A. Stampolidis

Analysis of potential field anomalies in Lavrion mining area, Greece

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.

Investigating behind the lining of the Tunnel of Eupalinus in Samos (Greece) using ERT and GPR

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.

Gravity data inversion for Moho depth modeling in the Hellenic area

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 (Mohorovičić discontinuity). The selected density contrast and mean depth of the Mohorovičić 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.

A focusing approach to ground water detection by means of electrical and EM methods: the case of Paliouri, Northern 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.Firstly, the Very Low Frequency (VLF) electromagnetic method was applied since the majority of the area was dominated by the formation of ophiolites and water flow was possibly expected only in fractured zones at a relatively small depth. Secondly, at the locations of the conductive zones detected by the VLF survey additional Electrical Resistivity Tomography (ERT) sections at different scales were measured to provide more detailed information about the geometrical characteristics of them. Finally, Self-Potential (SP) measurements along the same profiles were conducted in order to provide supplementary information concerning the nature of the conductive zones such as the possible relation with electrokinetic sources.The combined interpretation of the geophysical data proved very efficient for deciding the most promising locations for the construction of hydro wells.

Ground penetrating radar and electrical resistivity tomography for locating buried building foundations: A case study in the city centre of Thessaloniki, Greece

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.

Edge Detection of Magnetic Sources Related with the Philippi Granitoid in N. Greece

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.

Waste Disposal Sites Investigation by the Use of Electrical Resistivity Tomography

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.

Ground Water Detection by Means of Electrical and EM Methods – The Case of Paliouri, Northern Greece

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.