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Near Surface Geoscience 2016 - 22nd European Meeting of Environmental and Engineering Geophysics
- Conference date: September 4-8, 2016
- Location: Barcelona, Spain
- Published: 04 September 2016
1 - 100 of 189 results
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Hydrogeophysical Survey of Groundwater Flow Pathways in an Alpine Headwater Basin
Authors C.W. Christensen, M. Hayashi and L.R. BentleyAlpine regions of the Canadian Rocky Mountains are important sources of freshwater for the semiarid Canadian Prairies. Yet, only recently have studies demonstrated that groundwater plays an important role in storage and subsequent release of snowmelt and rain. With limited case studies available in this region, a general understanding of groundwater flow processes in the alpine zone remains elusive.
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Groundwater Discharge along the Southern California Coast - Geophysical Images of Three States of Salt Water Intrusion
By J. JansenThe interface between fresh groundwater and saline water in coastal areas is frequently complex. The natural discharge of groundwater to the near shore zone is controlled by multiple factors including the permeability of the aquifer system, faults, confining units, and the hydraulic gradient in the aquifer. The natural balance is often disturbed by heavy pumping that can cause significant intrusion of salt water into the on-shore portion of the aquifer. The shape of the salt water wedge is affected by the pattern of pumping, the properties of the aquifer, and hydraulic boundaries like faults and confining units.
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Inversion of Frequency Domain Loop-loop Electromagnetic Data in 3D at Arbitrary Induction Numbers
Authors L. Cox, M. Endo and M. ZhdanovNear surface geophysics often uses man-portable electromagnetic instruments which can relatively quickly and inexpensively probe the earth for the 3D conductivity distribution.
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Evaluating Seasonal Variation of Groundwater Flow through an Alpine Meadow Using Passive Electrical Potential Measurements
Authors E.B. Voytek and K. SinghaAccurate quantification of groundwater flow patterns, both in magnitude and direction, is a necessary component of evaluating any hydrologic system.
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High-resolution Reflection Imaging for the Planning of a Double Train-track Tunnel in the City of Varberg, Sweden
Authors M. Dehghannejad, A. Malehmir, E. Lundberg, H. Möller and M. SvenssonA newly developed broadband MEMs-based seismic landstreamer system was employed for the planning of a double train-track tunnel in the city of Varberg, southwest Sweden. In addition to the refraction analysis and velocity tomographic modeling, reflection processing of the data was considered given the good quality of the data and realization of reflections in some raw shot gathers. Bedrock is strongly reflective in most cases and only at occasions when reaches near the surface it disappears in the reflection section. Bedrock undulation is clearly noticeable in most reflection sections and at one occasion it appears to be strongly diffractive. The diffraction signature is now known to be associated with a buried water tank used in fire emergency situations. Reflection seismic data greatly complements tomographic models and may support a deep bedrock at where the tunnel is planned to be excavated in the downtown Varberg.
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P- and S-wave Seismic Imaging of Overdeepened Alpine Valleys
Authors H. Buness, T. Burschil and G. GabrielOverdeepened valleys and basin can be found in glaciated regions worldwide. Due to their geological, ecological, and societal relevance they constitute a relevant geoscientific target. In preparation for an ICDP project (Drilling Overdeepened Alpine Valleys, DOVE), we carried out several reflection seismic surveys using high-resolution P-wave, horizontally pola¬ri¬zed SH-wave, and multi-component (SV- and SH-wave sources, 3-component re¬ceiver) techniques at a test site in the Tannwald basin north of Lake Constance. The first results of the P- and SH-wave reflection profiles are presented here. The seismic sections image well the internal valley structure of the Tannwald Basin; different facies are also distinguishable in the glacial sediments. The combined inter¬pretation of P-wave and SH-wave reflection seismics reveal more details than just one technique on its own by providing complementary information. P-wave seismics show a more coherent image with a higher penetration depth, while SH-wave seismics partly resolve more details due to their higher resolution. The combination promises to be an enhanced tool to investigate sedimentary successions in advance of scientific drilling.
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Surface-consistent Residual Statics Estimation with Genetic Algorithms - An Application to a Near-surface Seismic Survey
Authors M. Aleardi, E. Stucchi, A. Sajeva and B. GaluzziIn this work we apply a Genetic Algorithm (GA) approach to the residual statics computation problem. This type of geophysical optimization problem is characterised by many local minima produced by the so-called cycle-skipping phenomenon. The application of a global optimization method is particularly suitable in this context as it is able to jump out from local minima where gradient-based methods can easily be entrapped. We use an analytical objective function to test the capability of GA in finding the global minimum in case of highly non-linear multi-minima objective function. Because the residual statics optimization problem involves many unknown model parameters, in this analytical test we are particularly interested in analysing the rate of convergence (that is the number of evaluated models required to reach the global minimum) as the dimension of the model space increases. We then show the use of this methodology on a field seismic reflection data set acquired for near surface investigations. The application of the residual statics derived by the GA method produces final CMP gathers with flatter reflectors and a final stack section in which the continuity of the observed events increases.
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Rayleigh Waves Modelling Complexities in the Perspective of Full Waveform Inversion of Surface Waves - Synthetic Examples
Authors Z. Xing and A. MazzottiFull waveform inversion (FWI) has recently been considered for extracting detailed near surface information through the surface waves inversion. But the need of long computing time and the risk to get trapped into local minima make FWI cumbersome. Both these shortcomings are strongly dependent on forward modeling. In fact, forward modeling must yield very accurate seismograms and be computationally feasible. In this study we use an elastic finite difference modeling and discuss means to address, at least partially, these two conflicting requirements. In particular, we illustrate the possibility of attenuating the computing time problem by implementing the convolutional perfectly matched layers (CPML), and by performing the 3D to 2D correction on the observed data, thus allowing for using simple 2D forward modeling. It turns out that CPML has the ability to accelerate the computations compared with the standard tapering method, while maintaining the same efficiency in attenuating the unwanted artifacts from the model boundaries, and that 3D to 2D correction gives satisfactory results. Both of them result very useful in the perspective of surface waves FWI applications, also in view of the fact that other features, such as irregular topography, which cannot be neglected, require additional computing efforts.
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Towards 3D Inversions with Full System Modelling
Authors K.R. Andersen, E Auken and A.V. ChristiansenWe describe the setup for inversion of ground based TEM data using a 3D forward code and a full description of the measurement system. The response is calculated using a finite volume method where we solve for the electric field on the edges of a staggered grid and time step solutions using backward Euler steps. We convolve the calculated fields with the system response to compare with the measured data. In this way we include all system related effects in the calculation and this is important for the very early time signal. We describe how this is done for both forward and derivative calculations. For the forward calculation and the inversion we use an iterative solver. We show that the forward code is in good agreement with the analytic response from a half space.
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Determining the Depth of Gravity and SP Sources
Authors G.R.J. Cooper and R.C. WhiteheadCooper and Whitehead (2016) introduced a new method for determining the depth of magnetic sources that did not require a priori specification of the source type. This abstract shows that the method also works for various gravity and self-potential sources. References Cooper, G.R.J., and Whitehead, R.C., 2016. Determining the Distance to Magnetic Sources. Geophysics 81(2), p.J39-J48.
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Combined Land and River High-resolution Reflection Seismic Imaging of an Area Prone to Quick-clay Landslides in Sweden
Authors S. Salas-Romero, A. Malehmir and I. SnowballQuick-clay landslides are common in northern countries and the delineation of these materials is important when planning urban areas. High-resolution reflection seismic data were acquired on land along four profiles in an area prone to quick-clay landslides in southwest Sweden in 2013. These data complement previous investigations that show the influence of the underlying coarse-grained layers in the formation and thickness of the quick clays. The intercalation of the different glacial and postglacial sediments, and the structural information of the subsurface provide clues to the possible causes of a landslide. Apart from the land data, river seismic data, using one and six channels, were obtained. All the seismic sections show a clear undulating bedrock reflection, and signs of bedrock faults at shallower depth that maybe important in the generation of quick clays and landslides. The coarse-grained layer reflection is delineated on the land data, and several filled channels can be distinguished along the river. The presence of the coarse-grained layer indicates the possible large extension of the quick clays in the study area, which needs to be confirmed using geotechnical investigations.
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Detection and Analysis of Electromagnetic Radiation Emission from Macroscopic Fracturing of Cement-bound-granular Matter
Authors P.I.B. Ceralde and J.T. MaquilingCountries most prone to earthquake damage have been in search of a possible earthquake precursor. This thesis aims to detect and measure the magnetic field component of the Electromagnetic Radiation (EMR) emitted by quasi-brittle materials that undergo macroscopic fracturing. Cement-Bound Granular Material (CBGM) beam composites were prepared by mixing cement, sand and gravel. Fine sawdust was added to form another aggregate component of the CBGM variant. Impact loading was repeatedly performed on the beams to induce fracture until failure. Six Vernier software magnetic field sensors, with sensitivity range of ±6.4x10-3 T and 0.0002 mT precision, were strategically positioned around the beams to detect the magnetic field (MF) component of the EMR emission. Initial calibration was done to minimize noise in the laboratory. The time of impact was determined in the form of collision noise using a sound level meter at fast time setting. CBGM beams consisting of cement, sand and gravel produced magnetic field emissions measuring from 0.58-1.07 μT while the CBGM beams with dispersed fine sawdust emitted 0.55-1.28 μT. Increasing the input energy from the mass of weight drop by 150% resulted to a 10% increase on the mean value measurements of magnetic field emission magnitude.
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The Holocene Tordera Delta System - On/Offshore Sedimentary Sequences and Evolution
More LessThe Tordera River delta system is located on the NE coast of the Iberian Peninsula. It is a coarse-sand delta originated from the erosion of the granitoids in the Catalan Litoral mountain range system. The Tordera delta has originated in a Mediterranean fluvial regime and with the influence of coastal drift currents from the SW. The sediments carried by the Tordera, together with the contributions from local streams has originated the different sand bodies present in the Blanes inner shelf. From new marine seismic data we have described the internal structure of these sand bodies as well as defined three seismic sequences which are Ph, Sd2 and Sd3. At the same time, the seismic profiles have provided additional support to the correlation of these sequences with the sedimentary deltaic sequences, as well as detail to the evolution of these sand bodies during the last sea level rise. The samples obtained though vibrocores and dredges have allowed the sedimentary characterisation of the sand bodies and their correlation to the deltaic sequences (absolute and relative aging) as well as the absence of sedimentary drift transport from the NE.
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On the Characterization of a Geophysical Diagnostics Resolution Index within the Seismic Damage Scenario Construction
Authors A. Teramo, D. De Domenico, D. Termini, M. Romeo, C. Teramo, N. Morey and C. SaccàA methodological approach for selecting areas to be subjected to geophysical diagnostic is proposed to determine the damage susceptibility of territory elements within the construction of a seismic damage scenario for the city of Messina. The morphology of the urban context have made difficult the programming and execution of those geophysical surveys more consistent with the objective to be achieved. On the basis of different indicator typologies, an empirical relationship has been established to identify the territory elements of a higher significance where to focus a greater diagnostic commitment for the acquisition of specific data to be used for seismic vulnerability assessments at a large scale. To this end it was defined a diagnostic resolution index, related to the specific characteristics of the territorial system, stands out as a significant interest element in the study and evaluation of the regional multi-hazard conditions (shallow water-table, presence of debris of buildings referable to the past earthquakes, high level of heterogeneity of the lithotypes, the widespread presence of surface faults, ...) The analysis of preliminary results have made possible the assessment of the reliability of the proposed procedure in order to properly planning a diagnostic campaign related to the safety reducers of the area in study.
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TDR Measurements of Magnetic Characteristics of Materials
By R. PersicoIn this contribution, the possibility of measuring possible magnetic properties of materials by means of a TDR probe is studied. A transmission line model is adopted and data in time and frequency domain are exploited together. Simulation results are shown, at the moment based on a bifilar line model.
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Time Domain IP Profile by Multi-current Transmission Technique - Water Tank Experiment and SP Noise Effect Estimation
Authors Y. Yamashita and F. LebertWe conducted time domain chargeability measurement by multi-current transmission technique using a water tank and mineral ore which has certain IP effect in the purpose of verifying the method to calculate chargeability from the data acquired by multi-current transmission measurement using Code Division Multiple Access (CDMA) technique . We also evaluate the effect to chargeability calculation of SP noise thorough numerical experiment. We confirmed that time domain chargeability measurement is available through the experiment using water tank and mineral ore. We also evaluated the effect of SP noise to time-domain chargeability measurement by numerical experiment. The precise current control and appropriate SP management are important for reliable chargeability measurement with multi-current transmission measurement.
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Enhanced Characterisation of Radiologically Contaminated Sediments at Sellafield by MSCL Core Logging and X-ray Imaging
Authors O. Kuras, J. Shreeve, N. Smith, J. Graham and N. AthertonVisual observations and electrical geophysics alone showed limited ability to characterise a complex Quaternary sequence of glacial sediments at the Sellafield site with sufficient spatial detail, and conventional high-resolution logging was impracticable. By applying non-destructive high resolution MSCL and X-ray core logging we have parametrically characterised and imaged the stratigraphy in detail for the first time. This approach has allowed us to identify geological units with increased confidence, and link these units to a depositional process. The results open up the opportunity to link geological observations at Sellafield with regional type localities and the regional stratigraphy. The approach holds promise for applications where conventional high-resolution borehole logging is not possible, or not able to fully characterise the geology.
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2D Modeling of Controlled Source Radiomagnetotelluric Data Observed on Buried Faults Close to St. Petersburg/Russia
Authors B. Tezkan, I. Muttaqien and A. SaraevControlled source radiomagnetotellurics (CSRMT) is a new and innovative method of near surface geophysics. We applied this method for the detection of a buried fault beneath a test area close to St. Petersburg. During this survey, a rectangular current was injected into the ground using an electrical horizontal dipole with a length of 700 m and O.5, 11.5, 30 and 105 kHz – as well as their subharmonics - were used as main frequencies. The time series of two horizontal field components and three magnetic field components were observed at 97 stations with a station interval of 20 m in the near, the transition, and the far field zone of the electrical dipole. Transfer functions were derived in the frequency interval of 1 kHz to 1000 kHz from the observed electric and magnetic time series using the newly developed processing software. They showed a smooth dependence of frequency indicating the reliability of the observed CSRMT data. The CSRMT data were interpreted in the far field zone by using a 2D inversion algorithm and in the near zone by using 2D forward calculations. The derived 2D conductivity models showed clearly the location of buried faults as large resistivity contrasts.
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On One of Precise Solutions to Integrate Hydrocarbon Mobilization Rhythms, Dense Reservoir Development Stages and Sand Recovery Geological Evolution
Authors V.I. Popkov, A.M. Shterenberg, V.V. Gusev and Е.V. MitinaIt is quite possible to achieve the growth in efficiency of geo-exploration works through the increase in drilling operations and this is the strategy of permanent technology. The improved technology strategy supposes the growth of rate of success in each well and constant amount of drilling operations. The costs for technology improvement are significantly lower than exponentially increasing costs for well pad drilling. The authors present the systematic evolution/topological theory of global solution for Cis-Ural region hydrocarbon mobilization as subduction and generalized saturation of the middle chain of the Urals, deformation of tunneling, plastic decompaction of fracture porous geo-media. Migration deformation provides great effect upon the structure of fractured permeability in aqueous matrix, energy with sand recovery, ecology and economics. The paper presents analytical solution of Darcy-Fick’s energy law for secondary deformation moments, plastic saturation of miming concentrations and formation of oil and ore material fields. The authors substatiate the systematic methodology in search, exploration and development of decompacted reservoirs with classtic and unconventional traps. They also present lithological/facies rhythms of migration glimmering foamy structure, geological risks in drilling. The authors note unconformity of initial lithological stratification cycles and rhythms of secondary processes in neo-hydrodynamics and evolutionary sand production.
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Remediation Investigation of a Failing Retaining Wall Structure
Authors A.J. Verweerd, S. Williams and P. ArnoldThis presentation is a case study combining geophysical & geotechnical investigation as well as structural deformation monitoring of a failing drystone retaining wall structure in the United Kingdom. Data collected and interpreted during this project was used to design a remediation solution, stabilizing the structure while retaining the wall's original appearance. The approach chosen in this study includes seismics, ERT and GPR studies combined with a targeted intrusive campaign to limit further destabilization of the structure. The geophysical surveys were executed close to the retaining wall, on the highroad above the wall as well as on the wall face itself. Both data sets were combined into a geotechnical interpretation which formed the basis of the remediation solution. In addition to the geophysical and geotechnical investigation a remote structural monitoring system was deployed to monitor the behaviour of the structure, ensuring the safety of the general public and infrastructure.
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Seismic Investigation for the Characterization of a Gravity Concrete Dam
Authors P. Capizzi, R. Martorana, C. Pirrera and A. D'AlessandroMonitoring of large-scale infrastructures plays an important role for public safety and prevention. The control of the safety assessment of a dam is largely dependent on knowledge of the mechanical parameters of the actual construction, as well as its geological substratum. The application of geophysical methods can considerably contribute to the examination indicating the less consolidated material and the degradation of mechanical parameters. A seismic tomographic approach has been used in a typical gravity concrete dam without reinforcement to detect mechanical properties of the body of the dam and its geological setting. Three seismic travel time tomographies in the dam body as well as S-wave velocity values obtained by a down hole testify that the dam is composed of high quality concrete. Small variations on the P-wave velocities seem to be the effect of moisture and infiltration. In addition seismic surveys in the surrounding grounds of the dam confirmed the expected properties of the foundation terrain.
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Identification of Landslides Processes on the Slope Areas near Gas Pipeline Bovanenkovo-Ukhta Permafrost by GPR
By V. NoskevichIdentification of landslides processes on the slope areas near gas pipeline Bovanenkovo-Ukhta permafrost by the method of georadiolocation (GPR). SUMMARY The article presents the results of profiling radar scanning along the gas pipeline in sloping areas in the permafrost zone. The technique of GPR survey at two sites and describes setting choices of GPR emitting and receiving antennas, as well as methods of data processing. Criteria for the selection in the GPR cross-sections shifting blocks weakly bound soils, and set the curve slip line of these blocks, which is a boundary between the melt and frozen grounds.
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Tunnel Assessment with Borehole Radar
Authors V. Perez Gracia, O. Caselles, J. Clapes and J.A. CanasThe collapse of a tunnel and the damage in a second tunnel during the construction works, forced to the assessment of the ground in the front tunnel of the second structure, in order to avoid additional problems. The first evaluation was carried out with a borehole radar, because the structure was in a populated zone of a dense city. The uncertainty associated to the near surface studies is, in this case, greater because the unshielded antennas produce a rotational ambiguity. The imprecision in the location of the targets was reduced using seven non-parallel boreholes. The results shows the anomalies that could be associated to faults and also an irregular area of the B-scans that could be related to heterogeneous materials and the existence of a large number of voids.
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Using the Resistivity Method for Leakage Detection at Sant Llorenç de Montgai Embankment (Lleida, NE Spain)
More LessThe infiltration through the core of foundation of embankment dams is a main concern for maintenance and safety. The mechanism of infiltration induces internal erosion which can be progressive and can disturb the stability and the durability of the structures. Internal erosion occurs when water flows through a cavity, crack, and/or other continuous void within the embankment. Geophysical survey at Sant Llorenç de Montgai embankment has evinced the effectiveness of the ERT technique in assessing the state of the dam embankment. In particular, the method has revealed areas with high electrical resistivity values related with mortar injection. In the other side, we have registered areas with very low electrical resistivity values correlated with areas with possible abnormal seepage.
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Study of Integrated Geophysical and Geological Research Methods on Mapping Weakness Structures in Bedrock at Urban Areas
Authors T.K.T. Huotari-Halkosaari, M.H. Wennerstöm and I.A.S. SuppalaThis abstract present one example site from a short project where the idea was to develop integrated geophysical and geological research methods for the urban studies for detecting fracturing and mapping weakness structures in the bedrock. The sample case is located in the route of planned west metro line in the City of Espoo. The area is called Hannusjärvi. The geophysical methods included old airborne interpretations as well as different ground geophysical test measurements together with geological interpretations from existing data and interpretations. Bedrock drilling data for this project was distributed by the West Metro Project. The old interpretations of weakness zones were produced in two earlier projects using aerogeophysical data and topographic models combined with structural geological analysis. The use of different ground geophysical methods was considered according to methodological and geological features. Magnetic, gravimetric, ground penetrating radar, electrical resistivity tomography and electromagnetic methods were utilized in test with new geological mapping. The combined geological and geophysical interpretation gave promising results and new information about the possible fractures and weakness zones in the vicinity of the new metro line. The ongoing excavation of the metro tunnel gives data to verify the geophysical and structural geological interpretations made in this project.
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Investigation with Seismic Methods of the Sedimentary Cover of an Astrobleme at Outskirts of Sao Paulo City, Brazil
Authors R.L. Prado, I. Ullah and I.C.E. FenollThe paper shows the results obtained from seismic reflection and HVRS/MASW (horizontal and vertical ratio spectrum and multichannel analysis of surface waves) data acquired in a circular structure whose formation is attributed to a meteorite impact. The structure, known as Colonia crater, is partially located in urban area at São Paulo outskirts. The aspects presented here are related to data processing and interpretation.
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Landfill Geophysical Imaging - Babica Landfill Case Study
Authors R. Putiška, D. Kušnirák, I. Dostál, V. Vybíral, R. Pašteka and J. PapčoOne of major environmental challenges in Slovakia is to deal with numerous contaminated sites polluted by improper waste management in the past. We present a case study from Babica landfill located in western part of Slovakia near the village Bošany. The landfill was established in 1970, in a very inappropriate environment of abandoned meander. Waste composition of the Babica landfill is mainly formed by waste from the leather and footwear production. Broad spectrum of geophysical methods were applied on several profiles in order to describe the spatial limitation of landfill materials and to monitor the spread of contamination from the landfill in the surrounding environment. Combination of several geoelectrical methods (EMI, ERT, VES and SP) allows us to define the resistivity model of the area, where the contaminated area was clearly outlined by low resistivity values. Moreover VES measurements were sorted in four elementary classes defined by the shape of the VES curve, which allows us to create schematic model of the area. Self-Potential method proved the active connection of the abandoned meander with the river. Additionally, soil vapour method survey revealed three outbreaks of methane gas generation that are connected to the area near the old meander.
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Comparison of Fracture Models for Seismic Wave Propagation in a Medium with Multiple Parallel Fractures
Authors E. Parastatidis, M.W. Hildyard, G.W. Stuart and D.A. AngusRock fractures create a secondary porosity giving new fluid paths due to the increased permeability. Seismic waveforms can provide useful information on the fracture network of a rock as a result of wave interaction with the fractures. This study is targeted at improving the understanding of wave propagation modelling in fractured media. For this purpose we use numerical modelling to model wave propagation through multiple parallel fractures based on an experiment with ‘simulated’ fractures in a steel block from (Pyrak-Nolte et al. 1990). Three models (Transversely Isotropic, Heterogeneous Transversely Isotropic and explicit fracture representation), each one using a different solution to the wave propagation in fractured medium, are developed in order to compare the similarities and differences. We use a P- and S-wave source which we have inverted from the experiment to study propagation in two different orientations perpendicular and parallel, to the fractures.
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Geoelectrical Monitoring at the Reclaimed Landfill of Derveni, Thessaloniki (Greece)
Authors F. Kapeti, G.N. Vargemezis, P. Tsourlos, N. Kazakis, A. Tatsi and A. VoumvourakiInfiltration of rainwater is of major importance for old waste disposal sites where production of leakage is taking place even after reclamation. In this work we present an ERT monitoring case study in a reclaimed Derveni Landfill. Previous studies in the area showed that important amount of water flows within the waste volume or by lateral groundwater flow or by direct infiltration of rainwater. Maag permeability measurements showed differential behavior of the top soil. Thus, geophysical monitoring of resistivity changes during injection of known conductivity water in high resolution 2D and 3D tomographies has been applied in two selected sites according permeability distribution map. 4D inversion of 2D and 3D data sets showed the flow paths of the injected salty water within the top soil up to the depth of almost one meter. At the same time increase of the resistivity has been observed deeper than one meter that cannot be easily explained. A possible explanation, except the case of disturbed current flow which could lead to artefacts, could be the biogas flow that is interrupted by the water cap of the injection. Both explanation are to be examined as a next step to the integration of the geoelectrical monitoring.
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Comparison between the Measurement of SP and Resistivity Method to Detect Wastewater in the North and South Bantar Geban
Authors B. Prasetyo and M.T. AlfiansyahThe problem of waste day by day more noticeably for many people. Garbage heap from households in DKI Jakarta is the cause pollution and health problems, so the rest of the household garbage heap is collected and transported to Final Disposal (TPA) Bantar Gebang, Bekasi which far from residential areas in order to keep the environment clean. Now, in fact the problem is not only on the surface like the smell of garbage wafted until the hundreds of meters, but also below the surface. Many residents are complained that several wells have bad odor, and allegedly a result of polluted by leachate water. The garbage are mounting (open dumping) without a thick layer of skin geotextile and channel leachate container, so that oozes down the surface. Based on the study, leachate water conductivity higher than groundwater which means the resistivity value was low. Utilization of SP and resistivity method is used to review and determine the distribution of the leachate below the ground surface which already oozes to the well of residential areas. Keywords: resistivity, conductivity, SP, leachate water, waste
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Microtremor for Evaluating the Effect of Shallow Sediments on Earthquake Ground Motion at Quseir City, Red Sea, Egypt
More LessRecording microtremor data is increasingly used in determining the site effect on earthquake ground motion especially in regions of moderate to low earthquake activity. In this study we used microtremor data to evaluate the effect of shallow sedimentary layers on earthquake ground motion in Quseir city which is located in the Red Sea coast, Egypt. The increasing in urbanization and land use planning, and the constructions of tourist resorts in Quseir city are the motivation of this work. The microtremor data was recorded by single seismic stations and by array of seismic stations at number of sites at Quseir city. The single stations microtremor data was analyzed based on the horizontal-to-vertical (H/V) spectral ratio technique in order to get the fundamental site frequency (f0) and its associated amplitude of ground motion (A0). The raw data of array was analyzed by using the SPatial AutoCorrelation (SPAC) technique to infer the shear-wave velocity structure beneath Quseir city. The results demonstrate that the value of f0 is ranging between 0.56Hz and 2.5Hz. The retrieved shear-wave velocity profile is characterized by significant interfaces at depths 20m, 50m, and 80m corresponding to velocities 170, 240, and 365 m/s respectively. The resulted f0 values were used in the calculation of bedrock depth at the measured sites. The parameters obtained in this study show a good agreement with the geological setting of Quseir city.
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History of Geophysical Work for Potash Salt Investigation in the Catalonian Potash Basin - ICL Iberia Súria & Sallent
Seismic surveys have been used for potash prospection in the Catalonian Potash Basin since the early 1970’s. More recently, 3D high-resolution seismic surveys have proved to be a powerful tool for potash mine evaluation and planning when professionally designed by geophysicists in collaboration with mining companies. Interpretation by mining geologists for mining engineers is key to achieving an improved geological understanding of the mine. In this case study in-depth seismic interpretation made it possible to obtain a structural geology model as well as produce isobath and isopach maps. The resources were evaluated after a drilling campaign and a calculation of on-site resources was made using geostatistical methods in compliance with International Standard Codes for Reporting of Exploration Results, Mineral Resources and Ore Reserves (JORC Code).
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Near Field Modeling of the Explosion Waveforms and the Key Contributing Factors
Authors M. Saeidnezhad, A. Sadidkhouy and S. KeshavarzipourtaftiFor modeling the blast wave, first its Green function must be solved. Therefore, we use the Green function solution of explosive source by Herman (1979). Study area, was located around the gas pipes in high-speed rail project Qom – Isfahan, with the longitude of the 50.5 to 51 degrees north and the latitude of the 33.5 to 34.5 degrees east. In this study, was used the number of four-digit seismograph machine type CMG-6TD. Sort seismograph machines around the blast site in such a way that the three-component seismic energy radiation patterns of blast were recorded in the vertical, radial and transverse. A condition that has a component (the radial component) was placed in the site of the explosion; also the distance between two consecutive samples was determined at a digitize of 10 milliseconds.
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Case Study of Seismic Surveying and Data Processing for Small-scale Carbon Capture and Storage in the Pohang Basin
More LessCarbon capture and storage (CCS) can be manipulated in subsurface sediment, which is a porous and permeable interval, after geological characterisation. We conducted multichannel seismic surveying to image the subsurface for geological interpretation of the Pohang Basin, Korea. The length of the streamer could not stretch to a far offset, due to the limited area of Pohang Harbour. The 24-channel streamer allowed six folds, which provided a low signal-to-noise ratio for conventional seismic data. Investigation of the seismic processing enhanced the quality of the stack section, which showed a reflector at the 800-ms TWT time domain. Geological interpretation using the seismic investigation mapped the thickness of the sedimentary unit for feasible CO2 injection.
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Mapping the Thickness of Gyttja by Using the Pull-down Effect on Shallow Reflection Seismic Data
Authors E. Nørmark, H. Sabra, H. Lykke-Andersen, K.J. Andresen and O.R. ClausenA reflection seismic survey has been carried out in Vejle fjord in Denmark in order to map the thickness of organic rich gyttja sediments. The reflection seismic data was severely contaminated by multiples and suffered from high absorption in the near surface sediments. Consequently, a direct and reliable interpretation of gyttja in the entire survey area could not be accomplished. Alternatively, the interpretation has been based on the pull-down effect on reflections which in the present case is the only way to achieve a coherent estimate on sediment thicknesses. Borehole information has been used to estimate the velocity in the gyttja layer.
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Combination of Active and Passive Seismic Methods for Subsoil Characterization of Seismic Stations
Authors A. Macau, B. Benjumea, S. Figueras, R. Puig, A. Gabàs, F. Bellmunt and A. RocaWithin the framework of Alertes-RIM (Regional and on-site earthquake early warning system for the Ibero-Maghrebian region) project twenty five seismic stations located in this region have been characterized. The aim of this work is the application of a methodology based on combination of active and passive seismic techniques in order to study potential soil effects at these stations. During the first step of this study, seismic noise recordings are extracted from seismic stations in order to apply the H/V spectral ratio technique and classify sites as rock or soft soil. Once identified seismic stations installed on soft soil the second stage is done. This phase consists on carrying out the fieldwork in the location of seismic stations. Surface wave analysis (MASW) and linear seismic noise array analysis are performed to get the shear-wave velocity model of soil column. Seismic refraction tomography (SRT) provides a 2D P-wave velocity model to identify bedrock geometry and soil parameters. The H/V spectral ratio is used in different places along the seismic profiles in order to obtain soil fundamental frequencies and compare these values with the fundamental frequency obtained from seismic stations recordings. The proposed methodology ensures a good characterization of seismic station subsoil.
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Shallow Seismic Reflection Survey by Using Accelerated Weight Drop as Seismic Source
Authors A. Alfian, M.R. Sule and A. PriyonoOnshore reflection seismic surveying for shallow objectives is a challenging task in Indonesia. The use of AWD (accelerated weight drop) as seismic source for an eco-friendly onshore shallow seismic survey is tested. The experiment was conducted around Jepon-1 well in Central Java, Indonesia which is a candidate for CO2-injection. This experiment is as initial investigation before baseline seismic survey is carried out around mid-2016. The CO2-injection itself will be started end-2017. This site was chosen as the first carbon capture and storage (CCS) pilot project in Southeast Asian region. The purpose of this survey is only to study the effectiveness of the AWD source for shallow seismic survey. Moreover, this survey is intended only to test the performance of AWD (ESS-200) seismic source and determine the optimum survey parameters for subsequent seismic baseline survey for monitoring CO2 injection in wells Jepon-1 and its vicinity. We found that the deepest reflections that could be imaged is only 650 m below the surface. To complete the data acquisition of 500m, it took only two operation days with a total cost of about USD 2,000. Thus, the use of AWD needs much less investment than similar surveys that use dynamite or mini-vibroseis as source.
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New Airborne Methods and Procedures for the Exploration of Mineral Resources - An Overview of BGR Activities
Authors U. Meyer, B. Siemon, M. Becken, R. Stolz, U. Noell, M. Frei, P. Buchholz, A. Steuer, S. Costabel, T. Martin, M. Ibs-von Seht and C. NittingerOne of the major tasks of the Federal Institute for Geosciences and Natural Resources (BGR – Bundesanstalt für Geowissenschaften und Rohstoffe) is to contribute to a sustainable future supply for Germany with minerals for industrial use. Part of the BGR’s strategy is to develop innovative ways of mineral exploration. The presented study focusses on airborne technologies, being applied and developed in ongoing projects. The methods used can be classified in established methods and newly evolving systems. The repertoire of established methods includes airborne electromagnetics, magnetics, radiometry and hyperspectral imaging. Systems based on latest technologies are full tensor magnetic gradient (FTMG) systems and audio-frequency magnetics (AFMAG) systems. Since a single airborne system usually cannot reveal the whole complexity of mineral bearing structures, new combinations of survey systems are being tested and new techniques are under development. The projects used to demonstrate and develop new systems, combinations and designs are E3 (Ore exploration in the Ore Mountains of Saxony, Germany), HYPGEO (New procedures for exploration of mineral raw materials using hyperspectral and geophysical sensing systems) and DESMEX (Deep Electromagnetic Sounding for Mineral Exploration). HYPGEO is being introduced as a new conceptual project combining different sensing systems and resources of BGR and partners.
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Test Airborne EM Surveys at a Black-shale Type Uranium Deposit in Korea
Authors M.J. Yi, J.H. Kim, N.H. Sung, M.H. Han, K. Motschka, R. Supper, A. Ahl and A. Johmorilogy in Korean geologic environment, test airborne geophysical surveys were conducted over a known uranium deposit using two AEM systems; GSA’s frequency domain loop-loop EM system and time domain EM system with grounded electrical source (GREATEM system). The main geologic feature of the test site is the phyllite formation with uranium mineralization in a graphitic zone and AEM surveys by two systems successfully delineated the graphitic conductors in this site. Considering the field condition with tough topographic variation, GREATEM system seems to have better performance in terms of data acquisition and depth of investigation, while GSA’ system provides better resolution for shallow subsurface structures, which is due to underlying EM principles used in the two systems. By this comparative study, we could convince that AEM technology is a very effective tool to the exploration of mineralized zone in Korean geologic environment.
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Archaeological and Resources Assessment of Sand and Gravel Deposits Using 3D ERT and Automated Interface Detection
Authors S.S. Uhlemann, J.E. Chambers, P.B. Wilkinson, M. Kirkham and M. BeamishRiver terrace deposits form one of the major sources for Palaeolithic artefacts and are of economic importance for the groundwater and aggregates industry. Their depositional history and thus structure can be highly complex. We present automated interface detection techniques applied to 3D geoelectrical data in order to guide archaeological prospecting and mining activities. Three different interface detection techniques were applied, which were based on resistivity iso-surfaces defined from clustering techniques and comparison to intrusive investigation, and on the steepest gradient in resistivity depth sections. Their results were compared to intrusive investigations. All three methods successfully imaged an incised channel underlying 3 – 8 m of sand and gravel deposits. The results showed good agreement with bedrock depths obtained from boreholes. The extracted bedrock topography was used to define archaeological trenching locations, within which Palaeolithic artefacts were recovered. The remaining sand and gravel resource of this extraction phase was estimated to be more than 1 350 000 m3.
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Mapping Alteration Zones over Botija Deposit, Using Reinterpretation of TDEM Data Flown for Geotechnical Purposes
Authors A. Viezzoli, V. Kaminski, A. Menghini and M. HopeCurrent study describes a case of reinterpretation of legacy TDEM geotechnical data for mining purposes. This reinterpretation allowed to extract new valuable information about alteration in Botija Cu porphyry deposit (Panama) and shine light on such phenomena as airborne IP effect and Cole-Cole modelling of airborne TDEM data.
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Application of Joint Inversion of Seismic and Gravity Data for Geological Characterization of Near Surface Zone
Authors A. Cygal, J. Pilch, M. Stefaniuk and T. MackowskiA comprehensive research on developing P-wave near-surface velocity models conducted during classic seismic data processing enabled not only a calculations of reliable values of static corrections, but also obtaining a detailed geological characterization of the shallow deposits and structures. Such a solution was possible to obtain by application of joint inversion of seismic refraction and gravity data and aimed to deal with complex geological and hydrogeological conditions of the Polish Lowlands. The presence of large thickness of glacial and post-glacial deposits typical for this region became an essential challenge for the presented experimental seismic study. This Quaternary formation comprises problematic for seismic acquisition unconsolidated material: gravel, sand and clay, which are additionally characterized by remarkable lateral and vertical lithological heterogeneity. In order to improve the quality of near-surface interpretation, it was inevitable to support the traditional interpretation methods, mainly seismic refraction tomography, with incorporation of the other, independent geophysical data. High-quality seismic data together with gravity anomaly gave an opportunity for the wider application of the joint inversion method to near-surface imaging for groundwater aquifers and mineral deposits prospection.
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Localization of Underwater Objects Using DC Resistivity Method with Two Detection Line
More LessSeveral methods were introduced as a technique to detect underwater objects such as submarines. Acoustic methods were generally exploited for underwater objects detection. However, they are prone to be disturbed by acoustically noisy marine conditions. To solve this problem, a new method adopting the geophysical DC resistivity method is introduced. Detection feasibility of underwater objects using this method was verified through numerical modeling and physical scale modeling. When we use a detection line, a peak point of responses indicates an object position along a detection line, however, the position along the perpendicular direction is not verified. However, fast localization of the target object is required since the final goal is real-time tracking of underwater object. In this study, a localization method for moving underwater objects is introduced using two detection lines and localization algorithm is developed with response library. A feasibility of detection and localization using the algorithm is confirmed through the experiments using physical scale modeling data.
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pyDFERM - Towards a Versatile and Efficient Environment for ERT Monitoring Data Management and Processing
Authors O. Kaufmann and A. WatletWe developed a Data Format for Electrical Resistivity Monitoring alongside a Python package (pyDFERM) as a novel approach for managing long-term ERT monitoring experiments. Large datasets produced in such experiments are indeed quickly difficult to handle with conventional data storing techniques. In parallel, long-term experiments are subject to changes in experimental conditions that are not always easy to report. Our approach covers 4 aspects that aim at improving the management and processing of ERT monitoring measurements. These can be listed as (1) checking and logging data acquisition job status, (2) structuring, documenting and storing incoming data, (3) efficiently retrieving and processing subsets of stored data, (4) structuring, documenting and storing processed results. Current developments show the added value of the project for subsurface imaging and data management in long-term ERT monitoring.
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Optimizing Geoelectrical Arrays for Special Geoelectrical Monitoring Instruments
Authors P. Tsourlos, B. Jochum, R. Supper, D. Ottowitz and J.H. KimIn this work we adopted an array optimization scheme for a special geoelectrical monitoring instrument for which no standard geoelectrical arrays exists. Optimized measurements are selected on the basis of their Jacobian matrix values. Application is demonstrated though model and real examples from a landslide site in Austria. Synthetic and real tests demonstrated that though measurement optimization it is possible to reduce the number of collected data without reducing the overall geoelectrical imaging quality. This is a very important for reducing both the power consumption as well the time-lapse data processing time.
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Modelling of Seismic Amplitude Anomalies Observed During Sub-surface Gas Injection Monitoring
Authors H. Perroud, P. Pezard, J. Lofi, N. Denchik and H. AbdoulghafourSeismic amplitude anomalies have been observed at the Maguelone site in the course of sub-surface gas injection experiments. To allow the interpretation of the seismic monitoring in terms of physical parameter changes, various modelling attempts were conducted that all share the elastic wave theory principles. We show in this presentation that we cannot reproduce the experimental results with this theory, thus some form of anelastic energy dissipation would be required.
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Time-lapse Electrical Resistivity Monitoring of Subsurface CO2 Storage at the Maguelone Experimental Site (France)
Authors N. Denchik, P. Pezard, H. Perroud, J. Lofi, H. Abdoulghafour, D. Neyens and G. HenryCO2 geological storage remains a recent research field and many questions are still open, particularly for saline formations, which are expected to provide over time a larger storage capacity than depleted hydrocarbon reservoirs. The Maguelone shallow experimental site for shallow CO2 injection (Mediterranean coastline, Gulf of Lions, France) has been developed to study in an integrated manner surface and in-situ (downhole) monitoring methods. The presence of two small reservoirs with impermeable boundaries (R1: 13-16 m and R2: 8-9 m) provides an opportunity to study a saline formation for gas geological storage both in the field and in a laboratory context. During the shallow injection experiment (~48 m3 of CO2 was injected over ~2 hours on December 4, 2014), traces of the CO2 plume were detected by time-lapse downhole and surface electrical resistivity monitoring techniques, although some of the injected CO2 appeared to leak along the new injection hole, which should be corrected in the future with additional cementing around the new holes.
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Monitoring Transport of Contaminants During Snowmelt Infiltration with Invasive and Non-invasive Techniques
Authors E. Bloem, H.K. French and A. BinleyThe impact of agriculture, industry, airport activities on soil and water quality is strongly influenced by soil heterogeneity. At Oslo airport large amounts of de-icing chemicals are used for removal of snow and ice. The objective is to quantify how the different processes occurring during snowmelt infiltration of meltwater contaminated with de-icing chemicals affects the geophysical signals. The study describes two field experiments were tensiometers, suction cups, and multi- compartment sampler (MCS) techniques have been combined with non-invasive time-lapse electrical resistivity measurements (ERT). The MCS combines variable-suction with multi-compartment aspects to measure spatial and temporal distribution of water flow and solute transport. The tracer experiments were performed at the research station at Oslo airport. The low resistivity values at the top of the ERT profiles on day 6 and 12 are explained by rapid increase of water saturation (Day 6), derived from tensiometer data, and infiltration of tracer (Day 12), derived from suction cup data. The low resistivity is also explained with MCS by saturation conditions at day 3 and increased electrical conductivity at day 12. By combining ERT, tensiometers, water sampling via suction cups or MCS, we can observe the contributions from water content and solute concentration to ERT.
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Seasonal Monitoring of Soil Water Content and Infiltration Using Soil Temperature Measurements
Authors A. Tabbagh, R. Guérin, B. Cheviron, H. Henine and M. BechkitWe use high precision Pt 100 sensors and apply numerical models of convective and conductive heat transfer to temperature experimental data recorded versus depth and time along a vertical soil profile. After having determined the thermal diffusivity and the convective flux rate it is possible to calculate the water content and the Darcy’s velocity using empirical soil properties models. The results obtained at Boissy-le Châtel site between April 16, 2009 and March 8 2010 are presented here. The ten day period results are reliable in accordance with local rain and potential evapotranspiration data.
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The Use of Surface Geophysics to Determine the Aquifer Characteristics in the Folldal Mining Site, Norway
Authors S. Puig, C. Duque, T. Pabst and P. AagaardOver two centuries of mining activity in Folldal area (Norway), now an industrial cultural heritage site, led to large amounts of uncovered waste materials. The exposure and subsequent oxidation of these materials produces acid mine drainage, which is discharging into the River Folla. Integration of surface geophysical and hydrogeological field methods was necessary to further obtain hydrogeochemical numerical models to assess the fate of the acidic groundwater, its contribution to the river and predict the effect of remediation. Seismic refraction and electrical resistivity tomography (ERT) were essential tools to characterize the aquifer geometry, locate the water table and obtain an overview of the topsoil sedimentological changes without altering the historical site. From the integration of the methods, the aquifer was characterized as a one single sedimentary layer aquifer of 30-40 m depth and areas with different hydraulic conductivity were defined, which permitted to obtain accurate groundwater flow.
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Analysis of the Water Content Variation in Different Timber Species Using the Nondestructive GPR Technique
Authors R. Martínez-Sala, I. Rodríguez-Abad and J. Mené-AparicioDeveloping a nondestructive system is crucial to inspect water contents in timber structures because the amount of water, beyond a certain point, can compromise the structure strength. With this in mind, the present work is aimed at analyzing the capability of ground penetrating radar technique (GPR), with a 2 GHz antenna, to detect water content variations in timber. To do that, GPR measurements were conducted on timber samples at two water content states: at hygroscopic equilibrium (HE) and after 72 hours of complete immersion in water. Given the anisotropic nature of timber, the data acquisition was performed in two directions respect to the grain, parallel and perpendicular. The obtained results highlighted that GPR can be a very suitable technique to monitor water content in timber structures that are in service, since it was confirmed that propagation velocities decreased as the water content increased for all samples and acquisition displays (parallel or perpendicular to the grain). Moreover, the dielectric anisotropy is more evident when the samples had been immersed in water than when they were at their HE.
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Electrical Resistivity Monitoring of Saline Tracer Fingering at Pore Scale under Partially Saturated Conditions
Authors D. Jougnot, J. Jiménez-Martínez, Y. Méheust, T. Le Borgne and N. LindeTime-lapse electrical resistivity tomography is a widely used geophysical method to remotely monitor water saturation and the migration of contaminant plumes. The effects of heterogeneous solute concentrations below the resolution limits of the tomogram are commonly ignored. We have adapted an experimental set-up to study the effects of sub-resolution solute heterogeneities on the effective bulk electrical resistivity. We used a 2D analogous porous medium consisting of a Hele-Shaw cell. We monitored simultaneously the bulk electrical resistivity and the spatial distribution of the water/air phases and the saline solute concentration field in the water phase using a fluorescent tracer injected together with the saline solute and a high-resolution camera. We performed saline tracer tests under full and partial water saturations. The bulk electrical conductivity measured at the scale of the medium were confronted to electrical conductivity computed numerically from the measured spatial distributions of the fluid phases and the salinity field. We find that the air distribution, saline tracer fingering, and mixing phenomena all result in large changes in the measured and simulated bulk resistivities by creating preferential flow paths or barriers for electric current at the pore scale.
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3D Resistivity and Induced Polarization for Leachate Plume Identification at a Challenging Field Site
Authors P.K. Maurya, A.V. Christiansen, G. Fiandaca and E. AukenIn the present study, we have used 3D ERT for detailed mapping of a polluted site at a challenging river site in the southern part of the Denmark. The survey layout involves several crossings of the meander of a river where a leachate plume from an old chemical factory site is expected to reach the river. Both resistivity and time domain induced polarization data were acquired, and full 3D inversion was performed for the resistivity data and 2D inversion of the IP data. Two sets of 3D data were acquired; one at a larger scale covering total area 410x90m2 and one at small scale covering 126x42m2, which enabled both details in the shallow part while covering a large area. 3D DC data were inverted using the inversion package BERT and 2D DC-IP data were inverted using AarhusInv. 3D DC inversion models show the presence of low resistivity anomaly at the northern bank of the stream interpreted as a contaminant plume. The contaminant plume is also seen in a deeper aquifer, which is separated by a low permeable clay layer to the upper aquifer. We could not discriminate the clay-lithology from the contamination using only resistivity model however, including the 2D inversions of the IP data we clearly separate the clay layer from the contaminated aquifer.
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Geoelectrical Characterization of Hydrological Processes in a Buried Braided River System
Authors A. Guinea, S. Hollins, K. Meredith, S. Hankin and D.I. CendónThe Macquarie Marshes (NSW, Australia) cover approximately 200 square km of the Macquarie River flood-plains. The marshes are one of the largest remaining inland semi-permanent wetlands in south-eastern Australia. Diversity of fauna and flora has decreased in the wetlands while the flood-drought cycles controlling these ecosystems have been affected by recent human activity. An Electrical Resistivity Tomography survey has been carried out to provide insight into the surface water/groundwater interactions occurring at the north-western part of the marshes and to identify potential recharge areas of the aquifer systems. In the resistivity sections three main units can be identified: 1. A top unit of low-resistivity (1 to 6 ohm.m) with about 5 meter thick on average. 2. A middle unit of higher electrical resistivity (6 to 20 ohm.m) that continues to a depth of approximately 20 metres and is discontinuous laterally. 3. A bottom unit below a depth of 20 to 25 metres with resistivity decreasing to values similar to those of the top unit. The resistivity results has allowed to identify clay dominated and sand dominated materials. The groundwater is recharged from surface water following sandy windows in the clay created by modern channels on the surface of the marshes.
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Potential for Reconstruction of the Subsurface Salinity Distribution Using the Frequency Domain Electromagnetic Method
Authors S. Delefortrie, T. Saey, P. De Smedt and M. Van MeirvenneWe explore the usefulness of FDEM conductivity mapping for hydrogeological investigations by surveying farming land overlying a salt plume. Specifically the potential for reconstructing the salinity distribution of the subsurface is researched. To this end, calibration of the collected FDEM data and accuracy of the inverted responses are looked into. In addition, ancillary data were collected to validate the results.
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Seismic Imaging of Esker Sediments within the Satakunta Sandstone Depression in Köyliö, SW Finland
Authors E. Ahokangas, G. Maries, J. Mäkinen, A. Pasanen and A. MalehmirThe Satakunta sandstone depression infilled by the Pori-Koski interlobate esker sediments hosts a major high-quality groundwater reservoir in Köyliö, SW Finland. These up to 100 m thick sediments were delineated for the first time down to bedrock level by high-resolution reflection seismic method using a newly developed landstreamer consisting of 80-3C MEMs (micro electro mechanical) broadband sensors together with 50 wireless recorders connected to 10 Hz geophones to obtain greater depth penetrations. The 5-day survey resulted in about 5 km long seismic data (2-4 m receiver and shot spacing) and two profiles. Indications of crystalline basement are lacking in the tomography sections, implying that the (fractured) Rapakivi granite area extends further southeast than expected. The sandstone contact position was also ca. 500 m further to the east than expected. The sandstone depression and infilling esker sediments and the bedrock level were shown with good accuracy in both tomographic model and the reflection section. The hydraulically conductive esker core does not follow the sandstone contact and is underlain by older sediments. This case study illustrates the capability of high-resolution seismic surveys with the parameters used in this study for hydrogeological investigations and in particular in thick glacial sediments.
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Fault Zone Imaging with Seismic Refraction Tomography
Authors S. Ostrowski, B. Rybak-Ostrowska and M. LasockiThe authors applied seismic refraction tomography (SRT) for imaging geometry, surrounding medium and internal details of fault zones. The applicability of the SRT technique to structural analysis of fault zones is demonstrated. Typical effects of fault zone occurrence on seismic velocity field distribution is described and discussed. Three examples of fault zones from southern Poland are presented, illustrating the description. A phenomenon of seismic velocity increase in some fault zones is introduced and is ascribed to presence of residual stress in recently active fault zones.
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Monitoring of “Contaminant” Flow Using Time-lapse Optimized 3D ERT in a Supervised Experimental Test Site
Authors K. Simyrdanis, P. Tsourlos, N.G. Papadopoulos and S. KirkouMonitoring of subsurface contaminants is crucial for environmental purposes. Electrical resistivity tomography has been extensively used the last years for spatial-temporal mapping and monitoring of various contaminants. In order to explore different aspects of survey planning regarding the employment of ERT in monitoring conductive contaminants, a supervised field test site was considered thus simulating more realistically the actual field conditions. A 3x2x2.5 m ditch was dug in the subsurface and equipped with an apparatus made of plastic pipes resembling four vertical and two horizontal boreholes, each one carrying 12 electrodes. The ditch was carefully backfilled with the same clay soil extracted by the ditch. A step-like sandy target was placed between the boreholes to control the contaminant flow and a saline tracer was injected on the top of the sandy target. The mapping and monitoring of the contaminant flow was made through optimized focussed ERT protocols compiled with the Jacobian matrix approach. The contaminant flow is represented using 2D and 3D inverted images, through space and time. Time-lapse 4D inversion presents with considerable accuracy the contaminant’s movement through the different time phases signifying the effectiveness of the borehole setting and the employed measuring protocol.
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An Assessment on the Recent Seismicity in the North Anatolian Fault Zone, Turkey
More LessA statistical assessment of recent seismicity in the North Anatolian Fault Zone, Turkey, is made by using seismotectonic b-value and precursory seismic quiescence Z-value. The catalogue including 28,420 earthquakes between 1970 and 2016 is used. Using the Reasenberg declustering process and the earthquakes with MD≥2.7, 51.4% of the events are removed and so, 13,815 events are used for a quantitative evaluation of seismic quiescence in the NAFZ in the beginning of 2016. Completeness magnitude is estimated as 2.7. Resulting values show that significant anomalies are observed in both b- and Z-values in some parts of the NAFZ. The larger b-values are calculated in Silivri, Black Sea, Izmit and Düzce whereas the smaller b-values are estimated in the western, the eastern and the middle parts of the NAFZ, covering Gulf of Saros, Gelibolu (Çanakkale), Ismetpaşa segment, Bingöl, Erzincan, Amasya and Çankırı. Several quiescence regions in and around Tekirdağ, Gulf of Saros, İstanbul, Marmara and Black Sea, İzmit, Düzce fault, Mudurnu, Çankırı, Amasya are observed. Consequently, the same regions including Gulf of Saros, Çankırı and Amasya where the smallest b-values and the largest Z-values are obtained may give important evidences to reveal the future earthquake potential in the North Anatolian Fault Zone.
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Airborne TEM Measurements Used As Reconnaissance Tool for Mapping Areas with Quick Clay in Sweden
Authors L. Persson, M. Bastani, H. Löfroth and C.A. SmithAn airborne transient electromagnetic (ATEM) survey was carried out over four test areas to evaluate the method for mapping potential quick clay areas in Sweden. The first results from an area located in southwestern Sweden are presented here. Previous geotechnical investigations confirm the presence of both quick clays and un-leached marine clays in the area. Based on the results from the ATEM survey, additional geotechnical investigations (including CPTU-R) and ERT measurements were also carried out. Comparison between ATEM results and the geotechnical investigations show that, over low resistivity areas (around 1 Ohmm) the clay is generally low sensitive, while in areas with resistivities higher than 5 Ohmm, high sensitive quick clay is identified. The resistivities obtained from the ATEM survey also correlates well with the results from ERT and CPTU-R measurements. The results show that the ATEM method can be used as an effective tool in mapping potential quick clay zones. Geotechnical sampling is always needed for comparison and confirmation of results from ATEM measurements.
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Numerical-experimental Study of Seismic Surface Waves Observables on Horizontal-vertical Components for Cavity Detection
Authors C. Filippi, D. Leparoux, G. Grandjean, A. Bitri, D. Pageot and P. CôteThe detection of underground cavities is still a challenging problem despite the good potential of geophysical techniques. The seismic surface waves analysis method can be acceptable for the cavity localisation if observables in data are affected by the void. We propose here a combined approach based on numerical 3D simulations (Spectral Finite Element Method) and reduced-scale experimental data to assess the possible observables affected by the cavity presence. The measurement bench MUSC is designed to effectuate seismic data measurements on reduced scale models on the two component of a P-SV configuration. We highlight different observables all visible in numerical or experimental cases: 1) the diffraction event is higher on the horizontal component; 2) there is a perturbation of the direct wavefield amplitude above the cavity and after the cavity position; 3) the analyse of the elliptic particular movement is perturbed in terms of amplitude and direction above and few meters after the cavity. Test results demonstrate the capability of using different observables of the Rayleigh wavefield in presence of a cavity to detect the object. These qualitative characteristics confirm the interest to study and compare observables on the horizontal and vertical components in a medium containing a cavity.
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Application for Capacitively Coupled Resistivity Surveys in the City of Messina
Authors D. De Domenico, G. Garilli, A. Teramo and A. MarinoThe electrical surveys by means of the OhmMapper Geometrics were carried out in the urban centre of the Messina city. The obtained results show an increased level of vulnerability of sediment areas due to the reduced depth of the water table in zones close to the coastline, also according to the hydrogeological characteristics of the urban area, which is crossed by nine seasonal streams. An additional safety reducer was highlighted by the presence of large area of the city where the buildings, also strategic buildings, have foundation partially or totally immersed in ground water table or water leakage from the municipal water. The CCR measurement can therefore be a useful supplement during the delineation of groundwater protection areas in urban sites where the telluric noise and the very dry shallow layer make the more traditional galvanic method impracticable. The main advantage of CCR is a more simple experimental setup, which allow a deeper insight into underground structure and results in a more time and cost effective geoelectrical logging.
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Evaluation of KTU Farabi Hospital Building Strength Comparing of the Ground by Using Single Station Microtremor Method
More LessDetermination of ground and building characteristics is important to provide against earthquakes. KTU Farabi Hospital is located in Trabzon and approximately 150 km distance from the North Anatolian Fault which is the most dangerous fault system in Turkey. In this study, 10 microtremor recordings were collected in the building and ground. The measurements taken in the building were recorded at (-2)nd, 1st, 4th, 7th, 11th floors and repeated day and night except 1st and 7th floors. The recordings were evaluated with Geopsy program according to Nakamura Method. The predominant frequencies were obtained averagely 1.66 Hz for the building and 7.65 Hz for the ground. The resonance risk is low because these two average frequencies are not close to each other. The damping ratios were calculated by using Half Power Method. The damping ratios are matching with the predominant frequencies and averagely 0.09% for the building and 0.23% for the outside points. Finally, the horizontal components of the all measurements were divided by each other to detect transfer function of the building to Floor Spectral Ratio Method. According to this dividing it can be said that the predominant frequencies are almost the same with the predominant frequencies obtained from Nakamura Method.
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Odd-even Pole-pole Array and 3D Resistivity Surveys in Urban and Historical Areas
Authors F. Almeida, N. Barraca, R. Moura and M.J. Senos MatiasModern and historical buildings may show some degree of subsidence resulting from foundation deterioration and local geological conditions. Hence, buildings stability can be affected and restoration plans must be envisaged. Resistivity methods have been used to investigate local conditions, providing 3D images of the soil under man made structures and hence contributing to the delimitation of hazardous areas and pathologies. However these techniques require the deployment of a grid of electrodes, which can be difficult to accomplish because of physical limitations and of the buildings nature that cannot be damaged. To overcome these problems special arrays have been used (L, Corner, Square arrays, etc). Here in it is proposed to use the “Odd-Even Pole-Pole Array” to study the ground under a contemporary building and under a high historical value XIV century Abbey, both showing evidence of subsidence. Field data quality is also addressed and it is proposed to identify low quality data to be expunged so that modelling is improved. It is also shown how to estimate resistivity values from data quality tests, to carry out further zonation, locate hazardous areas and to enhance modelling.
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Megalopolis Influence on Geophysical Field Variations
Authors S.A. Riabova, D.N. Loktev and A.A. SpivakThe research of geophysical fields in the conditions of megalopolis attracts particular interest not only in terms of their influence on the operation of precision equipment and technological processes associated with nanotechnology, but also it is perhaps the most important in terms of the formation of special habitat of human and other biological objects. Indeed, megalopolis causes significant changes in mode of the physical fields both directly and indirectly. The violation of upper layer of soil in large-scale construction leads not only to change in landscape and groundwater regime, but also causes increased flow of underground fluids, including highly natural radon emanation which is dangerous for human. The results of instrumental observations indicate a significant influence of the megalopolis on the physical field in the surface atmosphere. The presence of man-made continuous and pulsed sources causes a significant increase in the amplitude of the physical fields, their spectral characteristics, as well as a violation of natural, nature-defined periodicity.
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Linearity Analysis of the Random Noise in Land Seismic Prospecting
More LessThe existence of the random noise is one of the main obstacles for getting higher-accuracy seismic records. The investigation of the seismic random noise properties is the pathway for improving the performance of noise attenuation algorithms. Here, we use the statistical testing methods to investigate the linearity of land-seismic-prospecting random noise, whereas the linearity, to some extent, can reflect the complexity of the generating process of the noise. The results show that the noise cannot be considered as a linear stochastic process. By analyzing the behaviors of the dataset, we obtain that the non-linear noise always have more energy in high frequency bands, and the energy distributions of the non-linear noise are disordered in high frequencies. Thus, the linearity of the random noise should be improved by attenuating the energy in high frequencies. We use an experiment to prove the correctness of our results. Based on the generating mechanism of the random noise, we also give a reasonable explanation for the results of our study. The findings have implications for future noise reduction and signal detection algorithms.
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ERT-SIP versus Seismic Tomography - Geophysical Mapping of a Planned Highspeed Railway Track, a Case Study from Norway
Authors J. Scheibz, A.K. Lysdahl, H. Anschütz, S. Kalstad and A.A. PfaffhuberWithin an infrastructure offensive in Norway the authorities plan and will build many hundred kilometers of new roads and rail tracks. One of the focuses is towards a high speed railway (HSR) system as a sustainable future transport. Due to the complex geology of large parts of Norway drilling campaigns often lead to a big question mark. To fill the gap between these drillings, reduce costs and improve planning security there is a demand in high resolution geophysical methods. NGI had the possibility to test, among other methods, high resolution ERT-IP and seismic refraction tomography to determine shallow bedrock (1-20 m) below a glacial infill on two test sites. While we assumed seismic refraction tomography to be the most reliable tool our study shows that our high resolution ERT model results in a lower deviation from existing drilling informations and supplementary revealed two steep weakness zones which were completely hidden in the seismic model. Additionally we calculated the spectral information of the IP data using the Cole-Cole relaxation model. The model provides additional information about the sedimentary cover but reveals contradicting informations about the weakness zones which cannot be further explained due to currently non-existing petrophysical models, especially for hardrock.
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Comparing Automatic and Manual Methods for Determination of the Bedrock Interface Using AEM Data
Authors H. Anschuetz, M. Voege, A. Kydland Lysdahl, S. Bazin, G. Sauvin, A. Pfaffhuber and A.L. BerggrenAn extensive airborne electromagnetic (AEM) survey was carried out in Norway with the primary purpose to obtain information of depth to bedrock in areas with little or no prior geotechnical knowledge. We present different approaches to extract a bedrock model from the high-resolution time-domain AEM data, including both automated and manual procedures. It is found that in the area of investigation a user-driven approach of manual bedrock picking is most suitable, taking into account the strongest vertical resistivity gradient and geological information as additional information. A semi-automatic, statistical method, called Localized Smart Interpretation (LSI), is presented and discussed in addition. This method, while not included in the original bedrock model for the entire area, proved promising and should thus be implemented in future projects of similar scope.
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Combination of Geophysical Technques to Characterize Sediments (Ebro Delta, Spain)
Authors B. Benjumea, A. Gabàs, A. Macau, F. Bellmunt, S. Figueras, M. Vilà and R. PiThe Ebro Delta (Spain) faces anthropogenic and climate changes that can cause a significant decrease on its subaerial surface. One of the causes of this reduction is subsidence that take place due to the compacting of the sediments. In order to identify zones vulnerable to subsidence, we have defined several targets such as: characterization of Holocene sediments (sands versus clays/silts and location of organics) and delineation of the bottom of deltaic sediments. Regarding these objectives, we have acquired geophysical data sets at different environments of the Ebro Delta (from delta plain to marshes among others). The methodology includes combination of seismic methods (surface waves, refraction and reflection methods) and electrical resistivity tomography for sediment characterization as well as the use of the H/V spectral ratio of microtremor measurements to delineate the base of the Holocene sediments. We show the results for one line located on the delta plain and close to alluvial fans. Geophysical models are characterized by a high-resistivity and high-velocity layer at around 25 m depth interpreted as the base of the deltaic sediments. H/V results provide evidence of maximum thickness of deltaic sediments located at the right side of the river mouth.
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Empirical Correlation of Shear Wave Velocity (Vs) with SPT of Soils in Madrid
Authors I. Pérez-Santisteban, A. Munoz Martin, A. Carbó and J.M. Ruiz-FonticiellaEmpirical correlations are usually used as a predictive tool in geotechnical engineering. However, equations calculated for soils very different to the ones to be characterized are frequently used, and so they are not representative of their mechanical properties. This fact, added to the increasing interest of civil engineering in knowing the shear wave velocity (Vs) of the ground, has led to the calculation of different empirical equations to predict the Vs value of the soils of Madrid. In this study this has been achieved by calculating the empirical correlations between the Vs value obtained through the ReMi (Refraction Microtremor) technique and the Standard Penetration Test (500 NSPT values). The empirical correlations proposed are applicable to the whole metropolitan area of Madrid, and have an excellent predictive capability due to the incorporation of the measurement depth to the equations, which has an important influence in the resistance properties of soils.
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The Rock Physics Template to Estimate Clay Content, Porosity, and Vulnerability of River Levees
Authors C. Konishi and Y. HashimotoWe propose to use the rock physics template to estimate clay content and porosity, and also introduce a new quantity that can be calculated from estimated clay content and porosity to represent vulnerability for the seepage failure of river levees. The rock physics template can be generated for a certain range of porosity and clay content by selecting appropriate rock physics models. This methodology provides clay content section, porosity section, and vulnerability sections from the integrated geophysical survey. We demonstrate the methodology to detect the most vulnerable location from the integrated geophysical investigations. The location identified as the most vulnerable point is verified by drilling and SPT. The location consists of very loose sand; therefore we concluded that the vulnerability section is beneficial to judge a priority of a treatment to stabilize the river levee.
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Combined GPR and Conductivimeter Prospection to Detect Internal Erosion under Mataró - Dike and Quay
Authors J.O. Caselles, J. Clapes, V. Perez-Gracia and J.A. CanasThis paper presents a case study of the Mataró port combining GPR and conductivimerter surveys. Mataró port has lots of slab drop off in the dike that was supposed to be produced by sea flow wash out fine soil particles. The combination of both methods applied at the dike and a quay has permitted to detect perfectly the location of voids and disturbed layers in it foundation. Also, results seem to indicate that the internal erosion it is not only produced by sea flow but also by interflow water form two old streams.
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GPR Analysis of Water Content in Concrete Specimen - Laboratory Test
Authors S. Santos-Assunçao, S. Krishna and V. Perez-GraciaApplications of Ground Penetrating Radar (GPR) in civil engineering context are popular and it has been widely used to characterize the media in terms of structural arrangement and pathologies. This work presents some tests carried out under laboratory conditions on a concrete slab. The aim of this study is to evaluate the moisture content in a homogeneous medium (concrete) using data obtained with a 1.6 MHz GPR centre frequency antenna. The evaluation process includes detailed analysis of the signal in both time and frequency domains. The key parameters are amplitude of surface reflection, changes in the centre frequency and attenuation of signal. The central frequency decreases in the A-scans obtained from zones with high water content. The amplitude of the first signal (reflection on the surface of the specimen) exhibits an increment. These results could be useful in the assessment of foundations and slabs, as well as in the evaluations of buried geological channels.
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A Magnetotelluric Study in La Rosa Diapir (Murcia, Spain)
Authors E. Gorriz, A. Marcuello, F. Escosa, P. Queralt, A. Martí, J. Ledo and E. RocaThe study of salt structures is an important challenge because of its economic implications. In this work La Rosa Diapir has been taken as an example of salt structure because is still active showing an outcrop in good conditions. This diapir is located on Eastern External Prebetic (in Jumilla, southeast Spain). The aim of this work was to perform a reconnaissance MT survey to obtain a first interpretation of the diapir area with this technique. This area is moderately populated and its geological structure is complex. The profile ran along NW-SE direction, and 16 stations were collected on it. The distance between them was approximately 800 m. The effect of the power lines were detected in the apparent resistivity curves, and the shift filters showed its capacity to reduce it. The dimensional analysis confirmed that the geoelectrical structure is 3D. Since the data have been recorded along a profile, the interpretation is based on the determinant of impedance. The results in the area indicate that the geoelectrical structure is quite conductive and no clear traces of resistive bodies can be seen.
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Can We Really Detect Cavities Using Seismic Surface Wave?
Authors A. Bitri, K. Samyn and C. FilippiShallow cavities, such as karstic caves in carbonate bedrock, near-surface underground mine workings and tunnels, constitute serious hazards for people and existing constructions due to the risk of collapse and subsidence. This phenomena is growing fast with climate change involving damages to buildings and increasing urban development costs. Karstic features, voids, surficial dissolution, alteration and unconsolidated material are thus major challenges for geophysical methods which could play a major role for their detection. Recent investigations have reported good results for cavity imaging using surface wave seismic methods (Sloan et al. 2015, Samyn et al., 2013, Leparoux et al., 2000, Nasseri-Moghaddam et al. 2005, Gucunski et al., 1996, Park et al. 1996). But in spite of successful case histories, business as usual void detection is still challenging due to the complexity of near surface materials and probably the limited resolution of geophysical methods. The propagation of Rayleigh waves in homogeneous layered media is well understood and has been addressed in depth by several authors (Thomson 1950, Haskel 1953, Graf 1975). The derivation of analytical solutions for the scattering of Rayleigh waves around heterogeneities is complicated and researchers often perform experimental tests or develop numerical models to study this problem (Gelis et al. 2005, Gucunski et al. 1996). These numerical studies have shown reflections from the heterogeneities (even in the cavities) and perturbations in the dispersion curves. Leparoux et al. (2000) applied the MASW test to locate two cavities: masonry at 3.0 m below the ground surface, and the other one embedded at about 8.0 m beneath the surface, without masonry. Xia at al. (2007) demonstrated using 2-D surface wave modeling that the diffractions due to a void on a homogenous half space were Raleigh-wave diffractions because of their amplitude, velocity, and frequency. They derived a travel-time equation of surface wave diffractions based on properties of surface wave and solved this equation for a phase velocity and depth to a void. Sloan et al. (2015) demonstrated the capability of using P-wave diffraction and surface wave backscatter techniques to detect subterranean tunnels. Despite these convincing arguments, we have been recently confronted to disheartening results leading us to the question: Can we really detect cavities using seismic surface wave? The objective of this study is to pose the problem for understanding interaction between a cavity and a Rayleigh wave by measuring the wave field in surface on the roof and on the floor of a known cavity. For addressing this issue, we have focussed on a study area located in Souzay-Champigny, France. This consists of an abandoned underground quarry network in cretaceous chalky limestone (Bitri et al. 2014). We have chosen these cavities because they are accessible underground and partly mapped.
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Determination of the Ground-building Relationships in the KTU Campus Area with Microtremor Measurements
Authors Y. Beker, N. Sayil, O. Akin and K.H. CobanMicrotremor measurement obtained by ground vibrations is one of the useful methods for determination of ground characteristics. Also the method has been using to specify building resonance risk during earthquakes in the last decades. In this study, single station microtremor recordings have been taken on the ground and at the 6 buildings in the KTU campus area. The measurements taken on the ground and in the buildings have been evaluated by Nakamura (H/V ratio) method. The eastern of the campus area presents Class-IV and the middle and western part of the campus present Class-II- Class-III according to Kanai and Tanaka ground classification. The predominant frequencies of the buildings are not in a harmony with the values of the ground. It can be deduce that the resonance risk is low for these buildings during the earthquakes. The H/V ratios of the ground change between 1-3 and lower than the buildings ratios which change between 5.0-8.5.
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Geophysical and Seismological Investigations around Cairo, Egypt
More LessCrustal movement studies are considered very important in the geodynamical research tools, which help in understanding the properties of the Earth in regional, global and local scales. The worldwide tool for such studies is the repeated geodetic measurements performed at chosen localities or regions. Recently, in Egypt, in order to monitor local, regional and global movements of crustal blocks, methods of space techniques were applied. There are two purposes for the study of crustal movements. The practical purpose includes checking the stability of structures, assessment of the degree of geological hazards and the detection of earthquakes. Scientific purpose is very important for understanding the deformation mechanism, testing new theories, which are applied to the design of structures. The most important applications are monitoring of the behavior of seismic active areas, deformations of the earth’s surface, earthquake prediction and deformation of huge constructions.
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Geotechnical Modelling of the Riyadh Metro Line 3 Using Multi-technique Geophysical Survey
Authors M. Cueto, S. Mayordomo, M. Martín, P. De La Puente, J. Olona and D. AriasThe Riyadh Metro Project is currently the largest public rail infrastructure project in the world under implementation. Metro will become the backbone of the city's public transport, significantly improving the life quality of citizens. We helped to carry out an exhaustive geophysical survey along the entire corridor of the Riyadh’s Metro Line 3. Among all the six Lines that the System comprises, Line 3 is the longest. It runs along 42 km, of which we identified about 13 km long underground sections (TBM EPBS and cut and cover) and 11 underground stations (cut and cover). The geophysical survey comprised a variety of field tests: seismic refraction, electrical resistivity tomography, ground penetration radar and seismic tests in boreholes (downhole and cross-hole testing). We correlated the results of the geophysical surveys with data coming from geological, hydrogeological and geotechnical investigations. This way, we delivered a continuous subsurface profile, which became the raw data for developing a full detailed geotechnical and hydrological model for the Line 3. The said model anticipated potential geotechnical risks (layers owning poor engineering parameters, karstic areas, faults or weaker rock volumes within the rock mass). Then, mitigations helped achieving, reliable, durable, safe and efficient designs and construction works.
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Application of Ground Penetrating Radar to Detect Sinkholes and Ground Subsidence in Beryanak, Tehran
Authors H. Gharahi, B. Yousefi and U. AladinAfter occurring two dangerous subsidence in both Arab and Pahlavani Streets located at Beryanak in the 10 districts of the municipality of Tehran, the GPR Department of Geotechnical & Strength of material study centre of Tehran had decided to use ground penetrating radar method to detect possible sinkholes and aqueducts on the site. The GPR data acquisition had been performed by a 50 MHz GPR antenna made by MALA Company. GPR data gathered in 7 longitudinal profiles parallel to the street directions. In the processing of the GPR data, different filters such as background removal, Migration, Band pass filter, and horizontal and vertical smoothing are applied to the data. The final result shows that the most of detecting sinkholes which cause to the subsidence were created due to the scouring. GPR profiles from Arab Street indicate that those anomalies were detected at shallow depths (between 2/5 to 5 m) are due to the subsidence caused by excavation and placement of sewer pipeline. But at some areas were identified from depths 8 to 15 meters can be some sinkholes and may lead to a big subsidence. These areas are very important for both studying and reconstructions.
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Engineering Foundation Characterisation of Wind Farm Site Using Integrated Data Approach - Clyde Perspective
By A. RichardWind Farm development across the UK has been on the rise for the past decade with potential for more works in many years to come as drive towards renewable and clean energy demands continue to grow. The challenges faced in poor ground conditions such as clay gouge underlying site infrastructure such as turbine foundation, access track, hardstands, control building etc can be key to providing a sustainable design option across the site. This study covers an integral approach using multiple site investigation datasets to inform design in both shallow and deep foundation solutions. The study revealed incorporation of multiple ground investigation data at a Wind Farm site with different juxtaposing local geology formations and the use of an informed decision to implement a shallow foundation option even in weaker ground conditions. Integrated data such as resistivity, seismic, borehole and trial pit logs, geotechnical laboratory results and in-situ testing were used to characterise Wind Farm sites in providing a more cost-effective and sustainable foundation solution. It is also important to note that data correlations generated from this study could well be extended into other sites where similar ground conditions exit.
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Detection of Permeability in Irrigation Dams with the Electrical Resistivity Methods
More LessIt was aimed to identify the permeability of the dam area by collecting the information of 15 boreholes with 450 m depth in totally previously made along the dam axis line and the electric resistivity measurements along four lines vertical to the same axis line. Kırklartepe Dam, planned to be an irrigation dam for agricultural purposes, in the Central district of Bayburt province located in the northeastern region of Turkey was selected as the study area and it was tried to identify the permeability of the units forming the dam area. 2D and 3D underground views of the measurement lines were determined by implementing the inversion process to the electric resistivity measurements. While examining these sections, it was interpreted that anomaly areas with low resistivity values categorize an alluvial cone with permeable slope wash character, while anomaly fields with high resistivity categorize an impermeable metamorphic unit. Moreover, it was tried to reveal the permeability of the dam area by associating with the information of the present boreholes in the study area and creating section maps of 3D views obtained for each 10 m. Thus, it was observed that current boring information and electric resistivity measurement results supported one another.
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Determination of the Dynamic Characteristics of the Faculty Building of Law at KTU Campus with HVSR and FSR Methods
Authors Y. Bekar, K.H. Coban and N. SayilSeismic response characteristics of structures can be estimated by spectral ratios of microtremors measured on structures and their foundation ground surface. The microtremor horizontal-to-vertical-spectral-ratio (HVSR) technique has received great attention from all over the world with its simplicity together with quick information about dynamic characteristics of ground and structures. The HVSR of microtremors gives a good estimation of natural building frequency. In this study, Horizontal-to-Vertical-Spectral-Ratio HSVR method and Floor Spectral Ratio Method (FSR) has been applied to microtremor records taken with three component broad band velocity seismometers in three different locations inside the building and one at outside with the aim of determining the dynamic characteristics of Faculty building of Law at The Karadeniz Technical University (KTU), in Turkey. The average predominant frequency, period and amplification values for the Faculty building of Law are calculated. The vibration frequency and period is around 3.5 Hz and 0.283 s, respectively. The amplitude values increase to the upper floors.
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Imaging of Internal Structure in Landing Fields of Planes at Erzincan Airport (Turkey) with GPR Method
Authors I. Saricicek, Z. Ogretmen Aydin and A. SerenAt this investigation, it is aimed to display the internal structure including intensely landing points of planes (observed fracture, joint and deformation from surface) at Erzincan Airport with the ground penetrating radar (GPR) method. To view whether the observed deterioration at the surface continues under the landing field horizontally and vertically or not, at the observed fracture-joints part of study area GPR data were collected by using 800 MHz center frequency antenna at 20 lines. Measuring range was selected 1 m and the lines were selected 18 m long to parallel each other. After applying the standard data processing steps to obtained data, 2D and 3D views were determined. When these views analyzed; generally high quality landing space conditions are monitored, there are attenuation parts of electromagnetic waves locally and especially observed joints at 2.7 and 15 meters from surface was determined to continue at horizontal and vertical extension of the acquired GPR views. It was suggested to carry out maintenance to relevant institution.
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Physical Experiments on Detection of the Simulated Cavities Using GPR
More Less3-D GPR technique was applied to conduct the physical experiments for roadbed cavity detection. The physical experiment has employed the soil characteristics of mainly sand-sized soils. The simulated cavities with dome-shaped structure were installed at regular intervals in spatial distribution. The land surface of the site was not paved with asphalt concrete at the current stage of the experiments. The results of the experiment at the current stage show that the reflection patterns from the simulated cavities are hyperbolic returns typical to the point source in 2-D perspective. The signal noises such as clutters attributed to the soil compaction differences are widely present on the 2-D and 3-D data. A closer inspection of 3-D GPR volume data has yielded more clear interpretation than 2-D GPR data regarding where the cavities are situated and what kind of shape the cavities are imaged in space. Careful inspection of the 2-D and 3-D GPR data should be applied to the cavity detection. This study is an ongoing project of KIGAM and more realistic conditions of the underground environments in the physical experiments would be prepared for future studies.
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Tracing the Source of Water Leakage in Towhid Street (Center of Tehran) Using Ground Penetrating Radar Method
Authors B. Yousefi, H. Gharahi and U. AladinAfter observing two water seepages in Towhid Street in the 2 districts of the municipality of Tehran, the GPR Department had decided to use ground penetrating radar method to detect possible scouring area on the site. In this study, GPR method has been used to identify the source of water seepages in different parts of in Towhid Street. The GPR data acquisition had been performed by the Mala-HDR 80 MHz GPR Shielded antenna. The data collected in 14 longitudinal profiles. At the next step, the collected data have been processed by the GPR experts of the Geophysics Department at Geotechnical & Strength of material study center of Tehran. In the processing of the GPR data, different filters such as background removal, migration, band pass filter, and horizontal and vertical smoothing are applied to the data. The results obtain from this research work indicate that the GPR method, in addition to its speed and simplicity in data acquisition, is very successful in detection of leaking areas in which electromagnetic properties change rapidly.. It seems two parts of water pipe which is passed under in Towhid Street and along to the tunnel path have been damaged.
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The Contribution of Geophysical Data for Investigations of the Hatrurim Complex, Israel
Authors S.E. Itkis, Y.A. Vapnik and B.E. KhesinUnusual rocks of the Mottled Zone (MZ) are known in Israel and Jordan in the vicinity of the Dead Sea Transform. The genesis of the complex is problematic. The recent studies suggested the deep inflow and surface combustion of hydrocarbon gases that provided the heat for pyrometamorphism. MZ rocks are characterized by high differentiation in magnetic properties and density. Integrated geophysical studies of MZ areas included ground magnetic measurements, study of physical properties and reprocessing and reinterpretation of available aeromagnetic and gravity data. MZ outcrops are correlated with residual gravity minima, showing zones of disintegration and possible hydrocarbon accumulations. One of the several MZ outcrops, the Nabi Musa area, located in the Judean Desert, northwestern of the Dead Sea gives an exclusive possibility for the study of cross cut section, rock types, and near-surfaces processes. Obtained geophysical results produce information on remarkable features of MZ complex and allow us to outline areas with hydrocarbon potential.
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Advanced Machine Learning Methods for Copper Ore Grade Estimation
Authors B. Jafrasteh, N. Fathianpour and A. SuárezOre grade estimation is one of the most important tasks in the design of effective strategies for the exploitation of mineral resources. In this work, we compare the accuracy of ordinary kriging with advanced machine learning techniques in the estimation of mineral grade as a function of the location in the deposit. As a case study, we analyze data from the Sarcheshmesh porphyry copper mine located in the Southwest of Iran. The learning machines considered include multilayer perceptrons (MLP), a type of feedforward neural network, random forests (RF) and Gaussian processes (GP). The testing protocol explicitly takes into account the fact that the available data are grouped in boreholes. Specifically, the test instances are assumed to represent unexplored locations. Therefore, they belong to boreholes that are different from the ones in which the training instances are located. From the analysis carried out a Gaussian Process yields the best results. The improvement with respect random forest, which is the second most accurate predictor, is statistically significant.
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Mineralized Structure Prospection Using HGM and TAM Techniques with Magnetic Data in Gaziantep Southern Turkey
By A. ElmasThe aim of this paper is the edge detection and the depth estimation of the possible mineralized structures of an area in Gaziantep-Southern Anatolian region, Turkey. To achieve this, horizontal gradient magnitude (HGM), and tilt angle map (TAM) methods with a Reduction to the Pole (RTP) magnetic data have been used. The results indicated that depth values from these sources have ranged between 15 and 30 m. Key words: Reduction to the Pole, horizontal gradient magnitude, tilt angle, edge detection, depth estimation
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Prospecting the Lenticular Manganese- Ore Deposit (Um Bogma, Southern Sinai) Applying Gravity Survey
By K.H. ZahranManganese ore in this region was observed as lenticular, banded and pockets forms. Moreover, it is frequently distributed with different proportion, thickness, length and forms within the Paleozoic sediments in Um Bogma area. traditional mining techniques are not the optimum way for manganese ore exploitation at Um Bogma areas. Micro-gravity survey has been proposed as a geophysical method for Mn ore exploration at UM Bogma. Two locations have been selected as case studies. Selection has been subjected to previous geological and morphological information of Um Bogma region. The two selected has different Morphological features. High resolution micro-gravity survey has been carried out along both locations. Interpretation of observed gravity data delineate the existence of lenticular high gravity anomaly, suggested to be Mn ore deposit. After removing the regional trend from the gravity observation, the residual Bouguer gravity anomaly shows significant Mn ore formation. It was possible to determine depths, width and density contrast of the reported anomaly.
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Mineral Deposits Assessment of the Jabal Tays Ophiolite Complex, Eastern Arabian Shield, Saudi Arabia
Authors S. Alhumidan, O. Kassem and M. AlmutairiAl-Amar-Idsas fault is one of the most important tectonic features in the Eastern Arabian Shield and is a major effect in Jabal Tays ophiolite complex. This study aims to the assessment of mineral deposits and petrographic characteristics of the Jabal Tays. Through field investigation, rock sampling and microscopic examination we accomplished a better understanding of the nature of tectonic evolution in the area. Mafic-ultramafic rocks at Jabal Tays include a large amount of serpentinite, subordinate amounts of gabbro intruded by mafic dikes, mélange, serpentinite schist, and listwaenite. The serpentinite makes up the bulk of Jabal Tays variably sheared and typically consists of relatively massive serpentinite cut by shear zones marked by serpentinite schist. Mafic-ultramafic rocks generally confined to brittle-ductile shear zones, which are sub-parallel to the prevailing NW or NNW structural trends confined to the metamorphic terrains, especially to zones intruded by mafic volcanic rocks (gabbro, serpentinites and talc carbonate). Based on these results, we concluded that the contacts between Abt Schist at Ad Dawadimi Terrane and metavolcano-sedimentary rocks formed during progressive thrusting under a brittle to semi-ductile deformation conditions by simple shear, which is, also involve a component of vertical shortening, causing sub horizontal foliation in Jabal Tays area.
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Geophysical Investigations to Support Soil Organic Contamination Assessment in a PCB Historically Contaminated Area
Authors L. De Carlo, V. Ancona, M.C. Caputo, C. Campanale, A. Calabrese and V.F. UricchioNowadays due to the worldwide increase of environmental contaminations, the characterization of polluted sites has become very important. In light of this/As a consequence, the development of new methodologies, able to quickly and cheaply evaluate contamination is an arduous challenge but necessary. The use of geophysical techniques combined with the direct measurement techniques (such as groundwater and soil analysis) can be useful adopted as an integrated approach for a rapid pollution detection and assessment. In this work, a PCB historically contaminated area located close to Taranto city (Southern Italy) was investigated by chemical pollutant analyses and geophysical surveys in order to characterize and evaluate the pollution, which is occurring since years. Particularly, Electrical Resistivity Tomography (ERT) profiles were carried out close to the soil sampling points to image electrical structures in the upper part of the soil, severely contaminated by organic pollutants. The obtained results evidenced that geophysical surveys can efficiently support soil contamination assessment in an area of Southern Italy severally affected by high recalcitrant organic contaminants (PCB).
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Simulation of Low Frequency Responses of Dual Laterolog Using Numerical Method
Authors S. Keshavarzipourtafti, M. Nabi Bidhendi and M. SaeidnejadAlthough on account of reducing contact-impedance noise, DLL tool tends to work at non-zero but low frequencies, to date, most simulations of DLL have been carried out on the basis of assuming zero-frequency electrical current. In this work, we simulate low frequency DLL measurements of axially symmetric, invaded and isotropic formations using finite element method. Due to Groningen effects arising from frequency effects, we witness unusually high LLd readings of resistivity in layers lying directly under layer with high resistivity. In this study, we also simulate such effects.The results indicate that the DLL measurements are highly affected by the resistivity of the surroundings such as shoulder beds and invaded zones. Also, with decreasing layer thickness, the difference between the resistivity reading and true resistivity will increase; In infinitely thick beds, the LLS and LLD pseudogeometrical factors curves are widely separated for all invasion radii.
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Analysis of the Response of the Electrical Resistivity Tomography Method to Soil Cracks
Authors A. Dolinko, B.N. Losinno, N. Zunni and F.A. LemeilletIn this paper, the sensitivity of the electrical resistivity tomography (ERT) method for characterizing the cracking of soils is investigated. Due to the difficulty to produce cracks of known profile, the ERT method was tested by using synthetic soil profiles with known cracks shapes artificially generated. For this, a computer simulation method that allows reproducing the distribution of electric current density and electric potential in a synthetic resistivity profile, where cracks are introduced with specific length parameters and thickness, was developed. The simulation is based on a large rectangular grid of resistors that can be considered as a continuum medium. The electric currents and potential in the circuit is solved iteratively by applying the Kirchoff’s laws of electric circuits. In addition, small-scale experimental tests were performed in the laboratory using a high resolution geoelectric surveys in pots with real cracks. Synthetic and experimental data were processed by software investment DCIP2D (UBCGIF), which uses a method of least squares fit for the model apparent resistivity profile. The obtained results are used to define certain indexes indicating parameters of interest, such as depth, grosos and air volume of detected cracks.
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Characterization of an Iranian Aquifer in Terms of Suitability for Underground Gas Storage
Authors S. Bairamzadeh, S. Sona Naserian, E. Ghanaatpisheh and A. SafiarSeasonal variations in the natural gas consumption of Tehran and the steadily growing demand in the gas supply rate, require effective means for cold season’s peak shaving and balancing such variable trend of gas consumption. Underground storage of natural gas is considered as the most favorable solution to cope with this problem and vital to Iran's domestic and industrial energy supply. The goal of this study is to characterize an Iranian aquifer in terms of suitability for underground gas storage reservoirs by means of geophysical, petrophysical, geological and reservoir investigations. A 3D geological model, containing porosity property upscaled to 20 proportional layers has been built. The seismic interpretation was focused on the three following elements: PSTM (Post Stack Time Migration) output, Wells pseudo calibration, PSDM (Pre Stack Depth Migration) data-set and semblance cube. Finally, a reservoir numerical model considering the integrated available data was generated and calibrated by history matching with last results of performed Interference test. Based on the prevailing status of exploration and the results of the studies performed, it is concluded that the aquifer is suitable for storage of natural gas. This suitability is evidenced by the conclusive results of the performed geophysical, geological and reservoir investigations.
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Multi Sensor Soil Sensing Tool for Farmland in Spain
Authors F.M. van Egmond and R.L. KoomansIn the EU LIFE+ project ‘Crops for better soil’ the aim was to increase the (financial) yield of Spanish farmers on low-yielding rainfed soils and improve the soil itself by applying several agronomic measures and by better understanding the soil itself. Medusa Explorations and Universidad Politécnica de Madrid (UPM) were responsible for soil monitoring and acquiring soil information. To this purpose Medusa developed an efficient and effective soil sensing system (gamma-ray and GPR) on a 4x4 car to be able to measure >100 fields, 300 ha throughout the north of Spain in 3 weeks. The sensing data was combined with open data (DEM, geology) and soil sampling results (by UPM) to acquire information about soil texture, soil organic matter, tillage layer depth, compaction, altitude, slope, nutrients. This provided a good understanding of the soils and is a powerful communication tool for farmers and agronomists.
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An Algorithm for the Adaptive Optimization of ERT Measurements
Authors K. Tsakirrbaloglou, P. Tsourlos, G. Vargemezis and G. TsokasIn this work we propose an algorithm for producing adaptive optimized geoelectrical protocols related to the time lapse monitoring. The optimization method is based on the direct use of the Jacobian matrix as a metric for selecting the optimized data sets. The algorithm was developed into the Matlab environment and was tested with synthetic data. The tests showed that the method is effective and seems to produce improved results. The method is fast and it does not require the calculation of the resolution matrix and thus it can be applied effectively in real-time. The algorithm was also applied into a field example demonstrating its applicability in practice.
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Multivariate Statistical Analysis - An Alternative Method to Time Lapse Inversion Process for Electrical Tomography
Authors J. Riss, S. Xu and C. SirieixA method based on a multivariate analysis coupling principal component analysis (PCA) and hierarchical ascendant clustering (HCA) is proposed to interpret electrical images acquired during long surveying The method is an alternative to the time lapse process. The method was applied to 21 electrical models results from ERT carried out in the vicinity of the Lascaux Cave during two years. In this paper we focus our attention on the characterization of a particular zone we guess it participates to the feeding zone of the flow rate in the cave. The electrical behavior of the feeding zone and its surrounding areas let us assume a progressive weathering of the geological formation with decreasing resistivity, increasing permeability going far from the feeding zone to the feeding zone.
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Magnetic Investigation and 2½ D Gravity Profile Modelling across the Beattie Magnetic Anomaly in the Southeastern Karoo
More LessThe southeastern Karoo Basin is considered to be one of the most prospective area for shale gas exploration in South Africa. The basin has several igneous intrusions and an interesting magnetic anomaly, the Beattie magnetic anomaly (BMA) is seen on the magnetic map of South Africa crossing the basin in a NE-SW direction. To date, the source of the BMA and interconnectivity of the igneous intrusions are not well understood. In this study, we investigate the interconnectivity of the igneous intrusions and possible location of the source of the BMA using magnetic and gravity methods. The gravity model results showed that the igneous intrusions are interconnected at depth, which probably pose threat by increasing the risk of fracking the Karoo for shale gas exploration. The modelling result reveals that the BMA tends to divide into two anomalies and continue to trend in an NE-SW direction. The anomaly become stronger and or broader with depth which could be an indication that the source(s) is deep, possibly a buried magnetic body in the basement. The average depth to the top of the shallow and deep magnetic sources was estimated to be approximately 0.6 km and 15 km, respectively.
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New ERT Arrays to Increase the Depth of Detectability
Authors S. Szalai, A. Novák, K. Szokoli and E. NadasiDepth of investigation (DOI) has always been in the focus of geoelectric measurements. The DOI of the different DC arrays can be an important question, especially when the survey should be performed in built-up areas where space is limited. A lot of definitions exist about the DOI thanks to its significant role in geoelectric investigations. The authors of this study consider important the definition based on the detectability of small-size inhomogeneities. Thus, the so-called depths of detectability (DD) values were calculated of the different arrays. The newly investigated 11n arrays were compared with the traditional arrays and they gave consequently higher DD values than the pole-dipole and dipole axial arrays. This is very promising for the future, mainly because 11n arrays can get useful information in less time than the traditional ones. It is also conceivable that these arrays have better imaging properties, because the high DD value usually indicates this feature. A dyke and a square prism model was the inputs for the forward modelling, both having resistive and conductive variants.
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Time and Spectral Multiresolution Remote Sensing for the Study of Ancient Wall Drawings at San Salvatore Hypogeum, Italy
Authors L. Piroddi, G. Ranieri, M. Cogoni, A. Trogu and F. LoddoHistoric and prehistoric sites are often a serious challenge for geophysical techniques, which could give enhanced and essential information to define identity and health of cultural heritage assets. Multispectral remote sensing techniques have been applied to ancient wall pictures of a hypogeum actually under a rural church in San Salvatore (Italy). Multispectral survey was jointly done with state of art surveying for historic architecture and was compared with a 40s’ photographic survey. This integration has been the way to fully explore and exploit the signs present in wall drawings evidences of hypogeum frequentations. Adopting multiresolution approach for the construction of scientific datasets and maintaining full dimensionality for their evaluation and interpretation, jointly with some synoptic images, allowed us to build a user friendly Decision Support System potentially used by authorities assigned to the conservation, restoration and management of ancient heritage goods. In this case study, the informative layering showed to be a very effective method to find cross-information present in different surveys data, which are essential for planning restoration activities but also for dissemination and fruition of cultural heritage sites. The application of applied geophysics techniques to cultural heritage and artistic targets proved to be a disciplinary strategic application field.
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