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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
21 - 40 of 185 results
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Analysis of Ground Motion Parameters from the 2011 Earthquake in Lorca (SE Iberian Peninsula) Based on Seismic Data
Authors J. Pérez-Cuevas, P. Martínez-Pagán, M. Navarro and A. García-JerezSummaryIn the present work we study how the ground motion parameters had a relevant influence on the buildings structural damages due to the 2011 earthquake in Lorca city. We quantified the severity of subsurface motion through the estimation of peak ground acceleration (PGA), peak ground velocity (PGV), and Arias Intensity (AI) at bedrock level. Those values were obtained by means of S-wave velocity data from Multichannel Analysis Surface Waves (MASW) method which was conducted along the streets of Lorca city. Remarkably, PGA and PGV maps present high values in those urban areas which reported severe building damages. Besides, the highest PGA, PGV and AI values are located in the easternmost area of the city. In fact, in that area was reported significant building damages by the 2011 earthquake. These ground motion maps add some insights into both the interaction soil-building and the type of structural damages associated to buildings during the occurrence of an earthquake.
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Combined Geophysical Survey for the Detection of an Archaeological Theatre in Amphiareion of Oropos, Attica, Greece
Authors G. Apostolopoulos, G. Amolochitis, S. Stamataki, A. Giannopoulos and P. KofakisSummaryThe Amphiareion of Oropos, a sanctuary dedicated in the late 5th century BCE to the hero Amphiaraos, among the ancient monuments, a theatre not whole been revealed by excavation is to be detected by geophysical investigation. Electromagnetic (EM) measurements with conductivity meter in a certain field design but most important by a suggested processing and interpretation have outlined the area of theatre seats that have been covered by loose sediments. In addition other probable features been detected by EM indicate the position of subsequent ERT profiles. The later show in detail all features of the underground proving what EM has indicated along with other very useful information for the archaeologists in order to design their further research.
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Investigating Pre-Columbian Ceremonial Features at El Caño Archaeological Site, Panama, through Geophysical Surveys
Authors A. Mojica, M. Lezcano, J. González, J. Thiesson, L. Pastor, C. Camerlynck, N. Florsch, A. Tabbagh and R. VanhoeserlandeSummaryBetween 2005 and 2006, a series of magnetic and electrical surveys were conducted over the site El Caño, one of the most important pre-Columbian ceremonial site of the Isthmus of Panama (Central America). This site, of 3.4 ha in area presents a set of alignment of columns of carved basalts and tuff and mounds, with a first organized occupation between 100 and 400 BC. Today, these surveys have been extended to electromagnetic prospecting with the aim of identify with accurately the spatiotemporal organization of the site, funeral archaeological features of the mounds and surrounding. Integration and interpretation of the geophysical data allowed us to identify a set of circular magnetic anomalies in the base of mounds due to the strong runoff during the rainy season and topography, but in the base the runoff is weak (by flatness) and infiltration is higher; these results explain the difference between the calculated resistivity values obtained inside and outside of these mounds through electrical resistivity tomographies. Another larger circular magnetic anomaly was identified in the flatness southeast zone of the mounds; this result allowed the discovery of one of the most important pre-Columbian funerary complex in Panama.
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Three-dimensional Ground-penetrating Radar and Magnetic-gradient Surveying of the Roman Castle Irgenhausen (Switzerland)
Authors C. Schmelzbach, H. Horstmeyer, K. Scanlan, M. Kälin, S. Brändli and P. NagySummaryCombined three-dimensional (3-D) ground-penetrating radar (GPR) and magnetic-gradient (vertical gradient of the total magnetic field) surveying were used to investigate the remains of an older Roman villa complex buried under a surface-exposed younger Roman castle. Magnetic-gradient measurements allowed for efficient mapping of a large area around the castle in short time, whereas the 3-D GPR provided detailed information at depth of a selected area. The 3-D GPR data volume revealed several linear and rectangular features within the topmost around 2 m below the surface interpreted as walls and floors of houses belonging to the villa complex. Some of the identified walls could be correlated with the remains of a house with floor heating excavated and re-buried in the early 20th century. Furthermore, the joint interpretation of the 3-D GPR and magnetic-gradient data allowed identifying an extensive and rectangular, highly reflective feature in the GPR data collocated with a prominent magnetic anomaly as the fire place/oven used to drive the floor heating.
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Joint Analysis of Self Potential and Electrical Resistivity Tomography Data for Studying Alexandrovsky Settlement
Authors V.A. Shevnin, A.A. Bobachev, S.V. Ivanova and K.I. BaranchukSummarySelf potential (SP) method was used to study archaeological Alexandrovsky settlement, filtration anomaly and diffusion-absorption (DA) anomaly. Electrical resistivity tomography (ERT) data allowed estimating layered structure, lithology of layers and helped to prove DA origin of SP anomaly. Quantitative interpretation of filtration anomaly gave derelict spring yield estimation that could be used for water supply of the settlement in old days.
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ERT and VLF Measurements Contributing to the Extended Revelation of the Ancient Town of Trapezous (Peloponnesus, Greece)
Authors J.D. Alexopoulos, S. Dilalos, A. Tsatsaris and S. MavroulisSummaryA geophysical survey was carried out in the archaeological site of Kyparissia (Megalopolis, Greece) applying the Very Low Frequency technique, as preliminary combined with highly detailed Electrical Resistivity Tomography. Settlements of the ancient city of Trapezous (limestone slabs 0.5m height × 0.5m width) have already been uncovered from the local Ephorate of Prehistorical and Classical Antiquities, revealing a regularly planned town of the classical period. The geophysical research was performed at the non-excavated area of the plain, vicinal to the already exposed remaining, where, according to the expected geometry, the buried walls and drainage channel should be continued to. Fifteen parallel sections with distance 5m and spacing interval 1m were carried out. The processing with the application of Fraser and Karous-Hjelt filters led to the construction of respective maps, indicating some resistive lineation which could be a result of the buried settlements. Moreover, two detailed ERT sections were carried out with spacing 0.20 and 0.25m and total length 200m. The processing using the robust inversion, which is indicated for such environments, adumbrates quite clearly a sharp resistive target that could be the limestone slabs of the ancient walls or drainage channels, confirming the expected lineated geometry of the town.
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Detecting Shallow Medieval Features in the Church of St. George, Slovakia
Authors J. Panisova, J. Haličková, P. Brunčák, R. Pašteka, V. Pohánka, J. Papčo and P. MiloSummaryIn the framework of OPIS-Operational Programme Information Society co-funded by the European Regional Development Fund (ERDF) the most important monuments of Slovak cultural heritage are recorded using modern geodetic techniques. More than two hundreds objects, e.g. historical bridges, cemeteries, sacral buildings, folk architecture reservations, rock-cut dwellings, have been documented so far. The Church of St. George was recorded using laser scanning combined with very precise geodetic measurements. We present here the results of microgravity and GPR surveys carried out in the nave of this church in order to delineate the position of burial vaults beneath the floor. In microgravity data processing we focused on the calculation of the building correction. For this purpose a detailed polyhedral model of the church was created. Integrated interpretation of geophysical results has confirmed the presence of two medieval crypts predicted from historical archives. Moreover, the remains of the oldest Romanesque construction stage of the church were successfully detected by both methods.
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How to Characterize a Recharge Area by ERT Time Lapse and Cluster Analysis - Application to Lascaux Cave
Authors S. Xu, C. Sirieix, J. Riss and P. MalaurentSummaryThe decorated cave in Dordogne needs more attention while being studied and conserved. Geophysical methods enable in a non-invasive way to detect the underground environment of the decorated cave. Associated with the analysis of the effective rainfall (groundwater recharge) in this site and the flow in the cave, the Electrical Resistivity Tomography monitoring using pole-dipole and gradient arrays has identified a zone which probably stores water in relation with the cave. There is a high electrical contrast between the surrounding limestone and the probably recharge zone. Then, with a multivariate analysis through the resistivity values allows us to characterize the model blocks showing a specific behavior over time, especially the blocks the lowest electrical resistivity. The main result of this study is that these blocks are assumed to be probably a part of the recharge area; systematic electrical survey after raining event could be used to predict the beginning of the underground flow in order to give advice for preserving the Lascaux Cave.
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Improving Near Surface Characterization by Combining Reprocessed Vintage Seismic and Geophysical Passive Datasets
Authors B. Benjumea, A. Macau, A. Gabàs, M. Esquerda and S. FiguerasSummaryThis study reveals the importance of reprocessing vintage seismic data, originally focused on deep targets, in order to retrieve near-surface velocity model and structure. This information can be verified and complemented using cost-effective geophysical methods (passive seismic and audio-magnetotelluric -AMT data technique). This methodology has been applied to the Empordà Neogene basin (NE of Spain) where oil reflection datasets are available. 41 H/V stations were deployed along one seismic reflection profile to detect seismic impedance contrast between Quaternary/Neogene sediments and basement (Palaeozoic and Mesozoic). In order to calculate this contrast depth, shear-wave velocity profile has been obtained using seismic noise array technique. The final model obtained from the different seismic datasets show a basin shape with a gentle dip at the SW end of profile and an abrupt dip at the NE side interpreted as the Roses Fault. Bedrock depth reaches 660 m at the center of the profile according to H/V results. Finally, an AMT survey was undertaken at 10 sites to report a detailed 2D geoelectrical image across the Roses fault. The electrical resistivity model allows to characterize both structure and fluid properties associated with fractures network within the fault.
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Introducing Particle Swarm Optimization (PSO) to Invert Refraction Seismic Data
Authors R. Poormirzaee, R. Hamidzadeh Moghadam and A. ZareanSummarySeismic refraction method is a powerful geophysical technique in near surface study. In order to achieve reliable results, processing of refraction seismic data in particular inversion stage should be done accurately. In this study refraction travel times inversion considered by Particle Swarm Optimization (PSO) algorithm. In this year PSO algorithm, as a metaheuristic optimization method, is used in many fields of studies. Application of this method in different geophysical data inversion shows that this algorithm is powerful, fast and easy. We developed PSO code in Matlab for inversion of seismic refraction data. For efficiency evaluation of developed code, different synthetic models are inverted. Finally PSO inversion code investigated in a case study at the part of Tabriz city in north-West of Iran for hazard assessment. Then field dataset inverted by PSO code. Obtained model was comprised by the geological information of study area. The results emphasize the reliability of the PSO code to invert refraction seismic data with an acceptable misfit and convergence speed.
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Vibroseismic Acquisition with Long Landstreamer on Disko, Greenland
Authors E. Nørmark, P. Gulbrandsen, H. Sabra and O.R. ClausenSummaryA seismic landstreamer with a length of 500 m, has been applied for a reflection seismic survey on the island of Disko in the western part of Greenland. As source signal a vibrator has been used. The surface consisted of snow and ice and in some places of the exposed surface from a dry riverbed. Sledge mounted geophones and gimbaled geophones were used for the survey. In total 192 geophones channels were applied. Both types of geophones worked well but the gimbaled geophones performed slightly better in the present terrain. In total 10 km seismic profiles have been acquired. Conventional seismic processing has been applied. FK-filtering has been applied in order to suppress surface waves. The present survey has demonstrated that it is possible to use the landstreamer technique with a relatively long streamer in a terrain with snow and ice and exposed surfaces.
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The IGGE UAV Aero Magnetic and Radiometric Survey System
More LessSummaryThis paper expounds the advances in the development of a novel prototype UAV aero magnetic and radiometric integrated survey system developed by IGGE. The magnetometer consists of a CS-VL cesium vapour sensor and an AARC-510 real-time compensator and data logger. The gamma-ray spectrometer has 5 NaI(TI) crystal detectors. All the instruments were set up onboard a middle size UAV which can take off and land autonomously and fly for 10 hours with a 145kg payload at 180 km/h. A field trail survey of 3000 line-km was carried out at a exploration altitude of 120m AGL in 5 days to test the exploration performance of the system. Four flights were accomplished during the night. The survey data quality are competitive over traditional airborne survey system and meets the CGS survey specifications. However, some more optimization research will be required to improve the reliability and safety, simplify the operation, lower the costs, and make it a commercially usable system.
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Comparison of Different Stabilizing Functional in 3D Regularized Inversion of Direct Current Resistivity Data
Authors N.Y. Gundogdu and M.E. CandansayarSummaryIn this study, a new three dimensional (3D) direct current resistivity (DCR) data inversion algorithm is developed. In the developed algorithm, Tikhonov parametric functional is used for regularized inversion. Mostly, smoothing stabilizer is preferred in 3D inversion algorithms of DCR data. In the developed algorithm, different stabilizers are used and their effects on the inverse solution are investigated. It is showed that, inversion with "minimum support" and "first-order minimum entropy" stabilizers gives results with sharper boundaries than inversion with smoothing stabilizer. The algorithm is tested with synthetic data and also field data which is collected in archeological area.
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Classification of Unexploded Ordnance Using Geophysics – A Practical Reality
Authors D. Mortimer and N. ValleauSummaryDuring an unexploded ordnance (UXO) clean-up project, most of the items excavated are not UXO, but are harmless scrap metal. If these items can be determined to be non-hazardous without digging, the cost of a site clean-up can be cut by a substantial amount.
Reliable classification of suspected UXO targets using geophysical survey data is now possible. This paper provides a summary of new advanced electromagnetic sensors and related software technologies to consistently classify suspected UXO and buried munitions vs. non-hazardous buried metallic objects. The technology and the tools have matured to the point where classification can be (and are) routinely applied to UXO clean-up projects in a transparent and reproducible approach. This methodology is now being accepted and required by US government program managers and regulators in clean-up projects that span a range of site conditions.
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Geoelectric Reference Technique, Efficient Tool to Eliminate External Noise in SIP Data
By T. RadicSummaryExternal noise disturbs measurements carried out with the method of Spectral Induced Polarization (SIP), and lessens its data quality. In densely populated areas the disturbance signals mostly originate from high voltage power lines and the electrical devices supplied by them. However, disturbances (tellurics, lightnings) also appear in remote areas. At frequencies up to 250 kHz, disturbances through VLF and LW transmitters are also be taken into account. Stacking techniques are very time-consuming. We have implemented and tested the novel Geoelectrical Reference Technique, which with reasonable additional hardware costs effectively reduces most noise types without loss of time. External noise is characterized through a high spatial coherence. The signals of disturbance source can be observed in a large area. The Geoelectrical Reference Technique uses this fact by recording the noise at one or more remote locations. In doing so, the technique predicts and eliminates the coherent noise components contained in the SIP records. In order to use the Geoelectric Reference Technique in a wide frequency band, we developed a completely new hardware (SIP-Fuchs-4). Field measurements show that the Geoelectric Reference Technique improves the data quality at medium frequencies by a factor of up to 40.
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Time-domain Induced Polarization Profile with Multiple-current Transmission
Authors Y. Yamashita, F. Lebert, J.C. Gourry, B. Bourgeois and B. TexierSummaryWe propose the method of calculating time-domain chargeability on multi current transmission using Code-Division Multiple-Access technique. The multi current transmission technique is proposed for highly efficient resistivity surveys aiming at lowering costs in large number of measurements or improving time resolution in monitoring applications for example. In the purpose of expanding multi current transmission technique to time-domain IP survey, we developed the method for calculating time-domain chargeability using measured potential data obtained by multi-transmission resistivity measurement. We conducted a simple numerical experiment and a field experiment of multi-transmission measurement for confirming our method. We showed it is possible to obtain time-domain chargeability from multi-transmission data. Currently, it is needed to be improved for adapting practical situation such like instability of current injection.
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Non-conventional 3D Electric Resistivity Tomography Arrays
Authors D. Vargas, G. Cifuentes, J.E. Hernandez and R.E. ChavezSummarySpecific conditions of the studied area, where natural or anthropogenic obstacles do not allow carrying out conventional Electric Resistivity Tomography (ERT-3D) arrays, employing parallel transects. It is necessary to construct new ERT designs able to be adapted to any particular zone under investigation. ‘L’-and ‘Corner’-arrays were designed to surround the target to acquire reliable geophysical information from the subsurface. Combinations of these arrays employing more conventional settings (Wenner-Schlumberger, Dipole-Dipole, and so on), are applied to design alternative electrode geometries. The circle, the triangle and the horseshoe arrays are investigated to study the subsoil of different types of scenarios. The efficiency of such alternative arrays was verified on the examples considered. Such studied areas are: a pre-Hispanic circular pyramid, a seawater intrusion and a small urban neighborhood. Results are quite encouraging, where coverage at depth was adequately obtained, and inverted results computed were very interesting.
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Mapping and Migrating Reflected Surface Waves
Authors C.W. Hyslop and R.R. StewartSummaryIdentifying sharp lateral change in the near-surface is needed to accurately locate anomalies. We directly account for sharp lateral change by imaging surface wave reflections. We first show synthetic and field results from a processing flow that produces a space-depth reflectivity map across a seismic survey line. Then we use wave-equation migration to image surface-wave reflections adjacent to the survey line. Our results indicate that reflectivity images from both imaging methods can be used as an attribute in highlighting the location of anomalies and faulting. Using wave-equation migration with an imaging condition based on deconvolution resolves sharp discontinuities at high resolution while preserving polarity of the reflection. Frequency dependent surface-wave reflectivity is converted to depth resulting in 2D and 3D images.
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Three-Dimensional Advanced Fluxgate Magnetometers for Near Surface Geoscience Measurements
More LessSummaryThree new types of fluxgate magnetometers are presented in this paper, able to monitor the vector of the ambient field, all of them being based on the principle of rotational excitation field. The first type employs Yttrium- Iron Garnet (YIG) single crystal film, magnetized with rotational field on its plane, where the 2nd, 4th and 6th harmonics offer the three components of the ambient field with sensitivity better than 1 pT at 0.2 Hz, its size being 25 cubic centimeter. The second type is based on permalloy film, where the rotational excitation field on its plane offers change of magnetoresistance with sensitivity better than 10 pT at 1 Hz, uncertainty of 1 ppm and size ∼ 8 centimeter. The third type, is based on amorphous film, where the rotational field mode offer sensitivity better than 100 pT at 1 Hz, uncertainty of 10 ppm and size ∼ 10 cubic millimeter.
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On the Very Low Frequency (VLF) Measurements Using an Unmanned Aerial System (UAS)
Authors B. Tezkan, R. Eröss and J.B. StollSummaryWe performed very low frequency measurements by employing an unmanned aerial system as an innovative geophysical measuring platform. An appropriate suspension system had to be developed to carry out VLF measurements using the super high frequency coil triple (SHFT) sensor from Metronix and the ADU-07 logger. The survey was realized on a test site in Neuchatel/Switzerland on several profiles crossing a buried pipeline and a power cable. The locations of the buried anomalies were successfully detected by the UAS-VLF data and compared with conventional ground VLF measurements. Finally, the UAS-VLF data were interpreted by 2D conductivity models.
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