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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 - 50 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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