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– Resistance and magnetic mapping, ERTs and aerial photography put together. – Fusion was attempted through curvelet transform. – The useful information of all methods is given in a combined image at the site of Philippi in Greece.

– We use a new approach to combine magnetic and electrical geophysical data from two different archaeological areas in Greece (Europos & Doriskos). – Using the curvelet transform we express the feature of the images as a function of spatial coordinates, scale, and orientation. – A combined image is created in the curvelet domain through the objective selection of the most salient features. – The results show several potential archaeological structures.

The study area is a part of Dammam Dome that is situated at King Fahd University of Petroleum & Minerals (KFUPM) campus, Dhahran, Kingdom of Saudi Arabia. The gravity survey was conducted as a pilot case study to explore part of Dammam Dome in greater detail. Gravity data were collected solely during night hours due to low noise levels. A significant part of the survey was conducted during the summer holiday period, , when there was no student are on campus. A total of 235 gravity measurements were made using a Scintrex CG5 gravitometer, while a Trimble R10+ differential GPS (DGPS) was used to measure the stations’ location and elevation with the highest accuracy. All gravity data were reduced using several algorithms, and their outcomes were cross-compared. The Complete Bouguer anomaly map for the campus was then generated. Several enhancement filters including edged detection and shallow to deeper source separation were applied. Data were inverted, and 2.5D and 3D models were created to image the subsurface conditions. The main purpose of this study is to better understand the subsurface geology, tectonic settings of the Dammam Dome by applying the high-resolution gravity method before carrying out any comprehensive geophysical (seismic) 3D survey.

Summary Image fusion between different types of overlapping data offers significant advantages in archaeological research. For example, it complements the information that exists in images from dissimilar geophysical methods, enhances elusive yet systematic features and can reduce the effect of noisy spurious signals. Such improvements allow the identification of buried structures of archaeological importance with higher accuracy and greater confidence. In this work we use the curvelet transform to combine geophysical images from different modalities to detect possible archaeological targets in Philippi, Northern Greece. We jointly interpret overlapping data from two surveys, one utilizing the method of magnetic gradiometry and another measuring the apparent electrical resistivity. The images show several possible rectangular anomalies whose dominant orientation lies along the azimuths of 0 and 90 degrees which coincide with prior knowledge about this region. We utilize one of the main advantages of the curvelet domain that is the ability to express the imaged features as a function of their orientation and wavelength and we produce fused images that exploit the prior information about dominant building orientations. Our initial results are promising, showing several prominent features and possible excavation targets with sharp rectangular boundaries that possibly depict buried masonry of archaeological interest.

This paper presents a general overview of gravimetric measurements carried out for the first order gravimetric network of Albania. Data compensation, correction methodologies, interpretation and related results have been presented as well. Relative gravimetric measurements were carried out in 42points, with two CG-5 instruments. Real Vertical Gradients have been measured at all the points of first order network which together with other corrections, are used in the final data compensation in order to bring the final values at reference point as absolute ones. Apart from the first order network, other 38 second order and 138 third order gravimetric points have been measured in a grid 2x2 km, in the flat and most dense area (Tirana-Durresi) of Albania, with the scope the determination of Geoid Gravimetric Height on that region. The gravimetric measurements were realized with two Scintrex CG-5 gravimeters for three orders. For the first order points were used two gravimeters simultaneously, whereas for the points of second and third order only one. In this paper we present the results for only the first order measurements. The measurements were carried out during the period from August to October 2018, in collaboration with Aristotle University of Thessaloniki, Department of Geophysics. The project was supported by the Agency of Geospatial Information of Albania.

Uranium is a naturally occurring element that can be found almost everywhere in rocks and soils throughout the earth's crust. One of its decay products, radon, is of gaining concern in recent years because this colourless, odourless, tasteless gas is proven to be responsible for many lung cancer cases each year. Analysing the spatial distribution of the uranium concentration in the ground surface can help predict radon hazard regions. In this study, two types of uranium measurements – airborne gamma-ray spectrometry (AGRS) and ground-based rock sample analysis via inductively coupled plasma mass spectrometry (ICP-MS) – are calibrated for the purpose. The two types of data with different sampling schemes are found to have a reasonable correlation to each other when using the mapped geology as categorical units. This finding confirms the feasibility of using geological maps as a first-order predictor to map uranium, and further radon, in a larger scale. We then apply the self-organizing maps (SOM) technique for a data-driven classification of rock types based on the measured uranium content. The presented study area is located at mid-Norway in the Trondelag county, the same study will be performed in other regions across Norway where both types of measurements are in abundance. This study contributes to an on-going project to map radon hazard zones throughout Norway. While the radon hazard is defined by the indoor radon level which is affected by two folds of factors – geogenic (uranium-rich subsurface) and anthropogenic (dwelling type, indoor air exchange, etc.), our work aims to single out the geogenic factor. Comparing to the current national Radon Awareness Map of Norway (URL: http://geo.ngu.no/kart/radon/ ), where bedrocks were categorized by their likelihood of hosting elevated indoor radon, our approach utilizes measured uranium concentration of the ground which has a more direct link to the bedrock types.

The main objective of this study is the determination of the Moho discontinuity in the Hellenic area based on gravity data inversion. High-resolution (2 arcmin) and accuracy (±2 to ±3 mGal) gravity data were used in the computations following the Parker–Oldenburg iterative method, and a low-pass filter was applied to gravity information towards the convergence of the final solution. To determine the cut-off wavenumber of the filter, we tested different mean depths and density contrasts of the crust and the mantle (Mohorovicic discontinuity). The selected density contrast and mean depth of the Mohorovicic discontinuity are those which agree with the Moho depth interpreted from deep seismic imaging data. By comparing the Moho depth estimated, covering both land and marine areas and including the Ionian and Aegean Sea, with those interpreted from previous studies, it is shown that our solution is consistent with the available seismic data interpretation. Moreover, the resolution of the gravity data and the appropriate filtering used in this study contributed to the representation of local features of the Moho discontinuity. Finally, area-dependent discrepancies detected between the Moho depths of the current solution and those derived from previous studies are extensively discussed.

The 2.5-km-long Eupalinian Aqueduct in the island of Samos, Greece, comprises the most impressive sample of ancient Greek engineering surviving almost intact. The main construction is a tunnel 1036 m long and almost 1.8 m wide excavated from both ends into mainly the massif limestone. In some parts of the overall length of about 240 m, the tunnel is dressed by lining of archaic and Roman age. This is of remarkable quality, and presumably, it protected the parts of the tunnel that were affected by subsidence and cave-ins. At some particular locations, it suffers deformations and other failures. Thus, prior to its restoration and protection measures design, an integrated geophysical survey was carried out on the faces of the supporting walls, consisting in ground-penetrating radar and electrical resistivity tomography works. The survey aimed to investigate the structure at the unseen area behind the lining. The thickness of the lining walls was accurately assessed by the ground-penetrating radar method and proved to be about 0.3 m–0.5 m on average. On the other hand, the width of the excavation behind the walls was predicted and checked at some particular locations with the electrical resistivity tomography works.

In this article we provide a preliminary report of the work carried out between 2010 and 2012 as part of the Makrakomi Archaeological Landscapes Project (MALP). The programme of research is carried out in co-operation between the Swedish Institute at Athens and the 14th Ephorate of Prehistoric and Classical Antiquities at Lamia. The interdisciplinary project started in the summer of 2010, when a pilot survey was conducted in and around the hill of Profitis Elias, in the modern municipality of Makrakomi, where extensive traces of ancient fortifications are still visible. Systematic investigations have been conducted since 2011 as part of a five-year plan of research involving surface survey, geophysical survey and small-scale archaeological excavation as well as geomorphological investigation. The primary aim of MALP is to examine the archaeology and geomorphology of the western Spercheios Valley, within the modern municipality of Makrakomi in order to achieve a better understanding of antiquity in the region, which has previously received scant scholarly attention. Through the archaeological surface survey and architectural survey in 2011 and 2012 we have been able to record traces of what can be termed as a nucleated and structured settlement in an area known locally as Asteria, which is formed by the projecting ridges to the east of Profitis Elias. The surface scatters recorded in this area suggest that the town was primarily occupied from the late 4th century BC and throughout the Hellenistic period. The geophysical survey conducted between 2011 and 2012 similarly recorded data which point to the presence of multiple structures according to a regular grid system. The excavation carried out in the central part of Asteria also uncovered remains of a single domestic structure (Building A) which seems to have been in use during the Late Classical and Hellenistic periods. The combined data acquired through the programme of research is thus highly encouraging, and has effectively demonstrated the importance of systematic archaeological research in this understudied area of Central Greece.

In this paper the main results from the implementation and interpretation of a geophysical survey carried out in Chalkidiki (Northern Greece) are presented. The objective of the geophysical survey was to study the general geological conditions of the area (stratigraphy and tectonism) and to focus on the hydrogeological behaviour of the geological formations in the area. The ultimate target was to point out the most promising locations for the successful construction of hydro wells. Since direct hydrogeological information was not available, three different geophysical techniques were applied in order to follow a step by step approach to the exploration of the study area.

Various edge delineating methods (edge mappers) are tested on different types of synthetic data produced by calculating the response of a model of buried ancient ruins. The model was constructed to resemble a commonly occurring situation with ruins of two historical phases buried one beneath the other. These weak signals of relatively small wavelengths of the archaeological prospection comprise tough tests for the mappers considered. Additionally, a particular mapper, the balanced horizontal gradient magnitude scaled by the analytic signal is introduced in this study. An example of applying the mappers to real data is also presented. All the mappers proved capable of locating the lateral limits of the subsurface targets but with varying success. Also some of them are very sensitive to noise, rendering them useless for practical application. Some others proved robust in the presence of noise. For a number of them, the varying strength of the aligned maximum values proves an indicator of the variation of the burial depth of the targets. Their merits and drawbacks are demonstrated and discussed with respect to their application on the various types of magnetic archaeological prospection data. Also, relative comparisons are presented. Copyright © 2012 John Wiley & Sons, Ltd.

New findings on the deep origin of the geothermal field and volcanic centres at the North Euboean Gulf (or North Evian Gulf), Central Greece, were obtained by combining a three-dimensional traveltime inversion of microseismic data recorded by an on/offshore local seismic network with a Curie Point Depth analysis based on aeromagnetic data. A magma chamber was detected from low seismic P-wave velocity values and high Poisson ratios at depths below 8 km also coincident with a Curie surface estimated at 7–8 km depth. Furthermore, it was also observed that local geothermal anomalies are generated by hydrothermal flux facilitated by NW–SE and NE–SW oriented faults. Microseismic activity is also associated with these fault systems.

In his journey through Achaea in the second century AD, Pausanias mentioned the destroyed Classical site of Helike on the sea and noted that its ruins were still visible underwater near the southwest shore of the Corinthian Gulf. In 2001, the Helike Project excavators discovered on the coastal plain of Helike southeast of Aigion the first ruins of Classical buildings, buried under lagoon sediments 3 m deep. They also found segments of a major Roman road oriented NW–SE and buried 1–1.50 m deep under the contemporary surface. Pausanias referred to the main road through the Helike plain, which he followed during his visit. According to his description, he saw the submerged ruins of Helike toward the sea north of the Roman road. Tracing the exact location of the road would, therefore, help to locate the lost city. We employed resistivity tomography to explore the areas between trenches where the road had been unearthed and also to investigate its possible extension beyond those locations. Since 2004, resistivity studies performed by grids or single profiles have been carried out at 11 locations. As a result, the ancient road was detected for a length of about 2 km. It was also imaged either in two-dimensional or three-dimensional contexts at all the locations where it was detected. Copyright © 2009 John Wiley & Sons, Ltd.

The area around the Church of Protaton at Karyes on Mount Athos (Holy Mountain) in northern Greece, was explored by means of resistance mapping and electrical tomography. Ruins of foundation walls were detected and mapped around the Church, and additionally geological information was retrieved by the tomography. The floor of the Church was investigated with ground-penetrating radar transects wherever was possible. The presence of reflection patterns, which appeared aligned in parallel transects, led to the conclusion that they were caused by structures concealed beneath the floor of the Church. The survey, which took place in and around an existing monument, required different geophysical methods, used in a synergetic manner. Copyright © 2007 John Wiley & Sons, Ltd.

Ground total magnetic field data of Albania were used to produce estimates of the Curie point isotherm. The strategy followed was to estimate the depth to the bottom of the deepest magnetic sources. Firstly, the average depth to the top of the deepest crustal block, z t, was computed by linear fitting to the second lowest-frequency segment of the azimuthally averaged power spectrum of the total magnetic field data. Then, the depth to the centroid of the deepest crustal block, z 0, was computed by linear fitting to the lowest-frequency segment of the azimuthally averaged power spectrum of a distribution of magnetic dipoles. Finally, the depth to the bottom, the inferred Curie point depth, z b, was calculated from z b=2z 0−z t. Curie depth estimates for Albania vary from about 17 to 25.5 km (below sea level). These results are consistent with the depths inferred by extrapolating geothermal gradient and heat-flow values, suggesting that the Curie point depth analysis is useful to estimate the regional thermal structure. It also suggests that the approach was valid and that ground total magnetic field data can be used for this purpose.

— The aeromagnetic data of Macedonia and Thrace were used to produce Curie point estimates. The data were high pass filtered to remove components arising from topography and magnetic core fields which were not adequately modeled by a DGRF. The depth to the centroid, z 0, of the deepest distribution of the magnetic dipoles was obtained by computing a least-squares fit to the lowest-frequency segment of the azimuthally averaged log power spectrum. The average depth to the top of the deepest crustal block was computed as the depth to the top, z t , of the second lowest-frequency segment of the spectrum. The depth to the bottom of the deepest magnetic dipoles, the inferred Curie point depth, was then calculated from z b =2z 0 − z t . The Curie depth estimates for Macedonia and Thrace range between 11.2 and 17.3 km. These results are consistent with the depths inferred by extrapolating known geothermal gradient and heat-flow values.

Magnetization differences in rocks are related with differences in the content of magnetic minerals within rock units. Assuming that magnetic properties (susceptibility and/or remanence magnetization) are discernible between the various rock units, magnetic field anomalies could provide valuable information for the texture of lithological units and even be correlated with distinct lithologies. Delineating edges of magnetized structures is a common application of magnetic data to geological interpretation. We evaluate a number of edge mapping techniques in order to study the magnetic anomaly caused by Philippi granitoid and to estimate its lateral extension. Edge mapping methods can definitely improve the interpretation of magnetic data. They can delineate the locations of the edges of the subsurface magnetic sources. Applied on the magnetic data of the Philippi granitoid edge mappers succeed to map the edges of the granitoid. The PSG-HGM mapper is a robust method that can detect contacts even in the presence of noise. TDXAS filter was able to detect signal from shallow and deeper contacts.

Mining activities in Lavrion began during the first millennium B.C. after the decline of ancient Athens and then restarted more deliberately during the nineteenth century. Aeromagnetic data from a 1967 survey of the mining area was recompiled, processed, and interpreted for the present study. The original flight lines were digitized and leveled, and the international geomagnetic reference field (IGRF) was removed. The data were inverted by means of a terracing technique that defines separate domains of uniform distribution of physical properties that cause the magnetic anomalies. The log power spectrum was computed; along with the results of terracing, it suggested the existence of two sources of the magnetic anomaly. The long‐wavelength anomaly reflects a large, concealed body that is most probably a granitic intrusion, consistent with local geological evidence. The source of the short‐wavelength anomaly is a strongly magnetized body attributed to the net effect of various thin, magnetite‐bearing sulfide zones. The anomalies were then separated in the wavenumber domain. Magnetic susceptibility measurements were made in situ on the exposed parts of the local formations. Three‐dimensional models whose effect simulates the observed anomalies were calculated. Results of the modeling show that the large magnetic body is buried at 0.68 km depth. The small, relatively shallow body is about 0.035 km thick and buried at 0.6 km depth. The bodies do not show any corresponding gravity anomaly on the regional Bouguer gravity anomaly map.

The Strymon basin is one of the most important sedimentary basins in Northern Greece where significant geothermal fields are located. The SW part of the Strymon basin manifests geothermal interest. Available geophysical data (seismic, gravity, magnetic and electrical data) contributed to the identification of major faults that control the fluid-flow paths of the geothermal field and the estimation of depth to the metamorphic basement. The former is of great importance because the geothermal aquifer is expected to be at the contact of the basal conglomerate with the metamorphic basement. The highest thermal gradient values (10-15o C/100 m) were observed in the western part of the study area near the known geothermal field of Therma – Nigrita. Other important geothermal anomalies (>6o C/100 m) occur in the Patriki area, north of the village of Ivira and in the area between the villages of Patriki and Achinos. Geothermal interest manifests itself in the following areas: north of Mavrothalassa (>4o C/100 m), southwest of Ivira and east of Agios Dimitrios. It appears furthermore that the main thermal anomaly is associated with two NW-SE fault systems that affect the basement in the areas of Patriki and north of Achinos - Ivira correspondingly. These faults have been detected by the use of geophysical surveys. The presence of NE-SW faults extends the anomaly southwestwards.

Management of waste disposal is a major issue that authorities had and still have to deal with. The construction of landfills used to be the main way to manage the great volume of waste. At the present time, the construction of sanitary landfills is the dominant option in Greece, while old waste disposal sites where no protection standards had been followed still exist. In both cases, geological and hydrogeological setting of these areas is of a major importance. In this paper, two cases studies are presented. One case refers, to the active sanitary landfill of Thessaloniki where during the remediation of a new cell, underground water has been found. This was a major problem for the construction of the new landfill since water flow beneath the geomembrane can be destructive. The detection of the flow path and the confrontation of the problem was very important. Resistivity survey allowed the mapping of the underground water flow and appropriate measures have been taken according to the suggestions of the geophysical results. In the second case, an old waste disposal site has been investigated since outflows of leakage occurred. The flow paths of the leakage have been detected and remediation measures have been suggested.

Πραγματοποιήθηκε γεωφυσική διασκόπηση με τις μεθόδους του Ραντάρ Υπεδάφους και της Γεωληλεκτρικής Τομογραφίας, στο κέντρο της πόλης της Θεσσαλονίκης (Β. Ελλάδα) για τον εντοπισμό πιθανών οικοδομικών λειψάνων. Οι γεωφυσικές μέθοδοι είναι μη-καταστροφικές και χρησιμοποιήθηκαν σε αυτή την έρευνα μιας και η συγκεκριμένη έκταση λειτουργεί ως πάρκινγκ και είναι καλυμμένη με άσφαλτο. Οι γεωηλεκτρικές τομές σε συνδυασμό με τις οδεύσεις του ραντάρ μας έδωσαν λεπτομερείς εικόνες του υπεδάφους. Οι μεγάλες τιμές στις γεωηλεκτρικές τομογραφίες σχετίζονται με θεμέλια κτιρίων ενώ οι χαμηλές τιμές αποδίδονται στις γεωλογικές αποθέσεις της περιοχής. Επιπλέον, οι μετρήσεις του ραντάρ αποκαλύπτουν τις θαμμένες ανθρωπογενείς δομές. Παρά το γεγονός ότι οι δύο μέθοδοι χαρτογραφούνδιαφορετικές φυσικές ιδιότητες του υπεδάφους, εντούτοις αποκαλύπτουν παρόμοιες δομές. Τελικά, οι γεωηλεκτρικές ανωμαλίες και οι ξεκάθαρες ανακλάσεις στις μετρήσεις ραντάρ παρατηρούνται σε συγκεκριμένες θέσεις της περιοχής που ερευνήθηκε και αποδίδονται σε θαμμένα θεμέλια κτιριακών εγκαταστάσεων αλλά και υφιστάμενες γεωλογικές δομές., Ground penetrating radar (GPR) and electrical resistivity tomography (ERT) surveys have been carried out in the city centre of Thessaloniki (N. Greece), for investigating possible locations of buried building foundations. Geophysical survey has been chosen as a non-destructive investigation method since the area is currently used as a car parking and it is covered by asphalt. The geoelectrical sections derived from ERT data in combination with the GPR profiles provided a broad view of the subsurface. Regarding ERT, high resistivity values can be related to buried building remains, while lower resistivity values are more related to the surrounding geological materials. GPR surveying can also indicate man-made structures buried in the ground. Even though the two geophysical methods are affected in different ways by the subsurface conditions, the processed underground images from both techniques revealed great similarity. High resistivity anomalies and distinct GPR signals were observed in certain locations of the area under investigation, which are attributed to buried building foundations as well as the geological structure of the area.

The ground magnetic measurements in Albania were used for the compilation of the Total Magnetic Field (TMF) anomaly map of Albania. The magnetic data were processed and interpreted in order to study the structure of the ophiolitic belts of Albania. The ophiolites of Albania are placed at the Mirdita zone and are divided into two parallel alignments which are called the eastern and western ophiolitic belts. They are associated with strong potential field anomalies and their characteristics are considered crucial for a better understanding of the tectonic settings of Albania. The ground TMF data used in this study were acquired over various campaigns (1990-1994) and cover most of Albania's territory. The data were compiled to a map after reduction to the epoch 1990.4. The strongest magnetic anomalies in Albania appear along the known ophiolitic belts which trend NE-SW to the north and NW-SE to the south. Several processing steps were applied to the unified and gridded data in order to obtain information on the distribution of the magnetic sources. The magnetic sources were subsequently modeled using a 2.5D inversion technique. The magnetic properties of the ophiolites determined from laboratory measurements on rock samples, while their lateral extent was calculated from the processing of the magnetic data and used as constraints to the inversion procedure. The bottom of the ophiolitic belts is considered to be predominated by harzburgites. They exhibit lower magnetization than other rocks of the complex, i.e. gabbros, basalt. In fact gabbros are associated with the observed high frequency magnetic anomalies. The modeling results indicate that the thickness of the ophiolites is reduced from east to west. The eastern ophiolitic belt has a maximum thickness of approximately 12 km at its northern section (Kukesi and Lura massifs). The magnetic sources appear with relatively small thickness at the western ophiolitic belt. Boundaries of the eastern ophiolites are characterized by vertical contacts.

In the vicinity of the waterfalls area in Edessa (North Greece) a new tunnel has been decided to be constructed to connect the surface with an existing tunnel. For design and geotechnical reasons the formation of travertine sould be studied. Electrical resistivity tomographies have been measured in very complicated crooked lines because of the rough terrain. As a result the best location concerning topographic and geotechnical reasons revealed from geophysical data has been proposed.

In this study the resuls of the application of electrical methods (Electrical Resistivity Tomography and Self Potential) and VLF method are presented. Since underground water resources were expected mainly in faulting zones of the ophiolithic outcrops, initially the VLF method has been applied in order to detect faulting zones. In a second phase SP and ERT measurements have been conducted in order to further study the characteristics of the faults. Finally, positions for the wells to be drilled have been proposed.

Total magnetic field data measured for geophysical exploration purposes comprise the superposition of the effects of all underground magnetic sources. Usually the targets in magnetic exploration are small, shallow buried bodies, and their magnetic field is superimposed on the regional field that arises from larger and/or deeper source or sources located further away. Sometimes inaccurately removed core fields or large scale topographic features also give rise to regional components. The regional field is generally smooth, adding a trend to the data. The estimation and subtraction of this trend field yields the residual field that corresponds to the target sources. Evidently, the reliability of the interpretation of the residual field depends on the correct estimation of the regional field. In this work the regional-residual separation in the wavelet domain is performed with the aid of the discrete wavelet transformation (DWT) realized with the use of compactly supported wavelets (Daubechies, 1990) with two or three vanishing moments. These wavelets are orthogonal to first or second order polynomials. This means essentially that the regional field (usually represented by a first or second order polynomial) is invisible to the wavelets and thus the regional field is almost entirely hidden in the coefficients of the coarser level of the wavelet transformation. However, in the realization of the DWT as decimated and periodized, the periodic assumption produces some non-zero contribution in a few detail coefficients. Therefore the suppression of all detail coefficients degrades the calculated regional field. To avoid such a distortion we can process a relatively large symmetrical extension of the data sequence from both sides. Alternatively, we can use an internal model for the polynomial field that controls the separation. Because of the spectral overlap, the approximation of the regional field contains some of the energy of the residual field. We can tackle this problem by analyzing the reconstructed approximation of the regional field in a proper new wavelet basis (with the same number of vanishing moments) and repeating the separation procedure. The choice of the model is empirical; thus it depends on the interpreter’s experience. The wavelet that concentrates the energy of the regional field in the low-resolution coefficients and spreads the energy of the residual field in the high-resolution coefficients gives best results. A good choice of wavelet pairs for the first order model is the Db4 and the triangular biorthogonal wavelet. For the second order model, the combination of the Db6 and Villasenor2 wavelets gives a very good separation. The proposed method preserves the signal’s features and has the ability to detect the possible local variations of the regional field. The same method can be used for the detection of overlapping magnetic field anomalies. Although the method may have application in more general settings we are mostly focused on archaeological geophysics, a fact that limits the kind of regional-residual problems which occur in certain ways.

Στην παρούσα εργασία παρουσιάζεται η εγκατάσταση και οι αρχικές μετρήσεις ενός συστήματος Ηλεκτρικής Τομογραφίας για την παρακολούθηση της εισπίεσης επεξερ­ γασμένου νερού στην περιοχή της Σίνδου (Ν. Θεσσαλονίκης). Ο σκοπός είναι, μέσω διαχρονικών μετρήσεων Ηλεκτρικής Τομογραφίας, να παραχθούν γεωηλεκτρικές ει­ κόνες υψηλής ανάλυσης γύρω από και μεταξύ των γεωτρήσεων ώστε να μελετηθεί κα­ λύτερα η διεύθυνση ροής και η διάχυση του εισπιεσμένου νερού στους υπόγειους υ- δροφορείς. Στην εργασία παρουσιάζεται ο γενικός σχεδιασμός της διαδικασίας εισπίεσης και η κατασκευή και εγκατάσταση των καλωδίων της ηL·κτpικής τομογραφίας. Παρουσιαζονται οι προκαταρκτικές μετρήσεις ηλεκτρικής τομογραφίας σε μονή γεώτρηση οι οποίες ερμηνεύτηκαν με ειδικό αλγόριθμο δισδιάστατης αντιστροφής ώστε να παρα­ χθούν εικόνες της μεταβολής της πραγματικής αντίστασης γύρω από τις γεωτρήσεις. Τα αποτελέσματα δείχνουν έναν πολύ καλό συσχετισμό μεταξύ των εικόνων της Ηλε­ κτρικής Τομογραφίας και των λιθολογικών στηλών ενδεικτικό της αξιοπιστίας της προσέγγισης. Η χρήση ηλεκτροδίων στις γεωτρήσεις αυξάνει την ανάλυση και χωρική κάλυψη της πληροφορίας που λαμβάνεται σε σχέση με τις ηλεκτρικές επιφανειακές με­ τρήσεις ή και με σημειακές μετρήσεις μέσα στις γεωτρήσεις. Η μόνιμη εγκατάσταση διατάξεων ηλεκτρικής τομογραφίας σε γεωτρήσεις είναι χαμη­ λού κόστους, γίνεται εύκολα και μπορεί να χρησιμοποιηθεί για να την αξιολόγηση των αποτελεσμάτων της εισπίεσης., This work describes the installation and preliminary measurements of an electrical resistivity tomography (ERT) system to monitor the injection of recycled water into a confined aquifer in the area of Sindos. The aim is to provide, through time-lapse electrical resistivity tomography (ERT) measurements and processing, geoelectrical images of rather increased volumetric sampling around and between the holes and to obtain improved understanding of the flow and transport of the injected water. The details about the general setting and the design of the injection utility are presented and the construction and installation of the ERT cables into the boreholes are explained in full. Preliminary measurements involving single-hole ERT measurements were obtained and processed with a 2D inversion algorithm to produce images of the subsurface. Results depict a very good correlation between ERT images and the lithology logs an indication of the reliability of the approach. This images offer increased resolution and spatial coverage compared to traditional approaches. The entire ERT permanent installation is of low cost, easy to implement and can be used to understand and evaluate the effects of the water injection process.

New findings about the deep origin of the geothermal fields and volcanic centres of the North Evian Gulf area, Central Greece, were arisen by combining a three-dimensional traveltime inversion study of a microseismic dataset recorded of 37 portable stations together with a Curie depth point analysis based on aeromagnetic data. A possible magma chamber can be presumed by the detection of a low seismic velocity volume with high Poisson ratio values at depths below 8 km and the Curie point depth estimation at about 7-8 km depth as well. Besides, the analysis gave information about how the main large tectonic structures (NW-SE) and other important NE-SW faults can facilitate the hydrothermal flux of the local geothermal field.