Meriç A. Berge

3D resistivity imaging from an archaeological site in south-western Anatolia, Turkey: a case study

A large-scale resistivity imaging survey was performed in the acropolis area of Archaic Cnidos, south-western Turkey. This survey was a part of the geophysical studies conducted between 1999 and 2004. Two-dimensional resistivity data were acquired along a number of parallel lines using a pole–pole array. The data was processed using a 3D inversion algorithm based on a robust technique. We also applied shaded-relief processing to enhance the representation of the images of apparent-resistivity data and inversion results. In addition, the inverted resistivity data were visualized by a volumetric representation technique to display both the horizontal and the vertical extents of the archaeological structures. The inversion results revealed that a rectangular gridding pattern and a dense structuring existed in the depth range 0.35–1.5 m in the acropolis. Moreover, the bedrock was the base of the archaeological structures in the area. Based on the resistivity survey, four test excavations were carried out in various localities in the acropolis in 2004. These excavations yielded results supporting those obtained by the resistivity inversion. This indicated that large-scale 3D resistivity imaging can be a useful tool in archaeological prospection.

Electrical resistivity tomography monitoring studies at Balçova (Turkey) geothermal site

This investigation examines the electrical resistivity tomography (ERT) monitoring performed at geothermal sites. It includes two phases of time-lapse ERT studies of the shallow geothermal liquid transportation that results from the circulation of injected and re-injected liquids: synthetic modelling and field surveys. The synthetic modelling stage indicated that the injection process in the horizontal layered environment could cause temporal variations. The field investigation was performed between March 2010 and February 2011 at the Balcova geothermal site, Izmir-Turkey, which has supplied in-house heating since the 1990s. The time-lapse ERT investigations were performed on a shallow aquifer system near two boreholes used as injection and re-injection. In this study, the percentage changes in the synthetic models were determined and compared to the observed inverted time-lapse monitoring data. We propose that time-lapse inversion results are more reliable than the standard inversion approximation. However, the resistivity artefacts were significant, and were dependent on the selection of the comparison model and the inversion parameters. Also the selection of the initial model was shown to be the most important step in constraining the later temporal datasets. During the monitoring period, we observed very substantial decreases in the resistivity of time-lapse results. We conclude that these observed decreases are a result of subsurface temperature or salinity changes associated with the hydrothermal system and fault zone. As a result, this study indicates that time-lapse studies could be important in the characterisation of the subsurface changes that are connected with geothermal operations and climatic fluctuations.

Mapping aquifer geometry using electrical resistivity tomography: a case study from Şanlıurfa, south-eastern Turkey

A shallow aquifer system was investigated with 2D electrical resistivity tomography (ERT) to determine the hydrogeological setting of the Balikli Lake region, Şanliurfa, Turkey. Many spring waters are found in the study area where groundwater flow paths merge and reach the surface. A recreation complex was planned near the Balikli Lake by the Municipality of Şanliurfa. Therefore, an ERT survey was carried out to reveal the subsurface characterization, particularly to investigate the possible shallow aquifer system beneath the recreation area. Consequently, 2D resistivity data along thirteen profiles were acquired in the study area and the data were inverted by a tomographic inversion technique. The conductive layers in the ERT results indicated a shallow aquifer zone probably related to a karstic environment. The high conductivity observed in this layer might be caused by pollution resulting from the industrial and domestic wastes of the residential areas. The high resistive bottom layer was considered to be the basement in the study area. The geometry of the shallow aquifer environment was confirmed by slicing maps obtained from the ERT data. To build the conceptual geological model, a 2D forward resistivity modelling study was also achieved after the inversion studies. The inversion parameters and borehole result underlie the background of the forward model. Field and synthetic data were compared to each other and tested in means of calculation of the misfits to determine the reliability of these models.

Integrated geophysical investigations at a sacred Hittite Area in Central Anatolia, Turkey

In this paper, an integrated geophysical investigation of a sacred area in the archaeological site of Sapinuwa is presented. Sapinuwa was one of the important cities in the Hittite Empire. The archaeological site of Sapinuwa is located in the Corum region of Central Anatolia, Turkey. The goal of the here presented integrative archaeological prospection investigation was to explore buried structures inside the so-called sacred Tasdosem area (Tasdosem means “the stone pavement”) by employing a number of different near-surface geophysical prospection methods. To this purpose, magnetic gradiometry, ground-penetrating radar, electrical resistivity tomography, seismic refraction tomography, and multi-channel analysis of surface wave tomography were applied in this specific area. Overall, the results of the individual geophysical investigations were superimposed in order to obtain more detailed and comprehensive integrative interpretations on the burials contained inside this sacred area. Electrical tomography depth slices revealed the presence of an important structure buried inside the Tasdosem area. Surprisingly, the Vs velocity variations observed in the depth slices of the multi-channel analysis of surface wave tomography provided important information on the character of the burial structure. Additionally, seismic refraction tomography sections and depth slices confirmed the presence of the structures in the same locations. The result of the groundpenetrating radar investigation did not present sufficient certainty regarding the possible deeper burials, whereas the magnetic gradiometry survey gave some insight into near-surface structures. The combination of the employed geophysical prospection techniques was successfully able to characterize the structures that are assumed to have been buried within the Tasdosem area. It is concluded that the integrated non-invasive geophysical archaeological prospection study conducted at Sapinuwa provides a good example on how to approach the investigation and documentation of sites similar to the Tasdosem.

Applications of the GPR Technique to indoor, bridge deck and pier structures: case studies in Turkey

This paper presents the results of three ground-penetrating radar case studies applied to indoor, bridge deck, and pier construction types in Turkey. In these studies, 270-MHz and 1600-MHz antennas were employed to determine the ability limits for construction materials and diagnostic problems associated with the materials. In addition, the importance of the selected survey direction was tested during measurement. Analysing the significance of the migration technique during the data processing stage was another important goal of these case studies. The first case study analyses the indoor applications (e.g., house, villa, and fabric) of ground-penetrating radar and aims to identify possible cracks, structural defects, and corrosion damage. The second case applies ground-penetrating radar to a bridge deck. The third case investigates pier construction by establishing the layout of the construction materials. Identifying possible defects, including structural problems within the pier structure, was another goal. These case studies provide interesting results in terms of physically characterizing the concrete structure and the locations of rebar and slab conditions; the work also reveals the moisture and corrosion effects inside the construction materials on indoor, bridge and pier applications of ground-penetrating radar.

Ground penetrating radar (GPR) studies in the Agios Voukolos church, Izmir, Turkey

The Agios Voukolos church is one of the unique Orthodox constructions in Izmir. Ground penetrating radar (GPR) study was carried out to define the crypts, ossuaries and other subsurface structures under the church. Regular GPR investigations were performed by using a Ramac CU II instrument with 500 MHz center frequency shielded antennae. In addition, two small parts of the Katholikon were measured with 1000 MHz shielded antennas. Data acquired in continuous mode was processed by standard GPR processing steps. The results were given important information about deformation variations (floor cracking and the distortion of architectural elements) and subsurface relics (crypts, ossuaries etc.) inside the church.