behaviour of resistivity and chargeability vs. supplied current density can be met in field measurements, provided they are carefully planned. In a site located in Northern Apennines, where a saturated sandstone outcrops, different values of resistivity and chargeability were obtained at different supplied electric current whose achieved results agree with the forward model. Moreover, the non-linearity can also perturb TEM data as being affected by this IP effect, as the model predicts a dependence of non-linearity also on the current supply length. An example of anomalous TEM data collected in Northern Apennines is also presented and discussed.
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Pumping Tests of Layered Aquifers - A Numerical Analysis of Self-potential Signals
Authors P.K. Konosavsky, K.V. Titov and M.A. NarbutSummaryBased on numerical modeling we studied Self-Potential signals associated with pumping test experiment with a layered aquifer containing a main aquifer, a thin aquitard and a shallow aquifer. We show an unusual behaviour of SP signals, which are not linearly correlated with the hydraulic head distributions. However when plotted as a function of time, the SP signals and drawdowns where found to be coherent. In both distributions three time stages of the pumping test were determined: at early times the pumping occurs from the main aquifer and the aquitard, at intermediate times the downward flow from the shallow aquifer occurs, and at late times the layered aquifer acts as a whole. These three stages are clearly seen in the SP distributions. Moreover the SP signals react to the changing of these stages much faster then the drawdowns.
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Total Chargeability versus Full Wave Form Time Domain IP Inversion - A Case Study from a DNAPL Contamination in Norway
Authors J. Scheibz, S. Bazin, A.A. Pfaffhuber and G. FiandacaSummaryERT-IP measurements were carried out to delineate a creosote (DNAPL) contamination at a wood preservation plant in Southern Norway. Despite of 56 shallow drilling, geochemical sampling and 6 ERT/IP profiles the interpretation of the results showed a high uncertainty. One of the reasons for that is the changing electrical behaviour of DNAPLs during biodegradiation and weathering. We therefore used a TD SIP inversion to retrieve the Cole-Cole relaxation model for a detailed interpretation and a comparison to standard chargeability inversion results. While resistivity and chargeability results are good comparable the additional parameters τ and C seem promising to decrease interpretation uncertainties. Nevertheless these have to be used with care as long as the petrophyscial relationships for DNAPLs are not well understood.
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ERT Monitoring Sheds Light on the Hydrogeological Behavior in a Landfill
More LessSummaryAn engineered landfill is a very complex media. The internal structure of the waste mass (resulting from the compaction mode, the landfill growth and the waste complexity itself) is generally poorly documented and very difficult to figure out. Measuring and modifying the water content of the waste mass is a challenge in order to optimize biodegradation of evaluate landfill mining opportunities.
During the ERT monitoring of a recirculation experiment, numerous observations were made regarding the landfill hydrogeological features.
On one hand, time laps ERT during water recirculation is an interesting tool to characterize the heterogeneity of the waste mass. The media appears strongly anisotropic (water flows mainly horizontally). The underground flow pattern is also governed by the existence of preferential flow paths (old wells, drain, roads …).
On the other hand, observation of major rainfall events clearly demonstrates the role of the cover layer morphology and composition and the vegetation density and type on the water balance. Reverse slope in the cover layer induces local high infiltration rate. Electrical geophysical method could be used to control the permeability of the cover layer and estimate the water balance of the site or the efficiency of infiltration pounds.
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