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8th EEGS-ES Meeting
- Conference date: 08 Sep 2002 - 12 Sep 2002
- Location: Aveiro, Portugal
- ISBN: 972-789-071-7
- Published: 08 September 2002
1 - 50 of 131 results
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Cave detection with GPR and seismic methods
Authors B. Neducza, L. Hermann and M. Pattantyús-ÁIn the last few years building sites have been extraordinarily overestimated on the hilly part of Budapest, where protected caves can be found. Thus, new buildings are built on the unbuilt areas, while on the already built-up houses are enlarged. If we close the swallers we stop the growth of voids and stalagmites. It’s important to know the size, position and depth of natural voids and cavities before building or reconstruction. We used Ground Penetrating Radar (GPR) and shallow seismic measurements to detect these objects.
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Engineering geological and geophysical investigation at the dam site, Cine/Turkey
Authors S. Sirri Seren, J. Kleberger and O. SimsekCine Dam in South West Turkey will be the first major roller compacted concrete (RCC) dam in Turkey and with the height of 135 m one of the highest in the world. When completed it will perform a number of functions such as water supply, power generation and flood control. Excavation works of dam foot print area are almost completed. The dam is located along a narrow section of the Cine river valley. The cross section along the designed dam axis shows a slightly asymmetrical V-shaped profile, with a steeper left than right bank. The area of Cine dam is dominated by gneiss bedrock, which belongs to the Menderes complex. Foliated augen gneiss prevails, with subordinate massive gneiss beds of more homogeneous texture and highly foliated and intensively sheared gneisses with micaceous schists. The rock mass is gently folded, intensively jointed and locally intensively faulted with the most prominent faults dipping almost vertically and persisting several kilometres. Within the faults and adjacent to them the rock mass is largely disintegrated and locally rich in kaolin. Grain sizes in the core zones of faults are dominated by sand to silt. Site investigation for Cine Dam was developed and executed in several phases. Main aim of the geophysical investigation in the dam site area is to define the boundary of the engineering geological units, location of fault zones, which are covered by slope debris and soils, dynamic elastic parameters of the materials in the core zones as well as in the damage zones of the faults, velocities and dynamic elastic parameters of the soil and rock mass to be encountered at both side of the dam foot print area. Geophysical investigation was correlated with the core drill holes, which were carried out during same investigation campaign, and geological mapping results.
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Spectral analysis of surface waves and seismic refraction for the inspection of tunnel walls
Authors O. Abraham, J. Lagarde, Ph. Côte and O. MagninIn many fields, e.g. civil engineering, mining engineering and underground disposal, it is very important to be able to quantify the extension of the rock mass zone disturbed by underground excavations. In multi-layered plan media a combination of Seismic Refraction (SR) and Spectral Analysis of Surface Waves (SASW) can be used to determine shear modulus and compression modulus profiles. Both techniques cannot be transferred to circular tunnels without questioning the limit of a plan geometry approximation. Indeed, in the following we show that the curvature of the tunnel cannot be neglected even for a thin damage zone compared to its radius. Special attention is given to the SASW for this technique will work even if the tunnel walls are covered with a concrete lining. Both experimental and numerical results are presented. The error introduced by the curvature on the SR interpretation is of the order of precision required for the investigation but its influence does not show clearly on the experimental data. For the SASW, the influence of the curvature on the experimental data cannot be ignored for the global trend of the dispersion curves is greatly changed. The experimental SASW dispersion curves are matched with numerical dispersion curves calculated with the finite element code CESAR_LCPC in an error and trial process.
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Multimodal interpretation of surface wave data
Authors S. L. Valentina, S. Claudio and F. SebastianoSurface Wave Methods become quite popular tools for geotechnical characterization since they supply the stiffness profile of the sites with a cost effective testing procedure. Several acquisition and processing approaches have been developed to infer the Rayleigh wave dispersion curve which is then inverted (Nazarian and Stokoe, 1984; Park et al., 1999). Independently by the chosen procedure, the inversion is mainly carried out assuming that the experimental dispersion curve is actually the first Rayleigh mode. It is a rather diffuse commonplace among geophysicists that, for normally dispersive site, the first mode is in fact prevailing and that only for inversely dispersive site the role of higher Rayleigh modes has to be taken into account (Tokimatsu et al., 1992). By using a multi-modal modelling it can be easily shown that higher Rayleigh modes contribute to the effective dispersion curve not only for inversely dispersive stratigraphies but also in presence of quite high velocity contrasts. Beside this, since one of the main advantages of surface wave methods is to be effective even in case of velocity inversion, when for instance seismic refraction fails, it is quite important to overcome the limitation due to the influence of higher modes, considering them in the interpretation process. Furthermore it can be also shown that the analysis of higher modes can help to obtain much reliable information also in cases of normally dispersive sites (Foti et al., 2002). As far as concern the dispersion curve interpretation some further considerations are deserved. The simplest approach is to transform the dispersion curve from the phase velocity vs. frequency into the phase velocity vs. wavelength domain and to attribute the velocity values (multiplied by a factor of 1.1) to a depth approximately equal to one-third or half the wavelength. This approach, quite popular in the professional practice of surface wave testing is usually considered an approximated approach but can be easily demonstrated that it is in fact erroneous because the energy distribution with depth can strongly vary depending on stiffness contrasts among layers. A more rigorous approach, which is also widely diffuse, is to invert the experimental dispersion curve considering it as the first Rayleigh wave mode. This procedure can be effective and supplies reliable results only in those cases in which one can be sure that the first mode is prevailing within the considered frequency range. Otherwise it can lead to some degree of error in the estimation of the stiffness profile. The experience carried out at more than 50 different sites, where surface wave test results could be compared with other reference data, has shown that, in the majority of the encountered cases, to perform a reliable interpretation the influence of higher Rayleigh modes could not be neglected. Multi-modal interpretation involves the possibility of recognising experimentally the modal curves but this is usually impossible by using traditional acquisition and processing approach. Another possibility is to invert the experimental dispersion curve but, since it depends also on the acquisition layout, it has to be considered as an apparent curve (Foti et al., 2000). Furthermore its pattern can change dramatically also for quite small changes of the model parameters. For this reason is not easy to use the apparent dispersion curve in an iterative inversion process and trial and error inversion (Tarantola, 1987) can be preferred.
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Development of a new fast remote controlled 3D geoelectrical monitoring system for subsurface surveillance
More LessDuring recent years the dc-geoelectric method has been used widely to investigate the structure of landslide areas, thus gaining the status of a state-of-the-art-method in civil engineering for this However so far the dc-geoelectric method was hardly used to detect structural changes with time in active landslide areas, and no application is known to us where this method was used as a permanent online monitoring system with a sampling interval of several times per day.
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Detection and characterisation of underground cavities using high resolution seismic reflection (HRSR)
Authors L. Driad and B. PiwakowskiOld underground mining works are subjected to risks of collapse of which the assessment is a complex process. In the case of inaccessible underground mines, the difficult task for the risk assessment is to classify the already collapsed zones (no further risk) from still stable structures which may collapse in the future. The knowledge of the characteristics of the underground cavities and hosting rock mass can provide relevant information. However, accurate underground cavities detection and characterisation based on geophysical techniques are still a scientific challenge in the subsoil prospecting domain. Among these techniques, the high resolution seismic reflection is the most successful in the frame of underground cavities detection. The study presented in this paper, is a part of an extended research program aiming at prediction and controlling ground motions induced by underground cavities. The objective is to identify the most appropriate geophysical technique to localize and characterize the underground cavities at variable depths (several meters to 300 m). Thus, to meet these goals we have investigated the high resolution seismic reflection technique (HRSR). The selected test site is located close to Gréasque municipality in south France (figure 1). In this region, the underground works undertaken during the last two centuries consist of two mines: coal mine and cement stone quarries1 (marl limestone). The geological setting is characterized mostly by coal layers and massive limestone formations of the upper cretaceous with alternated coal strata of variable thickness dipping westwards.
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Experience of karst localization using magnetic resonance soundings
Authors A. Legchenko, J. M. Baltassat, Y. Albouy, J. M. Vouillamoz, M. Bakalowicz and W. Al-FaresThe main advantage of the Magnetic Resonance Sounding method (MRS), compared with other geophysical tools for water prospecting is that the MRS is sensitive only to subsurface water (Schirov, et al., 1991). Inversion of MRS field data reveals the water content and the relaxation time T with r being the coordinate vector (Legchenko, and Shushakov, 1998; Legchenko, et al., 2002). In a porous medium the relaxation time T is proportional to the mean pore size 1 (Kenyon, et al., 1997), where and V are the surface and volume of pores respectively.
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Magnetic resonance sounding method applied to catchment study
Authors A. Legchenko, J. M. Baltassat, C. Martin, H. Robain and J. M. VouillamozLogs of the water content and relaxation times T and derived from Magnetic Resonance Sounding (MRS) measurements reveal the depth and thickness of subsurface water-saturated layers. Furthermore, using experience acquired through Nuclear Magnetic Resonance (NMR) logging (Hinedi, et al., 1993; Kenyon, et al., 1997), MRS data allow estimation of the effective porosity and hydrodynamic properties of aquifers. Once calibrated (definition of empirical constants C and for a given geology), MRS provides the effective porosity )z(w)z(*2)z(T1wpC )z(wC)z(wMRS=φ, (1) the permeability )z(T)z(wC)z(k12pMRS=, (2) and the transmissivity ∫=zdz)z(kTMRSMRS, (3)
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GPR Tomography for mapping soil moisture and roots
Authors Sh. Hanafy and S. A. al HagreyFor high resolution georadar tomography inverting of arrival times or amplitude data yields a distribution of electromagnetic velocity or an attenuation-related parameter that images anomalous subsurface features, e.g., voids, moisture content or clay heterogeneities. Tomographic reconstruction technique is widely used in geophysical and geological field investigations (Bregman, et al., 1989; Daily & Owen, 1991; Cai & McMechan, 1999). Solving the tomography problem depends mathematically on solving a system of linear equations iteratively (Peterson et al., 1985). The principle of the tomographic method shows a typical ray path from the transmitter (Tx) to a receiver (Rx) Ri (Fig. 1). Multiple Tx and Rx locations yield a number of such rays crossing the intervening material in different directions. The region between Tx and Rx lines are discretized into cells and the slowness sj of the cell j is assumed to be constant over the area covered by a single cell. The recorded travel time can be expressed as integral over the ray path Each of these integrals, in discrete form, becomes one equation in the linear tomographic system that is to be inverted for velocity and/or layer shape (from travel times) or for attenuation (from amplitudes). The linear system of equations has the form: t=As, where t is the GPR time vector, A is the distance matrix connecting Tx-Rx locations, and s is the GPR slowness vector. We used this principle to develop a new GPR tomography algorithm (SeismoRad computer program) for inverting surface and crosshole data (Hanafy, 2002).
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Application of electrical imaging for borehole siting in hardrock regions of India
Authors R. Barker and T. Venkateswararao and M. ThangarajanAround seventy-five percent of India is underlain by granitic and gneissic basement rocks with a thin covering of weathered material. Many of these areas are semi-arid to arid and do not have high enough rainfall to support agriculture throughout the year. Here, groundwater is not difficult to find as the water table is generally within 10 m of the ground surface; however, the yield of boreholes is frequently low and supplies do not have long-term sustainability, so it is important to locate boreholes in the most productive areas possible. One of the methods found to increase the efficiency and effectiveness of borehole siting investigations is geophysics, with electrical imaging becoming an increasingly popular survey technique. Here we present the results of trials of a manual imaging system applied to groundwater investigations in the Dindigul area of Tamil Nadu and show how electrical imaging can provide much more meaningful and reliable data than is possible with other types of survey. It is the first use of electrical imaging in borehole siting investigations in India.
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Controlled laboratory experiment to test the validity of time-lapse electrical imaging
By J. MooreAs legislation imposes tighter constraints on the identification and remediation of contaminated land, so the demand for reliable, detailed and preferably inexpensive techniques with which to monitor subsurface conditions has increased. The electrical resistivity method is a particularly appropriate technique to implement in the study of groundwater movement and contamination, as it is sensitive to contrasts in saturation and to contrasts in groundwater conductivity. The resistivity method has additional benefits in the monitoring of groundwater conditions as it is non-invasive and provides continuous spatial information, properties lacking from all traditional hydrogeological monitoring techniques. However, interpretation of resistivity data can be ambiguous, as many subsurface models of resistivity distribution can give rise to similar results measured at the surface. A means of negating the need for a definitive interpretation of resistivity data is to examine only the changes in resistivity over time. This concept of time-lapse electrical imaging involves repeat measurements of resistivity at a time interval appropriate to the rate of change of subsurface conditions expected at the study site. It has been shown that time-lapse electrical imaging carried out during groundwater drainage (Berry, 1996) and infiltration (Barker and Moore, 1998; Hatzichristodulu, 1999) events can provide a description of the changes in saturation occurring within the subsurface. However, interpretation of these studies remains qualitative and often difficult to validate. One means of validating the fundamental concept of a technique is through the use of laboratory modeling, as it is possible to select the properties of the media under investigation and to visually record the physical processes occurring during the experiment. This study describes a laboratory experiment, designed to simulate a groundwater pumping test in a porous media aquifer, with concurrent measurements of electrical resistivity. The aim of this experiment is to validate the interpretation of electrical resistivity measurements recorded during subsurface changes in saturation and to establish the scope of this technique for other hydrogeological settings. Initially the tank is filled with a well-sorted sand to represent a homogeneous model. A body of contrasting hydraulic properties is then implanted to observe the effects of heterogeneities.
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Integration of VSP and TDEM data for hydrogeological characterisation
Authors A. Godio and C. StrobbiaThe hydrogeological characterisation often needs great detail and resolution to plan the drilling phase and to evaluate the possible interference between wells. We describe an integrated approach to analyse a complex formation of argillite and sandstone hosting an aquifer of great interested for mineral water supply: Time Domain Electromagnetic and borehole seismic methods are used.. Electromagnetic and electrical tomography measurements from the surface allowed estimating the geological set-up of the area for the optimal positioning of the borehole. The subsequent VSP (vertical seismic profiling) permitted to analyse the main fractured zones inside the sandstone: a full-wave analysis is performed to improve the resolution and reliability of the seismic data. The paper introduces some aspects of seismic data processing to separate and analyse the different wavefields involved in the VSP measurements.
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Water exploration on the Lastove Island (Croatia) by electrical tomography and seismic methods
By F. ŠumanovacWater exploration was carried out at the island of Lastovo, situated farthest from the Croatian Adriatic coast. The investigated area is situated in a tipical karst field, close to the Lastovo town, with the name Prgovo Polje (Prgovo Field). There are several exploited water wells in this area, which produce 2-3 l/s of water, but this is not sufficient because of the growing demands for water. The main goal of this water exploration was to capture more water, minimum of 5-6 l/s. Previous explorations and wells made in the sixtees were aimed at very shallow aquifers, mainly fine-grained sands, but because of the strong pumping, water has become brackish and has to be desalted by adequate technology. With respect to the fact that more water can only be captured from deeper aquifers, target rocks were fractured carbonate rocks in the bedrock of clastics. Since the infrastructure in the area of Prgovo Polje is mainly completed, the first goal was to discover new resources in this area. The secondary goal was to get the water of as low a salinity as possible, since the price of desalinization technology depends on the water salinity.
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The use of ERT for the characterization of a thermal karstic aquifer
Authors A. Bratus and D. Nieto YabarThis is a case history of an ERT survey in a karstic aquifer characterized by the presence of thermal water having a temperature > 35° C. The aim of this survey was to define the best position of a well for exploiting thermal water, in order to restore the old thermal bath. ERT was used to define: o The depth and the morphology of the carbonated bedrock o Different aquifer features o Thermal water concentration The positioning of the well defined by the ERT survey result was successful. Thermal data logging agreed with the ERT model.
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Analog modeling of streaming potential during well-pumping
More LessElectrokinetic potentials, also called streaming potentials (SP), are natural potentials between sets of points on the surface or within the soil. They are produced by the flow of a fluid, generally water, in a porous media. SP being the only surface method able to give indications on the direction of flow, it is used in several applications involving water movement, as in volcanic and geothermic areas, dam and lake leakage, landslides and well-pumping. The electrokinetic phenomenon, the relative motion of ion species producing an opposite conductive current, is well-known, as is the double layer model of Helmholtz-Smoluchowski. Furthermore, from the mathematical point of view, the thermodynamical set of equations allows the distribution of the SP to be modelized (Revil et al. (1999a, 1999b)). Although the overall theory is known, as soon as mineral species are involved, the subject becomes much more complicated. Many laboratory surveys (e.g. Ishido et al. (1981)) had been conducted in order to understand which parameters, in what manner and to which extent, act upon the production of SP. But after more than forty years of research, the authors still do not agree completely on the results. On a larger scale, field measurements, even less is understood. The main reason is that there is no way to know the exact values of the influencing parameters and, moreover, they are likely to change over distance and time. Besides, few field cases are presented in the literature, so it is difficult to know how other research groups cope with these problems. There is a gap between the laboratory and the field measurements that has been rarely studied (e.g. Sato et al. (1998)). We are trying to fill it partially by the analogical study of a scale model of a pumping-well.
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Electric and electromagnetic response patterns of fault zones in granites
More LessGroundwater percolation in granitic terrains is highly conditioned by fault zone type structures where the rock has been disrupted to a point as to increase the overall porosity and local permeability. This is particularly the case where a surface sedimentary or weathered layer is nearly absent. For practical purposes that is the situation in granitic terrains in central Portugal where the weathered layer is no deeper than 3 m. In such a situation the variations in geophysical parameters may be considered to be related to variations in the bedrock itself. The geophysical methods considered below include “classic” electrical sounding, multidirectional electrical sounding and VLF/VLF-R profiling.
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Integrated geophysical/hydrogeological study in the Danish-German border region – An Interreg project
Authors R. Kirsch, S. Thomsen, W. Scheer, W. Voss and R. FriborgAs groundwater reservoirs are crossing national boundaries transnational efforts are required to ensure a sustainable use and an effective protection of these water resources. This is the background of a Danish-German project for the mapping of aquifers and covering layers in the border region Sønderjylland / northern Schleswig-Holstein (Fig. 1). This project was funded by the European Community under the INTERREG-programme. The use of geophysical methods to establish a geological model of the project area is shown in this paper.
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Analysis of helicopterborne electromagnetic data for hydrogeological investigations
Authors N. B. Christensen and R. J. TølbøllTraditionally, frequency and time domain airborne electromagnetic (AEM) systems have been used for mineral prospecting, often in parts of the world with little environmental electromagnetic disturbance. However, the increased focus on hydrogeological investigations in many parts of the world has led to a growing interest in the possibility of using airborne systems for such purposes, even in densely populated areas (Sengpiel and Siemon 1998). This raises questions about the resolution capabilities of AEM systems and their sensitivity to disturbing influence from ambient electromagnetic noise and the presence of man-made structures such as power lines, buried cables, and fences. The data quality of earlier AEM systems was such that they were mainly used as "bump detectors" capable of indicating the presence of good conductors. Quantitative interpretation of the data was often not warranted (Huang and Fraser 1999). Traditionally, helicopterborne frequency-domain electromagnetic (HEM) data have been processed to produce iso-resistivity maps using lookup-tables, and transformations of the apparent resistivity and the centroid depth obtained from the table lookup have been used to produce pseudosection images. With the general improvement of HEM systems quantitative interpretation has become an option (Sengpiel and Siemon 1998). In general, the objectives of a hydrogeophysics survey are; detection of non-permeable boundaries of a potential aquifer, often coinciding with the clay-sand boundaries, discernment of internal structure in the aquifer and mapping of near-surface capping clays reducing the vulnerability of the aquifer. This paper presents quantitative analyses using one-dimensional (1D) models of the resolution capabilities of a modern HEM system with 5 frequencies. Because a frequency domain ground system equivalent to the HEM system does not exist we have chosen a profile oriented, multi-electrode DC geoelectrical system (CVES) with a comparable depth penetration and compared the resolution capabilities of the HEM system to that of the CVES system for a number of hydrogeologically relevant models.
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First experiments on solid transport estimation in river-flow by fast impedance tomography (SOTEBIT).
Authors L. Sambuelli, G. Lollino, G. Morelli, L. Valentina Socco and L. Bidoneayleigh (1892), studied the effect, on the overall conductivity, of particles with conductivity σ included in a medium with conductivity σ0 ; Fricke (1924) extended the Maxwell's formulas from spherical to ellipsoidal particles. Geophysics and chemistry literature is reach of studies dealing either with the conductivity of saturated grainy materials or with the conductivity of suspensions: from the work of Archie (1942) to the model of Wyllie and Southwick (1954); from the one of Hanai (1960) up to those more recent of Waxman and Smits (1968) taking also in account for the clay content. More recently the papers of Clavier et al. (1977), introducing the dual water model; of Sen et al. (1981), working with the complex dielectric; of Bussian (1983), Garboczi and Douglas (1995) and Chinh (2000) can be cited. The interest on the subject is still high, as the many papers constantly published on scientific geophysical journals demonstrate, and a consistent scientific background on the relations among fluid, grain, mixture conductivities is available. Moreover the recent, fast development of hardware and software related to electric impedance tomography (EIT) allows for the possibility of performing fast tomography acquisition and processing (Barber and Brown, 1984; Barber and Seagar, 1987) so that the so called “process tomography” has become a leading field of research (Dickin and Wang, 1996). In as much as process EIT allows for fast resistivity or capacity imaging of sections through rapid flows (Xie et al., 1992), to test the possibility of getting resistivity images crossing the rivers and containing information on the solid transport distribution becomes a worthwhile research target. This paper reports the first tests performed within a real scale model with quasi-static flow to verify the possibility of Solid Transport Estimation By fast EIT (SOTEBIT).
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Avoiding miss-interpretation of GPR measurements in forested areas
Authors H. Paasche, N. Ormuz, J. van der Kruk and J. TronickeGround-penetrating radar (GPR) is a common method for investigating the shallow underground. Subsurface reflections are usually associated with variations in dielectric properties. Unfortunately, reflections and diffractions from above-surface objects may contaminate GPR data. We have conducted a dual-component GPR survey across a shallow aquifer situated beneath a forest. Strikingly different reflection patterns are obtained for the two antenna orientations. To understand better the observed patterns, we first describe key characteristics of the dipole radiation emitted by GPR antennas. This is followed by the results of a simple modelling exercise designed to determine the effects of diffractions from numerous trees on GPR data recorded with the two antenna configurations. Based on these results, it is then possible to distinguish between subsurface and above-surface features recorded in a field data set, thus leading to a more reliable image of the shallow subsurface.
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Combined high resolution magnetics and GPR surveys of the roman town Flavia Solva
Authors S. S. Seren, A. Eder-Hinterleitner, W. Neubauer, S. Groh and P. MelicharArchaeological problems as considerations on the extent, the structure and the preservation state of an archaeological site can be solved very quickly and cost effective by archaeological prospection. The use of both prospection methods, high resolution magnetic and ground penetrating radar (GPR), became very successful in investigating Roman sites in Austria. High resolution magnetic prospection delivers not only information about the extent and structure of a Roman town, but also important indications of former wooden- and burned archaeological features. Prospecting 30.000 square meters a day even large sites can be surveyed within reasonable time applying magnetic
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Analysis of high resolution GPR time-slices from archaeological sites in Italy
Authors S. Piro, D. Goodman and Y. NishimuraRecent developments in 3-D high-resolution multi-image processing and contouring, as opposite to destructive testing, have greatly contributed to improve the quality of geophysical information in archaeological reconnaissance surveying. Nowadays non-destructive ground-surface geophysical prospecting methods, which involve detailed physical and geometrical reconstruction of hidden ambient, are increasingly used for the investigation of archaeological sites. Ground Penetrating Radar (GPR) offers very high resolution sounding capability with detection of features of the order of a few tens of millimetres thickness at ranges of several metres. In this work, the results of two high-resolution GPR surveys carried out in order to detect superficial walls and floors, in two archaeological sites in Italy, characterised by different geological environmental conditions, are presented.
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Archaeological prospection of clay-brick walls using resistivity methods and GPR at San Julián Bay, Argentina
Authors E. Lascano, A. Osella, M. de la Vega, S. Buscaglia and J. LanataIn this work we present the geophysical prospection done in Florida Blanca archaeological Site, in San Julián Bay, Santa Cruz province, Argentina. Ground Penetrating Radar and the resistivity method were applied to find very shallow clay-brick archaeological structures. An optimization in the resolution of both methods was necessary to detect the low contrasts in the electrical response of the soil and the clay-brick walls. Profiles were carried out in the zone of interest and outside it to compare results. A periodic distribution of low contrast shallow anomalies was found with both methods indicating the presence of the walls of the houses.
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Intensive survey, geomagnetic, excavation and GIS for the intrasite study of the Roman site of Terlamonte I (Teixoso, Covilhá, Portugal).
Authors A. J. M. Silva and P. C. CarvalhoThe Roman site of “Terlamonte I” is lies in the natural region of “Cova da Beira” (East Central Portugal), belonging to the Zêzere’s river basin side system, tributary of the Tejo river. The region was intensely occupied in the Roman period, certainly due to its mining wealth in tin and gold, to its remarkable agricultural capacity and to its geo-strategic position on the Roman road system of the province of Lusitania. The “Centum Cellae tower” and the “Orjais” temple are certainly the most important of the standing Roman monuments of the area (Frade, 1998). The site of “Terlamonte I” stands on a gentle slope, about 500 m from the river Zêzer, which flows down in the valley. The landscape, now loosely settled, being a prairie drained by many little lines of water, running in fields of moderate declivity. The landscape’s monotony is broken by the presence of oak woods in spots, where more often the coarse porphyroide granite crops out. Many streaks of quartz, sometimes "brechóides", cross that granitic mass which is the geological substratum (Teixeira, 1974). Trial excavation on this site began in the spring of 2000, under the direction of one the authors of the present paper (PCC), as part of a research project on the “Roman’s occupation the ‘Cova da Beira’ region” (enrolled in the “National Archaeological Program: 2000-03 – IPA”). The excavations fell upon the main building area and, as a result of these, the type and chronology of the site were determined. The “Terlamonte I” is a rural site dated to the 1st and 2nd centuries AD.
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Magnetic interpretation of gradient field in archaeological prospection
Authors F. Almeida, A. Silva, J. Alarcão and P. CarvalhoArchaeological magnetic exploration had been intensively used to investigate different occupational periods in various geological environments. Today, magnetic acquisition is very rapid, processing data can be easily done and large areas can be surveyed making this method one of the most popular among archaeologists. When magnetic material properties contrast in low noisy magnetic environments mapped images can be obtained showing linear patterns that can be sometimes architectural related. Notwithstanding the archaeological importance of the surveying plan view, generally, the image only shows a kind of projection over the surface where the measurements were done and depth is not directly evident as well as horizontal localization is biased. Much more information can be obtained from the anomalies if their wavelength and earth magnetic induction direction and inclination are taken into account. Quantitative approaches are known like reduction of the magnetic image data from the geographical coordinates of the measurements to the Magnetic North Pole, and direct or inverse magnetic body models. The self-explanatory images generally obtained in archaeological geophysical exploration may justify why in this area of Humanity/Science, quantitative methods are sometimes neglected that lead the field archaeologist to dig with no planned depth and right emplacement. The objectives of this communication are: to define qualitative rules for interpretation and to show, for point anomalies, an easy and rapid method based on the inversion of the location and depth of two opposed poles (bi-pole).
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The airborne ramses radar experiment for archaeological prospecting in a temperate climate region
Authors R. Chapoulie, M. Martinaud, P. Paillou, D. Barraud and P. DreuilletIn less than ten years, microwave remote sensing techniques have provided unexpected insights in the Earth surface structure and processes, and triggered the development of entirely new research fields. Using space-borne Synthetic Aperture Radar, SAR, theoretically three characteristics of the Earth surface can be observed : the slope (topography), the surface roughness (vegetation, geology, ocean surface), and the dielectric properties (nature of soils, moisture content). Low frequency SAR (L and P-bands) represents a promising future for remote sensing, since it allows to investigate the sub-surface down to several meters and penetrates the vegetation cover. In particular, P-band radar can achieve penetration capabilities which could be used for accurate mapping of sub-surface characteristics such as moisture content or geological structures. The region near Bordeaux in France was chosen as a suitable laboratory site for fieldwork validation of the new P-band RAMSES airborne SAR, the so-called PYLA’01 experiment (Paillou et al. 2001). Several flights were performed over the region during April and May 2001. This experiment was planned within the “low frequency radar working group” set up by the French space agency CNES in order to explore potentials of low frequency radar for sub-surface moisture detection, biomass evaluation, mapping of the ocean bathymetry, mapping of ocean salinity and for archaeological prospecting. The results will be used to promote a future P-band RAMSES flight foreseen in Egypt for the end of 2003, which will validate potentials of low frequency SAR in an arid context. The data quality of the PYLA’01 experiment is high, with no UHF interferences. Moreover calibrated data are available. The aim of this article is to present the first results of this airborne radar campaign over an archaeological site.
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Non invasive controls of balcony corbels by means of GPR investigations
Authors P. L. Cosentino, D. Miraglia, L. Romano and M. ScopellitiThe aim of this research is to optimize a non-destructive control procedure, studied and already used by authors, carried out with electromagnetic method (high frequency GPR) to control the security of balcony corbels of historical and monumental masonry buildings, built since many centuries ago until the incoming of reinforced concrete.
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Geophysical researches in the Roman villa del Casale (Piazza Armerina, Sicily)
Authors P. L. Cosentino, P. Capizzi, R. Martorana, D. Miraglia, S. Pellerito, V. Sanfratello, G. Anselmo, C. Genovese and P. Messina“Piazza Armerina” is a very important archaeological site in Sicily and many excavations have been carried out during the last century. One of the most important findings is the well known “Villa del Casale” (Fig.1). Fig. 1 – Aerial photography of “Villa del Casale”. The excavations started in 1929; took back in the '40s and more deeply in the ‘50s and they aren't finished yet. "Villa del Casale" was built between 330 and 360 A.C. and it had its period of shine during the 4th and 5th century, when disappeared under the mudflow. The villa is 3500 square meters large, and it was once Maximilian Hercules’ haunting house. He was one of Diocletian's collaborators and both of them managed the Roman Empire. Its interest is mainly due to the mosaics of the floor, among the largest and most beautiful ones of the Roman epoch. Techniques, style and the figures call to mind the floors of Northern Africa, and there are certainly works of African artists. The Villa can be divided into four main groups: main entrance and spa; peristyle with dining room and guest room; private rooms and basilica; triclinium and elliptic courtyard. They are not on the same level because the structure was built following the topographic profile.
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Comparative application of gravimetry ground penetrating radar and high-resolution seismic reflection surveys for the detection of shallow archaelogical vestiges
Authors P. Palacios, J. Cartel, C. Macedo, E. Loiseau, B. Piwakowski, M. Gouyegou, J. Mania, D. Roger, F. Loridant, P. Herbin and C. LouvionThe city of Bavay, in the North of France, has been, since the Roman Empire, an important place for trade, and the main crossroads before the Boulogne’s harbour. Its population was, at that time, mainly composed of rich traders and of a garrison force. Bavay had an extended waterworks system that was supplied by a 30 kilometers long underground aqueduct built in 96 A.C. This is one of the only monuments of that kind known in the North of France. The location map of this aqueduct is shown in Fig.1 The little part of this monument that has been discovered showed that the aqueduct was constituted of a brick and stone masonry. Its section is approximatively 1 m². It is burried at depth varying from 1 to 2 meters in a clay layer which is followed by limestone. A cross-section of it is shown in Fig.2 The goal of this paper is to check the possibilty of the detection and the localisation of the aqueduct. Between the various geophysical methods, three methods were chosen in order to test their availability for the aqueduct detection: gravity, ground penetrating radar (GPR) and high resolution seismic reflection (HRS). We point out that the tested methods are non destructive methods, compared with the classical commonly used destructive archaelogical exploration. Other methods like electro-magnetics, electrical coring were tested in the past and did not give any promising results. The experiments were conducted in the site where the position of the aqueduct was partially suspected. The test site was chosen as a 8 x 12 m rectangular area (Fig.3).
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Integrated geophysical methods for the characterisation of an archaeological site (Massenzio Basilica - Roman forum, Rome, Italy)
More LessThe Massenzio Basilica was built by Emperor Massenzio in the AD 308 until AD 312, it is one of the biggest Monuments of the Roman age after the Coliseum. It spreads in 100x65 square meters and 40 meters high. Now only an aisle remains to evidence the size of the Monument. A general study has been performed in the frame of co-operation between Superintendence of cultural heritage of Rome and University of Rome with the aim to have better knowledge of the Monument both historic artistic as structural point of view. At first bore-hole investigation was performed then to improve and increase the knowledge of the site the study was implemented with a geophysical survey. To characterise the soil where the Monument was built we used electrical resistivity tomography (ERT), vertical electrical survey (VES) and seismic refraction technique, to obtain information about the foundation structures ERT surveys and ground penetrating radar (GPR) were used. The data obtained with the bore-hole investigation were interpolated with the results of 15 VES performed with Schlumberger array having maximum distance between the electrodes AB=100m. The VES were located inside and outside the Basilica (Fig.1). Electric data were inverted by using the steepest descend method (Koefoed 1979). The interpretation of SEV performed inside the Basilica indicated the presence of three layers, characterised respectively from the top to the bottom by a resistivity of about 200ohm.m 2 meters depth, 20ohm.m 16 meters depth and 5ohm.m. The first layer was identified with the concrete floor of the Basilica, the resistivity values of second layer were ascribed to silt clay materials typical of fluvial lacustrine formation and the third layer was identified as clay formation. Resistivity curve of Mas15 with the interpretation is shown in the fig.2. To confirm the results obtained with the VES a multielectrode dipole-dipole array was performed inside the Basilica, (line C).
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Electrical resistivity by electromagnetic slingram mapping, electrical 2D and 3D imaging, and electrostatic logging: A tool for studying an old waste landfill
Authors R. Guérin, P. Begassat, Y. Benderitter, J. David, A. Tabbagh and M. ThiryMany brownfields and mine sites contain acid waters which are responsible for an important mobility of the metallic ions in the environment. To plan site remediation, it is necessary to locate, estimate and describe with non-destructive methods the areas where contaminated materials are present. The aim of this study, funded by ADEME, is to define a geophysical measurement protocol which can be used on contaminated landfills in order to: i) map the distribution of contaminated materials, ii) locate the water table and its seasonal variation, iii) evaluate the water mineralization and its spatial variation, and iv) identify the water leak toward the river drain.
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Dam hazard inspection by nuclear and resisitivty measurements
Authors H. Lindner, R. Käppler, V. Patzold and W. ThießenThe task is to explore hydraulic conductible ranges in a dam. This object is situated near the Rhine, Germany, for flood prevention. On the one hand it is necessary to detect these ranges which are destabilising the dam. On the other hand, this knowledge is important for technical reconstructions. The exploration of such embedments was done by resistivity measurements in a first step. We validated the indications by nuclear geophysical soundings in a second step. In an experiment hydraulic conductivity coefficients were computed.
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Environmental seismic measurements on inland waters
More LessThe latest development of electronics and computer sciences made possible to create special devices to solve special engineering problems. Environmental tasks on inland waters require methods and equipment with low penetration but very high resolution, in many cases less than 1 cm. Because the expression “ultra high resolution” is often used for boomer seismic sections let’s call the VHF seismic method simply sonar. The source, receiver and the data acquisition system was tested systematically on Lake Balaton (Hungary) in connection with the Limnogeologic Project of the Hungarian Geological Institute. Two case histories are presented to show the capabilities of the method in environmental applications.
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Geophysical measurements in volcanic areas: vulcano and lipari
Authors R. Supper, A. Römer, B. Meurers, R. Di Maio and K. AricAs part of the European Community project “TOMAVE” airborne and ground geophysical measurements were carried on the islands of Vulcano and Lipari. In this talk new results and interpretation of ground geoelectrical, seismic and gravity measurements are presented.
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Gradient and Mid-Point-Referred measurements for multi-channel 2D resistivity imaging
More LessResistivity imaging now becomes more and more popular in electrical exploration, due to its ability to efficiently and effectively produce images of the subsurface as a result of the availability of automated data acquisition systems and efficient user-friendly inversion software. One of the major limitations of the technique today is the time-consuming measurement process that tempts data acquisition teams to reduce the data density in order to save expensive field operation time, which in turn can be devastating for the imaging quality. In this paper, two electrode configurations suitable for multi-channel-recording, called gradient array (GD) and the midpoint-potential-referred measurement (MPR), were numerically examined for 2D resistivity imaging. These electrode configurations are well suited for multi-channel data acquisition systems, so that many data-points can be recorded simultaneously for each current injection, so as to reduce fieldwork time very significantly without compromising the data density. First, numerical experiments were conducted to examine the spatial resolution and surveying efficiencies for different data acquisition schemes. The results are compared with the results achieved for the same models with the Wenner-α (WN), Schlumberger (SC), dipole-dipole (DD) and pole-dipole (PD) arrays (Dahlin and Zhou 2001). Then field experiments were done, and results from at a waste dump are presented here.
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Geophysical investigation of the large séchilienne gravitational movement, The Alps (France)
Authors J. M. Vengeon, D. Jongmans, M. Jeannin, M. Wathelet, A. Giraud and O. MericMajor gravitational movements are common in the metamorphic formations of mountain ranges and show various types of failure, such toppling, sagging and translational or rotational sliding. The different failure processes are mainly governed by the characteristics of the discontinuities (foliation, schistosity, faults and fractures) affecting the mass (Antoine et al., 1990). In the Alps, most of the gravitational movements have probably been initiated or reactivated after the retreat of glaciers some 10,000 to 15,000 years ago, and have evolved at very different rates, depending on the initial geological and topographic characteristics, as well as on the other factors contributing to lower the stability (presence of water, earthquake ground motions, climatic cycles). The instability process progresses through periods of stabilisation and reactivation and leads to slope failure after decades or centuries. The Séchilienne movement, which is located in the French Alps near Grenoble, is affecting the right southfacing bank of the Romanche river (figure 1) The slope is homogeneously made of micaschists with subvertical foliation at right angle with the valley (except in the upper part of the slope where it is folded with an axis inclined of 30° in the north direction) and is affected by 3 sets of subvertical fractures. The main family runs ENE-WSW and delimits vertical slices in the rock mass. It is clearly distinguished by several hundred meters long depressions in the morphology associated with scarps of several meters high (Vengeon, 1998). Some of these depressions are 20 m wide, attesting the long duration of the gravity-induced processes. The slope angle is about 40° in the lower part of the hill (elevation between 330 m and 950 m) and decreases to 20° between 950 m to 1100 m (Mont Sec). Near the crest, a 20 m high scarp which is followed on a distance of several hundreds meters reveals an upper collapse. The non-freshness of the scarp and the absence of glacial erosion sign and deposits show that this movement is relatively old and occurred after the last ice age. The part of the slope which exhibits signs of current instability is located in the middle of the hill, at an elevation between 700 m and 850 m, and involves a rock volume estimated to about 3 million cubic meters (Giraud et al., 1990). This area was extensively instrumented since 1988 (Evrard et al., 1990) and the measured displacements are globally oriented in a SSE direction, perpendicular to the strike of the main fractures, and dip downhill between 10° and 20°. The movement rate varies from a few cm/year to a few dm/year. Besides geological surface observations and displacement measurements, a 240 m long gallery was excavated in 1993-94 at the elevation of 710 m. It showed a succession of blocks delimited by highly fractured and sheared zones parallel to the main fracture set. No sign suggesting the presence of a sliding surface has been observed (Vengeon, 1998). Numerical modelling with the discrete element method was able to retrieve the main field observations and suggest that the movement at Séchilienne is controlled by the main discontinuities cutting the mass into blocks and includes toppling and local sliding, evolving through progressive damaging to a potential large sliding of unknown characteristics (Vengeon, 1988). The data available at Séchilienne have led some authors to propose that the hill could be affected by a massive movement, delineated to the East by the active zone and to the North by the Mount Sec scarp. No western limit is clearly visible in the topography and the thickness of this moving mass is unknown. Consequently, the volume estimations for a rock avalanche scenario are highly variable and poorly constrained, ranging from 3 to 20 hm3 (Giraud et al., 1990 ; Antoine et al., 1994) with a global mass movement between 50 to 100 h m3. The aim of this study is to try to get information at depth over the movement area by using geophysical techniques and to confront the results with existing geological data.
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Geophysical surveys for detecting subsidence and collapse areas at Cardona salt diapir (Catalonia, Spain)
More LessSubsidence and collapse are major problems associated with salt mining, causing damage to surface structures. These processes can be associated with different processes as compaction of natural sediments, ground water dewatering, natural terrain deformations and underground material exploitation. Many of these factors are natural and have a long period occurrence, while human intervention can start or accelerate some processes. Consequently, to avoid adverse impacts of subsidence and collapse, reliable prediction is essential. Barla and Jarre (1991), Bell (1992) and Marino (1999) have conducted studies dealing this subject. Around the Cardona salt mine major problems related to this facts occurs and geophysical methods have been applied in order to gain information about the hazardous areas. Gravity and EM methods have been carried out to detect potential collapse areas, while GPS levelling has been performed for subsidence control.
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Monitoring of leakage in embankment dams through resistivity measurements – A 2.5D modelling study
Authors P. Sjödahl, T. Dahlin, B. Zhou and S. JohanssonThe study aims at improving current long term monitoring routines at two embankment dams in the north of Sweden and increase the understanding when interpreting existing data from these dams. For this purpose special software was developed as a tool for modelling resistivity distribution in earth embankment dams. The study comprises evaluation of the influence from 3D effects due to the specific dam geometry. Moreover a comparison between four different electrode arrays is carried out.
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Application fo geophysical methods for the evaluation of thermal centers and their structural controls in Boku, Nazareth, main Ethiopian rift
Authors T. Haile, G. Ranieri, T. Alemayehu, A. Vernier, E. Gavaudò, G. Barbieri and G. GhiglieriThe Boku thermal centres are located in the tectonically active axial part of the East African Rift system where the east and west rift margins are the narrowest. More specifically, in the part of the rift system known as the Main Ethiopian Rift (MER) where acidic and central volcanoes are erupted along NE-SW tectonic lines forming a region interspersed with fault scarps, volcanic scoria cones and collapsed segments (Figure 1). The topography is dominated by sunken strips of land between a series of normal faults forming part of the so called Wonji Fault Belt system. The area is also characterised by high geothermal gradient and thermal anomaly associated with the acidic volcanic centres. Steam temperatures as high as 72 °C has been recorded at the currently active thermal centre, although the steam temperatures has also been observed to show variations within a given day. Studies conducted in the area earlier specially in Aluto volcanic centres, which are currently being developed for power generation, and adjoining areas within the rift have shown that pyroclastc deposits are the major thermal aquifers. The main geological feature in the area, called the Boku caldera and its surroundings represent a typical example of central eruption from where peralkaline acidic and pyroclastic deposits have been erupted. The caldera shows rims of irregular geometry, indistinct at some places but well marked on the eastern side of the Boku. The prominent topographic high in the area is the Boku ridge which rises to an elevation of 1875 meters a.m.s.l. in the centre of the region. In a few places in the area, manifestations of steam of very high temperatures from the ground have rendered the area to be usable as a traditional steam bath centre. The major area currently used for the purpose, the Boku, has a small scale infrastructure connected to Nazareth town by gravel road and serving the local population as a bath/healing centre. Due to its geographic location connecting parts of Ethiopia between Addis Ababa and the large sections of the country in the east, Nazareth town is one of the fast growing urban centres of Ethiopia with future potential to be the centre of economic and industrial growth. It has recently shown large growth in population and has a future which will make it a trade and economic centre. The potential of the Boku to be involved in the future development of the town both as a source of recreational and healing centre and in the future for the supply of hot water to the town and the surroundings is therefore apparent.
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The effects of tree roots on the electrical properties of triassic clay
More LessA large percentage of housing in England is built on clay foundations, where clay shrinkage and swelling can lead to building subsidence and heave that result in insurance claims. As volumetric change due to absorption of water into clay mineral structure is a characteristic of some clay minerals, it follows that buildings situated on clay geology may be susceptible to heave and subsidence. This may be strongly amplified if trees are in close proximity, as root-induced changes in moisture content will also cause volumetric changes. The problem of clay and root induced subsidence really became recognised in the UK in the 1970s after the drought of 1975 and 1976 that affected the whole of North-western Europe (Driscoll 1983).
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Comparison of 1D laterally constrained inversion and 2.5D inversion of CVES resistivity data with drilling data as apriori information
More LessData collection with a multi electrode system, such as Lund Imaging System from ABEM, is usually arranged so the dataset is suited for inversion using 2.5D inversion algorithms (Loke and Barker, 1995). This data may not always be suitable for 1D inversion. However, with a 1D inversion approach it is possible to decide the number of layers to be used in inversion and also put in apriori information, where this is available, to lock layer boundaries. This approach is likely to give a result where depths to layers are better determined than with a 2.5D approach. This paper aims to compare inversion with a 2.5D least squares algorithm, Res2Dinv, and the 1D Lateral Constrained Inversion (LCI) algorithm (Auken et al., 2000). The comparison is based on a large dataset collected with a multi electrode system in Lockarp in Southern Sweden (LTH, 2000). There are a large number of geotechnical investigations available, such as auger and core drillings, which can be used as apriori information in the inversions. The geology in the area is sedimentary and consists of Quaternary deposits underlain by Danian limestone. The Quaternary deposits consist of four individually different units. On top there is a half to two meters of high resistive sediments. The second and fourth unit consist of low resistive clay till. In between these two units a third unit consisting up to three meters of high resistive intermorainic sediments can be found in parts of the area. The resistivity data was originally acquired for 2.5D inversion. For LCI inversion the data was divided into individual soundings, one every meter, and all soundings with midpoint within a four meter distance were gathered into one sounding. This results in a dataset with soundings every four meters containing exactly the same amount of data as the original dataset. This means that a sounding might contain more than one data point with the same electrode configuration.
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Interurban - geophysical assessment of water dynamics and solute transport in urban soils
Authors M. Müller, O. Mohnke, J. Schmalholz and U. YaramanciUrban soils are subject to strong variations of environmental conditions, like water flow, solute transport or heat budget. The research project INTERURBAN has been formed to clarify the dynamics of water and materials at urban locations with special consideration of the spatial heterogeneity, the organic soil substance, and soil-biological transformation processes. In order to achieve these objectives, we work on four interdisciplinary questions: 1st The evaluation of spatial heterogeneity and its interaction with sub-processes; 2nd The influence of biotic and abiotic factors on the characteristics of the organic substance; 3rd The recording of water- and material transport from heterogeneous urban locations and application to selected locations; 4th The recording of the interaction between biotic and abiotic factors and their participation in the dynamics of the release of pollutants. These goals of the research group define the target for geophysics: The development of a noninvasive conception to map the water distribution and important structural parameters. In addition to standard methods, like geoelectrics and Ground Penetrating Radar (GPR), Spectral Induced Polarization (SIP) and Surface Nuclear Magnetic Resonance (SNMR) will be used. SNMR is the only method that allows to determine water content and pore size distribution directly from the surface and therefore a special focus in the project.
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GPR Mapping toluene infiltration in a sand model
More LessThe high resolution GPR technique of 1.5 GHz antenna is applied for mapping infiltrated dense non-aqueous phase liquid DNAPL (here toluene) in a partially saturated sand medium with time. A model box (83*9.5*61 cm3) is filled with a medium sand which is saturated with water at the lowermost 18 cm. The model contains five prismatic objects of fine (objects 1, 4) and coarse sand (objects 2, 3, 5). A toluene is infiltrated from a single driplet at the centre of the upper surface. Georadar measurements (1.5 MHz) from the external surfaces show that mapping toluene is possible in the partially saturated zones of objects 1, 2 and 4 and hardly in the other areas. The weak reflections within the low saturated region may be caused by a weak electromagnetic impedance contrast at the interface to the toluene zone.
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Preliminary result of resistivity measurements for the name project (Nitrate from aquifers and influence on carbon cycling in marine ecosystems)
Authors B. Ludovic and D. ChapellierThe NAME project is an European research project which gathers hydrogeologists, geophysicists, geochemists and marine biologists belonging to different institutions: • DHI Water & Environment, Denmark; • Netherlands Institute of Ecology, Netherlands; • Max Planck Institute, Deutschland; • Ribe County, Denmark; • Technical University of Denmark; • University of Lausanne, Switzerland. The role of nitrogen in eutrophication of coastal marine environments is well documented (Horwarth et al., 1996). It is also well known that the application of fertilizer on agricultural fields causes nitrate concentrations in groundwater to increase (Postma et al., 1991). The nitrate bearing-nutrient that enters the marine environment in this way is monitored by measuring their fluxes in outlets of rivers and estuaries. Furthermore a significant part of the nitrate is removed by denitrification in the estuarine system (Nixon, 1996). However, at extensive sections along the European coast, the groundwater is discharging directly into the sea by upward transport throw the sea bottom. The importance of this direct nutrient flux into the marine environment is virtually unknown both with respect to its quantitative importance and with respect to the processes that take place at the freshwater-seawater interface. Given the steady increase in groundwater nitrate concentrations (Howarth et al., 1996), there is a strong need to investigate and document this matter and to evaluate its significance for coastal zone management. To illustrate the potential significance of processes occurring at the freshwater-seawater interface for the impact of direct discharge of nitrate containing groundwater on the marine ecosystem, two imaginary end-member scenarios may be envisioned: • In the first scenario nitrate bearing groundwater emerges unaltered through vents in the sea bottom. In this case there is a direct input of nitrate into the marine environment which may seriously affect the state of eutrophication in the coastal marine ecosystem. • In the second scenario, the freshwater is thought to mix dispersively with seawater below the sea bottom and in this case the emerging nitrate is reduced to free nitrogen while oxidizing organic matter that is deposited from above. The two scenarios described above are purely speculative, basically because of our current ignorance concerning real world processes. A recent research interest in this subject has lead to some reports describing the seepage of groundwater through the sea bottom (Moore, 1999; Hussain et al., 1999; Bussman et al, 1999). Generally, however, the current literature reveals a disturbing lack of knowledge concerning the quantitative significance of nitrate-bearing groundwater directly discharging into the marine environment and the biogeochemical processes involved.
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Georadar estimation of ground pollution degree as a result of leakage from main pipelines
Authors A. Dolgiy, Аn. Dolgy, V. Zolotarev and V. MarkulisThis report discusses the georadar technology application to problems occurring during operation with main pipelines. Two of the authors - V. Markulis and A. Dolgiy represent an operation service of a Latvian-Russian joint venture on transportation of oil and derivate products by main pipelines LatRosTrans Ltd (figure 1 – pipeline layout). The others two authors - V. Zolotarev and Аn. Dolgy represent Radar Systems Inc., Latvia.
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Induced polarisation survey at a waste site in southern sweden
More LessTime-domain induced polarisation and apparent resistivity pseudosections were measured on a former waste site in Southern Sweden, just outside the city of Kristianstad. The landfill is still in service, except an approximately 400 m x 400 m area, which has been covered by a rather inhomogeneous layer of clay and clay till. Since the landfill is to become a green leisure area, the aim of the study was to be able to assess the thickness of that covering layer with good precision in order to guide the rehabilitation process. A grid of auger drillings, down to a maximum depth of 3 m and placed approximately every 50 m yielded punctual information on the stratigraphy of the material covering the waste, and was used as reference. Apparent resistivity and chargeability pseudo-sections were measured to get a continuous picture of the distribution of the material.
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Signal optimization for electrokinetic metal decontamination: sample and fiels scale model experiments
Authors F. Cherubini, G. Losito, A. Trova and R. AngeliniAs well known, the decontamination of polluted soils by heavy metals is an environmental problem that concerns wide areas of the planet. The electrokinetic decontamination (Acar Y.B. et al., 1993; Acar Y.B. et al., 1995; Alshawabken A.N. et al., 1999) is a recent "in situ" method, but in the current technology it requests high levels of power (some MW), with consequent security and cost problems. So the main purpose of our research has been to find an experimental procedure that requests low voltage levels to obtain the metal mobilisation.
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An application of magnetic and ecletromagnetic methods for environmental research
Authors P. Barsukov, E. Fainberg and E. KhabenskyIn 1941 when the German armies invaded Sevastopol (Crimea), the Soviet sappers blew up the arsenals of the Black Sea fleet stored in the limy massif galleries known as the Inkerman galleries. However, when undermining only small part of the arsenal has been detonated, the massif was strongly destroyed and the basic part of the arsenal has remained under blockages galleries. According archive data the area of the galleries at the moment of explosion was more than 1 hectare, there were from 10000 up to 30000 tons of ammunition, mainly large aerial bombs, sea mines, torpedoes, charges for ship artillery of the big calibers, etc. At present, there are some crevices in the destroyed limy massif through which it was possible to penetrate into the blockages of the arsenal and to find kept ammunition on the area about 40 m2. The find state of the ammunition is quite satisfactory, that allows using the mine clearing and the further recycling technologies. At the moment of explosion the vaults of the galleries were destroyed and sank on 10-15 m. The rock massif has intensively cracked and turned to a congestion of limestone blocks in the volume up to 1000-5000 m3. Cracks are filled with the clay formations and water supplied. Intensively progressing karstic processes in cracked limestone create danger of explosive objects of the arsenal corrosion, which is situated within the city boundaries. On territory of Inkerman galleries SINECO Company carried out measurements of a full vector of magnetic field on a uniform mesh 5m×5m. Several powerful sign-variable anomalies were revealed there, however their locality and huge gradients (up to 200-400 nT/m) testified to the small size and small depth of bedding (not more than 1-3 m). As the goal of the magnetic survey was the detailed mapping of the ammunition’s value, the decision to involve in researches TEM-FAST sounding technology was accepted. This technology is used successfully to solve the engineering, geological, hydro-geological and environmental problems. Primary goals of the research were the following: 1) Mapping of the ammunition on the depth of 10-30 m from a surface; 2) Three-dimensional mapping of sluggies in the limestone massif. For the solution of these tasks TEM-FAST 48 HPC (AEMR ltd.) system with 25m×25m antenna has been used. This system defined transient characteristics of the media in a range of times from 2-4 μs up to 16 ms, both in one-loop configuration, and in configuration loop-in-loop. Preliminary full-scale test has shown that well conducting layers of limestone screen metal objects even of 5 ton aerial bomb size which practically are not visible at depths more than 10 meters. However the super paramagnetic effect (SPM), caused frequency dependence of a magnetic susceptibility of metals χ(ω), is confidently registered even for much big depths. When measurements of transient characteristics of an electromagnetic field the voltage on receiving antenna U(t) in case of SPM-effect [1] is inversely to time U(t) ~1/t1+δ (|δ|<<1). In regulation E (t) = t*U (t)/I the response of the media at t > 100 μs weakly depends on time E(t) ~ t−δ. At the same time the induction signal caused by attenuation of the curl currents in rock, attenuates much faster: E(t) ~ 1/tn, where n ~ 1-3. Examples of the transients for two sites: P-38 and P-44 in the above regulation are given in the fig. 1.
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Eigenimage analysis of shallow seismic sections
More LessThe appearance of seismic events related to various subsurface objects is to a large extent defined by their coherency on seismic sections. In particular, shallow subsurface inhomogeneities can be expected to appear as the areas of poor coherency. Identifying and separating coherent and non-coherent events on the sections can be performed using the technique of eigenimage analysis. This technique is based on the singular value decomposition (SVD) of the sections represented as data matrices. A similar approach is implemented in the Karhunen-Loeve (or principal component) reconstruction method (Hemon and Mace, 1978). The technique has been successfully applied to various geophysical problems (Jones and Levy, 1987; Freire and Ulrych, 1988; Jackson et al., 1991; de Franco and Musacchio, 2001).
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The use of constraints in 2D and 3D resistivity modelling
Authors M. H. Loke and J. W. LaneElectrical imaging surveys are now widely used to map areas with complex subsurface geology. The many applications include groundwater exploration, mineral exploration, environmental and engineering studies (Dahlin, 1996; Griffiths and Barker, 1993). While 2D surveys are more commonly used due to time and cost limitations, 3D surveys are also used in very complex areas such as in mineral exploration surveys (White et al., 2001). A cell-based inversion model is normally used to model such complex structures. The subsurface is divided into a large number of rectangular cells and an inversion algorithm is used to determine the resistivity of the cells. The inversion of resistivity data gives non-unique results. Thus some assumptions are made about the subsurface so as to limit the range of plausible models. The regularized least-squares optimization method where constraints can be easily added into the inversion procedure (Ellis and Oldenburg, 1994) is frequently used. The effects of constraints on the inversion results are discussed in the following sections.
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