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24th European Meeting of Environmental and Engineering Geophysics
- Conference date: September 9-12, 2018
- Location: Porto, Portugal
- Published: 09 September 2018
1 - 100 of 203 results
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Modern Electro-prospecting Technologies for Searching and Exploration of Ore Deposits
By S. ZaytsevSummaryThe emergence and widespread introduction of computer technologies and satellite navigation systems into various industries has led to the emergence of a new class of compact high-precision geophysical equipment. There has been a qualitative improvement of existing technologies and the emergence of completely new geophysical techniques. New directions in ground-based electrical prospecting are associated with the development of audio-magnetotelluric sounding (AMT), magnetovariance techniques (MVS, HMT), electrical resistivity tomography (ERT), spectral induced polarization (SIP), etc.
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Influence of the Ground Surface Relief on the Results of Electrical Tomography
More LessSummaryThe Soviet geophysics S.G. Komarov and L.P. Gorbenko first noticed to the problem of the influence of ground surface relief on the distribution of electric field. The main features of the electric field anomalies, which arise on the relief were clear already then. It was found that anomalies of apparent resistivity of the minimum type arise over a positive relief forms due to a decrease of the current density, and anomalies of the maximum type arise over negative forms of relief due to an increase in the current density ( Chanturishvili, 1983 ). At the moment, the electrical tomography has a complicated situation during observations in conditions of complex Earth’s surface relief. There are several commercial inversion programs ( Loke, 1997–2000 ; Günther at al., 2017 ; Kaminsky, 2016 ; ERTLab Solver, 2017; Zonge, 1997 ) and a small number of academic programs ( De-Bao Lu at al., 2015 ; Jian-ke Qiang at al., 2013; Erdogan at al., 2008; Pidlisecky at al., 2007 , Marchenko, 1999) available to a wide range of geophysicists. However, none of these programs is open, although these programs are often successfully used in practice. Therefore, there always arises the question of the degree of reliability of those calculations that we obtain using one or another inversion code. So, it should always be remembered that the construction of the result geoelectric section is usually obtained through solving a direct problem.
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Sunnyside Deposit: A Calibration Site for Airborne EM Systems
Authors A. Viezzoli, A. Menghini, G. Selfe and V. KaminskySummaryThe Sunnyside deposit is a part of the Selebi-Phikwe nickel mine (Botswana), which has a resource of 68 Mt at 0.8% Ni and 0.88% Cu ( Figure 1 ). It is small, but has some high grade intersections of up to 2.3% Ni and 1.12% Cu over 1 m. The nickel belt has been flown by several airborne EM systems including GeoTEM, Spectrem, VTEM, SkyTEM and XCite. Albidon (Pty) Ltd started the airborne surveys in 2008 by flying VTEM system. African Nickel Limited followed, having flown a Spectrem survey in late 2012, which was succeded by a SkyTEM survey in early 2013. At the same time, moving loop ground EM survey was carried out, and then in early 2014 two AMT surveys were performed. The sulphide body was drilled extensively to a depth of 200 m, but little deep drilling has taken place. In May 2016 NRG offered to fly Sunnyside with their new Xcite heli-EM system, as a test survey. The possibility to compare a generous selection of AEM systems, makes the Sunnyside deposit a defacto test site for airborne EM in southern Africa.
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Possibility of Distributed Acoustic Sensing (DAS) for Geophysical Problems Solution
By A. ShuvalovSummaryIn systems based on fiber-optic sensors, an optical fiber can serve as both a medium for transmitting information and a sensitive element. The DAS (Distributed Acoustic Sensing) technology deploys optical fiber as a sensor for measuring acoustic effects with high spatial resolution over entire length of receiving system. The range of application of this technology is very wide and includes the protection of perimeters of long objects, monitoring of roads and railways, monitoring of the pipelines condition, dams and other complex and highly sensitive engineering structures, microseismic monitoring, hydraulic fracturing monitoring, permanent monitoring of deposits, etc. The technology of distributed acoustic sounding for vertical seismic profiling (VSP) was applied relatively recently ( Mestayer et al., 2011 ; Mateeva et al., 2014 ).
Compared to classic borehole tools based on geophones, the fiber optic distributed measuring system is much lower in price, provides real time seismic data acquisition over the entire length of the well and limits operational risks, as it requires a one-time setup for all subsequent observations ( Barfoot, 2013 ).
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Different Scale Complex Airborne Geophysical Survey In the Central African Ridge Area
By E. MoilanenSummaryAirborne geophysical survey was started by 12th of October 2016 in Rwanda. EQUATOR ( fig. 1 ) technology ( Felix et al., 2014 , Karshakov et al., 2017 ) was used. A survey was fully completed by 12th of April 2017. A survey at a scale 1:50 000 and infill works was completed on a square of 26 000 km2. Total survey volume is 57 718 line km. About half of the survey time was in the rain season. And half of the survey area are situated in the rough terrain conditions. Average productivity of airborne geophysical survey is 9620 line km per month. Detailed characteristics of EQUATOR system are described by Karshakov et al. (2017) .
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Complex of Geophysical Methods During the Survey of the Underwater Diapir Volcano of the Taman Peninsula
Authors A.V. Kozlova, D.A. Korshunov and T.S. KlapyshevaSummaryMud volcanoes could be found almost everywhere on the areas with sediments thickness about the first kilometres. Their forms are conical structures with a truncated vertex. The vertex has crater, outer slopes could be strongly indented by radially diverging ravines. Cone’s form changes depending on the consistence of the erupting mud: if it is liquefied the cone is low with smooth slops, if consistence is viscous it leads to high cone formation with steep slopes. The mud volcanoes eruptions are accompanied by fire arising from spontaneous combustion of gases exhaled from the vents.
The main factors causing the possibility of occurring of mud volcanism: existence of tectonically dislocated intensely fractured clay rocks which are able to deliqate, confined groundwater and underground gas accumulation. The main principle of mud volcanism lies in the exhalation of combustible gases coming to the surface along weakened zones, blending gas flow with clayey breccia, which is liquefied by confined groundwater and mud mixture effusion to the surface ( Rakhmanov, 1987 ; Kholodov, 2012 , Mironuk, 2014 ).
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Assessment of the State of Stability of a Road Tunnel on the Basis of Data from a Multilevel Seismic Survey
Authors V. Pisetsky, A. Zudilin and S. ChevdarSummaryThe presented report discusses the results of a survey of the technical condition of the unfinished construction of a road tunnel on the object: Bashkortostan - a new exit from the city of Ufa to the federal highway M-5 “Ural” (Eastern exit).
The purpose of the work was to study the engineering geological and hydrogeological conditions within the zone of interaction of the enclosing mountain massif and all previously executed parts and tunnel elements to obtain the initial data necessary to verify the compliance of the design documentation and to assess the possibility of their further use during the continuation of construction and future accident-free operation or the need for their replacement, restoration, repair and reinforcement. Note that to date, along the route of the future tunnel from the beginning of construction (2001), three parallel galleries from the western portal have been traversed for a distance of about 900 m. Up to the design position of the eastern portal, about 200 m have been drilled. The side of the tunnel is partly finished by finishing, the rest - temporary.
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Engineering-Geological Conditions for Construction of Highways in the Cryolithozone
Authors I. Abaturova, I. Koroleva, I. Savintsev, L. Storozhenko and I. KovyazinSummaryAt the present time the expanses of Yakutia are becoming more and more active. This is due to the exploration and exploitation of deposits located in hard-to-reach places. Intensification of the development of natural resources has necessitated the construction of highways, paved in the most complex engineering and geological conditions. Underreporting, which will entail incorrect choice of design solutions, million construction costs and as a result the inability to operate is often the only transport route.
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Multiple, Concurrent GPR Data Acquisition - The WARR Machine
Authors Nectaria Diamanti and A. Peter AnnanSummaryGPR WARR (wide angle reflection and refraction) and the closely related CMP (common-mid-point) soundings have been a standard survey method since GPR first existed. Earliest efforts demonstrated the variation in ice sheet velocity versus depth. While a valuable survey method, the technique has seen little adoption.
Unlike seismic, commercial GPR systems with multiple concurrent data acquisition receivers have not existed. Multiple offset GPR data had to be acquired using a single transmitting and receiving antenna pair moved to the desired offset sequentially. With the recent advances in GPR timing and control technology, modern instrumentation with multiple concurrent sampling receivers enables continuous, rapid acquisition of WARR data. Two dimensional reflection surveys (i.e., simple, common offset profiles in the past) can now rapidly yield a multi-offset sounding at each recording station, providing WARR profiling at the same speed as a standard, single fold GPR sounding.
We have recently developed the first embodiment of a GPR WARR system called the WARR machine. We have dealt with design and implementation challenges as well as the concomitant issues of dealing with large volumes of WARR data. The key conclusions derived from the initial in-field deployments are that the approach is now viable, timing stability in distributed units is sufficiently reliable for multi-channel data to be merged, and that standardized work flow coupled to data processing is essential for the method to see broad adoption.
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Application of the Small-Loop TDEM Method to the Quantification of Both Electrical and Magnetic Parameters of the Subsurface (Numerical Approach)
Authors Cécile Finco, Cyril Schamper and Fayçal RejibaSummaryThe inductive electromagnetic geophysical method in the temporal domain (TDEM) allows, in certain conditions, the measurement of a signal integrating information from several physical independent parameters (electrical resistivity, magnetic viscosity, polarization). Being able to separate and quantify those physical and independent contributions is a real issue. It is particularly important when one of those contributions overwhelms the others which can happen depending on the geological context and the specific setup used.
The non-conventional use of this method with small transmission and reception loops (a few meters wide at most for the transmitter loop) increases the sensitivity to the magnetic viscosity in addition to the usual electrical resistivity. Through numerical modeling and field tests, we are designing a setup geometry that would allow us to discriminate between the influences of these parameters on the signal. The most promising option would be to make a measurement in the central configuration, which is very sensitive to the magnetic viscosity, and another one with an offset between the two loops as the sensitivity to the magnetic properties decreases with the distance separating the transmission and reception loops.
This use of small loops also increases the sensitivity to the noise from the system itself. The interactions between the reception and transmission loops and the measurement device create a distortion on the measured signal. This distortion depends on the setup geometry and on the electrical characteristics of the ground. Current work concerns the study of equivalent electrical circuits to model the mutual characteristic and complex impedance between both the transmitter and receiver coils of the TDEM setup. The accurate evaluation of the mutual impedance over a wide band of frequency is necessary to deconvoluate the instrumental response (including all electronic and coils parts) from the part of the measured transient signal coming from the subsurface.
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Sediment Volume Search Sonar
Authors Tom E. Blanford, Daniel C. Brown, Shawn F. Johnson and Cale F. BrownsteadSummaryThe Sediment Volume Search Sonar is a sensor whose goal is to improve buried unexploded ordinance (UXO) detection and classification performance through the design, build and demonstration of a sonar system that is deployed from a shallow-draft surface vessel. This sonar system produces a novel form of three-dimensional synthetic aperture sonar (SAS) imagery of surficial and buried UXO across a range of environments. The sensor is particularly suited for use in water depths less than 3 meters, and it provides sufficient detection and classification performance against objects of interest in water less than 5 meters depth.
The sensor’s hardware design was based in part upon data created in a modeling and simulation collaboration with the Applied Physics Laboratory at the University of Washington. This collaboration produced synthetic sensor data where the sensor/environment/target space could be modified to explore the expected operating conditions. The simulated data were also used to adapt a set of existing signal processing algorithms for formation of three-dimensional acoustic imagery.
Recently, the sediment volume search sonar has been integrated to a shallow-water surface craft, and experiments have been conducted at a trial site in the Foster Joseph Sayers Reservoir near Howard, PA. This test site has been prepared with several buried man-made objects. Results will be presented showing the use of the sensor for detecting and localizing these objects.
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Integrating Multiple Geophysical Methods to Understand Groundwater Storage and Discharge in Tropical Proglacial Catchments
Authors Robin Glas, Laura Lautz, Jeff McKenzie, Rob Moucha and Bryan MarkSummaryThe Cordillera Blanca in Northwestern Peru is home to a quarter of the world’s tropical glaciers, where hydrologic regimes are rapidly changing due to warming- induced glacier recession. Proglacial alpine meadows are storing a significant portion of annual basin discharge, and buffer dry season low flows as glaciers continue to lose their influence on the regional hydrologic cycle. We used integrated seismic (refraction, H/V passive seismic) and electrical (2D ERT and 1D soundings) in conjunction with borehole data to characterize the nature of proglacial talus aquifers in alpine meadows at elevations above 3500 masl. The meadow subsurface exhibits a transition from relatively slow (400–800 m/s) to fast (∼2500 m/s) seismic p-wave velocity at depths of 4 to 8m, coinciding with the top of a composite layer of buried talus boulders, according to borehole data. Artesian pressure head in piezometers screened at the boulders indicate the presence of an aquifer confined by clay sediments. Resistivity profiles suggest that the upper most portions of the buried talus deposit are infilled with saturated clay, which dissipates with depth where sediments become more electrically resistive. Passive seismic and 1D electrical soundings suggest that total sediment thickness extends deeper than 20 m, allowing for first estimates of talus aquifer storage volumes and groundwater residence times. Based on the results from this study, we present a refined conceptual model of talus aquifers, from their formation to hydrologic function. Throughout the Cordillera Blanca, buried talus aquifers have the potential to store between 7 and 20% of annual basin discharge, which will allow for future predictions of dry season base flow for the region’s principal river.
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Variability of Electrical Conductivity and Water Content in a Soil under Irrigation in the Pampean Region, Argentina
Authors C.M. Sainato, M.S. Iseas and J.J. Márquez MolinaSummaryThe complementary irrigation in the Pampean Region of Argentina may result in a deterioration of soil properties, such as sodification and salinization. It is important then to evaluate soil water content to decide the sheet of water to be applied. The aim was to study the distribution of electrical conductivity (EC) and water content, using electromagnetic soundings to evaluate the effect of irrigation on the soil. Two areas of a lot with corn were studied: one which had been irrigated since 2011 (1) and another one without irrigation (2). Volumetric water content (VWC) was measured with TDR (Time domain reflectometry) in transects along the areas. The geostatistical variograms were estimated for ECa and VWC. The range of correlation of ECa for Area 1 is approximately 8–9 m, while for Area 2 is almost 12 m. The TDR variograms showed pure nugget effect except for two transects with a range of 5 m and 7 m. The periodicity in the series of moving average of ECa and VWC is very similar at the first part of the transects. The TDR measurements of volumetric water content followed the trend of conductivity being the variability greater in the area without irrigation.
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Electrical Resistivity Survey to Locate Buried Colonial Structures in the Santo Domingo’s Historic Complex, Panama
Authors M. Lezcano, A. Mojica, G. Arosemena, F. Durán, C. Ho, M. Llubes, L. Pastor, C. Camerlynck and F. RéjibaSummaryElectrical resistivity tomography is a powerful tool for investigating hispanic structures in the tropic. This technique of geophysical prospecting was developed in one of the most important ruins that are part of the archaeological site of Panama Viejo: Santo Domingo’s complex. The prospection was carried out in three zones with the aim to detect buried archaeological structures linked to church and the convent. In all zones, we detected a set of strong electrical anomalies at shallow depths associated with debris from walls and fallen roofs, and deeper we detected high electrical anomalies linked to walls, pebble floors, stone pillars and footing.
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A Multidisciplinary Study of Soils from the Sha’ar Ha-Golan (Israel) as a Method for Determining Ancient Human Activity
Authors S. Itkis and L. BityukovaSummaryThe multidisciplinary study of soils is an important tool in the investigation of archaeological sites. In order to investigate the relationships between magnetic susceptibility (κ) and geochemical characteristics of soil a detailed study of two areas in the Sha’ar Ha-Golan Prehistoric site was performed. Magnetic and self-potential surveys were carried out prior to soil sampling. Soil samples were collected along a 2 ×2 m grid within revealed geophysical anomalies. The content of ten oxides (SiO2, Al2O3, TiO2, Fe2O3, CaO, MgO, MnO, K2O, Na2O and P2O5) was determined by bulk silicate analysis by X-ray fluorescence method. The concentrations of 12 trace elements were measured by optical emission spectrography. For the study of the relationships between main chemical components and geophysical data we constructed maps and profiles geophysical and geochemical data distribution and applied correlation analysis. Comparison of κ and geochemical elements distributions along with correlation matrix analysis enabled us to reveal different correlation models in areas of ancient human activities in different archaeological periods. The complex study of magnetic properties and the specific chemical characteristics of the topsoil is an additional tool in the investigation of archaeological sites.
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Can magnetometry detect sediment-filled caves? The case study of the Sierra de Atapuerca Sites (Burgos, Spain)
Authors L. Bermejo, A.I. Ortega, J. Thiesson, J.M. Parés, R. Guérin, I. Campaña, J.M. Bermúdez de Castro and E. CarbonellSummaryThis work evaluates the potential of magnetometry to detect the inaccessible sediment-filled caves of the Sierra de Atapuerca karstic system. This karst consists of numerous caves filled with sediments that bear outstanding archaeo-paleontological remains from the Early and Middle Pleistocene. In order to find the continuity of the caves, the Sierra de Atapuerca sites have already been the target of ERT and GPR surveys, which have revealed their suitability for detecting different karstic features. Although our expectations were to find positive anomalies when crossing these filled conduits, the results showed a negative anomaly of the magnetic field where these sediments were expected. So far, the only explanation for this phenomenon is that these sediments were deposited in a reversed magnetic polarity period. This theory is supported by the fact that the Matuyama-Brunhes boundary is present in many of the studied caves.
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Digital Museum from Integrated 3D Aerial Photogrammetry, Laser Scanner and Geophysics Data
Authors G. Ranieri, A. Trogu, F. Loddo, L. Piroddi and M. CogoniSummaryThe hypogeum of San Salvatore di Sinis (Sardinia, Italy) is one of the oldest signs of the presence of the first Christians in Sardinia (IV century a.C.). Its walls are finely decorated with drawings from different periods, today strongly degraded. The present knowledge of the monument and of the site is not complete therefore, to check the presence of buried remains that could be related to the hypogeum, an extensive geophysical survey using ground penetrating radar (GPR), 3D ERT, seismic survey was carried out in the area around the church and inside it. The walls and floor of the hypogeum were also investigated. The results of the survey shown numerous buried structures in the surround of the hypogeum, furthermore some other voids are probably present near the hypogeum.
The data collected were used to implement a tool that can be utilized both to explore the subsoil and to see the lost drawings on walls as a virtual archaeology. The system also allows the musealization and the use by disabled people.
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Automatic ERT Monitoring System Installation at Crater Lake, Deception Island, Antarctica
Authors M. Farzamian, G. Vieira, F. Monteiro santos, B. Yaghoobi Tabar, C. Hauck, M. Catarina Paz, I. Bernando, M. Ramos and M.A. PabloSummaryAn automated-electrical resistivity tomography (A-ERT) with repeated measurements at 4-hour intervals was installed in the vicinity of air and ground temperature boreholes in the Crater Lake site at Deception Island in 2010 in order to study the dynamics of the active layer. All apparent resistivity raw data, collected during one year, were analyzed regarding daily and monthly resistivity changes and then compared to the spatiotemporal temperature variability. Preliminary investigation of apparent resistivity data reveals that the thawing and freezing sequences of the active layer can be well identified using the installed A-ERT monitoring system.
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Electrical Resistivity Tomography of Celtic Burial Mounds in Nonnweiler (Germany)
Authors O.S. Al-Saadi, V. Schmidt and P. LendleSummary2D and 3D electrical resistivity tomography (ERT) measurements have been applied for the investigation of Celtic burial mounds. The results show the general structure of the mounds and also indications of previous excavations. The archaeological interpretation of the result is complicated by the complex geological structure of the subsurface and the effect of trees, which also prohibit a regular electrode layout for 3D measurements. A reference measurement on undisturbed ground helps to assess the anomalies in the resistivity tomogram.
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Geophysics Applied in Precision Agriculture – Experimental Resistivity Studies for Plant Root Detection and Analysis
Authors A.G. Gerea and A.E. MihaiSummaryThe aim of this study is to conduct new experiments with higher precision and building new complementary equipment in which we can detect the plant roots extent with more accuracy, their behaviour in natural environments by carrying tests in both laboratory and agricultural fields. We’ve been able to create ERT (electrical resistivity tomography) with electrode arrays both classical and new experimental types, using flexible equipment created in the laboratory and Matlab programming. We’ve developed new test settings for the experiments in order to minimize the human errors and come up with high quality data and a more precise interpretation compared to previous studies on plant root detection using resistivity measurements.
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Parametric Study of GPR Signals Numerical Model to Analyze Hardened Concrete Response at Different Antenna Positions
Authors I. Rodríguez-Abad, J. Mené-Aparicio, R. Martínez-Sala and Y. BotellaSummaryThe purpose of this paper was to apply a numerical model of a 2 GHz central frequency antenna, to understand the behavior of the waves generated with a GPR, when concrete samples were under study at different antenna positions. The GPR numerical model was created based on the FDTD method and GprMax software was used to provide the 2D numerical modeling. Numerical modeling results and their further parametrical analysis were very clarifying. Arrival times, velocity increments and relative amplitudes presented a pattern according to what it was expected, when the antenna was separated from the concrete sample more than 8 cm. Nevertheless, when this distance was closer than 8 cm, due to the signals overlap the concrete reflection arrival times were altered. Despite that, the relative amplitudes for these distances did present an exponential behaviour, in agreement with what it was expected.
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GPR Prospecting of Fluvial-Eolian Interaction Deposits in the Bermejo Valley, NW Argentina
Authors P. Zabala Medina, N. Bonomo, A.M. Osella, S. Salvo Bernárdez and O. LimarinoSummaryIn this work we present results of a prospecting carried out with GPR and field observations, to determine the composition and geometrical characteristics of an eolic-fluvial interaction environment in Argentina. Three depositional subenvironments were defined and investigated: 1) eolian channel, 2) eolian interchannel and 3) muddy interchannel. In each of them, we acquired GPR data with antennas of different nominal frequencies in order to evaluate their resolutions and penetrations. From the GPR data sections, it was possible to identify numerous reflectors that were interpreted in terms of the field data. The applied methodology resulted very efficient for describing the complex deposits and provided relevant information for later constructing models for reservoir characterization.
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Analysis of GPR Response to Cavities Simulated in the Physical Experiments
More LessSummaryFull-scale physical experiment was conducted to investigate the GPR responses to roadbed cavities using 3-D GPR technique. The experiment employed the testing ground with sandy soil, simulating cavities with dome-shaped structure attributed to old damaged underground facilities such as water supply and sewer pipes made of cast-iron and hume concrete, respectively. The surface of the testing ground was not paved with asphalt concrete at the current stage of the experiments. The GPR responses were investigated using 2-D profile and 3-D volume data obtained with 250 MHz antennas, and with HH and VV antenna orientations. The results of the experiment have shown that the simulated cavities responded with typical hyperbolic shapes reflected from the isolated reflector sources in 2-D and 3-D perspectives. The different antenna orientations have shown the different areal extents of the hyperbolic reflections patterns from the cavities. 3-D GPR volume data has provided better information on the locations and shapes of the cavities in 3-D space. This study is an ongoing project of KIGAM at a second stage of the experiments. More realistic conditions of the road surface with asphalt pavement would be prepared in the testing ground for the next stage of the experiments.
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Automatic Detection of Reflections at Ancient Walls in Simple-Offset GPR Images by Using Cascade Classifiers
Authors P. Bordón, P. Martinelli and N.E. BonomoSummarySimple-offset GPR reflection methodology allows obtaining very precise information in archaeological/historical sites. However, as large amounts of data are usually acquired, their processing, analysis and interpretation can be extremely time-consuming.
In this work, we present three algorithms for the automatic detection of reflections at ancient walls in SO-GPR images, based on cascade classifiers and well-known image feature descriptors: Haar, HOG and LBP. These algorithms were implemented using supervised learning, and experimental data from previous works. The best performances corresponded to the descriptor Haar. With only two cascade stages, remarkably accurate results were attained despite the complex characteristics of the signals of the walls. Almost all of them were detected near their actual positions, and only a few false positive predictions were obtained, mostly without any continuity across the profiles.
The main advantage of these methodologies is that once an accurate and reliable algorithm is implemented using data from an appropriate sector, it can be applied in all the zones of the site with similar characteristics, or even in other site of the same type. Thereby, a precise representation of the target structures is rapidly obtained, and the qualified interpreter only has to examine some parts of particular profiles.
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GPR Survey in Outcropping of the Guarani Aquifer System, Paraná Sedimentary Basin, Brazil - Preliminary Results
Authors J.L. Porsani, J.V. Coutinho, B. Poluha and E. WendlandSummaryThis work shows preliminary results of GPR survey in the Ribeirão da Onça Basin areas, located in outcrops zones of Guarani Aquifer System, in the Parana Sedimentary Basin, São Paulo state, Brazil. Studies had as objective to characterize the subsurface, aiming to obtain saturated and unsaturated layer thickness and other hydrogeological characteristics. Preliminary GPR results obtained with 200 MHz antenna shows strong reflections corresponding to the groundwater level and a subsoil horizon which can be associated with transition from Cenozoic to Mezosoic sediments of the Botucatu Formation. The results are important to improve the understanding about geological characteristics of unsaturated layer, aquifer saturated zone definition, besides of contribute to scientifical improvement in hydrology areas and hydrogeology of outcrops zones of Guarani Aquifer System.
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Eigenimage Filtering on Sudoeksa Field Data to Reduce Clutters
More LessSummaryWe compare the background-removal and eigenimage-filtering techniques in the perspective of suppressing clutters while preserving horizontal subsurface target reflections.
The background-removal technique is a simple but powerful technique to remove laterally invariant clutters. Therefore, it is widely used in GPR image processing softwares. However, in case horizontal subsurface targets exist, the background-removal technique has the risk of damaging the target reflection events.
One of the alternatives to this background-removal technique is the highpass-eigenimage-filtering technique. In some literatures, the effectiveness of the eigenimage-filtering technique has been proven for synthetic data sets. In this study, we compare the eigenimage-filtering technique with the background-removal technique for the field data set acquired at the testbed in Sudeoksa, Korea, for which we already have the information of subsurface target materials and locations. Through this study, we show the effectiveness of the eigenimage-filtering technique in revealing the horizontal subsurface target image.
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Enhancing Stratigraphic and Structural Features in GPR Images of Limestone Karst through Adequate Data Processing
Authors W.E. Medeiros, J. Oliveira Jr., F. Santana, F. Bezerra and C. CazarinSummaryThe demand for detailed understanding of karst formation process in carbonate rocks occasioned an accompanied demand for high quality GPR images. It is necessary to characterize from the images primary strata and to identify fractures, faults, and dissolution features, as an stage to establish spatial and genetic associations among these elements. However, materials infilling karst voids or resulting from carbonate rock weathering might be conductive and, as a result, penetration depth and signal resolution might be greatly reduced due to attenuation. Considerable effort must then be done to improve the image resolution in karst through data processing. We present a GPR processing flow highly tested in the limestone karst environment of the Jandaíra Formation in Potiguar basin, Brazil, composed by the following main steps: static correction, dewow, background removal, spreading and exponential compensation gains, spectral balancing, Kirchhoff migration, band-pass filtering, topographic correction, and amplitude-volume enhancement. The spectral balancing step is of particular importance because, when judiciously applied, it can replace approximately the high frequency content lost by propagation effects. We also exemplify how image improvements obtained in 200 MHz datasets help the interpreter to better visualize the karst geometric elements, thus contributing to a deeper understanding of its formation process.
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A Newly Developed GPR Receiver
Authors P. Annan and N. DiamantiSummaryGround penetrating radar (GPR) signal capture has been a challenge since the method first appeared. The capture of radio frequency signals has required some specialized receiver design and overall more complex system architecture than visible to the normal GPR user. As the field of GPR is evolving and moves towards more quantitative data analysis, there is a need for users to better understand the signal capture process.
We provide a summary of the underpinning aspects of GPR signals and an overview of the principles that have been involved in time-domain signal capture. The capture of wideband transient signals requires considerable hardware ingenuity and the concepts are illustrated with presenting data acquired by an older and new receiver from the same location.
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Analysis of Random Backscattering in Ground-Penetrating Radar Signals to Detect Subterranean Watercourses - Field Results and Laboratory Tests
Authors V. Perez Gracia, Y. Rovira and S. Santos-AssunçaoSummaryThe studies of seismic risk in Barcelona city required nanozonation because measurements of soil response in the plain of Barcelona present sudden changes in small areas, highlighting the importance of a most detailed study to determine the nanozones. The problem lies in the high number of vibration measurement points needed for an appropriate nanozonation that made the analysis time consuming or even unfeasible. Therefore, a previous GPR survey was carried out in relevant zones of the city in order to determine abrupt changes that requires high density of passive seismic measurements. Some previous GPR studies underscore the relation between the noise at consequence of clutter in radar data and the random heterogeneities of the medium. In this paper, GPR is used to detect noise as consequence of clutter due to clusters of materials associated to subterranean streams and paleochannels. In addition, some laboratory test were carried out with the objective of comparing with field survey results.
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Determination of Environmental Vulnerability Using GPR Data
More LessSummaryPluvial floods as a harmful effect of the global climate change process may occur more and more frequently in urban areas. With determination of environmental vulnerability the vulnerability pillar of the impact assessment can be given. The environmental vulnerability depends on three factors: slope, water coverage and the drainage capacity of the earth. Since the drainage capacity of the surface water depends on the soil’s clay content, with a careful calibration of GPR survey the soil factor can be derived from the attenuation of EM waves. This study presents the determination process of environmental vulnerability and with a field example illustrates its applicability where the designation of vulnerable zones was done by using conventional method and the based on GPR survey as well. The field test showed that based on the attenuation of EM waves more precise and reliable vulnerability assessment can be carried out than with the conventional delineation method of the endangered areas.
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Study of Structural Elements in Heritage Buildings with Ground Penetrating Radar Images
Authors S. Santos-Assunçao and V. Perez-GraciaSummaryMaintenance and repairing or ancient buildings requires efforts and a wide knowledge of the structures. However, in many cases, the constructive methods, the distribution of supporting elements and the materials are unknown. There are two main causes of this uncertainty: the lack of information and drawings due to the age of the buildings, and the misinformation about past restorations, damages and alterations of use and structures. This paper presents a GPR assessment of two terraces of ancient buildings, placed in the Eixample neighbourhood of Barcelona city (Spain). Common offset radar data was used to acquire data on the terraces of the buildings, with an 800 MHz centre frequency antenna. In one case, GPR images show structural changes as consequence of rehabilitation. The other case study is characterized by significant variations in the built structural supporting structures, including orientation and material types. In both cases, GPR images allowed to determine the structural supporting structures. The results highlight the capability of the method to determine the position, orientation and shape of structural elements and, also, to differentiate between wooden and metallic members.
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Enhancing Crosshole GPR Data by Analysing Travel Time Differences of Reciprocal Tomographic Measurements
Authors S. Hellmann, P. Giertzuch, M. Grab, A. Bauder and H. MaurerSummaryCross-borehole radar (XBHR) systems have been employed successfully in recent decades in a broad range of geophysical applications from glaciology and hydrogeology to peatland gas development. Especially the high contrast between water and any other material and the high resolution of crosshole measurements allow a detailed investigation of the near subsurface.
During data acquisition the position of the antennas can only be controlled from the surface. While moving the antennas in their boreholes positioning uncertainties are unavoidable. We provide a straightforward algorithm to analyse and correct for depth increment errors by using reciprocal multi-offset gather measurements. Systematic travel time differences due to slightly incorrect depth registration, i.e. due to slip or cable tension while using a common trigger wheel can be analysed and a more realistic depth increment in terms of reciprocal travel times can be determined. Artefacts and velocity errors in the final data can be suppressed. Additionally due to technical reasons randomly occurring zero-time drifts have been investigated. Using a common zero-offset profile and the multi-offset gathers we show how to correct for zero-time drifts in each multi-offset gather individually.
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Development of Drone-Assisted Electromagnetic Prospecting System for Automobiles Buried by Landslides
Authors Y. Mitsuhata, T. Ueda, A. Kamimura, S. Kato, A. Takeuchi and C. AdumaSummaryWe have developed an electromagnetic prospecting system using a drone for searching for automobiles buried by a landslide. The system consists of an drone, an 1.6 m long electromagnetic (EM) sensor with a GPS receiver, an ultrasonic distance sensor for monitoring the height of EM sensor from the ground surface and a WiFi serial transceiver for controlling the EM sensor and monitoring the measured data. The drone suspends the EM sensor and EM data are acquired during the flight. The distance of drone-sensor separation is crucial to avoid EM noise caused from the drone motors and to stabilize the flight of drone On the basis of field experiments, we adopted a separation of 4 m and attached a vertical tail to the aft end of EM sensor witch can stabilize the flight at a speed of at least 2 m/s. The height of EM sensor should be monitored because it affects the EM data significantly. We have tested the system at an experiment site where there are two cars embedded at depths of 1.5 m and 3 m respectively. The close-area search clearly indicated the location of the shallow car, and there was a slight indication of the deep car.
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Electrical Soundings Applied to the Contamination at a Feedlot in Buenos Aires Province, Argentina
Authors C.M. Sainato, P. Zarragoicoechea and B.N. LosinnoSummaryThe cattle fattening in corrals (feedlot) is an activity that has expanded in the last years. These activities may contribute with contaminants to environment through waste water and manure, such as Nitrogen and Phosphorous, pathogens, between others. The aim was to identify and characterize physically, chemically and microbiologically the phreatic aquifer at a feedlot, at the zone of Saladillo, Bs. As. Province, Argentina. A topographic survey was carried out to describe the directions of superficial runoff and to locate the wells. Samples were taken for laboratory analysis. Electrical resistivity tomography was carried out to characterize the extent of the potential contamination. Near the corrals there is a decrease in the resistivity in unsaturated and saturated zone (NSZ, SZ). In the sense of groundwater flow and decreasing topography, an increase of EC of SZ is observed, associated with water salinization. The concentration of nitrates and phosphates increases in the sense of groundwater flow. The Pseudomonas and E coli, in some wells, added to the amount of detected coliforms, demonstrates the deterioration of the groundwater quality. The integration of geophysical survey allowed corroborating the extent of the salinization of the NSZ and SZ by the effect of leachate from the corrals.
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Analysis of Soil Gas and Their Correlation with Seismic Events along Indo-Burmese Subduction Zone
Authors R.C. Tiwari, S. Singh, H.P. Jaishi and R.P. TiwariDespite the fact that no strong earthquake (> M6) occurred during the investigation period in the region, some meaningful relationship between anomalies in radon/thoron concentration and seismic events have been found. It was observed that both soil radon and thoron data seems to be affected by variation in the meteorological parameters. During the investigation period there are two radon peaks (≥ +2SD) and these were correlated with the relevant seismic events. The so-called postquake reduction was observed for radon minimum value during the measuring period. It is interesting to note that most of the seismic events occurred along the Indo-Burmese arc during the investigation period (Fig. 2) suggesting significant disturbance between the plate tectonics along the Indo-Burmese subduction zone. It can be seen that continuous soil radon/thoron measurements at weekly intervals were not frequent enough to obtain a precise interpretation of the data. A long term database is needed for better results for which work is in progress.
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Preliminary Analysis of Strong Motion Data from Nepal Earthquake - An Input for Structural Designing
By M. DagarSummaryStrong ground motion records of an earthquake provide the basic information for evaluation of seismic hazard of an area in order to reduce the considerable loss to life and property. It is an important input for earthquake engineering for perfect designing practices so that the structures can withstand maximum possible shaking. Several earthquake characteristics are studied for qualitative evaluation of seismic hazard of an area. These cover characteristics such as Epicentral distance, Peak ground acceleration and site conditions. Analysing average spectral response on the basis of these characteristics shows three major factors such as strong ground motion source, path and site effects. Further, the comparison of average response spectra with existing BIS code shows the current Indian code is applicable for the entire country is well within the structural limits proposed for the seismic forces at all periods for alluvium sites. If the buildings are designed as per the norms given by the BIS (2002), then a considerable amount of loss in terms of life and property can be reduced.
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Effect of Heterogeneity on Estimation of Permeability Using Lattice Boltzmann
By S. RezaieSummaryIn this study, pore-scale simulation is carried out utilizing the lattice Boltzmann method by taking into account the direct effect of all pores. The smooth profile method [22] is employed for liquid-solid interaction in the pore-scale simulation of the dual porosity porous medium. In REV scale simulation, the effect of micro pores, after homogenization, is combined with the effect of larger pores. In addition to fluid flow simulation, the effects of micro-pore permeation are also examined on the main parameters governing fluid flow.
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2D and 3D Inverse Modeling of the Residual Gravity Field for a Buried Deposit Mass
More LessSummaryGravity surveys have been used in investigations of wide range of scales such as tectonic studies and mineral explorations and in engineering and environmental problems. Geometric shapes and especially prisms are useful in geophysics for modeling two and three dimensional (2D and 3D) underground bodies that produce gravity anomalies. Modeling in 2D and 3D are an important procedures enabling 2D and 3D information about mineralization to be leveraged for the computation or extraction of the key parameters. In this paper, we employ the inversion algorithm of Li and Oldenburg (1998) for 3D inverse modeling and a 2D nonlinear inversion method for a real gravity data set related to metal deposit from Iran.
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Magnetotelluric Responses in Layered Medium
Authors I.V.S. Chanakya and A. KumarSummaryMagnetotellurics, Electromagnetics, Modelling, Synthetic data
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Impact of Small Shear Wave Velocity Variations on Surface Wave Phase Velocity Inversion
Authors A. Wang, M. Le Feuvre, D. Leparoux and O. AbrahamSummarySurface wave methods have attracted a lot of geophysicists’ attention for the purpose of monitoring civil engineering structures, because they represent the most energetic part of the seismic signal, and contain information on shallow media. In order to infer the mechanical properties of the medium as a function of depth, an inverse procedure is required that minimizes a misfit function between observed and modeled data. However, a small change of model parameters can have low effects on observed surface waves data. This study focuses on the inversion of phase velocity dispersion curves of two-layer media with small to moderate variations of shear velocities. We use a simple two-layer model, where the shear velocity and thickness of the top layer are respectively 600 m/s and 8 m, and the shear velocity of bottom layer is 1100 m/s. Results show that it is difficult to distinguish inversion results when variation of shear velocity of the shallower layer is lower than 2%, and 10% for the deeper layer in our study case. These results emphasize the difficulty of estimating small to moderate evolution of medium, especially for deeper layers.
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Geophysics in the Prospecting Hydrogeological of Santiago
Authors J. Duarte, A. Pina, M. Cunha and F. FigueiredoSummaryThis work aims to be a further contribution to the numerous studies that have been carried out under the prospecting of groundwater in the Cape Verde archipelago ( Pina, 2009 ; Duarte, 2017 ). The application of the method has aimed to evaluate acquisition geometry in volcanic environments, to maximize and contribute to the geological, structural and hydrogeological interpretation of the area of research, and evaluation of the model of distribution of Resistivitys with lithologies distribution model (probing holes). The spatial distribution of the surveys was chosen in such a way as to coincide with the places where this drilling was effected. The work carried out was carried out in the locality of Ribeirão do Chiqueiro, the Santiago Island, where electromagnetic probes were performed 1D using the TEM-FAST. For visualization and interpretation of the geophysical models and the data of the subsurface surveys, they were integrated with high resolution aerial image.
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The Application of ANFIS in determining the Optimum Exploratory Boreholes Points by Using Exploratory Data
Authors M. Azizi, S. Nourbakhsh Bahreghani and A. MohammadiSummaryIn this research, the application of adaptive neuro-fuzzy inference system (ANFIS) was investigated in determining the optimum exploratory boreholes points, using exploratory data. The study area is Vertaveh iron deposit that is located in the south of Kashan and 8 kilometers away from south-east of Ghamsar city. The input layers to adaptive neuro-fuzzy inference system consisted geomagnetic data and iron grade that obtained from powder drilling (RC). After the preparation of input layers, 30 percent of data selected as test data and remaining 70 percent as training data. The training data was done for three function of adaptive neuro-fuzzy inference system, then these three functions were compared by two error indices and the best function with minimum error indices was selected. Finally, the best regions were identified in terms of grade and thickness and also the optimum exploratory boreholes points were determined.
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Enhanced Interpretation of Continuous Dipmeter Logs in Formation Fracture Study
Authors M. Mavaddat, Y. Mavaddat and M.G. Akbari fardSummaryAn integrated data acquisition and log interpretation method was used to achieve the fracture study of a very old cased hole abandoned well. Accordingly, by using continuous dipmeter logs and core samples; fracture dip, density, direction and fracture intervals were determined. Results were used along with seismic interpretation and drilling history as a tool to transform recently unused continuous dip meter logs from old drilled wells into valuable information that can highly help in formation fracture studies. It can also be used in combination to drilling rate of penetration, drilling cutting logs and mud losses to get a better insight into the fracture network in the reservoir formation.
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A Combined Approach of Electrical Resistivity and Physicochemical Methods for Mapping of Hydrocarbon Contaminated Site
Authors K. Ishola, O. Bamidele, K. Oyedele and L. AdeotiSummaryAn investigation of the contaminants of the environment especially groundwater with hydrocarbon leakages from pipelines has remained a major concern globally. The purposes of this study were to map the extent, analyzed the chemical composition of the plumes, and estimate the water quality index of the water samples collected in the study area using geophysical and physicochemical methods. Six traverses were occupied and a total of thirty VES data were collected. The sixth traverse was designated a “control” traverse. Some water samples from hand dug wells and boreholes were collected. For this study, four to five geoelectric layers were delineated indicating topsoil, contaminated sand, sandy clay/clayey sand, sand and clay. The physico-chemical analysis revealed that BH-1 to BH-7 have anomalously high BOD, TDS,and conductivity above the acceptable level. At present, the groundwater in the area is not potable; therefore, concerned agencies or government should embark on remediation to salvage the groundwater aquifer system in the area from a total damage. The electrical responses from the resistivity measurements using both vertical electrical soundings(VES) and 2D electrical profiling were good at imaging the contaminated zones. For this study, the electrical techniques reveals that relatively high resistivity associated with the supposed contaminated zone.
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Field and laboratory Validation of ERT-Detected Subsurface Heterogeneity at the Meter Scale
Authors E. Bloem, A. Dathe, A. Nemes, P. Fernandez, H.K. French, M. Patterson and D. GimenezSummaryAgriculture, industry, airport activities all have impact on the quality of soil and water. To improve risk assessment, monitoring, design and implementation of cost-effective preventive or mitigation measures and/or policies we require a better understanding of the underlying environmental processes. Spatial heterogeneity plays a critical role for describing water and solute transport processes in the unsaturated zone. Heterogeneous water flow in soils is complex and challenging to quantify due to changes in soil hydraulic properties across different spatial scales.
We conducted an experiment involving different field and laboratory sensory techniques and measurements to examine 3D functional heterogeneity and its physical drivers in natural soil. We compare the spatial heterogeneity of the soil from ERT measurements at two scales with the observed spatial distribution of hydraulic properties calculated from soil samples and TDR data.
ERT helped to visualize the heterogeneity of the studied system. Although at first the high resistive feature observed with ERT could not be explained by tensiometer and/or TDR data, there was a distinct difference in the retention curves inside and outside the feature, which creates difference in resistivity values. These observations help us to better understand the links between soil hydraulic properties and heterogeneous water flow.
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Monitoring of In Situ Remediation with the Direct Current Time-Domain Induced Polarization Method
Authors A. Nivorlis, T. Dahlin, M. Rossi and H. WeiSummaryIn Alingsås, a dry-cleaning facility was operated for many years, and huge amounts of the solvent PCE was spilled into the ground. This contributed to an increasing concentration of PCE over the years until the use of PCE was stopped, resulting in the formation of a DNAPL plume beneath the building. Treatment of contaminated soils in Sweden often includes excavation and landfilling, however in Alingsås this is not applicable. In situ remediation methods (thermal, biological, chemical) are the only alternative however, there is a need for tools to monitor the effectiveness of those methods. One method of particular interest in this context is the Direct Current time-domain Induced Polarization (DCIP). For that purpose, a fully autonomous and automatic monitoring system was installed in Alingsås, to perform frequent automated measurements and to provide information about the changes in the subsurface. The geophysical data should be ideally acquired, analyzed and verified with automated routines as part of a larger monitoring system. It is of great importance, especially in the early stage, to verify events that appear to show interesting changes with sampling data to evaluate the level of reliability of the system.
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Differential Acoustic Spectroscopy for Low Frequency Laboratory Measurement of Compressibility and Attenuation
By J. HarrisSummaryDifferential Acoustic Resonance Spectroscopy (DARS) was developed as a laboratory method for measuring compressibility and attenuation of small samples of materials at low acoustic frequencies. The DARS concept begins with a baseline measurement of resonance frequency and resonance linewidth of a fluid-filled but otherwise empty cavity. When a small sample of rock or other material is placed inside the cavity, shifts in resonance frequency and linewidth occur. The changes in resonance can be inverted for sample compressibility and attenuation. Previous DARS studies focussed on the estimation of compressibility. In this paper, I report the first quantitative estimates of attenuation (Q) from the DARS system. The paper begins with a brief review of the DARS concept, followed by a summary of the DARS theory developed to support Q analysis, and finally measurements and analysis of non-porous and porous samples.
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Analysis of the Frequency-Time Characteristics of Seismic and Electromagnetic Fields over a Gas Condensate Field
Authors V. Potylitsyn, D. Kudinov, G. Shaidurov, E. Kokhonkova and V. RomanovSummaryThis article presents data on the analysis of frequency-time characteristics of seismic and electromagnetic fields obtained in July 2017 at the Bystryansky gas condensate field (Russia, Krasnoyarsk Territory, Minusinsk District). Spectrograms of signals measured both in the center of the deposit and at its periphery are given. The optimal frequency range for recording seismo-electric effects is obtained.
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First Land Application of the Differential Electrical Dipole Method together with Transient Electromagnetics
Authors K. Lippert, B. Tezkan, J. Boekmann and A. HaroonSummaryThe newly developed DED-transmitter consists of two horizontal electrical dipoles that share a common central electrode which has one polarity, while the outer ones have the opposite polarity. Thus, the current in each dipole flows in opposite directions. The differential signal is recorded by electrical receivers at a certain distance. This feasibility study, realized along the beach of de Panne in Belgium, is the first land-based application of the DED system of its kind. The freshwater distribution has a thickness variation of 8–15m in a depth of up to 30m. 24 DED measurements were conducted at the beach at low tide, utilizing two 75m transmitter dipoles in an inline configuration parallel to the beach. Six transmitter locations were assembled parallel to the beach with a spacing of 50m along with four electrical receiver stations at different offsets. Additionally, 40 inloop TEM stations were measured. Previously performed 1D modelling studies suggested an interpretation of the DED Step-On signal as more suitable compared to the DED Step-Off signal. A joint inversion algorithm is for DED and TEM data was developed. Based on these results a freshwater distribution underneath the Belgian coastline is confirmed with a varying thickness between 8 and 30m.
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Feasibility of 3D Random Seismic Arrays for Subsurface Characterizations in Urban Environments
Authors B. Brodic, A. Malehmir, M. Svensson and J. JonssonSummaryTo test new and cost-effective methods for 3D subsurface characterization in urban and near-surface environments, along with mapping bedrock morphology and zones of weaknesses at a contaminated site, a seismic survey was conducted in the city of Varberg, southern Sweden. The survey consisted of 12 active-source landstreamer seismic profiles, 89 randomly distributed wireless seismic recorders along an area of 350×300 m and 46 wireless recorders deployed along the train tacks crossing the site. In this study, we analyzed the properties and potential of two datasets obtained only from the wireless recorders for seismic imaging. One dataset consists of recordings of shots done along the active-source profiles, while the other one consists of 5 days of passive seismic data recording. The first dataset was used for first-break traveltime tomography with the picked data indicating uniform source-receiver azimuth-offset distribution and minor acquisition footprints. P-wave velocity model obtained from the inversion was successful in imaging bedrock surface and indicated two preferential directions from which contaminants may migrate away from the main contaminated site. Preliminary analysis indicates that the site’s noisy nature limits 3D reflection seismic potential of the dataset with active source recordings while the passive dataset shows promising results for site characterization.
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Three-Dimensional Ambient Noise Tomography Based on Common Midpoint Spatial Autocorrelation
Authors K. Hayashi and C. KonishiSummaryWe developed a passive surface wave method that delineates 2D or 3D near-surface S-wave velocity (VS) structure from ambient noise obtained from dozens of receivers on the ground surface. A new cableless (nodal) seismograph that includes CPU, A/D converter, GPS clock, Wi-Fi, batteries and SD card was developed and used for data acquisition. The GPS clock permits units to be synchronized over any distance without cables. Ambient noise was recorded using a receiver spacing small enough to avoid spatial aliasing. A common midpoint spatial autocorrelation (CMP-SPAC) method was used to process ambient noise. First, coherencies were calculated for all pairs of receivers. Next, coherencies having common midpoint (CMP) were grouped together and a dispersion curve was calculated at each CMP. A one-dimensional inversion with horizontal constraint was used to estimate a 2D or 3D VS model. This paper summarizes the equipment and method and provides a field example.
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A New Towed Ground-Based TEM-System for 3D Mapping of the Top 50 Meters of The Subsurface
Authors P.K. Maurya, E. Auken, A.V. Christiansen, N. Foged and T.T. EiskjærSummaryThe top 0–50 m of the subsurface are critical for infrastructure, water supply, artificial infiltration, farming, waste deposits, construction, etc. Yet, the tools for imaging this zone are limited to boreholes or geophysical methods such as electrical resistivity imagining (ERT) with a limited applicability for area-covering surveys larger than a few hectares. We present a new highly efficient towed transient electromagnetic system, tTEM, which bridges the gap in coverage and resolution between point or line measurements and airborne electromagnetics. The system yields images in full 3D with a lateral resolution down to 10 × 10 m. The system is towed by and All-Terrain Vehicle, uses a 2 × 4 m2 transmitter coil and has a z-component receiver 9 m offset from the transmitter. The first bias-free gate is as early as 4 µs from ramp beginning (1.4 µs after ramp-end). The turn-off time is 2.6 µs. Data are processed and inverted using methods directly adopted from airborne electromagnetics. We discuss the system design and present a case study where the system has been used to map complex subsurface geology in large detail to build 3D geological/hydrogeological models.
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Cross-Hole ERT Measurements in Slotted PVC Cased Boreholes - A New Perspective in Geoelectrical Prospection
Authors A. Almpanis, P. Tsourlos, G. Vargemezis and C. PapazachosSummaryIn this work we study the case of performing cross-hole ERT measurements in plastic PVC cased slotted observation boreholes by inserting a multi-electrode cable directly into the borehole. We present results from an experimental study by setting up simulations in a water tank using different PVC casings, with various number of slots and by testing them using different electrode array configurations.
The findings of the experimental test were also tested by field data. We conclude that the applicability of this measurement set-up depends on the density of the slots on the PVC casing, with denser slot configurations leading to a better data quality. Among the tested configurations, the pole-dipole array is shown to be the most preferable array. The previous findings are verified by the field data results, giving a new perspective for geoelectrical prospecting, since the obtained results suggest that slotted PVC cased observation wells can be efficiently employed for ERT mapping, reducing the overall survey costs, reliability and effort, especially in urban environments.
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Estimation of Anisotropy Parameters in VTI Media Using the Ray-Based Tomography
By G. BohmSummaryIn this paper a new procedure to estimate the Thomsen parameters ε and δ in VTI (Vertical Tranversely Isotropic) media is presented. The approach used in this work exploits the angles of the ray segments computed by the anisotropic ray tracing in travel time tomography using direct, reflected and refracted arrivals. The reliability of this technique is demonstrated by two synthetic examples related to transmission tomography (cross-hole) and reflection/refraction tomography.
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Shallow Cavern Detection through the Acquisition and Interpretation of Airborne Full Tensor Gradiometry
Authors A. Morgan, S. Payton, G. Jorgensen and K. StaffordSummaryEvaporite sediments within the Delaware basin of west Texas are known to be significantly karsted through the action of surface and subsurface water. Surface geomorphology offers indications of subsurface karsting, but such features may be occluded by more recent sedimentary cover. Recent drilling efforts have penetrated shallow caverns resulting in the loss of drilling fluids and the abandonment of the borehole after mitigation methods failed to stem further fluid loss. Airborne Full Tensor Gradiometry (FTG) is acquired to locate the known karst penetrated by the wells and to assess further risk in the adjacent leased acreage. FTG acquisition is rapidly acquired, processed and interpreted in order to allow risk assessment to take place within the strict time frame imposed by drilling commitments. Such data acquisition could not take place through ground methods due to the extent of the acreage and the time required to secure multiple permits which are not required by airborne data acquisition.
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Geological Modelling Implications - Different Inversion Strategies from AEM Data
Authors A. Rapiti, F. Jørgensen, A. Menghini, A. Viezzoli and G. VignoliSummaryData from AEM survey, carried out in the Peace Region of NE British Columbia to support groundwater investigation, were used in this study. An understanding of the geological structures can have significant implication in groundwater management decisions. Previous studies have demonstrated the presence of shallow aquifers specifically those within paleovalleys. In this study we present different inversion strategies and their geological modelling implications. The aim was to obtain geophysical models that have better resolved electrical resistivity units. This, therefore, should allow more straightforward geological interpretation.
Different types of geophysical inversions on synthetic data have been performed. Testing different settings, for each inversion strategy permitted to study how the final geophysical model could change. This workflow was applied to real data over a subset collected in the south-western part of the Peace Region, an area characterized by different buried valleys.
Sharp Laterally Constrained inversions have been thoroughly investigated. The sharp result is very sensitive to settings choice: sharp inversion with tight settings allows to recognition of the basic electrical resistivity blocks of the model, on the other hand, sharp-inversion with loose settings allows to obtain resistivity variations within the blocks. We present a rough geological interpretation on a representative cross section.
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The Heavy Mineral Indicator Adds a New Dimension to Airborne Radiometrics
Authors I. Hooshyari-Far, A. Kepic and M. CarsonSummaryFor many years the output of radiometric surveys are maps of total count gamma activity and estimations of K, U, Th. Our work puts the focus upon using the long neglected aspects of the radiometric spectrum: the scattered gamma ray radiation. The heavy mineral indicator (HMI) is computed form a ration of low energy versus high energy scattered gamma rays. It is in effect the ratio of Photoelectric effect versus Compton effects. The Elashgin case history demonstrates that low-level and high resolution full spectrum radiometrics provides good data for the HMI technique. HMI values are dominated by Fe concentration due the abundance of Fe over other high atomic number elements. Areas composed of higher atomic numbers, mostly due to the iron content, such as ferricretes and laterite show up clearly in the Elashgin data without the need to be “interpreted” with respect to geological context. With the high resolution of modern radiometrics on planes and future drones this technique works well for remote sensing. An exciting aspect of HMI analysis for airborne radiometrics is not just the future, but the past: many high quality full spectrum data sets already exist and may be easily reprocessed to reveal new geological insights.
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A Drone as Platform for Airborne Gamma-Ray Surveys to Characterize Soil and Monitor Contaminations
Authors S. Van Der Veeke, R.L. Koomans, F.M. van Egmond and J. LimburgSummaryGamma-ray spectrometers are an invaluable tool in the field of geophysics where they are used for geological mapping and mineral exploration. Recent technological advances introduce the emergence of a new platform for gamma-ray surveys: Unmanned Airborne Vehicles (UAVs) otherwise known as drones. This new platform enables the fast and efficient collection of environmental radiometric data in otherwise inaccessible areas. An overview is given of the technological and data-analysis developments to realize the use of a spectrometer under a drone.
As a result of weight and power optimization a spectrometer system based on a 1.0L NaI crystal can be used under a drone. The system collects gamma spectra with sufficient statistics to perform full spectrum analysis and determine variation in geophysical soil parameters. The platform can autonomously measure and process data giving real-time insight in the collected data and results. Two test cases are discussed in which the use and accuracy of this platform is validated for precision farming as well as locating and monitoring radioactive contaminations. It is concluded that a self-contained gamma-ray measurement system under a drone combines the best of two worlds by maintaining high resolution while increasing the ease of use.
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Near Surface Conductive Zones in Hessdalen Valley (Norway) Inferred by Preliminary VLF Surveys
Authors G. Vargemezis, J. Zlotnicki, B. Gitle Hauge, A. Kjøniksen and E. StrandSummaryDuring the last four years VLF surveys have been performed in Hessdalen valley during four wide geophysical field campaigns including Total Magnetic Field surveys, time recordings of the electrical field, and magnetotelluric soundings. VLF measurements have been carried out on a 20 m average spacing along a large number of traces totaling 70 km length. The covered area is now about 100 km2. Hereafter, we focus on the results of the VLF upshots. A part of the conductive zones have been found to be related with mineral deposits (mainly sulphites). The distribution of these conductive zones could suggest that they draw an ellipse of 6×12 km dimensions related with the anticline in the area. These results combined with the other geophysical results will contribute to understand if and how these, very superficial, structure could participate to the genesis of the so-called Hessdalen lights.
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Geophysical Investigation of the Malga Archaeological Park (Carthage, Tunisia)
Authors A. Jrad, C. Jallouli, Y. Quesnel and P. RochetteSummaryA non-invasive multitechnical geophysical survey, using magnetic cartography, seismic and electrical resistivity tomographies, was carried out at the Malga archaeological park of Carthage in Tunisia. The goals were to understand the geological stratigraphy of the subsurface and to locate buried archaeological relics at the high-potential archaeological area of El Malga site. A potential linear magnetic anomaly was observed at the eastern-north side of the prospected area and which can be related to ruins probably made of sandy bricks like those of the Carthage-Zaghouan Aqueduct. Numerous bipolar magnetic anomalies are also characterized suggesting the presence of magnetized bodies in the subsurface. Seismic tomography profiles crossing magnetic anomalies show four main stratigraphic layers which are from the top to the bottom; the weathered zone with the lowest seismic velocity, a more compacted layer which deposited above the layers with the higher seismic velocity. The enhancement of the velocity can be related to enrichment with limestone or the impact of the phreatic table water. A depth of about 1 m was defined for potential archaeological features with strong electrical resistivity contrasts.
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The ERT-3D Method as a Tool to explore the Pyramid of La Luna and the Main Plaza subsoils, Teotihuacan, Mexico
SummaryThe Pyramid of La Luna is found within the archaeological site of Teotihuacan, located to the NE of Mexico City. A big Plaza is found to the south surrounded by pyramids of different ages. These two areas were restored until the beginning of the 60th’s and few archaeological investigations have been carried out in this zone. A geophysical work was performed to characterise the subsoil of La Luna and her Main Plaza. The ERT-3D method was applied in both areas. The base of the Pyramid of La Luna was surrounded by 105 electrodes and different electric arrays were applied to cover adequately her subsoil. The main Plaza was covered with 4 ERT profiles employing a special roll-along technique to obtain a 3D view of the plaza subsoil.
A very interesting low resistivity signature was determined at 8 m deep beneath La Luna, towards her central part, which may indicate the presence of a cave. Two possible passages were identified. One of them seems to be heading towards the eastern end of the pyramid. The ERT-3D study at La Luna Main Plaza did not find evidences of a buried tunnel, nevertheless several resistivity anomalies were found that are of archaeological interest.
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Seismic SH Full Waveform Inversion as New Prospection Method in Archaeogeophysics
Authors D. Koehn, D. Wilken, T. Wunderlich, D. De Nil, W. Rabbel, L. Werther, J. Schmidt, C. Zielhofer and S. LinzenSummaryA successful and efficient archaeological excavation campaign requires a high resolution seismic imaging approach to resolve small scale near surface structures. The resolution of classical first arrival traveltime tomography (FATT) is limited by the first Fresnel zone, while the inversion of surface wave dispersion spectra requires a (local) 1D medium approximation, a significant problem in 2D heterogeneous media. To overcome these limitations, we introduce in this study the seismic SH full waveform inversion (FWI) of the Love- and refracted SH-wavefield as promising archaeogeophysical prospection tool. The applicability of this approach is demonstrated for SH field data from the transect over a medieval canal structure in southern Germany. Compared to FATT, the FWI is able to improve the definition of the canal shape and resolves small scale structures within the canal. These features are qualitatively compared with sub-surface structures revealed by an archaeological excavation along the SH profile.
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Comparison of Apparent Conductivity to Ground Displacement and Surficial Geology for Continuous Permafrost
Authors G. Oldenborger, N. Short and A. LeBlancSummaryInformation on thaw susceptibility is important for predicting the behaviour of permafrost as an engineering substrate. We compare apparent conductivity surveys to ground displacement obtained from differential synthetic aperture radar and surficial geology, with the objective of improving the regional characterization of terrain stability and permafrost conditions along the western coast of Hudson Bay, Nunavut. For certain field conditions, seasonal ground displacement, conductivity, and seasonal conductivity ratio are related to surficial geology, and there is a correspondence between high displacement, low conductivity, and high conductivity ratio, inferred to be indicative of high ice content and thaw-related displacement. For other conditions, results suggest heterogeneity of permafrost conditions, thaw susceptibility and conductivity that are not easily understood in terms of surficial geology alone.
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Soil Salinity Assessment Using Electromagnetic Induction and Inversion Technique – A Case Study in Portugal
SummarySoil salinization limits agricultural productivity and can ultimately cause desertification and land abandonment. Salinity mapping represents a good contribution to control soil salinization. Recent research is revolutionizing how soil information can be obtained quickly and cheaply. By using a state-of-the-art electromagnetic (EM) instrument and inversion techniques, it is possible now to generate high-resolution EM conductivity images and, in conjunction with soil sampling, to obtain quasi 2D and 3D maps of soil salinity. In this study EM surveys were conducted in four experimental plots located in Portugal, with different levels of salinity. EM models obtained from joint inversion of EM data, collected at different heights and orientations, shows good agreement with soil sample electrical conductivity of the saturation extract (ECe) in the study area. The significant correlation between EM models and ECe permits therefore a rapid characterization of the spatio-temporal variation of soil salinity, allowing to further predict salinization risk under different conditions.
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Ebro Delta Geometry and Structure Characterization Using the Electrical Resistivity Imaging Method
Authors F. Bellmunt, A. Gabàs, A. Macau, B. Benjumea and S. FiguerasSummaryThe Ebro Delta is currently a place of interest due to the presence of zones vulnerable to subsidence. Determining the type of sediment that favours the subsidence and its identification in the subsoil is a critical task for planning protection actions in the Ebro Delta. In this point the geophysical methods can help providing subsoil information. The subsidence mainly relies on Holocene sediments (clays, silts, sands and organic deposits). All these materials are affected by salty, fresh or brackish water. For this reason, one of the best geophysical techniques to describe the geometrical structure of complex lithologies, and its spatial variation, is the electrical resistivity tomography (ERT). The used geophysical parameter is really sensitivity to the presence of ions, and efficiently detects fresh water and saline water zones. The application of ten ERT long profiles (355 m - 1km) distributed around the studied area are a well-suited way to study the different environments inside the delta and to understand its evolution, from coast to margin side. In addition, the established geoelectrical boundaries have been used as a reference to build the 3D geological model surfaces, which will be used to assess the subsidence of the whole delta plain.
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Karst Imaging Using a Fuzzy C-Means Data Clustering Approach (Montgrí Massif, Spain)
Authors B. Benjumea, A. Gabàs, A. Macau, J. Ledo, F. Bellmunt and S. FiguerasSummaryIdentification of karst zones can be critical for hydrogeological or geotechnical studies. We present a case study carried out at the carbonate coastal Montgrí Massif (Spain) characterized by a well-developed karst system. The karst is covered by Quaternary sediments in the study area. The objective of the work is to image karst structures using geophysical techniques. Both electrical resistivity and seismic tomography (ERT and SRT) datasets have been acquired on five collocated profiles. Karst filled with clays produce seismic and electrical signature difficult to interpret. The Fuzzy c-means (FCM) data clustering approach is a way of producing an integrated model that can help to constrain lithological interpretation. In this study, FCM has been applied as a first step to one of the profiles with available ground-truthing from a near borehole. The resulting zonal model and cluster distribution has been used to interpret the integrated models obtained from applying FCM data clustering to the five datasets as a group. In this way, karst areas have been identified in three of the profiles in the near surface.
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Study of Small Earthfill Dams Structure Using Seismic Refraction, ERT and Self-Potential Methods
Authors W. Malagutti Filho, J.C. Dourado, C.A. Moreira, M.M. Coura and F.A. BergonzoniSummarySmall dams are used mainly by cities, industries, mines and agro-industries as a means to discipline the use of water, for diverse purposes. The need for constant monitoring and maintenance of this kind of structure is essential to guarantee its integrity, detect fractures, infiltrations, leaks, etc and therefore helps preventing accidents which can have catastrophic proportions. This paper presents the results of seismic refraction, electrical resistivity tomography and self-potential methods, performed in an integrated manner, on two earthfill dams, located in the cities of Cordeirópolis and Ipeúna, inland São Paulo state, Brazil. The objective was to aknowledge the geophysical signature to deduce geotechnical and hydrogeological parameters such as bedrock, layer length and disposition, possible weak spots in the bodies of the two earthfill dams as well as ground water preferential flow inside them.
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Electrical Resistivity Methods with Petrophysical Analysis of their Results
Authors D.A. Kvon, V.A. Shevnin and A.A. RyjovSummarySoil resistivity can be calculated from petrophysical soil properties. That gives possibility estimate petrophysical properties on soil resistivity. Now we use forward petrophysical problem, petrophysical modeling and inverse petrophysical problem to analyze relations between soil resistivity and some petrophysical parameters. We show examples of petrophysical approach application in different situations of water resistivity, rocks composition, influence of lithology and permafrost.
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A Novel Analytical Approach to Estimate Sand Production in Unconsolidated Reservoir: Case Study in Oil Field “N”
By D. AriantiSummarySand production is the migration of formation sand caused by the flow of reservoir fluids. This paper aims to develop an analytical model to predict sand production in oil field and validate it using 4 wells in Field “N”. Coupled sand failure mechanism considering static and dynamic criteria is used to models sand production. Rock particles strength is predominantly acting by drag and buoyancy forces. To capture fluid flow and pressure drop in porous medium, Darcy’s law is applied. The result of this study is the proposed analytical equation successfully models sand prediction accurately in 4 wells at range of cavity height 12–25 ft. At oil rate 1000 STB/day, calculated sand production in Well 1 is 0.005 lb/bbl, Well 2 is 0.007 lb/bbl, Well 3 is 0.005 lb/bbl, and Well 4 is 0.002 lb/bbl. This study shows good agreement on sand production trend in the moderate production rates of 2000 STB/day and low production rate of 500 STB/day with discrepancy varies of 2–3%. Sensitivity studies resulted is fluid viscosity and sand radius very sensitive to the sand production value. This study suggests cavity height in the proposed analytical method is applied at 10–25 ft.
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Angle Dependant Interference Patterns for Blast Vibration Minimization
Authors C. Tauchner, J. Zeiß and F. BleibinhausSummaryThe project focuses on reducing blasting vibrations at sensitive targets with phased source arrays in the far field. An interference pattern is naturally created by the geometrical setup of blasting arrays and the delay time between each single blast within the array. The aim is to create focusing effects with angle dependant interference where constructive energy hits sites of lesser interest and destructive interference is directed to neighbouring infrastructure. This work applies an analytic solution, which utilizes Dirac-Delta impulses, to better understand the basic relations between certain blast configurations and the resulting frequency radiation patterns. This is important because it signifies an additional constraint to the global search for optimized patterns in a later stage of the project.
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Multimethod Geophysical Survey of a Sinkhole - The Case Study of São Mamede
Authors N. Barraca, D.R. Rodrigues, S. Oliveira, F. Almeida and M. MatiasSummaryThis paper presents a case study dealing with the characterization of an area where a sinkhole developed. Several geophysical techniques (ground penetrating radar, 3D electrical resistivity tomography and seismic refraction) were used. The geophysical survey is intended to understand the origin of that sinkhole developed under a public road in São Mamede, Batalha (Portugal).
The integrated geophysical data point out to the existence of anomalies associated with the sinkhole and local infrastructures that could contribute to the occurrence of the phenomenon. The joint data interpretation shows high-velocity anomalies on the seismic refraction data the coincide, specially, with a high resistivity anomaly in the 3D resistivity model. These anomalies can be interpreted as corresponding to a concealed underground drainage system that could originate the sinkhole visible at the road surface.
Therefore, the integrated use of the three geophysical methods allowed to propose a model to be considered for the remediation of the problems caused by local water infiltration and sinkhole development.
Only the integration of data from different methods can enhance the interpretations and models obtained from the solely use of a single method. Thus, this strategy allows to propose more complete and detailed modes to describe the area under investigation.
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Applications of Data Fusion for Estimating Water Saturation at the Basis of Seismic, GPR and Resistivity Methods
By K. CzajaSummaryThe paper presents possibilities of applications of data fusion techniques for estimating water saturation at the basis of seismic, GPR and resistivity methods. The main purpose of this works was to test few data fusion techniques in order to obtain objective rules which first of all allow to estimate the value of water saturation with as high accuracy as possible. The tests were based on the results of computer modelling for the geophysical measurements for geological layers with different thickness and petrophysical properties.
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A Seismic Reflection Signal Recognizing Algorithm Based on the Stationarity Testing
More LessSummaryIn seismic prospecting, tracking the reflection events is the pathway for getting the accurate strata information. However, the existence of the seismic random noise prevents the recognizing of the reflection signals. Recently, the properties of the seismic random noise have been comprehensively discussed, especially in the statistical properties. It is shown that the random noise can be considered as a stationary process in a short period. In contrast, the seismic reflection signals are typically non-stationary. Here, a reflection signal recognizing algorithm, which is based on the stationarity testing, is proposed. The basic idea of the recognizing algorithm is to take advantage of the differences between the reflection signals and the random noise in terms of the stationarity. The experimental results demonstrate that the proposed method can recognize the reflection signals effectively, even the signal-to-noise ratio is low. Furthermore, the proposed method also has further application in the seismic noise attenuation.
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Contribution of Deep Deposits to Estimate Site Effects in the East of Mexico City
Authors D.F. Zepeda Fernández, R. Rojas Hernández and M. RodríguezSummaryThe damages in Mexico City (CDMX) associated with September’s 1985 and 2017 earthquakes are symbolic cases of the modifications that local geology can impose to strong ground motions received by buildings in Mexico’s basin. Site effects within the CDMX are predicted considering a simplified unidimensional model, in which the amplifications of the movement are generated by a high contrast of acoustic impedance between a homogenous layer and a semi-space. In this study we advance in the discussion of the origin of the amplification within Mexico City by including the observation of shear velocity models at the east of the city, which indicates the absence of a high contrast of shear velocity in the area, even when the deep deposit formation was reached. Results show a contribution of underlying formations to the superficial deposits in the observed dominant period; this suggests that site effects are probably associated to greater shear velocity structure thicknesses, than soil thickness over deep deposits.
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Crosshole Seismic Tomography to Assess Rock Mass Foundation of Dams - Alto Ceira II Dam Case Study
Authors R. Mota and M.J. CoelhoSummaryCrosshole seismic tomography is a widespread geophysical method to estimate the elastic properties of materials in the crosshole section, for a variety of applications, including engineering site characterisation and foundation treatment evaluation.
This method was applied to Alto Ceira II dam in three phases: Phases 1 and 2 – before and after rock mass foundation treatment, and Phase 3 – after the reservoir first filling. The resulting time-lapse seismic tomographies allowed assessing the schist and greywacke rock mass foundation treatment, and the influence of the reservoir filling.
This study demonstrated that the method can be used as a management tool to evaluate the rock mass behaviour along the dam’s construction phase and during its working lifetime.
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Integration of Geoengineering Techniques to Map Hidden Qanats at Shahid Bahonar University of Kerman
Authors A. Hojat, L. Zanzi, M.H. Loke, H. Ranjbar and S. Karimi-NasabSummaryIn this paper, we present integration of remote sensing, GIS, GPR and ERT techniques to detect underground qanats at Shahid Bahonar University of Kerman, Iran. These studies were defined because of the subsidence problems and cracks of some building walls at the main campus of the university due to unknown hidden qanats. The results of remote sensing studies tracked eight qanat systems passing under the university campus. These results were validated by field visits. GPR studies performed up to now in some parts of the campus showed the depth of qanat systems to vary in the range of 8–15m. Detailed geophysical surveys including GPR and ERT measurements are still to be completed with the aim to reconstruct the maps of underground qanat galleries. Our results and observations have inspired the new idea to construct a geotechnical-geophysical test site of natural qanats at the university main campus. We propose an area in the southeastern part of the university that is not likely to be significantly included in the future construction plans and it also hosts a sequence of non-collapsed shafts which can be used to better evaluate the site.
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Geometrical and Induction Electromagnetic Soundings Resolution Capabilities for Geological Engineering Investigations
Authors I. Mendrii, I. Ingerov and A. LozoviySummaryRecently developed and currently available on the market multichannel broadband multifunction EM instruments of the generation 5+ have levelled the costs of one measuring channel as well as field survey productivity during investigations of shallow geoelectric sections (up to 200m) with geometrical and induction EM soundings methods. Hence, it raises question of comparing resolution capabilities, sensitivity, productivity of geometrical and induction EM soundings methods during investigations of shallow sections. Research carried out by the authors has shown that the control source frequency domain electromagnetic sounding method (CSFDEMS or formerly FDEMS-IP) is the most sensitive to variation of parameters in the geoelectric sections, and subsequently, the most accurate for mapping boundaries of geoelectric section’s layers. The FDEMS method was developed in former USSR in the 50s of previous century together with MT and TEM and was mainly unknown in western countries. Since then, extensive FDEMS method field application experience has been accumulated and with new capabilities of recently developed equipment and software it became sensitive, highly productive and EM noise resistant method.
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Hybrid Surface Wave Survey - A Combined Active and Passive Seismic Survey Using a Linear Array
Authors T. Inazaki, H. Kisanuki, T. Kita and K. HayashiSummaryWe developed a combined active and passive surface wave survey method and named it Hybrid surface wave survey method. The Hybrid survey method deploys a linear geophone array to measure active and passive seismic data sequentially. Surface hitting using a wooden hammer is adopted as the active seismic source. In addition, traffic noises are measured using the same linear geophone array. A number of geophones are placed along a line at 0.3 to 2 m intervals to record active and passive data. Two dispersion curves, one is for a higher frequency part calculated from active data, the other is for a lower frequency part calculated from passive data, are combined to form a single dispersion curve to a specific CMP in a survey line. The method enables us to reconstruct a dense 2D S-wave velocity profile along a line up to 50 m in depth. One of the advantages of hybrid surface wave survey is its robustness to the traffic noises or active utilization of them vice versa. We have applied the hybrid surface wave surveys to more than 30 survey lines since 2013. Our field tests demonstrated the capability of the hybrid surface wave survey method in urban areas.
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How to Detect Disorders During Tunnel Digging with a Muons Telescope Mounted on a TBM
Authors P. De Sloowere, B. Carlus, A. Chevalier, J.-. Ianigro, J. Marteau, D. Gilbert and M. Rosas-CarbajalSummaryThe fact that the earth is constantly bombarded by an isotropic flux of cosmic rays has permitted to develop a new detection method that can only look over the observation point, but powerful enough to detect anomalies in front of a tunnel boring machine (TBM) digging a gallery. To do that, a cosmic ray detector, a muons telescope is set up on a TBM, looking towards.
Cosmic radiations generate very short-lived particles in the upper atmosphere, muons, whose diameter is small enough to penetrate the ground to depths of several hundredths of meters. Muons propagate without changing direction and disintegrates when it hits a proton or a neutron. So it’s a mass detector like gamma ray, and is able to measure density variations. It is used to study volcanoes and galleries. Experiments are occurred in galleries in France and Switzerland, especially in the Croix-Rousse tunnel (Lyon). Since April 2018 a muons telescope is installed on a TBM of the “Grand Paris Express”, moving with the TBM and permanently providing results.
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How to Detect Density Anomalies in Mining Activities with Cosmic Rays Detected by a Muons Telescope
Authors P. De Sloovere, B. Carlus, A. Chevalier, J.-. Ianigro, J. Marteau, D. Gilbert and M. Rosas-CarbajalSummaryThe fact that the earth is constantly bombarded by an isotropic flux of cosmic rays has permitted to develop a new detection method that can only look over the observation point, but powerful enough to detect anomalies in front of a tunnel boring machine (TBM) digging a gallery. To do that, a cosmic ray detector, a muons telescope is set up on a TBM, looking towards.
Cosmic radiations generate very short-lived particles in the upper atmosphere, muons, whose diameter is small enough to penetrate the ground to depths of several hundredths of meters. Muons propagate without changing direction and disintegrates when it hits a proton or a neutron. So it’s a mass detector like gamma ray, and is able to measure density variations. It is used to study volcanoes and galleries. Experiments have been occurred in France at Tournemire tunnel and Switzerland in the Mont-Terri underground Laboratory, showing fault and geologic contacts. Since April 2018 a muons telescope is installed on a TBM of the “Grand Paris Express”, moving with the TBM and permanently providing results.
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Detection of Buried Mine Shafts by Ground Conductivity Mapping - Two Examples from the Walloon Coalfield (Belgium)
Authors N. Dupont, T. Martin and O. KaufmannSummaryThe presence of numerous buried mine shafts in Wallonia (South Belgium) causes significative post-mining hazards and geotechnical risks. Recently, the locations of thousands of buried mine shafts have been estimated with some uncertainties. To eliminate these uncertainties, the most suitable solution is to relocate precisely the buried mine shafts. Geophysical surveys could provide an efficient way to detect such buried mine shafts. However, the applicability depends on the local context and needs to be assessed.
In our study, we applied ground conductivity mapping to detect and locate buried mine shafts expected within two distinct sites (Sambreville and La Louvière). The application of this method gave very convincing results, with some nuance according to the site geology and to the mine shaft abandonment (backfilling or not). In addition, a significant number of unknown mine shafts was also discovered. In the future, development projects in these areas could benefit from investigations such as the ones presented here.
This is why this work could be seen as a milestone in dimensioning ground conductivity surveys to detect buried mine shafts in the regional context of the Walloon coalfield.
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Geophysical Study to the Port of Kos Island (Greece) after the Earthquake of 21st of July 2017
Authors G. Apostolopoulos, G. Amolochitis, K. Leontarakis, D. Merziotis, D. Karaiskos, A. Kamilakis and A. StergiouSummaryOn 21st of July 2017 a 6.5-magnitude earthquake between Bodrum and Greek islands ( Fig. 1a ) strikes injuring more than 200 people. Kos’s port was put out of action due to damage at the harbor. Greek Authorities commissioned ISTRIA Ltd. and the Laboratory of Applied Geophysics of NTUA to conduct sampling drilling and geophysical research to provide the appropriate information to engineers for the port repair study. The initial design of the geophysical survey was for P and S refraction seismic survey in order to detect the depth to bedrock and identify the loose formations above through their seismic velocities. The actual field conditions resulting to hidden layer problems and noisy data have led to the use of MASW method exploiting the 5 shots and all the respective seismic data. The depth to bedrock was found well as borehole data indicated but details in the loose sediments above couldn’t be found with such a seismic array setup. ERT sections have shown the top of semi-impermeable zone to saline water and lateral inhomogeneities and GPR sections near surface loose sediment zones with higher presence of saline water and zones with regular presence possibly related with hidden anthropogenic structures.
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Geophysical and Geotechnical Data Fusion for Levee Assessment - Interface Detection with Biased Geophysical Data
Authors T. Dezert, S. Palma Lopes, Y. Fargier and P. CóteSummaryTo prevent disastrous consequences imputed to levee breakage, assessment methodologies have to be improved. Geophysical and geotechnical investigation methods are usually used to make such assessments. However, the effective combination of these two specific types of data remains a challenge. We propose the fusion of geophysical and geotechnical data by means of Belief Functions. Here we demonstrate our approach on a synthetic case study including geophysical (electrical resistivity) and geotechnical (cone-bearing) data and by implementing Smets and PCR5 normalization rules. This new data combination approach allows the characterization of horizontal interfaces and of a geological structure initially hidden by the effects of a highly conductive body.
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S-Wave Imaging of Glacial Overdeepened Alpine Valleys – Multi-Components
Authors T. Burschil, H. Buness, D.C. Tanner and G. GabrielSummaryS-wave seismic imaging complements the application of P-waves with benefits, e.g., in resolution and petrophysical parameters. However S-wave imaging strongly depends on subsurface conditions. We investigate two overdeepened Alpine basins with P-wave and S-wave seismic methods using single-component and multi-components: (1) The Tannwald basin, located in the Alpine foreland, and (2) the inner-alpine Lienz Basin. These basins have a 3-D shape and a spatially-varying internal structure that constitute promising study areas.
Here, we present two profiles of S-wave seismic reflection imaging using 6-components, i.e. 3-C geophones and a horizontal vibrator sources exciting in two directions. The interpretation of coincident P-wave profiles benchmark the S-wave data. The seismic S-wave sections show most geological structures on the components that have same source-receiver orientation and, thus, corresponds to the SV- and SH-domains. We are able to detect S-wave reflections and diffractions of the basin base down to 600 m depth (2 s TWT). Reflectivity on the other (mixed) components indicate a large amount of wave conversion. The application of S-waves increases the resolution and is able to improve seismic imaging in these environments.
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Integrated Geophysical and Geotechnical Analyses at a Landslide Area - Case History in Lopare, Bosnia and Herzegovina
Authors K. Suto, J. Sugawara, M. Urosevic, S. Arsenovic and S. KomatinaSummaryA heavy rainfall in May 2014 caused an extensive damage in the Balkan area.
A combination of seismic reflection, MASW and electric resitivity surveys are carried out to supplement a surface geotechnical observation at an area in Bosnia and Herzegovina for potential of further landslides. This is a Geoscientists without Borders project.
Surface observation found soft and low strength layers in the area with multiple scarps and cracks.
The depths of slip surface are estimated at 10m at the upper part of slope and about 2m at the lower part of slope. These are indicated by low reflectivity on the seismic reflection, low S-wave velocity in the MASW and high conductivity in the resistivity tomography sections.
According to these results, several suggestions are made to local government to mitigate landslide disasters.
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New Gravimetrical Map of The Rieti Intra-Mountain Basin (Central Apennines, Italy)
Authors K. Skrame, M. Di Filippo and M. Di NezzaSummaryThis paper describes the acquisition of the gravity data and their analysis to model and map the bedrock configuration of the Rieti Basin (hereafter RB); a typical intra-mountain tectonic depression of Central Apennines in Italy, related to a still active tectonic extensional regime.
The study involved a test area of 35 km2 occupied by 110 gravity stations. The new gravity measurements were merged with the gravity data of the 358 gravity stations collected during the 1995 gravity survey ( Ciccollella et al., 1995 ). The gravity data resulted from the network adjustment were used to calculate the Bouguer anomaly map. To realize the 2-D gravimetric models of the RB, a realistic density of 2,15 g/cm3 for the unconsolidated Quaternary deposits, a density of 2.50 g/cm3 for the Travertine and a density of 2.60 g/cm3 for the Meso-Cenozoic pelagic basin deposits were used ( Skrame, 2011 ).
The models obtained matched quite well with the exiting geological and geophysical data.
The new bedrock surface topography map of RB provides a new more detailed and representative image of the buried morphology, and gives a more accurate evaluation of the thickness of the Plio-Quaternary sedimentary infilling.
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Development of Geophysical Methodologies for the Assessment of Coastal Concrete Infrastructures
Authors C. Sachet, P. Sentenac and D. LerouxSummaryDue to the geometry and sea effect, an adaptive methodology is required in the case of the geophysical assessment of coastal concrete infrastructures. Along with other observables, these distinctivenesses influence the resistivity and permittivity measurement. The procedure jointly uses the ERT and GPR geophysical methods and is directly taking into account the geometrical engineered particularities, and the presence of the sea water. With complex geometrical shapes addressing the engineering needs, measurements are directly under the effect of the general geometry and underlying structures. In order to identify the 3D structures, the acquisition and the processing steps have to take into account these complexities and the corresponding anomalies. The process considers the geotechnical and geometrical properties during the data processing and inversion problem in order to assess the coastal concrete infrastructure state.
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Selection of Field Parameters for Shallow Seismic Reflection Surveying and the Results of Two New Shallow Seismic Lines
Authors J.A. Meekes and V. VandeweijerSummarySeveral faults in the border area between Netherlands and Germany show a complex structure. Deep seismic lines do not reveal the shallow structure well enough and the density of the available lines is low.
We conducted two high resolution seismic reflection lines to clarify some of the geological questions about the fault structure. This paper presents a general discussion on the selection of field parameters for high resolution seismic surveys for shallow applications and the data acquisition and data processing of these two lines. Several aspects of the selection of field parameters for high resolution seismic surveys for shallow applications are discussed. The selection of a station interval is discussed in detail as well as the stack-array principle.
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The Contribution of Geophysical Methods to the Study of Vallcebre Landslide (Eastern Pyrenees, Spain)
Authors M. Himi, M. Sánchez, L. Rivero, R. Lovera, A. Urruela and A. CasasSummaryThe use of geophysical methods to study landslides may provide useful information on defining internal structure of a landslide, identifying geometry of sliding surface, determination of groundwater effect on landslide, physical properties of landslide material and landslide mass movement.
In this study, electrical resistivity tomography and seismic refraction tomography methods were used as complement to geotechnical and monitoring tests. The results from each geophysical study were very evident for clarifying the internal structure of the landslide, the physical properties of the rock mass involved and defining the sliding surface geometry.
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P- And S-Wave Seismic Imaging of Sinkhole Structures in the City Of Hamburg
Authors S. Tschache, U. Polom, H. Buness and C.M. KrawczykSummarySinkholes pose a natural hazard, especially in densely populated areas. In Hamburg-Groß Flottbek, two slowly subsiding sinkholes are known that lie above a salt diapir flank. The Wobbe See sinkhole is a collapse structure that has been buried and built up. The Flottbek Markt sinkhole is a suffosion sinkhole. We applied P-wave and S-wave reflection seismics on coinciding profiles to study the structure of the sinkholes and their causes. Additionally, a pseudo 3D P-wave dataset was acquired.
The P-wave and S-wave seismic sections show mostly a good accordance. S-waves enable a high-resolution imaging of the near-surface. Below the Wobbe See sinkhole, a deepening reflector interrupted by staggered faults can be interpreted, which confirms the outcome of a previous study. Down-bending reflectors and an internal bedding structure are imaged in case of the Flottbek Markt sinkhole. The P-wave data reveal reflections of the salt diapir and caprock due to their higher penetration depth. The results suggest that the combination of P- and S-wave reflection seismics is a suitable tool for the investigation of sinkhole areas, even in urban environments.
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3D-Borehole Radar - A Routine Tool for The Detailed Imaging of Salt Structures
Authors D. Orlowsky, C. Holst and B. LehmannSummaryDuring the last decade, the 3D-borehole radar technique has demonstrated to be a valuable tool for the localization of the edges and for the investigation of the internal structure of salt domes. This methodology evolved to an integral component of the standard investigation program for new cavern development projects at many salt dome sites in Europe. A 3D-borehole radar probe, which runs within a vertical drill-hole through the salt formation, emits omni-directional radar signals. To map the 3D spatial coordinates of radar wave reflectors (geological interfaces) within the salt, the directions of the incoming radar signal reflections are determined apart from the distance of the probe to the reflector. A so called cross loop antenna as receiver unit in the probe allows for the recording of three separate signal shares. Together with the knowledge of the probe’s orientation the incoming angle of each signal can be clearly set and thus the coordinates of reflectors in the 3D space can be determined
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High-Frequency GPR Investigations in Saint Vigilius Cathedral, Trento
More LessSummaryIn this paper, we present the results of high frequency GPR measurements performed on the pillars of Saint Vigilius cathedral in Trento to monitor the construction conditions as well as to detect the internal defects of the pillars. Tomographic measurements were performed using a pair of 1GHz Mala antennas at three heights along the pillars. The distribution of the propagation velocity was therefore determined in horizontal planes within the pillars and the data were then translated to images of the relative permittivity. Reflection measurements were performed using the very high frequency 3GHz IDS antenna. The results detected some minor spaces where the stones were not perfectly attached. However, significant internal defects with dimensions larger than 15cm should be excluded according to GPR results. Based on vertical profiles on all the accessible sides of the pillars, the size and layout of the stones used to construct the outer parts of the pillars were recovered. Thickness variations of two sample vaults were also monitored using the profiles measured across them.
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A Fast GPR Numerical Model Based on Machine Learning with Application to Full Waveform Inversion
Authors I. Giannakis, A. Giannopoulos and C. WarrenSummaryForward modelling of Ground Penetrating Radar (GPR) is often used to facilitate interpretation of complex GPR data and as a key ingredient of full waveform inversion (FWI) processes. As general 3D full-wave electromagnetic solvers are computationally very demanding routine application of advanced GPR modelling is not popular. A novel concept for creating a fast GPR forward model based on machine learning (ML) concepts is presented. This ML-based model is trained using a dataset obtained from a realistic 3D Finite-Difference Time-Domain (FDTD) gprMax model. The fast model is trained for a specific GPR application that can be easily parametrised and have a somewhat constrained variability. However, the training uses GPR A-Scans obtained from very realistic forward models that include all complex scattering effects and antenna coupling mechanisms. To demonstrate the efficiency of the approach an application, using real GPR data, of the fast forward solver within a FWI process, using a global optimiser requiring a great number of forward model calculations, is presented producing very promising results.
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Subsurface Utilities Mapping for Engineering Applications Using Ground Penetrating Radar (GPR)
Authors L. Adeoti, T. Oyeniran, K. Ishola, R. Adegbola and M. AyukSummaryGPR survey was conducted to investigate the presence of voids / cavities in the shallow subsurface that may compromise the construction of a landing pier/jetty/dock for small and medium sized ocean-going vessels. Two major parallel traverse lines and three minor parallel lines that cut perpendicularly across the two major lines were occupied. Panels (which are points of interest) were established on the two major traverse lines. A total of fifteen (15) GPR sections were produced and processed. Data editing, zero-offset correction, DC filtering, dewowing, automatic gain control (AGC), trace equalization, band-pass filtering in frequency domain, NMO correction and migration were applied to process the data. GPR data were constrained with a borehole log and interpreted in terms of the radar facies. Two intercalated radar facies namely; sand and clay are identified. The depth of penetration of the radar signals ranges from 4 m to 14 m. The thickness of the reinforced concrete hardstand across the study area is 0.15 m. Voids / cavities are suspected only at three sampled points with the depth range of 1.1 to 6.3 m.
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Tree Root Imaging by Ground Penetrating Radar Synchronised with Self-Tracking Total Station
Authors K. Takahashi and K. AoikeSummaryLocating tree roots in subsurface is an important task in the treatment of unhealthy trees. There are some examples of tree root imaging by ground penetrating radar (GPR) scanned in multiple straight survey lines. Tree roots tend to extend in radial direction from the trunk and the conventional straight line scanning is not optimum considering antenna polarisation. We developed a GPR system that records accurate position of antennas by tracking with a total station. The system is allowed to scan freely while data collection for 3D measurements and thus circular scanning can be employed in the tree root imaging. In this way, antennas directed normal to scanning direction can keep polarisation parallel to radially directed targets and thus receiving higher reflection amplitude from tree roots is expected compared to scanning in other directions. We used the system for trees in parks and major root systems were successfully imaged. The present paper illustrates the imaging results.
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Hydraulic Permeability Prediction from Induced Polarization Data at Field Scale
Authors G. Fiandaca, P.K. Maurya, N. Balbarini, A. Hördt, I. Møller, V. Rønde, N. Foged, P.L. Bjerg, A.V. Christiansen and E. AukenSummaryIn this study we present the prediction of hydraulic permeability (k) from time-domain spectral induced polarization (IP) data, measured in boreholes and along 2D surface profiles. The borehole data were collected with the El-log technique, which provides undisturbed “while drilling” measurements of the direct current (DC) resistivity, time-domain IP data and gamma radiation. Data were measured on unconsolidated formations at a landfill site in South Denmark, in three boreholes and along 16 2D profiles.
DC and full-decay IP data were inverted in terms of the BIC re-parameterization of the Cole-Cole model, which present smaller parameter correlations and disentangles bulk and surface conduction. Permeability values were computed from bulk conductivity and the maximum imaginary conductivity, using the empirically-derived formulae presented in a recent study without any calibration. The IP-derived k estimates were compared to those estimated using grain size analysis and slug tests, for a total of 157 comparisons.
A good correlation, on average within one decade, was found between the k estimates over four orders of magnitude, with similar depth-trends. In conclusion, IP can be reliably used for estimating hydraulic permeability on unconsolidated formations at the field scale, using the relations found in the laboratory without any further calibration.
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High-Resolution Shallow Seismic Integrated with Electrical Resistivity Method for Hydrogeological Prospecting
Authors E. Onyebueke, M. Manzi and R. DurrheimSummaryTwo perpendicular high-resolution shallow seismic and resistivity profiles were acquired to assist in imaging the near-subsurface sedimentary architecture for hydrogeological prospecting in the Nylsvley Nature Reserve. We deployed 48 channels of 14 Hz geophones with 1–2 m dense source-receiver spacing, providing fold coverage of 24. To enhance the reflected seismic signal, we employed an extensive seismic processing workflow which enhanced the seismic reflectivity on the stacked sections. The seismic reflection interpretation was constrained and integrated with refraction, resistivity tomography and the 1-D multichannel analysis of surface waves (MASW) to generate the model that best represents the real subsurface geological model. The integrated results show the bedrock-overburden contact at 8–12 m depth, which correlates well with boreholes, drilled in the area. In addition, reflection seismic and refraction tomography show the bedrock undulation and velocity changes associated with erosional surfaces or weathered/fracture systems. We further interpret these characteristics to be associated with groundwater movement and storage related to the fractured/weathered zone within the bedrock. The integrated data also delineate the interface between the unsaturated sand and saturated sand-gravel that represents the groundwater water table. This study demonstrates the potential of combining several surface geophysical techniques for near-surface investigations, especially for hydrogeological prospecting.
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Geophysical Surveys for Improving the Hydrogeological Conceptual Models in the Semi-Arid Region of Valle Alto (Bolivia)
More LessSummaryGeophysical methods provide important information for mapping the subsurface. In semiarid areas, a detailed knowledge of the aquifers geometry can assist to a better management of groundwater. In the Valle Alto (Bolivia), which is a semiarid region, there is gap in the knowledge about the aquifer system geometry and hydrogeological processes. Local reports indicated problems in some wells such as very low production and bad water quality (i.e. high concentrations of salts). In order to improve the knowledge about the aquifer system and identify the depth of the layers with saline water, the geophysical methods Electrical Resistivity Tomography (ERT) and Time Domain Electromagnetic (TEM) were applied. The main objective of this study is to refine the hydrogeological conceptual models and to delimitate the depth and thickness of saline layers. The TEM soundings are performed in a grid of 150 m separation, which provide significant information for proposing 2-D models that displays the lateral/vertical extent of the saline layers. While the ERT surveys were performed across the Valle Alto in order to obtain long cross sections where the aquifer geometry can be exposed. With the refined conceptual models, further planning and policies can be proposed for protection and sustainable groundwater exploitation.
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New Processing Schemes for the Removal of Harmonic Noise from SNMR Signals in Complex Multi-Frequency Noise Environments
Authors T. Kremer, J.J. Larsen and F. NguyenSummaryIn SNMR surveys, the electromagnetic (EM) perturbations originating from powerlines infrastructures is often the main EM noise source that contaminates the SNMR acquisition signal. The removal of these harmonic signals is therefore critical to extract the data and carry out the study. To date, some techniques exist that give satisfying results in many cases, provided that the assumptions of a harmonic noise based on a single and constant fundamental frequency are valid. However, when these conditions are not met and the characteristics of the harmonic noise become more complex, these methods will fail to remove it correctly. In this paper, we show how such complex conditions will affect the frequency spectra of the SNMR acquisition signal. Then, we address the issue of a harmonic noise composition based on two different fundamental frequencies, by solving the non-linear optimization problem simultaneously for the two frequency values, using a 2D grid-search. Then we investigate the case where the fundamental frequency of the harmonic signal is not constant but variates within the signal duration. We expose a new approach based on the Nyman and Gaiser estimator, which, associated with a signal bootstrapping strategy, efficiently handles this situation.
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Supplementary Geophysical Survey in Urban Park for New Metro, Fælledparken, Copenhagen
Authors O.F. Nielsen and K. MartinezSummaryThe new metro line in Copenhagen, Cityringen, is currently under construction and is expected finalized in July 2019. As part of the preinvestigations urban geophysical site investigations were carried out including 13.9 km of seismic lines, 29 VSP (Vertical Seismic Profiles) as well as a geo-electrical survey covering Fælledparken, the largest urban park in Copenhagen (ca. 400,000 m2).
The purpose of the geoelectrical survey was to provide detailed hydrogeological information in the urban park area where only sparse borehole information was available.
A total of 68 criss-crossing DC-soundings were collected and interpreted using a Spatially Constrained Inversion (SCI). Due to this approach and detailed planning only 4 out of the 68 soundings were affected by electrical coupling effects from buried cables.
The results showed a 5–10 m thick secondary aquifer underlaid by approximately 10 to 35 m clay till indicating a minimal recharge from the secondary to the primary aquifer. Below the lower till the top of the limestone was seen dipping from approximately 25 m depth in the eastern part of the park to approximately 35 m in the western part.
The results contributed to a detailed hydrogeological understanding of the area and therefore a more realistic hydrological model.
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