I. Fikos

Electrical resistivity tomography study of Taal volcano hydrothermal system, Philippines

Taal volcano (311xa0m in altitude) is located in The Philippines (14°N, 121°E) and since 1572 has erupted 33 times, causing more than 2,000 casualties during the most violent eruptions. In March 2010, the shallow structures in areas where present-day surface activity takes place were investigated by DC resistivity surveys. Electrical resistivity tomography (ERT) lines were performed above the two identified hydrothermal areas located on the northern flank of the volcano and in the Main Crater, respectively. Due to rough topography, deep valleys, and dense vegetation, most measurements were collected using a remote method based on a laboratory-made equipment. This allowed retrieval of information down to a depth of 250xa0m. ERTs results detail the outlines of the two geothermal fields defined by previous self-potential, CO2 soil degassing, ground temperature, and magnetic mapping (Harada et al. Japan Acad Sci 81:261–266, 2005; Zlotnicki et al. Bull Volcanol 71:29–49, 2009a, Phys Chem Earth 34:294–408, 2009b). Hydrothermal fluids originate mainly from inside the northern part of the Main Crater at a depth greater than the bottom of the Crater Lake, and flow upward to the ground surface. Furthermore, water from the Main Crater Lake infiltrates inside the surrounding geological formations. The hydrothermal fluids, outlined by gas releases and high temperatures, cross the crater rim and interact with the northern geothermal field located outside the Main Crater.

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.

Landfill Leakage Detection Using ERT

In this work we applied the electrical resistivity tomography technique in an attempt to locate areas of leakage in a lined landfill. A systematic ERT survey was carried out using dipole-dipole and pole-dipole forward and reverse arrays. Based on the explanation of the different inversion images obtained over the same line for the the different electrode arrays we propose an interpretation approach which can be used for identifying leakage within a geomembrane liner landfill. Further, the systematic survey with dipole-dipole and pole-dipole (forward and reverse) arrays and the combined graphical interpretation can be used to locate potential leakage area.

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.

High-resolution magnetic gradient and electrical resistivity tomography survey at the Plaka Petrified Forest Park in Lesvos Island, Greece

Lesvos Island, in the North Aegean area of Greece, exposes large accumulations of fossilized tree trunks. They are collectively known as the Petrified Forest of Lesvos, a designated protected natural monument. The paper describes the results of a geophysical study that has been carried out in the area of Plaka on the western part of Lesvos in order to investigate the near-surface geology and detect buried fossilized tree trunks. n In situ and laboratory measurements of magnetic and electrical properties of the trunks have been conducted. Considering the magnetic susceptibility distribution and the contrast between the trunks and the surrounding material, magnetic gradient anomalies of negative signature were expected to reflect the existence of trunks. Electrical resistivity tomography has also been conducted nin order to detect buried trunks, based on their resistivity contrast with the pyroclastic surrounding nmaterial. nFlow paths of the pyroclastic material that can be related to the tectonic features at the time have been detected. In general, petrified trunks have been detected as high resistive bodies. In one case, where the trunk was buried very close to the surface, the resistivity was lower than the surrounding material. n2D and 3D subsurface resistivity models of the surveyed area have been constructed, pointing out probable locations of buried petrified trunks. Excavations that followed the geophysical survey revealed petrified trunks in most of the cases although some of the excavated resistive targets proved to be surface fracture systems filled with resistive oxides.

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.