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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
21 - 40 of 131 results
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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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