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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
81 - 100 of 131 results
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Geophysical surveys in the capoterra coastal plain (Southern Sardinia - Italy)
Authors F. Ardau, R. Balia, G. Barrocu, E. Gavaudò and G. RanieriThe Capoterra coastal plain lies on the south-western tip of the Campidano Graben, few kilometers west of Cagliari, the main town of Sardinia (Fig.1). It was originated by the ancient Santa Lucia river delta and is bounded by salt-works and lagoons on the east, the seashore on the south-east and the Paleozoic basement on the west and south-west. The surface geology of the plain is characterized by Pleistocene and Holocene sand and alluvium; the Paleozoic bedrock is mainly constituted by Carboniferous granite and Cambrian-Ordovician schist (Fig.1). Concerning hydrogeology, to date the dominant theory is that two aquifers can be distinguished: a shallow phreatic aquifer and a deeper, multilayer, locally confined aquifer. Due to the large number of incorrectly drilled water-wells, these two aquifers, laterally recharged through the fractured Paleozoic rocks, are now communicating in several areas of the plain; moreover they are affected by saltwater intrusion coming from the sea and the neighbouring salt-works. In the past, several hydrogeological and geophysical surveys were carried out in the Capoterra plain , e.g. Balia et al., 1994; Barrocu et al., 1994; Godio et al., 1999; Montaldo, 1966; Sciabica, 1994; Vernier, 1999. Referring to most recent works, Sciabica (1994) afforded the the mathematical modeling of the aquifer system based on hydrogeological and hydrogeochemical data, while Vernier (1999) conducted a more general synthesis including all available data. However the overall information on the Capoterra plain is still inadequate for a reliable modeling of saltwater intrusion and its evolutionary trend, and very important aspects such as stratigraphy of Pleistocene-Holocene sedimentary cover, relationships between phreatic and confined aquifer and depth to Paleozoic basement must be further elucidated. Hence a new campaign of geophysical surveys including a gravity survey and then some seismic reflection profiles, properly designed on the basis of gravity interpretation, and TDEM soundings has been recently planned.
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Using geophysical methods for detecting seawater intrusion and waste plumes in the river Foix delta (Catalonia, Spain)
Authors D. Vázquez, R. Lázaro, M. Himi, N. Yilo and A. CasasGeophysical surveys, particularly electric and electromagnetic methods, have demonstrated to be useful for mapping inorganic conductive plumes and delimitating seawater intrusion into coastal aquifers (Frohlich et al., 1994). In the study area groundwater is affected both by salt-water intrusion and toxic industrial wastes. Therefore, the purpose of this study was to test a cost-effective geophysical methodology to detect saltwater in the shallow subsurface using electromagnetic ground conductivity and electrical imaging measurements to determine the immediate sources of leachate plumes flowing in the area.
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Geoelectrical survey at the water barrier of Elva river at the area of Havelberh (N. Germany)
Authors P. Sotiropoulos, P. Tsourlos, K. Buckup and G. SiderisA 2-D geoelectrical survey was carried out at locations at the water barrier (dam) of the west bank of river Elba at the area of Havelberg (Sachen Anhalt), Germany (Figure 1). The target of the geophysical survey was to provide lithological and hydrogeological information about the surveyed water barrier area and its surroundings. The localization of lithological variations (i.e. shale lenses) is of particular interest since these are associated with potential vulnerability zones in case of river flood. This information will be of use to geologists and engineers who are currently plan works, which will increase the safety of the dam. The sediments in the region consist of sands, mixture of sand and clays and lenses of shale. The dam is elevated on average 2.5m above ground and has relatively steep slopes.
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Location of buried valley aquifers using transient electromagnetic soundings
Authors K. I. Sørensen and E. AukenIn Denmark, 99% of the water supply is based on groundwater abstraction. Increasing problems with the groundwater quality due to urban growth and agricultural contamination in 1995 caused the Danish Minister of Environment to approve a plan for improving ground water protection. In July 1998, the Danish Parliament decided to launch an ambitious plan to significantly intensify the hydrogeological investigation of the Danish groundwater resources. This plan runs for the next 10 years and includes all areas characterized as groundwater recharge and aquifer areas, a total of 16,000 km2 or 1/3 of the country. In Denmark, a large number of aquifers are composed of Quaternary sand and gravel deposited in deep valleys eroded in Tertiary clays. The valleys are often covered by an inhomogeneous moraine cap. In order to protect the aquifers, it is necessary to delineate the buried valleys and to locate permeable sandy areas in the inhomogeneous clay cap. It is generally observed that variations in hydraulic conductivity of these formations are closely related to the variations in electrical formation resistivity. Numerous investigations during the nineties showed that the application of electrical and electromagnetic methods (Christensen N.B. and Sørensen K.I., 1998, McNeill, J. D., 1990, Meju, M. A., 1999) was successful and provided the hydrogeologists with detailed information on location of the buried valleys and the inhomogeneities of the protecting surface clays. In Denmark, the largest investigation of this kind so far is the transient electromagnetic (TEM) mapping of the municipality of Aarhus (Sørensen et al. 2003). The survey area is approximately 120 km2. In the period 1991 - 1998, more than 6000 TEM soundings were acquired with a density of 16 per km2. In 2000, the data were reinterpreted to ensure uniformity using current processing, modeling and inversion techniques. The investigation was carried out by cooperation between the Municipal Water Supply of Aarhus, the County of Aarhus and the Department of Earth Sciences at the University of Aarhus. The Department conducted the measurement, the data processing and the geophysical interpretation of the soundings, and the hydrogeological interpretation was performed by the County of Aarhus. The cost of the survey was approximately 1 million euro. In this presentation we give an overview of the gained experience and the new techniques developed through the investigation period. On a general level, it is development of standards which ensure enhanced data density and reliability, increased acquisition efficiency as well as standardization of mapping methods in a region. The latter provides the precise, detailed mapping needed to determine the extent, vulnerability and water quality of aquifers. The following geophysical developments have taken place: - Development of field methodologies for operating the TEM method in densely inhabited and culturally developed areas (Sørensen et al. 2003). - Development of new and enhanced TEM instrumentation. These are the PATEM method (Sørensen, 2000) and the HiTEM method (Danielsen et al., 2002). - Development of new data processing and interpretation software packages. This is enhanced modeling of instrument transfer functions (Effersø et al., 1999), MCI and LCI interpretation (Auken et al., 2001, Auken et al., 2000) and instrument calibration (Halkjaer et al. 2002).
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A Web based knowledge integration method: Application to data from multiple investigations on cultural heritage
Authors A. Castellano, R. Cataldo, G. De Nunzio, L. Marzo and A. TurnoneThe aim of this work is to suggest a method to explore relationships between features of chemical-physical variables that are distributed unevenly over space. Given a large number of data one could seek patterns that may not be visible without using advanced techniques of query, selection, analysis and display. For example, to access to the great variety of data available from multidisciplinary surveys on works of art, powerful tools are required to manage them. Exchanging and sharing are necessary to reduce time to be spent on low-end activities and to focus instead in higher-level thinking and problem solving. GIS (Geographical Information System) and MapServer, an OpenSource development environment for building partially enabled Internet applications (free available on http://mapserver.gis.umn.edu) are useful to perform the above task. GIS is a combination of robust hardware, powerful software, special data and thinking explorer. Through GIS one can manipulate hardware and software, work on the data, explore relationships between features and investigate important locations and topics. MapServer, beyond browsing GIS data, allows to create "geographic image maps", i.e. maps that can direct users. The same application serves as a "map engine" for other portions of the site providing spatial context where it is needed. This coupled software has never been applied to strongly multidisciplinary studies. In this work we attempt to fill this gap. Public administrators also have discovered GIS as an important tool for a wide variety of tasks; CAD-based maps of historical building can be maintained during many years. Furthermore by adding an intelligent interface to these maps the planning and analysis for safeguard management can be improved.
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Reduction of the archaeological risk by means of geophysical methods. An example from the south-west of peloponnese (Greece)
Authors S. Gaviano, C. Olivas, G. Korres and G. RanieriThe “a priori” knowledge of the physical and characteristics and the geometry of the subsoil is the basic element both for the optimisation of the design of engineering constructions, and the means to avoid or reduce the so called “archaeological risk” which can cause the interruption of engineering works. On the other hand the imperfect knowledge of the subsoil characteristics and the thoughtless or forbidden intervention that can follow, can produce the loss of the cultural goods without the “memory” of the archaeological remains. Practically that is very usual in the “urgency” condition and especially in urban areas and/or in a building construction. In such cases it is very hard to preserve the archaeological structures. It is well known that the subsoil knowledge can be obtained by the application of appropriate geophysical methods. They must be applied with care taking into account the context, the dimensions of the archaeological bodies, the presence of noise sources, the physical properties of the materials. The choice must also be made taking into account the economic aspect: the geophysical methods must be “convenient” in respect to the economic value of quality and cheaper than other methods like archaeological diggings or excavations. Normally in archaeological research it is necessary to acquire substantial data, which must be filtered, processed and interpreted in order to give a detailed reconstruction of the subsoil. All data must be ordered and normalized to give a pseudo 3D reconstruction: The quantity of data can make the direct excavation process long and expansive. Archaeological Heritage has different dimensions and characteristics, so the choice of geophysical methods depends on the type of archaeological structure that it needs to show. Type of measure, sampling rate, profiling distance, have to be compared to archaeological structure. To establish the convenience of Geophysics an economic parameter (Marchisio and Ranieri, 2000) can be applied: Monetary Expected Value of the archaeological heritage is the product of the probability to discover the object and its monetary value. Besides it’s possible to define the intrinsic value of geophysical information and value the quantity of methods to apply.
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Geophysical methods to recognise preexisting structures under an important archaeological site
Authors G. Ranieri, M. Boccone, R. Deiana and R. PorcuThe most characteristic Sardinian constructions are the “nuraghe”, all around the world there are examples only there. The nuragic period began from the Bronz Age to the Steal Age. A famous one is “Su Nuraxi” of the Barumini nuragic site (near Cagliari), that is the bigger between the 7000 nuragic sites in Sardinia. Researchers of several disciplines are studying to know more about their function, their constructive modality and their scope. Near the village there is a temporal stratification that probably continue under the surface soil. In some nuraghe site there are signs of pre-existing culture, with examples of neolithic villages. It would be possible that some nuragic sites were been chosen because of these pre-existing structures. The acknowledgement of those constructions near a such important archaeological site is very hard and often impossible. For the nuragic constructions were made without foundations we have applied geophysics methods, among them the seismic and the electric type, with emitters and geophones on the rest plan. We have used seismic tomography with P and SH waves to recognise probably pre-existing structures. High velocity zones are in correspondence of probably older constructions, while low velocity zone could represent poor resistance zones. The geophysical methods applied on the nuragic site have permitted to characterize the points in which take part with a static restoration, in some of them we have really found visible craks, in others not. These results have shown smaller resistance zones to take part for a static restoration. In Conclusion, the totality of the geophysical methods can be used to perform the static restoration and the electrical tomographies give important information on the groundwater paths, this is very interesting because the surrounding zones are devoid of water.
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GPR Survey to confirm the location of the Ronda castle wall (Andalucia, Spain)
Authors N. Yilo, D. Vázquez and A. CasasWith the increasing importance of the conscience for archaeological sites conservation, non-destructive methods of subsurface analysis are developed and becoming important. With the excavation budgets there are a lot of restrictions, political, economical and strategical ones (Scolar, 1990). Many times it is not possible to excavate, and the remote sensing and the geophysical methods could be a solution. Ground penetrating radar (GPR) is one of the methods that is gaining respect by archaeologists due to its capacity of give a high resolution results, wich allows the prospecting of small structures(Vaugha, 1986) and the location of underground objects at shallow depths, comparing it with others geophysicals technics (da Silva, 2001). We report here the results of a recent survey using GPR to search an Arabic castle wall that at the present is probably under the playground of a school in Ronda (Málaga), where a underground car-parking is projected.
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Non-Destructive testing on masonry structures: A series of different methodologies applied on the cathedral of Lucca.
Authors M. Marchisio, L. D’Onofrio, A. De Falco, V. Baroncini and D. MorandiA very dangerous situation of the West wall of the left transept of the Cathedral of Lucca was discovered by chance in 1994. The masonry structure is a typical three-layered one: the two external faces enclose an internal less regular brickwork, the so-called "muratura a sacco". During the eight centuries of life it underwent numerous interventions and repairs. Unfortunately in one occasion gypsum mortars were used. Due to water infiltration, in several areas the mortar was completely ruined. The damage was discovered by chance. Seismic tomographies were the first quantitative diagnostic tool to show the very critical situation of the structure. Very low velocity zones were very evident: they correspond to very low dynamic elastic moduli, less than 1000 daN/cm2. The tomographies put in evidence many structural details. The heavy loads due to the 30 m high structure of the transept act only on the external layers of the wall structure. The presence of an important portal makes the situation worst. Our description of the situation has been well confirmed by a series of other very accurate tests and historical investigations that were performed in the following years. A series of seismic tomographies were later performed across other parts of the wall of the church. Luckily the rest of the building did not show other problems. Since that period a number of different diagnostic tools were used and tested on this structure. The structures of this building in fact are a very interesting test-site, as there are very different situations in the different sides of the church and because of the very detailed information that were obtained by different methods. A number of microseismic and electromagnetic experiments are shown.
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Application of GPR and ERT in the archaeological site of “Palazzo di Teodorico” in Galeata (Forli’ – Italy)
Authors A. E. Bracci, C. Cesaretti and S. De MariaGaleata is located on the Bidente’s river valley (Tosco-Romagnolo Apennines), in the province of Forlì. The ancient urban area was located on a busy mountain pass. The first evidence of human presence at Galeata goes back to the prehistoric age, but the most ancient settlements are dated between the VI and IV century B.C. In the III century B.C., the Romans occupied the Celtic centre of Mevaniola, which became an important Roman municipality. The collapse of the Western Roman Empire caused the disappearance of the Roman town so the inhabitants moved downhill to what is now Galeata. During the Second World War an equipe of the German Archaeological Institute of Rome, led by Siegfried Fuchs and Friedrich Krischen, made excavations to find Teoderico’s Palace. The goth king raised his palace in order to use it as hunting resort in the beginning of VI century, A.D. The location of some shallower foundations can be partially identified in the area during the harvest time when the crops assume a lighter colour on the ancient walls, the picture suggests plan of the goth palace. The excavations had been resumed in 1998 by the Archaeological Department of the University of Bologna. Stratigraphical excavations revealed the existence of two main building periods: the first related to the Roman age, probably at the beginning of I century B.C., with an extensive installation of a large villa; the second period related to the late-ancient age. The activity of the Italian archaeologists partially confirmed the German excavation results and additionally found other important structures. These structures include a building with a complex planimetry, with polygonal rooms, apses and heated rooms which are probably the thermal area of a late-ancient “Palace” (extensive excavations in this zone are continuing and so the data are not confirmed yet).
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Geophysical investigation of a recent shallow fault
Authors J. B. Edel, G. Herquel and M. BanoThe surveyed area is located in the central part of the upper Rhinegraben, a few kilometres south of Wissembourg, close to the western border. A normal fault has been evidenced in the open sand quarry of Riedseltz. It was an opportunity for 1) practising geophysical prospecting, as part of the final year curriculum of Ecole de Physique du Globe, 2) testing various methods for imaging a shallow fault, 3) locate and follow the fault outside of the quarry. The study was partly supported by the BRGM.
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A First geophysical survey to investigate the Telóes basin
Authors J. M. Lourenço and M. S. MatiasAlong the major geological fault of Penacova-Régua-Verin, FPRV, (north Portugal, fig. 1) there are several tectonic depressions that have been interpreted as the result of recent reactivation of the fault. On the other hand these depressions are very important for water exploitation in a region where water resources are scarce. Generally, these basins are filled with undifferentiated sedimentary materials of unknown thickness. The “Telões Basin”, a grabben structurally controlled by the FPRV, is a typical and important economical example and its 3D study comprises a comprehensive geophysical project including Electromagnetic Mapping, Resistivity Imaging, Seismic Refraction and Gravity Mapping. Here in an account will be given of the Electromagnetic and part of the resistivity survey (Lourenço, 1997) that were the basis for the planification of the other geophysical techniques to be used.
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Joint interpretation of surface waves, refracted waves amd resistivity
Authors D. Orlowsky, R. Misiek, R. Elsen and B. LehmannTechniques to investigate the soil with the help of different geophysical methods increased rapidly during the last decade. Nevertheless, the use of different geophysical methods results often in different interpretations of the investigated area. This paper deals with the joint interpretation of surface waves, refracted waves (full waveform) and resistivity data acquired in an urban area of old coal mining where cavities or zones of loosening are expected in the near subsurface. Special anomaly indices are determined for each geophysical method. A weighting process combined these indices to a “Joint-Anomaly-Indicator” for the whole investigated area. This results in a map which clearly shows those locations with a high probability of cavities or loosening.
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Contribution for a better understanding in soil temperature
Authors M. A. R. Talaia and A. H. AmorimThis study allows us to understand how soil varies in depth and time when its thermal profiles are known. The research analyses the data of a twelve year period and contributes to the development of agricultural planning strategies.
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Geophysical characteristics of precambrian fracture zones - A case study from Rovaniemi, Northern Finland
Authors E. Lanne, J. Lehtimäki, H. Vanhala and U. VäisänenThe recognizing of fracture zones is important in the geological mapping, ore prospecting, ground water studies and in the applications of rock engineering. In environmental accidents fracture zones may also provide flow channels for groundwater contaminants. The aim of this study is to locate and characterize potential bedrock aquifers. The study is methodical and it is continuation of earlier works (Lanne et al., 1998).
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The Molasse fault zone in Lake Geneva, South-West Switzerland, From high-resolution seismic reflection data
Authors I. Chaudhary, D. Dupuy, M. Scheidhauer and F. MarillierThe Oligocene-Miocene Molasse basin along the northern rim of the Swiss Alps is affected by a major fault zone that separates Plateau Molasse to the north from Subalpine Molasse to the south. As a result of alpine compression, thrusts along this zone brought up Subalpine Molasse rocks by an amount of up to 1000 m. On the northern shore of Lake Geneva, near the City of Lausanne, the fault zone is well defined (Fig. 1). However, its extension in the lake and on its southern shore is not well known. Geology on both sides of the lake, however, indicates that major changes in the distribution of Molasse units occur in this region. Locating the Molasse fault zone across Lake Geneva would help to better understand geology and would provide important constraints on tectonic models of the Alps. In order to study the extension of the Molasse fault zone across Lake Geneva, we conducted a 2-D high-resolution multi-channel seismic reflection survey. Molasse units in the lake are overlain by Quaternary sediments up to 300-400 m thick (Vernet et al. 1974). Our data imaged these sediments and detected several faults in the Molasse units.
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Gravity anomaly map of the lower Vouga basin (Aveiro, North - Central Portugal)
Authors F. P. O. Figueiredo, M. J. Senos Matias and M. R. P. V. FerreiraSeveral studies have been carried out in the ‘Baixo Vouga’ area, near Aveiro, Central-North Portugal (Fig. 1), in order to investigate its geology and tectonics. However, so far it has not been presented an overall model for the behaviour of the bedrock (metamorphic and igneous) in the region. This work aims to contribute to the definition of the bedrock topography and deep geological structures in the ‘Baixo Vouga’ region. A gravity survey in an area of 560 km2 in the Estarreja, Murtosa, Aveiro, Ílhavo, Oliveira do Bairro, Albergaria-a-Velha, Vagos and Mira districts was done and a total of 653 gravity stations were measured over a non uniform grid.
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Geophysical investigation of a hydrogeological important fault structure
Authors H. Wiederhold, F. Binot, R. Kirsch, W. Scheer and C. StadtlerThe water supply in the northernmost part of Germany is mainly based on the groundwater reservoirs of Tertiary sedimentary layers. South of Flensburg these sedimentary layers are displaced by the north-south striking Flensburg-Sieverstedt fault zone with a throw of about 600 m at the base of Tertiary. The deeper part of this fault zone is well-known from earlier seismic investigations for hydrocarbon exploration. For an assessment of the groundwater reservoirs the near-surface structural feature of the fault was recently investigated through shallow seismic reflection and gravity surveys.
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Geophysical and atmogeochemical methods revealing old LNAPL contamination history of sandy aquifers
More LessDuring last years a series of papers was devoted to possibilities of geophysical methods in detecting long time residing LNAPL plumes in the granular sediments. Sauck (2000) developed a new conceptual geophysical model for this case taking into the account geochemical processes caused by the bacterial biodegradation of hydrocarbons. The existence of the low resistivity zone below the LNAPL plume is the only chance to estimate the extent of the plume by resistivity survey (multielectrode measurements, vertical electrodes) and ground penetrating radar. We combined the geophysical techniques with the soil vapour survey using the new method and instrumentation (ECOPROBE 5) based on the combination of total PID (photo ionisation detector) and selective IR (infra-red) analysers. The efficiency of this approach is documented on materials from an abandoned military area in the Cretaceous of Bohemia.
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Use of geoelectrical methods to evaluate undustrial contamination near Setúbal, Portugal
Authors E. C. Ramalho, R. Gonçalves, A. Nogueira, L. Torres and C. PenedaThis study consists on the estimation of contaminated soil volumes to be removed or remedied in a small industrial area near Setubal, Portugal, using geoelectrical methods. The area was used for a long period of time as a deposit of iron fillings impregnated with lubricating oil with high Zn content that can jeopardize its environmental quality. As a complement of a preliminary chemical analysis survey conducted to identify the problem, Induced Polarization and DC Resistivity surveys were also carried out, and results were related with Fe concentrations. Zn concentrations were estimated after Fe concentration and critical areas were identified using international standards. Bearing in mind these results, contaminated soil volumes were estimated.
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