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Near Surface Geoscience 2015 - 21st European Meeting of Environmental and Engineering Geophysics
- Conference date: September 6-10, 2015
- Location: Turin, Italy
- Published: 06 September 2015
1 - 50 of 164 results
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A Multidisciplinary Hydrogeophysical Approach Applied to the Chalk Aquifer Using MRS (North of France)
More LessFor several years LaSalle Beauvais has regularly carried out hydrogeological and hydrogeophysical measurements in order to characterize the chalk aquifer in the vicinity of Beauvais (Picardie, France), in terms of geometry, behavior and development (Zouhri and Lutz, 2010). A multidisciplinary approach has been chosen: piezometric and meteorological measurements, near surface geophysics measurements (electrical resistivity tomography, seismic refraction…), logging (gamma-ray, water conductivity, temperature), and since June 2014: Magnetic Resonance Sounding. The main hydrogeophysical results obtained on the experimental site of LaSalle Beauvais are displayed in order to show how geophysics methods can improve the hydrogeological knowledge. We insist in particular on the results of Magnetic Resonance Soundings. This method, little used in France because of its susceptibility to electromagnetic noise, allows us to estimate the water content, the permeability and the transmissivity. All of these results, which will be complemented by pumping tests and water samples study in the future, will be of great interest for the water management in the Beauvais area.
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Density Estimation Using Muon Imaging
Authors L.A. Preston, N.D. Bonal, D.J. Dorsey, D. Schwellenbach, W. Dreesen and J.A. GreenSummaryMuons are subatomic particles capable of penetrating the earth’s crust several kilometers. Muons have been used to image the Pyramid of Khafre of Giza, various volcanoes, and smaller targets like cargo. For objects like a volcano, the detector is placed at the volcano’s base and muon fluxes for paths through the volcano are recorded for many days to weeks.
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Geophysical Imaging at the U.S. Critical Zone Observatories
Authors W.S. Holbrook, B. Carr, J. St. Clair and J. HayesSummaryOver the past two years, the Wyoming Center for Environmental Hydrology and Geophysics (WyCEHG) has imaged the subsurface at five CZO’s: Calhoun, Boulder Creek, Eel River, Reynolds Creek, and Southern Sierra. Techniques applied include seismic refraction, electrical resistivity, downhole logging, ground-penetrating radar, magnetic gradiometry, EMI, and surface NMR. We will present results from these sites.
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Advances in the Application of Thermal Logging Techniques for Hydro-physical Characterization of Flow through Fractured Rock
More LessSummaryThe use of thermal techniques for identifying groundwater flow in fractured rock is experiencing a revitalization as a result of both advances in sensors and synergistic developments of other technologies. Multiple sensors with resolution approaching 0.001 C8 are combined to measure an orientated temperature field in the thermal vector probe (TVP).
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Chargeability from Airborne TDEM Data - Model Studies and Field Examples
More LessSummaryElectrical chargeability has been observed in time-domain EM data for many years, but mostly as a curiosity or considered to be interference, rather than a useful geophysical measurement.
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Spectral Analysis and Correlation of Ambient Seismic Noise. The Case Study of Madonna del Sasso (NW Italy)
Authors C. Colombero, L. Baillet, C. Comina, A. Helmstetter, D. Jongmans, E. Larose, J. Valentin and S. VinciguerraSummaryAmbient vibrations recorded on potentially-unstable rock slopes show that the temporal variations in the spectral content and in the correlation of seismic noise can be related to both reversible and irreversible changes within the rock mass. In this work, we analyzed the seismic recordings acquired at the potentiallyunstable granitic cliff of Madonna del Sasso (NW Italy) from October 2013 to November 2014.
The spectral content of noise systematically highlighted clear energy peaks at specific frequencies on the most unstable sector, interpreted as resonant frequencies of the investigated volume. Horizontal ground motion at the fundamental frequency was moreover found to be orthogonal to the main fractures observed at the site and consequently parallel to the potential direction of collapse. Cross-correlation was computed between the recordings of the sensors placed in the prone-to-fall compartment and a stable reference station.
Both the temporal variations of the resonant frequencies and the results of cross-correlation showed seasonal reversible variations related to temperature fluctuations. No irreversible changes, resulting from damage processes within the rock mass, were detected during the monitored period.
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Microseismic Monitoring of an Unstable Rock Face - Preliminary Signal Classification
Authors D. Arosio, L. Zanzi, L. Longoni and M. PapiniSummaryWe analyse signals collected by a microseismic monitoring network installed on an unstable rock face threatening the city of Lecco, in the North of Italy. We propose a classification process based on parameters computed in both time and frequency domains able to identify events possibly related to microseismic activity within the unstable rock mass and discard unwanted signals caused by meteorological conditions or other sources of noise. Our classification routine seems to be robust and the preliminary outcomes are in agreement with the findings reported in previous studies. We believe that further investigations together with the integration with a localization process of the significant microseismic events will improve our approach.
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Seismic and Resistivity Monitoring of Pont Bourquin Landslide in Switzerland
Authors S.R Carrière, G. Bièvre, E. Larose, D. Jongmans, T. Lebourg, L. Baron and M. JaboyedoffSummaryLandslides are natural and complex phenomena which can be encountered all over the world. They affect all types of geological formations and present a large variety of size, morphology and displacements rates. Among these phenomena, landslides in clay-rich formations are particularly complex due to the still unpredictable acceleration and fluidization that characterize them. In order to better understand this solid-fluid transition, the Pont Bourquin landslide in Switzerland has been continuously monitored with at least two vertical seismic sensors since the beginning of 2010, and 36 electrodes since the beginning of 2014 to assess the resistivity changes at different locations of the landslide. Relative velocities changes processed from ambient noise correlation show seasonal fluctuations between −2 and +2 % along the years. Only one drop of more than 7% was observed in summer 2010 preceding a major earthflow, showing that daily dV/V processing could be used as a precursor signal for landslide activation. Resistivity measurements show that certain parts of the landslide undergo strong electrical changes for which the causes are not yet determined. Because of the structural complexity of the landslide, further studies are requested to better understand the coupling between geophysical soil properties and environmental parameters.
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Role of Fracturing on Seismic Noise Measurements - The Case of the Bory Crater (La Réunion Island)
Authors P. Bottelin, J. Valentin, D. Jongmans, L. Baillet, F. Donze, O. Brenguier and A. MangeneySummaryIn recent years, ambient seismic noise measurements have significantly developed in gravitational hazard assessment for both investigation and monitoring purposes. The wide frequency range allows ambient vibrations to be applied for investigating geological and civil engineering structures in a great variety of sizes, from the lithospheric or crust scale to a few m-thick landslide and rock column or buildings. On landslide sites, several studies revealed significant spectral amplification at given frequency and polarization of the wave-field in the direction of maximum slope displacement. They show that different characteristics (resonant frequencies, polarization, and spectral amplification) could be used from the spectral analysis of the ambient motion or from spectral ratios for characterizing landslides.
This study aims to study a prone-to-fall column located at the top of a basaltic cliff in the Bory Crater (Réunion Island). Seismic prospecting profiles were performed on the plateau to characterize the basaltic lava deposits and the ambient seismic noise was measured using 3C sensors located on the column and at several distances from the cliff. The studied showed a clear resonance effect due to the column vibration, as well as larger site effect which could be related to the fracturing in the Bory crater.
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On the Use of ERT and AEM Resistivities for a Tunnel Pre-investigation
Authors S. Bazin, H. Anschütz, A.K. Lysdahl, J. Scheibz and A. A. PfaffhuberSummaryWe have investigated the applicability of resistivity derived either from surface electrical resistivity tomography (ERT) or airborne electromagnetic (AEM) surveys to a tunnel pre-investigation. We have exploited resistivity models to map the extent of toxic black shale along a tunnel alignment in central Norway. The resistivity models acquired before excavation and supported by laboratory measurements enabled us to map geological layers that are in agreement with the rock types subsequently observed from drillings and geological logging during tunneling. Our results highlight the potential of AEM surveys for such tunnel pre-investigations.
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A Study of Misfit Topography towards Waveform Inversion for Prediction Ahead of Underground Tunnel
Authors L.T. Nguyen and T. NestorovicSummaryThis work presents a synthetic study of misfit topography towards identification of geological structure ahead of the underground tunnel by waveform inversion. Simulation of viscoelastic waves is performed by the spectral element method implemented in SPECFEM2D package. By modeling a simple 2-dimensional underground tunnel model with a dip geological interface ahead of the tunnel face, we construct the misfit error landscapes with respect to geometric parameters defining the dip layer interface. As a result it is found that the misfit topography is very multimodal and therefore finding the true model by waveform inversion is likely to be very challenging. However, the choice of misfit definition, for example by using the envelope misfit, can help ease the toughness of misfit topography and facilitate the inversion task.
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Statistical Soil Type Estimation Based on Cross-plots of S-wave Velocity and Resistivity in Japanese Levees
Authors K. Hayashi, T. Inazaki, K. Kitao and T. KitaSummarySoil type of levee body and foundation are statistically estimated using cross-plots of S-wave velocity (Vs) and resistivity in Japanese levees. The Vs and the resistivity are collected from surface wave methods and resistivity methods. Total survey line length of the geophysical methods is about 600 km on 37 rivers in Japan. The blow counts and soil types are collected from about 400 boring logs carried out on geophysical survey lines. Vs and resistivity at the depth of the blow counts were extracted from geophysical sections. The total number of extracted data is about 4000. The data is grouped in levee body and foundation. A polynomial approximation was used to estimate the soil type from Vs and resistivity. Coefficients of equations are optimized by a least squares method. Accuracy of estimation was statistically evaluated by comparing estimated and actual soil parameters. Soil type sections were calculated from Vs and resistivity sections using the polynomial approximations.
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Ambiesta Dam - Geophysical Survey to Define the Cracks Patterns inside the Structure
Authors A. Masera, D. Donnaruma and D. MilaniSummaryThe paper describes the investigation using sonic tomography, performed on the Ambiesta dam (Italy) and aimed to characterize and identify the concrete cracking patterns inside the dam body, starting from the surevy of cracks visible on the downstream face.
The investigation had to define the depth of the cracks patterns and define the concrete caractheristics in the area affected by the cracks compared to healthy areas or free from cracks.
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GPR Assessment of Columns in the Pavilions and the Church of the Modernista Building Sant Pau Hospital, in Barcelona
Authors S. Santos-Assunçao, R. Gonzalez-Drigo and V. Perez GraciaSummaryThe work presents a case study applied to the analysis of columns in cultural heritage. The GPR assessment of columns in three different places of a Modernista set of buildings allows determining the differences in constructive solutions. The study of the church denotes that the columns are masonry structures with four metallic reinforcements along the shaft. The analysis carried out in the pavilions highlights differences between two types of masonry columns: some of them are built with regular arrangement of bricks and seem to be solid structures; others have a metallic pipe (a rain drainage tube) in the centre of the structure, and the inner elements are most likely portions of bricks with a shape similar to a triangles.
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Photogrammetry and 3-D Ultrasonic Tomography to Estimate the Integrity of Two Sculptures of the Egyptian Museum of Turin
Authors L. Sambuelli, G. Böhm, C. Colombero and A. FilipelloSummaryWe present a fruitful combination of geophysical tests (Ultrasonic Measurements) and photogrammetric processing (Structure from Motion) for the analysis of the integrity of a couple of statues from the Egyptian Museum of Turin. Aim of the study was to investigate the persistence of the exterior widespread fractures within the sculptures. More than one hundred ultrasonic measurements were acquired on selected travel-paths across each statue, using an ultrasonic pulse velocity instrument. Dealing with complex-shape objects of restrained dimensions, it was very important to accurately define the three-dimensional coordinates of sources and receivers, in order to precisely measure their distances. A 3-D model of the statues was obtained from photogrammetric techniques. The acquired data were analyzed with both a statistical approach and tomographic processing, comparing the use of classical and staggered grids, in order to obtain the best fit of the local resolution. The final results revealed a valuable tool to guide the procedures for the mobilization, transport and restoration of the sculptures.
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High Resolution Geophysical and Topographical Surveys for the Characterisation of Fumane Cave Prehistoric Site, Italy
Authors M. Obradovic, N. Abu Zeid, S. Bignardi, M. Bolognesi, M. Peresani, P. Russo and G. SantaratoSummarySmall scale prehistoric archaeological sites, such as the Fumane cave, located north of Verona city in north Italy, poses a lot of challenges both to archaeologists and geophysicists. The cave is considered as one of the most important Middle and upper Prehistoric sites of Europe, discovered in 1884. It contains a well-preserved and impressive stratigraphic sequence of more than 12m thick where human activity remains are accumulated. In this work, we applied high resolution geoelectrical resistivity tomography and seismic passive geophysical methods to investigate, on one hand, the electrical properties of the shallowest part of the deposit, where, a number of medium to low resistivity anomalies were localised. On the other, a test using microtremors provide evidences on the probable maximum thickness of the deposit (4–5 m). In addition a high resolution and georeferenced laser scanner survey was carried out so as to have an high resolution topographic model that shall be used as a container to allocate in 3D the position of the already achieved findings as well as the geophysical results. This shall constitute the first step for the planning of a smart protocol for results conservation and dissemination both for cultural and scientific interests.
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Archaeogeophysical Experiments in the Large Scale Laboratory
Authors F. Perciante, L. Capozzoli, V. Giampaolo, R. Luongo and E. RizzoSummaryThe ArchaeoGeophysical techniques are based on the investigation of buried cultural structures and surrounding materials in the archaeological framework. Unfortunately, the geophysical contrast between archaeological features and surrounding soils sometimes are difficult to define due to problems of sensitivity and resolution both related on the characteristic of the subsoil and the geophysical methods. An archaeological experimental activity has been performed in the Hydrogeosite laboratory, a full large scale controlled site consisting on a pool shape structures of 230m3 where archaeological remains have been installed. The laboratory experiment was performed to assess of the capability of EM geophysical techniques to detect archaeological remains placed in the humid/saturated subsoil. The archaeological test site was characterized by remains of Roman times (walls, tombs, roads, harbour, etc.) covered by sediments. In order to simulate lacustrine and wetland condition and to simulate extreme events (for example underwater landslide, fast natural erosion coast, etc.) the phreatic level was varied and various acquisitions for the different scenarios were performed. The integration of electric and electromagnetic data in that conditions allowed us to overcome the limits of each technique in terms of resolution and depth. Moreover, the experiment highlight the uncertainties related on the interpretation of geophysical analysis.
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Quality Assurance of Jet Grouting Columns Using Seismic Methods
Authors E. Niederleithinger, J.C. Galindo Guerreros, S. Mackens and T. FechnerSummarySealing and strengthening of the subsoil by injection is a major issue in the field of geotechnical engineering. This involves also jet grouting, which allows creating columns of grouted soil by eroding and mixing the in-situ soil with a thin cement suspension. A general difficulty of this method is to predict the column diameter and its material strength. Here, we present two-dimensional finite-difference numerical simulation results of a promising non-destructive quality assurance testing tool to evaluate the diameter of jet grout columns. This approach incorporates crosshole and downhole seismic measurements. Preliminary tests showed that this tool is applicable under real site conditions.
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Sensitivity of Seismo-electric Waveforms and Electric Noise to Electrode Configuration
Authors M.S. Devi, D.R. Dietrich and D. R. GaramboisSummaryThe seismo-electric exploration method aims to analyse the electromagnetic signals generated when seismic waves excite, and then propagate through a fluid-filled porous or fractured medium. Seismo-electric signals are obtained by firing a seismic source and recording the resulting electric fields. Such experiments usually allow one to detect the dominant contributions of the seismo-electric response, namely the electric signature of seismic surface waves and guided waves propagating in the near surface. Of more interest are the electromagnetic waves generated at depth when seismic waves cross an interface. These signals are much more difficult to discern due to their very weak amplitudes and because of the ubiquitous man-made electric noise that dominates the records. As a workaround, we investigate here the possibilities offered by multi-electrode arrays to enhance the EM interface response and mitigate the power line noise at the same time.
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Drones — New Technologies for Geophysics?
Authors A. D’Alessandro, F. Bucalo, M. Coltelli and R. MartoranaSummaryDrones, also referred as Unmanned Aircraft Systems (UAS), Unmanned Aerial Vehicles (UAV) or Remotely Piloted Aircraft (RPA), are aircraft without pilot on board. USA is today the leading country in the field of UAS but recently, seven European countries have pledged to launch joint programs for drones, with the aim of producing the next generation of UAS before 2020. According to some studies on the potential market of UAS in Europe, the geoscience sector is definitely one of the most promising. In this paper, we bring a short description and classification of drones, according to their sized and shaped, with particular attention to the advantages and drawbacks of each type in reference to the possible employment in geosciences applications. Currently the drones are used for geological and topographic mapping, coastal control, landslide inspections, etc., and are capable to integrate geophysical sensors like magnetic, electromagnetic, infrared, radar, natural gamma ray sensors and etc.
UAS technology have several advantage over conventional airborne geophysics like resolution, accurancy, cost, etc. We are witnessing the birth of a new branch of aviation, which could be profitably applied to geophysics measurements.
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The Use of Mathematical Models in the Control Environment of Underground Gas Storage
SummaryThe operation of underground gas storages may be accompanied by deterioration of the technical condition of wells. This is due primarily to the variables of temperature and pressure loads of the element in the wellbore during injection and extraction of gas, which most from the earth’s surface and to a depth of 500–700 m. Under the influence of these factors disrupted the adhesion of cement to casing and formation, occur the leakage of columns, gas leakage from the wellbore, the accumulation of gas behind the columns and headers, behind-the-casing flows from the storage reservoir into the overlying sediments. All this results in considerable industrial gas accumulations, the complication safe operation of UGS and disturbance of the ecological situation in the area. Therefore, the development of the technology search wells — sources of technogenesis, elimination of leaks and cross-flows of gas in them is an urgent task for underground gas storage. The work deals with the identification of cross-flows in the wells of underground gas storages. We consider mathematical models and algorithms for identifying cross-flows according to the thermometer wells. Examples of the interpretation and processing of data, previous studies of wells, underground gas storage.
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Fast Multi-channel Data Transfer System for Ultrasonic Borehole Tools and Others
By T. RadicSummaryReliable and high resolution information about the current state of radioactive waste repositories and their casing can only be gained on site with borehole tools. Ultrasonic sensors are such a tool, making it possible to characterise the surrounding ground (salt, clay, granite) by measuring the elapsed times of high frequency seismic signals. The arising data must be transmitted to an above ground or to a subterranean observation point. There, the data (mostly still analogue signals) are collected, plotted and quantitative evaluated. The quality of the transmitted analogue signal is, however, reduced through, amongst others, the excitation signal (which is usually transmitted through analogue means). This problem becomes more severe as the distance of transfer increases. We are currently developing a digital data transfer system, which will span a distance of up to 2 km. This system allows 7 analogue signals, with a bandwidth of 250 kHz each, to be transmitted within a single optical fibre at the same time. The same single fibre is used in the opposite direction to remote control gain settings and others. Further areas of use lie where rapidly changing analogue signals must be transmitted in real time over large distances.
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Comparison of Different Acquisition Patterns for 2D Tomographic Resistivity Surveys
Authors R. Martorana, P. Capizzi, A. D’Alessandro and D. LuzioSummaryA systematic comparison is presented between some 2D resistivity models and their images by the inversion of synthetic datasets relating to three different arrays, suitable for multichannel data acquisitions (dipole-dipole (DD), Wenner-Schlumberger (WS) and multiple gradient (MG)). The goal is to study how the measurement errors affects the resolution of the tomographic models and the ability to retrieve correct information on buried targets. We considered different data acquisition patterns, gradually increasing the complexity of the combinations of potential spacing and dipolar distance. To this end we increased the number of current dipoles to obtain approximately the same amount of measures, increasing the investigation time. Results from noise-free and noisy data are discussed and compared with those from field data. The results show that: the quality of the inversion models, for a fixed noise level, depends significantly on the data acquisition pattern; the information recovery and the resolution, being equal the number of measurements, is overall better for WS and worse for DD; the decrease of sensitivity with depth is lower for particular acquisition patterns that allow to better resolve deeper targets; the MG array can be preferred because it provides comparable results, using a smaller number of current electrodes.
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Site Investigation of Twin Tunnels by Joint Application of Seismic and Engineering Geophysical Soundings (CPTe)
Authors É.B. Bujdosó, E.H. Hegedűs, A.C.K. Kovács, I.T. Török, R.C. Csabafi and J.S. StickelSummaryThe near-surface geophysical data have become key components in the development of the engineering of major underground structures. Geological and Geophysical Institute of Hungary (GGI of Hungary) carried out a detailed geophysical survey along the twin tunnels of a new Metro line in Budapest, Hungary. Following the tunnel boring activity several sinkholes were detected at the surface along the path of the twin tunnels. GGI of Hungary carried out engineering geophysical soundings (CPTe) and non-invasive seismic technologies (3D seismic tomography) in order to mitigate the potential risk of any material damages in the future. The aim was to get to know the physical parameters of the soil layers. The joint application of the two methods was able to detect the known and the hidden potential sinkholes using state-of-the-art technology.
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MASW 2D Seismic Survey in Urban Areas - The Case of the Turin Metro 1 Line
Authors C. Alessio, R. Crova, E. Duò and M. NaldiSummaryThe present article discuss the results of seismic investigation conducted in Turin, Italy, to assess the geological and geotechnical modeling related to the planned extension of the underground Metro Line 1 from Collegno to Cascine Vica (about 4 km of length, from Collegno to Cascine Vica). The specific objectives were to map the thickness of the man-made ground lying upon alluvial soil made of gravel and sand and evaluate the stiffness property of the subsoil. To overcome the typical obstacles of the urban ambient (electromagnetic and vibrational noise, hard traffic management, high energy source required) we applied the shallow wave technique with a continuous profiling (MASW 2D) by means of a customized system of geophones array on a land streamer and a controlled source of energy mounted on a vehicle. The surveys were performed overnight in two sessions (two days), with a fast data acquisition for a total length 2000 m. The results of the survey, calibrated with boreholes positioned all along the survey line, has precisely mapped the contact between the shallow reworked ground and the alluvial deposits. Moreover, the survey results have highlighted many lenses of cemented gravel (conglomerate bodies) inside the alluvial deposits.
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Geophysics and Tunneling - The How and the Why - A Focus on the Why
Authors L. Sambuelli, P. Fargione, E. De Cillis and M. PatruccoSummaryTunnels should be constructed, maintained and used without neglecting the basic principia of Occupational Safety and Health (OS&H), environmental protection and economic efficiency: this involves a Prevention through Design approach both from the very first steps of the project, and during the tunneling operations. At the purpose, the identification and careful evaluation of a number of parameters are essential for a correct Risk Assessment and Management (RAM) during the various phases of the analysis. However, many of these parameters are “hidden into the mountain” and difficult to identify with the desired detail. This problem can affect the quality of the result, and cause accidents and work stoppages, with consequent dramatic economic losses.
In the Authors’ opinion, only a multidisciplinary approach can contribute to solve the problem. The already consolidated contribution of geophysics plays an important role, and represents an efficient means for a more efficient definition of the design parameters. Future developments in the research work in geophysics are advisable and precious for a more efficient predictive RAM, both at the preliminary phase, and during the tunneling operations, particularly if a fast response will become achievable.
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Geophysical Time-lapse Monitoring of Leachate Recirculation in a Bioreactor Landfill
Authors A. Arato, G. Cappato, F. Manfredi, M. Fischetti, E. Perissinotto and A. GodioSummaryThis work deals with the time-lapse geoelectrical monitoring of leachate re-circulation inside a municipal solid waste landfill. The studied landfill is exploited as an anaerobic bioreactor, and leachate is recirculated in order to maintain constant and high moisture content within the waste. The goal of leachate injection is to ensure optimal conditions for the anaerobic bacteria to rapidly degrade the organic fraction of the waste. The main objective of this study is to evaluate the electrical behavior of the wastes, for estimating the moisture content dynamics during time.
Electrical resistivity tomography (ERT) and self potential (SP) methods have been applied both on surface electrodes installed on the top of the landfill and along borehole which have been installed for cross-hole measurements.
Both the methods helped in locating the zones affected by the leachate flow, but ERT measurements suffered from anomalous long-term polarization phenomena. On the other hand, SP measurements were in good accordance with the injected leachate volumes, and they can be useful for helping numerical modeling of the leachate flow within the waste mass.
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Investigation Concrete Quality of Zigana and Torul Tunnels by Using GPR Method
Authors I. Saricicek and A. SerenSummaryThe GPR method which can display the shallow depth of the investigated surface with high reslution, is a widely- used method to investigate the concrete structure without any damage. In this study it is aim to investigate the leaking water risk areas and accordingly the evaluation of the content of the concrete structure of the Zigana Tunnel which located on the highway of Trabzon-Gümüshane and faracture-joint system, deterioration and stratigraphy of the Torul Tunnel walls. During examinations, GPR data were collected along totally 20 profiles at the entrance of the both sides of tunnels by using 500 MHz and 800 MHz shielded antennas. After applying essential data processing stages to the collected data, 2D and 3D images with ReflexW3DScan software were acquired. When analyzed amplitude-slice maps at various depths into the wall from these images; while has impaired in places of concrete structures in belonging to the Zigana Tunnel, those obtained from the Torul tunnel have been identified quite durable and high quality of concrete internal structure.
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Integrated Geophysical Investigations for Calcione Dam Safety Evaluation
Authors V. Giampaolo, L. Capozzoli, A. Caputi, C. Corradini, G. Zucco, T. Moramarco and E. RizzoSummaryAn integrated geophysical field investigations have been carried out at the Calcione earthen dam near Lucignano town (Arezzo, Italy), for the purpose of better understanding the hydrogeological conditions at the site. In winter 2002, the Calcione dam embankment has been affected by some landslides and a gabions drainage system was installed to mitigate the phenomena. Therefore, the purpose of the geophysical investigation has been to identify the presence of eventually seepage areas through the embankment materials and provide information about subsurface water circulation. These tasks have been accomplished through the use of self-potentials (SP), electrical resistivity tomography (ERT) and ground penetrating radar (GPR). The results obtained allowed to identify an area of interest in correspondence of the central area of the dam above the installed gabions drainage system. Moreover, future efforts will focus on an integrated hydro geophysical interpretation, where geophysical data will be directly incorporated into the dynamic estimation of hydrogeological parameters.
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S-wave Velocity Monitoring During an Artificial Rainfall Experiment Using Large Scale Rainfall Simulator
Authors C. Konishi, T. Ishizawa, T. Danjo and N. SakaiSummaryWe conduct the rainfall experiment using a large scale rainfall simulator and an artificial embankment consists of sand and silt in order to evaluate S-wave velocity monitoring for a prediction of a slope failure. The intensity of the rainfall is controlled to maintain 15 to 200 mm/hour for a certain time frame. S-wave velocity cross sections are acquired by MASW survey before, during, and after the controlled rainfall. The obtained cross sections show little change in the S-wave velocity and that is considered to reflect water filtration process in subsurface. The difference is not so significant, but it is confirmed by both waveforms and the dispersion curves calculated from common shot gathers at a fixed shot point. The dispersion curves are included various higher modes and that makes it difficult to evaluate the result; however, the complex higher mode would be useful to derive more information in the future. Compared to the resistivity monitoring, the S-wave velocity monitoring is not so sensitive to the water content; instead, it is relatively easy to be obtained by surface wave method. Therefore, it will be an effective monitoring tool to assess vulnerability of slopes and mitigate damage by natural disasters.
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Electrical Resistivity Tomography in Support of Geological Surveys of Landslides Involving Clay Slopes in Asti Reliefs
Authors D. Barbero, M.G. Forno, M. Naldi and A. TissoniSummaryWe report on the results of geological, geotechnical and geophysical surveys for the characterization of a landslide, occurred in the Asti Reliefs (NW Italy) during the first ten days of March 2011, just after an exceptional meteoric event. The investigated landslide is located in San Damiano d’Asti (15 km E of Asti) and involved a hilly side, gently sloping. The hazard situation in this area regards a landslide that involved the back of a building. This landslide was caused by excavations made in the time at the toe of the slope with the aim to extend the narrow flat spaces. The contribution given by Electrical Resistivity Tomography (ERT) was essential, in the first phase of the investigation, to recognize deep and localized water seepage, otherwise undetectable. The identification of saturated clays into the slope allowed us to design the correct re-profiling of the scarps and make digging operations in safely. The use of these methods of investigation has a significant economic savings in the choice of interventions for slope stabilization.
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Landslide Geophysical Imaging - Kapušany Landslide Case Study
Authors R. Putiska, I. Dostál, D. Kušnirák and M. BednárikSummaryGeophysical survey is very useful and popular tool used by engineering geologists to examine landslides. We present a case study from the Kapušany landslide, eastern Slovakia, where a broad spectrum of geophysical methods were applied on several profiles in order to compare the ability of the methods to detect as many landslide’s structural features as possible. The 2D Electrical Resistivity Tomography inverse model was capable to define the geological structure of the landslide and to define the shear zone, however the resolution of the inverse model does not allows us to identify cracks or other minor landslide’s features. These, however, were nicely recorded in the results of Dipole Electromagnetic Profiling and Self Potential method. In addition microgravity was employed to validate the results obtained from electrical methods and afterwards a final geological model, based on the integrated interpretation of all involved methods was constructed. This model will serve as a reference model for long term landslide monitoring using modern geophysical and engineering geological approaches.
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Detection of Landslide Plane by Using Refraction Seismic Tomography Method
More LessSummaryAn application of refraction tomographic method in order to identify a predicted landslide’s plane is presented. This method is applied to detect the existence and the geometry of possible landslide’s plane that is situated in a Seling Village, Kebumen City — Indonesia. This area experienced several episodes of landslide type of creeping several years ago. Although it has been observed that the displacement of the most upper part of surface is only several centimeters per years, but there is a tendency that bigger landslide could be occurred in the future.
The seismic data was acquired on the surface that has a total length of about 150 m. Twelve shots and 24 geophones are planted on the seismic line that is perpendicular to the predicted strike of landslide’s plane.
The result shows that the most upper part of surface has low P-wave velocity values. Higher P-wave velocity layer is situated below this layer. The plane between those layers is then interpreted as possible landslide’s plane. The result of this investigation is a P-wave velocity section, which correlates well with almost all available a priori data. Several resolution tests are conducted in order to increase the certainty degree of tomographic results.
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Geotechnical Risk Assessment at South Eastern Suburb of Cairo, Egypt Using Integrated Geophysical Techniques
Authors N.I. Medhat, M. Atya, E.A. Ragab, A. Ali and M. AbdelzaherSummaryThe reason for implementation of this research is the prevalent of incidences of structural damage around the area of investigation causing large number of casualties and loose of souls.
The location of the district is very close to the quarry blasting operations that can intensely produce stresses in the ground due to continuous artificial explosions and ultimately result in the instability of the area.
Geophysical reconnaissance surveys using seismic refraction, electrical resistivity and ground penetrating radar were carried out to measure near surface structure setting and follow up its activity upon time by delineating the major fault and other minor features such as cracks, fissures and water saturated zone.
Integration of the geophysical data shows that the main reason of fractures in the study area is the swelling of marly clay layer due to retention of the drainage water. Also, there is a near surface major fault cuts the southern part of the study area causing variation in thickness of the marly clay layer and consequently affect on the inhabitant buildings.
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Estimation of Alluvial Sediments Properties with a Multilevel Cluster Analyses of Spectral Induced Polarization Data
Authors S. Inzoli, M. Giudici and J.A. HuismanSummaryIn order to infer the sedimentological properties of saturated samples of alluvial deposits, a cluster analysis is applied on spectral induced polarization data (amplitude and phase resistivity spectra). The hierarchical tree of clusters is dissected and analyzed at different aggregation levels, comparing the electrical and sedimentological intra-cluster variability. A low number of clusters densely populated guarantees a perfect allocation into cluster on the base of a few electrical parameters but permits to obtain only a rough textural characterization of the sample, while increasing the number of clusters yields to reduce the variability intervals of the textural parameters and of the chemical properties of the saturation water within each cluster, thus reducing the uncertainty in their estimation. An excessively large number of clusters is ineffective since the uncertainly in the assignment of a sample to a specific cluster is too high. These results can be used as an indirect tool for sediments characterization and have been successfully tested on an independent sample. The cluster analysis allowed to use the whole spectral information to establish a link between geological and geophysical parameters, avoiding the use of one-to-one correlations, whose validity has not yet been confirmed for natural unconsolidated materials.
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Using Borehole NMR Data to Determine the Effective Porosity of Sediment for Groundwater Resource Estimation, Australia
Authors K.P. Tan, K.L. Lawrie, J. Abraham and R.S. BrodieSummaryEstimating groundwater storage volumes is important for assessing the potential capacity and recovery efficiencies of Managed Aquifer Recharge (MAR) strategies. However such volume estimates are vexed by poor characterisation of factors such as the effective porosity of the aquifer. These issues were faced by the Broken Hill Managed Aquifer Recharge (BHMAR) project which aimed to define key groundwater resources and aquifer storage options in the lower Darling River floodplain of western New South Wales, Australia. The aim of this study is to determine if the NMR free-water data depicts the effective porosity of the sediment and could be used in a workflow to estimate groundwater storage volumes in the target aquifer. 26 sonic drilled bores were logged using the Vista Clara Javelin system. An investigation ensued to validate these NMR results. This included examination of the NMR data processing parameters and optimal regularization factor, additional matric potential and gravimetric water experiments to determine the fractional water and total porosities of sediment. The laboratory experiments showed comparable results to the NMR free-water and total water for sand and muddy sand, but the NMR underestimated the total water in mud.
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Monitoring of Injection of Hydrogen Release Compounds in a Contaminated Site
Authors A. Arato, S. Fiore, B. Ruffino, A. Godio, M.C. Zanetti and C. RoatiSummaryWe present the set-up and results of a pilot-scale field test concerning the remediation of a site polluted by chlorinated solvents. The hydogeological setting is mainly compound by a first aquifer in silty and sandy material and a second fissured aquifer made of fractured grey marl and gypsum/sulphur formations. A preliminary characterisation of the area have pointed out the groundwater contamination by chlorinated solvents, at a depth of about 15–20 m b.g.l. Vinyl chloride was identified as the secondary pollutant, proving the occurrence of natural degradation phenomena. Hydrogen Release Compound (HRC-X, Regenesis) was selected to support the on-site biological activity. In a selected test site, we injected about 250 kg of reagent in three injection points at the depth of about 15–18 m.
The chemical and physical monitoring of the clean up activity was performed for about 6 month after the injection by groundwater sampling in the three observation boreholes (downstream with respect the injection points) and by time lapse cross-hole resistivity tomography.
The enhancement of natural attenuation phenomena is testified by the decrease of halogenated pollutants with higher number of chlorines, and by an enhancement of the amount of the reductive dechlorination secondary products.
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Detecting Contaminants in Aquifers through Modeling of Surface-downhole Geoelectrical Data
Authors M.V. Bongiovanni, V. Grünhut and A.M. OsellaSummaryMost of the world’s reservoirs are currently in the advanced primary or secondary recovery stage. Even though sinks wells used by oil companies are located much deeper than aquifers, they may eventually cause environmental damages contaminating the water with brine leakage, oil spill or other polluting agent. This is why it is extremely important to do vulnerability studies.
Since contaminants have different electrical conductivity than water, geoelectrical methods can be useful to detect and even monitor flow evolution of the contamination plume.
We want to analyze if it is possible to detect contaminations of an aquifer that lies above an oil reservoir, approximately at 300 m depth, with current injections on surface and voltages sensors in a well. In order to achieve this we have designed an electrical model of the reservoir including the contaminated aquifer with, either a conductive contamination such as saline brine or a resistive contamination such as oil spill, and numerically simulated the forward geoelectrical responses.
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High Amplitude SP Anomalies in Mountains of Electrokinetic Origin
Authors V.A. Shevnin, A.A. Ryjov and D.A. KvonSummaryIn different countries after 1967 were discovered local self potential anomalies above 1200 mV that didn’t related with redox processes in rocks. Such anomalies were found in mountains, they had inverse correlation with relief, and underground water had low mineralization and high electrical resistivity. Possible cause of these anomalies can be electrokinetic or streaming potentials due to water filtration. Calculation of electric field intensity on Helmholtz formula shows that these anomalies could appear at water resistivity above 100 Ohmm at filtration in loose sand-gravel- soil.
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Electrical Geophysical Monitoring of Organic Waste Contamination
Authors D. Ntarlagiannis, J. Robinson, P. Kirmizakis, P. Soupios and L.D. SlaterSummaryOlive oil production in the Mediterranean area is a major industry, with significant impact in the economy of producer countries. During the production of extra virgin olive oil, a substantial amount of waste is produced and is improperly disposed. since no regulation for the environmental deposition of olive oil mill waste exists. Thus, there is an urgent need for the development of methods that will allow efficient monitor waste management processes, and enable rapid recognition of environmental degradation incidents.
The most common disposal practice involves unrestricted damping of the olive oil mill waste in open evaporation ponds, leading to significant degradation of the environment including groundwater and surface waters. Geophysical methods could be used to monitor olive oil waste management processes, and identify olive oil waste plumes right at their inception times. We applied a series of electrical geophysical measurements at an olive oil mill waste (OOMW) site in western Crete to test their applicability as monitoring aids. Our results suggest that electrical methods are very efficient in accurately delineating young OOMW plumes due to their conductive signature.
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Modeling of Electromagnetic Soundings to Detect Groundwater Contamination by Intensive Livestock Farming
Authors C.M. Sainato, R.A. Espada, B.N. Losinno and J.J. Márquez MolinaSummaryThe feedlots, farms for feeding animals in corrals, are spreading at Buenos Aires Province, Argentina. It is important to evaluate the contamination by mineralization of organic matter. Geophysical exploratory methods give an important tool for monitoring groundwater and soil quality. The objective of this work was to perform electromagnetic soundings and to do a modeling of these data by an inversion procedure for different frequencies at a corral of a feedlot and the surroundings. The survey was repeated the following year. Bellow the corral, the unsaturated zone has lower resistivity (between 8 and 17 ohm m, more conductive) than the test zone. The second year, the test zone showed greater range of values for resistivity (up to 54 ohm m) but the layers bellow the corral showed an important decrease of resistivity. Groundwater samples were taken along four years. An increase of water conductivity was found at the lower well along the time.
The EMI modelling allowed characterizing the distribution of resistivity bellow the corral and the background, reaching the groundwater, detecting an increase of salinity bellow the corral which may be mainly due to leaching of nitrates.
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TEM Profile Using Fixed-loop Array in the Paraná Basin, Brazil: Preliminary Results
Authors J.D.R. Campana, J.L. Porsani and C.A. BortolozoSummaryIn this work the authors shows preliminary results of TEM profile by using fixed transmitter loop and a 3D coil receiver mobile in the Paraná sedimentary basin, Brazil. The objectives were to map the sedimentary and crystalline aquifers. The sedimentary aquifer is characterized by Adamantina Formation and the crystalline aquifer is characterized by fractures zones inside of the basalt layers of the Serra Geral Formation. 1D inversion results for component-Z for each sounding are presented as an interpolated geoelectric profile of 1000m long. Two low resistivity zones were observed: the first between 40 – 60m depth, being related probably to the Adamantina Formation (sedimentary aquifer), and the second between 150m and 300m depth, being interpreted as a probable fractured zone filled with water inside of the basalt layer of the Serra Geral Formation (crystalline aquifer). These results are in accordance with the local geological information.
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Electric and Electromagnetic Investigation of a Karst System
Authors M.P. Miensopust, J. Igel, T. Günther, R. Dlugosch and S. HupferSummaryThe limestone of the western flank of the Innerste Mulde in Lower Saxony, Germany, host a 27 km long karst water system which is surface-mapped by sinkhole and collapse structures. The karst water emerges at springs — one of them is a spring called Kirschensoog near the village of Altwallmoden which only temporarily yields water. From early March to mid March 2015 the water level fell visibly. During that time electric and electromagnetic methods were applied in the field and soil and rock samples were taken for laboratory studies. Field measurements comprise electrical resistivity tomography (ERT), ground penetrating radar (GPR) and 2D nuclear magnetic resonance (NMR) surveys. The laboratory measurements (e.g. NMR and spectral induced polarisation measurements, petrophysical studies, dielectric spectroscopy) are applied to support the interpretation of the field data. The preliminary results show that the covering, clay-rich soil has a strong attenuation restricting the investigation depth of GPR. The ERT models indicate a 3D subsurface structure and — as well as GPR — suggest dipping structures possibly related to the bedding of the limestone or fissures/ fractures. The rather low resistivity of the limestone might be an indication of disruption and presence of fluids.
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Seasonal Monitoring of Saline Intrusion in an Unconfined Coastal Aquifer in New Zealand Using DC Resistivity Traversing
More LessSummaryLong term time-lapse DC resistivity measurements along six 155 to 275 meter long traverses at the Kapiti Coast in New Zealand have been made to image a seasonal cycle in the saline interface movement. Two-monthly repetition of the measurements showed a continuous decrease of the bulk resistivity at depth and over an extended horizontal area when coming into the drier summer season. This observation is somewhat contradictory to the expectations and has its origin most possibly in a decrease of the fluid resistivity, likely due to a lower fresh water flow coupled with saltwater intrusion. Although, the changes from time step to time step are not always major on all profiles, ERT time-lapse monitoring proved itself a suitable tool to image the saline interface shape and movement along with changes in the subsurface resistivity distribution in an unconfined coastal sand aquifer and in a seasonal time frame.
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Prestack Depth Migration of Ultrashallow Seismic Data. A Critical Analysis
Authors G.P. Deidda, G. Satta, E. Battaglia, C. Strobbia and Z. HeilmannSummaryPSDM is increasingly becoming rule rather than exception in near surface seismic imaging when the goal is to get detailed sub-surface images and accurate velocity field. PSDM produces the seismic image of an earth model in depth converting the seismic reflection data into a depth section by means of a velocity field. Although different implementations of velocity model building tools exist, they usually start with an estimation of an initial velocity model using moveouts in the time domain and proceed with an iterative model refinement using residual moveouts in the depth domain and seismic reflection tomography. In addition, if available, a priori velocity/depth information, is also considered to improve the accuracy of the velocity model. In shallow seismic reflection imaging, instead, refraction tomography has been used not only to improve the velocity model built with PSDM but also as the exclusive tool to build the velocity model. In our tests, building a velocity model by means of a priori information unrelated with the recorded data or by means of the exclusive use of refraction tomography, PSDM produces depth images that have an imprint of the velocity models and not a result coming only from seismic reflection data.
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Groundwater Storage in a Karst Vadose Zone Evidenced Using Gravimetric and Surface-to-borehole ERT Monitoring Systems
Authors A. Watlet, O. Kaufmann, O. Francis and M. Van CampSummaryHydrogeophysical tools allow characterizing the heterogeneity of karsts and evidencing groundwater storage in their subsurface. A permanent gravimetric monitoring highlights seasonal variations in gravity that can be related to vadose zone effects after the discrimination of the saturated zone signature with direct measurements. A surface ERT monitoring improved with daily borehole-to-surface measurements through the vadose zone allows identifying preferential flow paths. Groundwater storage variation is then monitored by time-lapse inversion of the ERT datasets.
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Assessing Electrical Resistivity Tomography for Hydrofacies Detection Using a Sensitivity Dependent Probabilistic Method
Authors T. Hermans and J. IrvingSummaryAlluvial aquifers are generally composed of several facies with complex architectures and interconnections depending on the fluvial system. In this context, electrical resistivity tomography (ERT) may provide important information on the spatial distribution of hydrogeological parameters. However, ERT inversion introduces some bias in the resulting resistivity distribution due to regularization and resolution issues. In this study, we refine ERT inversions by incorporating prior information in order to improve the identification of facies through a probabilistic relationship derived from collocated measurements. We then analyze with synthetic cases the effect of spatially varying sensitivity on the probabilistic relationship. As expected, when sensitivity decreases, the distributions of resistivity for the different facies tend to be superimposed. A mean distribution thus overestimates the ability of surface ERT to discriminate hydrofacies in depth.
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Integration of Geoelectrical Imaging and Hydrochemistry Data in a Coastal Aquifer in India
Authors P.R. Pujari, R. Sanam, C. Padmakar and P. LabhasetwarSummaryGroundwater is a vital source of drinking water on earth. The quality of groundwater is under increasing stress due to various anthropogenic stresses. The impact of ash ponds has been a major concern and is a subject of research. The present study seeks to assess the impact of an ash pond on the near sub-surface through Resistivity and IP imaging survey. The Resistivity and IP imaging data has been acquired on profiles close to the ash pond and at some far off locations. Groundwater and surface water samples have been collected from the ash pond and also from the wells in and around the ash pond. The study indicates very low resistivity formations in the near sub surface at location close to the ash pond as compared to the profile approximately 1 km away from the pond. The water chemistry data from the monitoring wells indicates very high Total Dissolved Solids (8658 mg/L) and chloride (1402 mg/L).
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Ground Penetrating Radar Applications in Seismic Microzonation
Authors S. Santos-Assunçao, V. Perez-Gracia, R. González-Drigo, V. Salinas and O. CasellesSummaryThe work presents a methodology that combines a first GPR survey and a subsequent measurement of seismic ambient noise vibration. The GPR signal characteristics used in this analysis are two: the amplitude of the background noise in the A-scans, and the frequency content of the received signal. The background noise could be consequence of three main sources: clutter as consequence of external reflections, electronic noise and energy randomly scattered in the medium. The first source could be identify in the GPR B-scans and usually produce anomalies similar to those caused by reflections in the targets inside the medium. The second source produce a continuous noise in the A-scans characterized because the average value is approximately constant. The third source introduces noise in the A-scans but its amplitude depends on the randomly backscattered energy. As consequence, the amplitude of this noise could be used in order to identify sudden changes in the shallow geology, always depending on the grain size distribution. The frequency content depends strongly on the water content. The analysis of the spectrum, combined with the analysis of the B-scans and the backscattering noise in the A-scans could be used in order to locate active subterranean streams.
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