Tomographic Imaging of Ancient Wall Foundations in Thessaloniki, North Greece

Introduction A survey involving both surface and cross borehole Electrical Resistivity Tomographies (ERTs) is described. It was conducted at various parts of the western wall of the city of Thessaloniki (N. Greece) aiming to estimate the extent of the walls’ foundations. The Thessaloniki city walls have been initially erected during the Hellinistic and early Roman period. A second phase, which is partly preserved until today, was build during the Byzantine period. It runs parallel to the olde..

Near Surface Geophysical Archaeological Prospection at the Prehistoric Site of Akrotiri on Santorini/Thera

In February 2014 high-resolution ground penetrating radar and earth resistance tomography measurements have for the first time been used successfully for the distinct mapping of buried archaeological structures in the vicinity of the Bronze Age archaeological site of Akrotiri on Santorini/Thera in Greece

A hybrid optimization scheme for self-potential measurements due to multiple sheet-like bodies in arbitrary 2D resistivity distributions

Self-potential (SP) is a passive geophysical method that can be applied in a straightforward manner with minimum requirements in the field. Nonetheless, interpretation of SP data is particularly challenging due to the inherited nonuniqueness present in all potential methods. Incorporating information regarding the target of interest can facilitate interpretation and increase the reliability of the final output. In the current paper, a novel method for detecting multiple sheet-like targets is presented. A numerical framework is initially described that simulates sheet-like bodies in an arbitrary 2D resistivity distribution. A scattered field formulation based on finite-differences is employed that allows the edges of the sheet to be independent of the grid geometry. A novel analytical solution for two-layered models is derived and subsequently used to validate the accuracy of the proposed numerical scheme. Lastly, a hybrid optimization is proposed that couples linear least-squares with particle-swarm optimization (PSO) in order to effectively locate the edges of multiple sheet-like bodies. Through numerical and real data, it is proven that the hybrid optimization overcomes local minimal that occur in complex resistivity distributions and converges substantially faster compared to traditional PSO

3D Inversion of Automated Resistivity Profiling (ARP) Data

Electrical resistivity is a well established and widely used prospection method. The technique has also become a valuable and inseparable tool in archaeological site evaluation and excavation planning (Clark, 1990). Nowadays, it is routinely used in mapping the sub-surface resistivity variation of an archaeological site. The compilation of maps that transform the geophysical results into images that resemble a plane view of buried relics comprises the ultimate goal of geoelectrical prospectio..

3D Inversion of Automated Resistivity Profiling (ARP) Data

Electrical resistivity is a well established and widely used prospection method. The technique has also become a valuable and inseparable tool in archaeological site evaluation and excavation planning (Clark, 1990). Nowadays, it is routinely used in mapping the sub-surface resistivity variation of an archaeological site. The compilation of maps that transform the geophysical results into images that resemble a plane view of buried relics comprises the ultimate goal of geoelectrical prospectio..

Geophysical prospecting in the Krousovitis dam (N. Greece) by seismic and resistivity methods

Abstract: The use of two geophysical methods in the investigation of the geological setting in the area of a dam foundation is presented in this study. The seismic method was used in order to map the structure of the upper layers near the riverbed. VES and resistivity tomographs were also carried out. The depth to the basement was estimated by interpreting the VES curves. Interpretation of the topographic images, along with the inferred models from the seismic data, revealed the thickness of the colluvial deposits

Tumuli exploration using surface 3D Electrical Resistivity Tomography

Introduction The direct current resistivity method is nowadays a well established geophysical technique, used routinely and successfully in the detection and mapping of concealed subsurface structures, like walls, ditches and anthropogenic or natural cavities (Dahlin and Zhou, 2004). In archaeological geophysics, tombs constitute the most common subterranean manmade cavities of the greatest archaeological and historical importance. Several successful case studies in the detection of tombs hav..

Geophysical investigations of tumuli: a continuously challenging problem

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Measurement and inversion schemes for single borehole-to-surface electrical resistivity tomography surveys

Several measurement arrangements involving different electrode arrays are considered for the case of single borehole-to-surface ERT surveys. Synthetic data tests indicate that standard measuring and inversion techniques can result in reconstructed images that suffer from artefacts. Based on the measurement sensitivity analysis, we propose a modified inversion scheme that compensates for the symmetric sensitivity of the in-hole measurements and improves the quality of the image. The new scheme has been tested using both synthetic and field data. The best results were obtained using pole–dipole or dipole–dipole arrays. Finally, some recommendations are made to improve the efficiency of field measurement configurations