This paper discusses the geophysical survey conducted within the fortified settlement of ancient Pistyros in N. Greece. According to archaeological data and the ancient written sources, the city was founded at the end of the 7th century BC. Pistyros based its prosperity on the processing of metals, which were abundant in the surrounding area, and probably on the trade in wine and textiles. Its prosperity continued until the 1st century BC. The investigation employed electrical resistance mapping and magnetic gradiometry. Electrical mapping covered almost the entire fortified area of the settlement. Magnetic gradiometry was employed on a trial basis; however, it did not produce reliable results, due to the abundance of slag and metallurgical debris scattered across the site. In addition to traditional processing, image fusion was attempted, employing relatively recently introduced custom-built algorithms. The numerous geophysical anomalies recorded clearly reflect subsurface features, most likely corresponding to buried architectural remains. This interpretation is primarily based on the morphologies of the detected anomalies. Most exhibit linear patterns of finite extent, while, when considered collectively, they form rectangular geometric configurations. These features reflect the layout of the urban fabric and correspond closely with the ground view of the unearthed architectural remains.

This study aims to assess the quality of marble blocks after the extraction procedure, by analysing electromagnetic wave signals’ amplitude values obtained with the geophysical method of ground penetrating radar (GPR). To achieve this, we developed an algorithmic process able to process GPR data collected on marble blocks, named ‘Study Marble Blocks Quality’. This newly developed program consists of five different algorithms that were used—in a mainly automatic manner—to examine variations in the reflectivity of the prospected marble blocks. These variations were mostly attributed to internal block heterogeneities and/or fracturing. Our analysis highlights the importance of the GPR amplitude-based quality assessment of marble blocks, emphasizing on the careful selection of GPR data processing steps as well as the choice of the optimum spacing between measurement lines.

Mapping the integrity of standing monuments with borehole-to-surface Electrical Resistivity Tomography (ERT) measurements. Reconstruct the internal composition and identify positions prone to contain moisture. Contribution to the preservation of historical monuments.

Highlights: Mapping root system in church altar wall, Reflections from construction failures, tiles, plates, and wooden bonding, Some reflections likely due to tree's root system

Agia Bay is located on the southeastern coast of Lemnos Island. The coastal area today is characterized by aeolian sandy deposits (dunes). The systematic investigation of a 15.5-m long sediment core from the coastal plain of Agia Bay aimed to shed light to the paleoenvironmental evolution of the area that prehistoric groups occupied. The exhaustive study of the faunal and floral remains of the deposits including benthic foraminifera, ostracods, mollusks, pollen, and dinoflagellate cysts as well as plant remains was further supported by sedimentological, micromorphological, and elemental analyses, magnetic susceptibility measurements, ERT, and absolute dating. Four main evolutionary stages have been identified since the Late Glacial. At the base of the sequence, the fluvial activity dominated the sedimentation in the area forming a small shallow wetland, while after 12,500 cal BP, a marine signal was observed at the wetland. At 7500 cal BP, the wetland increased in size and depth, whereas at 6000 up to 4000 cal BP, a connection of the wetland to the sea was established, and an inner lagoon formed. After 4000 cal BP, a nearshore environment developed due to the sea-level rise. Pollen assemblages record the occurrence of a mixed deciduous oak forest in the island interior around 6000 cal BP, while after 5000 cal BP, an expansion of Mediterranean vegetation, shaped by human activity, is inferred.

This paper presents the combined application of electrical resistivity tomography (ERT) and ground penetrating radar (GPR) on studying the internal structure of standing monuments. The geophysical survey was conducted at the Rotunda, located in Thessaloniki, Greece, which is an UNESCO heritage monument that dates back to $4^{\text {th}}$ century AD. The main purpose was to perform multiple, three-dimensional (3D) ERT measurements and support the results with GPR data collected in a time lapse manner, to detect possible variations in both ERT and GPR signals. These variations could be related to rainfall and moisture infiltration inside the structure's walls. Raw ERT data collected daily for over a year and represented as apparent resistivities, suggest that the structure is affected by rainfalls and exhibit a strong correlation with them. Additional 4D inversion results indicate the main region of moisture infiltration. Furthermore, the GPR data which were collected on a monthly basis, support the results obtained from ERTs: reflectivity changes over time and fluctuations concur with the infiltration regions suggested by the ERT results.

The Anthemous Valley in Northern Greece underwent major landscape changes during the Holocene. Previous geoarchaeological research has shown that the western and central part of the valley's lower basin was subjected to marine transgression and river aggradation between the 4th and 3rd millennia BC. These changes influenced the Neolithic and Bronze Age habitation patterns in the area. Our study investigates the eastern part of the plain to explain the connection between the former landscape and the Bronze Age occupation of the Toumba Agia Paraskevi tell settlement. Using geoarchaeological methods (electrical resistivity, vibra-coring, radiocarbon dating, sedimentological and palynological analyses) we have revealed that the major alluviation period in the east started during the 1st millennium AD, providing evidence of gradual plain aggradation across the valley from west to east. As a result, we have been able to reconstruct the original location of the toumba, which lay on the edge of the former terrace. This location suggests the inhabitants of Toumba Agia Paraskevi shared a similar preference in settlement locations to those at other Bronze Age sites in the lower basin of the Anthemous Valley.

Time lapse ERT on standing monuments, Moisture detection using optimized 3D ERT arrays

Groundwater is a primary source of drinking water; however, groundwater depletion constitutes a common phenomenon worldwide. The present research aims to quantify groundwater depletion in three aquifers in Greece, including the porous aquifers in the Eastern Thermaikos Gulf, Mouriki, and the Marathonas basin. The hypothesis is to reverse the phenomenon by adopting an environmentally acceptable methodology. The core of the suggested methodology was the simulation of groundwater using MODFLOW-NWT and the application of managed aquifer recharge (MAR) by using water from small dams after the generation of hydropower. Surface run-off and groundwater recharge values were obtained from the ArcSWAT simulation. The predicted future climatic data were obtained from the Coordinated Regional Climate Downscaling Experiment (CORDEX), considering the Representative Concentration Pathway (RCP) 4.5 and the climate model REMO2009. Groundwater flow simulations from 2010 to 2020 determined the existing status of the aquifers. The simulation was extended to the year 2030 to forecast the groundwater regime. In all three sites, groundwater depletion occurred in 2020, while the phenomenon will be exacerbated in 2030, as depicted in the GIS maps. During 2020, the depletion zones extended 11%, 28%, and 23% of the aquifers in Mouriki, the Eastern Thermaikos Gulf, and the Marathonas basin, respectively. During 2030, the depletion zones will increase to 50%, 42%, and 44% of the aquifers in Mouriki, the Eastern Thermaikos Gulf, and the Marathonas basin, respectively. The simulation was extended to 2040 by applying MAR with the water from the existing dams as well as from additional dams. In all sites, the application of MAR contributed to the reversal of groundwater depletion, with a significant amount of hydropower generated. Until 2040, the application of MAR will reduce the depletion zones to 0.5%, 9%, and 12% of the aquifers in Mouriki, the Eastern Thermaikos Gulf, and the Marathonas basin, respectively. Apart from over-pumping, climatic factors such as long periods of drought have exacerbated groundwater depletion. The transformation of dams to mini-scale hydropower facilities combined with MAR will benefit clean energy production, save CO2 emissions, and lead to an economically feasible strategy against groundwater depletion.

Tumuli, ancient burial mounds, stand as intriguing archaeological features, offering valuable insights into past cultures and burial practices. This paper explores the significance of tumuli inspection and utilizes electrical resistivity tomography (ERT) as a noninvasive and powerful tool for inspecting these enigmatic structures, using a nonconventional array. Tumuli, spanning various shapes and sizes, serve as repositories of cultural and funerary traditions, and understanding their internal composition is crucial for unravelling historical narratives. ERT has emerged as a promising geophysical method for investigating subsurface structures, including tumuli. By imaging the electrical resistivity of the ground, ERT enables archaeologists to map variations in soil composition and identify buried features without excavation. This paper reviews the principles of ERT and its application in tumulus studies, showcasing a case study where ERT has successfully revealed internal structures, burial chambers and associated artefacts. The use of 2D ERT is common in tumuli inspection, ignoring accurate 3D effects from the topography. Here we highlight the benefits of the 3D inversion, while we provide a different way to measure which is cost efficient and provides increased spatial resolution to the area of interest. The integration of 3D ERT into archaeological investigations not only enhances our understanding of tumuli construction but also preserves these cultural heritage sites by minimizing the need for invasive excavation. This research contributes to the evolving methodologies in archaeology, emphasizing the synergy between modern technology and traditional archaeological inquiry to uncover the secrets held within tumuli.

The current paper describes the conduct and the results of the innovative (for the time of the survey) geophysical investigations carried out in Hamza Bey Mosque (cine Alkazar) in Venizelou station at Thessaloniki. The assessment of the geological structure and the detection of buried antiquities under the monument were accomplished by conventional GPR and ERT techniques and have been reported elsewhere. A fully 3-D survey is presented here. Further, since the investigations aimed also to precisely determine the depth of the foundations of the monument, innovative crosshole ERT was employed to accomplish this task. The use of geophysics to assess the burial depth of the foundations of buildings is a very difficult task because operating directly over the ground surface is impossible. Further, the manmade noise comprises an additional problem. These are the reasons led to a combination of conventional methods and a cross hole one. Thus, the investigations had a certain degree of innovation. During these investigations we introduced new surveying techniques, specific ways of data treatment and modifications to the mathematical inversion schemes. Practical and theoretical problems had to be faced which were addressed by the collaboration of all involved groups.

The Holocene marine transgression in the Aegean Sea area has significantly impacted prehistoric societies. Toumba Gona is a tell site located at the mouth of the Anthemous River, east of Thessaloniki Bay. According to earlier research, the site should be dated at most to the late stage of the Early Bronze Age. Geoarchaeological research by means of electrical resistivity tomography, vibra-coring, sedimentological analysis, and radiocarbon dating shows, however, that the direct proximity of the site witnessed the maximum marine transgression around 3000-2500 BC and the human habitation phase before the 3rd millennium BC, before the transgression. The coastline began to recede due to the delta progradation, which resulted in the formation of extensive marshes to the south of the Toumba. The increased fluvial activity since the end of the 4th millennium BC is relatable with the progradation of the Anthemous River's bay head delta. Human occupation was recorded before and after the marine transgression thus suggesting human persistence in the coastline environment.

Summary In this work, three-dimensional Electrical Resistivity Topographies are applied to an ancient monument to investigate its foundations. In this framework, we propose and test special measuring strategies based on optimized 3D measuring protocols that depict the foundations of building structures with electrodes located at both sides of the targeted area. The different 3D electrode layouts and protocols were tested extensively with synthetic data against more standard electrode configurations. In addition, the methodology was tested in real field conditions at parts of the Thessaloniki’s Byzantine Wall. Inversion results from the three-dimensional ERTs prove the proposed scheme’s ability to delineate the foundations’ depth while requiring a minimum footprint on the monument.

Summary This study investigates the efficacy of the Ground Penetrating Radar (GPR) method for quality assessment in the marble quarrying industry. GPR surveys were conducted in both quarry benches and extracted marble blocks, utilizing systems with various centre frequency transducers. The processed GPR data are analysed and interpreted through a combination of 2D radagrams and 3D visualization techniques. The results indicate that GPR is a reliable and effective tool in identifying fractures and discontinuities in the marble rock mass. Based on these findings, it can be concluded that appropriate implementation of the GPR technology can significantly improve quarrying techniques, leading to an increased recovery ratio of high-quality marble and enhancement of the overall quarrying operations.

Summary In this study and based on Mediterranean climate temperature data, we examined the subsurface perturbation depth of the seasonal and diurnal surface temperature oscillation, in conjunction with forward and inverse models of electrical resistivity tomography synthetic data. We investigated the influence depth of the atmospheric temperature changes that can be detected from the ERT method, the sensitivity of the ERT method to the temperature changes in terms of a different number of electrodes and spacing between them. Even in the case of high thermal diffusivity materials, the 3% change resistivity horizon cannot be found deeper than 9.5 m during a seasonal cycle, and it cannot be found deeper than 0.33 m during a diurnal cycle. For a typical value of thermal diffusivity formation (sandy CLAY 0.84•10-6 m2/s) and for array inter-electrode spacing of equal or larger than 10 [m] the ERT method is practically insensitive to the surface temperature oscillation effect. For the same thermal diffusivity and spacing of below 5 [m], the inversion results are highly influenced. The conclusions are valid only for the particular tested region; however, the same methodology can be applied to any other temperature oscillation profile from any geographic area.

A large‐scale geophysical survey was carried out at the foothills of a topographic table hosting the ruins of the ancient city ‘Trikorynthos’, in the area of Marathon, north of Athens. The explored site assumed to host remnants of ancient constructions belonging to the ancient city. Although the explored site is associated with the final phase of the famous Marathon battle, it was not expected to bear any signs of that event. Because the bulk of the survey had to be during the dry period, resistivity mapping could not be carried out. Further, tests of magnetic prospecting proved unsuccessful, leaving the electrical resistivity tomography (ERT) survey as the only alternative. Therefore, a total area of about 10 000 m2 was covered by ERTs during the dry months of 2001. A few months later, during the wet winter period, about 5500 m2 were explored by resistivity mapping. The electrical tomographic imaging was extensive, leading to the collection of a large volume of tomographic data. The distance between the measured electrical sections was ranging from 0.6 to 2.4 m at places, depending on the nature of the expected targets. The large number of ERTs carried out renders the survey as one of the largest worldwide of this kind. Processing and interpretation of the tomographic data was carried out in three‐dimensional (3D) using custom‐built algorithms. The inverted data were combined to produce depth slices and 3D images. A few months after the ERT survey, the wet winter conditions allowed the conduct of resistance mapping. Thus, spatially limited resistivity mapping was carried out to complement the ERT survey. The whole operation resulted in detecting and mapping various concealed structures, some of which were verified by the subsequent excavation. Therefore, the ancient use of the area is revealed by the combined result of the geophysical investigation and excavation. In fact, the area should had comprised a road network with extended cemetery westwards and rural premises at the TEST side.

The geophysical survey presented in this paper deals with the combined application of multiple geophysical methods in the area where the new University of Wester Macedonia is to be build. The aim of the survey was to investigate the optimal methodological approach regarding the detection of karst features on limestone rocks. Electric Resistivity Tomography (ERT), Seismic Refraction Tomography (SRT) and Multichannel Analysis of Surface Waves (MASW) were applied. All measurements took place at the area of building C, where a cavity was observed on the surface. ERT was initially applied in order to delineate known features and determine a 3D geoelectric model. Seismic exploration followed in order to evaluate the potential of seismic methods in karst environment and the overall combined interpretation. The results highlighted the main advantages and disadvantages of each method, confirming the importance of joint interpretation. Seismic methods were crucial for the clarification of ambiguous ERT results caused by a resistive environment. Synthetic modeling and real data inversion proved that refraction tomography is a useful and reliable tool in cavity detection. MASW can be used as a complementary technique as it still faces challenges in the delimitation of karst features.

Summary Underground storage tanks (USTs) are very common in urban areas since they can be used for water or hydrocarbon storage without occupying any space at the surface. In the case of the land use being changed, the existence of underground storage tanks turns to be a problem to be solved, especially when those used to be used for the storage of gasoline and other fuels. This is what happened in a former military camp in Thessaloniki (North Greece) that was moved, and the land has been given to the local municipality. Since the exact location of such USTs was not known, as all the surficial constructions and facilities of the camp were completely removed, geophysical investigation was called upon to solve the problem. The Ground Penetrating Radar (GPR), total magnetic field (TMF) and resistivity methods were used to detect the exact location of the USTs. Four locations were pointed out and three USTs were found and removed from the area. A pair of tanks were located in an underground room surrounded by stone walls and concrete floor while the other two were separate and buried directly into the soil.

ABSTRACTIn this work, we study the performance of cross‐hole electrical resistivity tomography measurements by employing different electrode array configurations in plastic polyvinyl chloride (PVC) cased and horizontally slotted observation boreholes by inserting a multi‐electrode cable directly into the borehole. Preliminary cross‐hole electrical resistivity tomography measurements in PVC cased boreholes related to an underground tunnel construction showed poor data quality. This was attributed to the borehole‐fluid effect caused by the PVC casings. An experimental study was conducted to support this hypothesis by setting up various simulations in a water tank, using different PVC casings with various slot densities, and different electrode array configurations. We conclude that the applicability of various measurement setups depends mainly on the acquisition protocol and, to a lesser extent, on the slot density of the PVC casing. Among the different array configurations considered, the pole–dipole array with the potential measuring electrodes being placed in a separate borehole to the current electrodes provide the most robust and reliable results, even for low slot density PVC casings. Besides, denser borehole slot configurations result in better data quality, though to a different extent for the examined protocols. A minimum slot density criterion of at least six slots/electrode spacing is proposed, regardless of the electrode array. The experimental findings are finally evaluated against real field measurements associated with the construction of an underground tunnel of the new Thessaloniki Metro, verifying the pole–dipole array's superior behaviour for this type of measurement configuration. Finally, for those cases where the aspect ratio (hole depth/hole separation) is limited, we propose a modified borehole‐to‐surface configuration with the current electrodes placed outside the boreholes. The overall results indicate that slotted PVC cased observation boreholes (e.g., conventional piezometers), typically constructed as part of many infrastructure monitoring projects, can be efficiently employed for electrical resistivity tomography mapping, generating a new perspective for geoelectrical prospecting. This measuring approach exhibits a significant advantage. The use of pre‐existing boreholes reduces the overall survey costs, reliability, and effort, while also providing high‐resolution subsurface images, especially in urban environments.

Ancient Poliochni is one of the oldest excavated cities in the Aegean Sea and its connection with the sea is indisputable and diachronic during the city habitation from 3500/3300 BC to 2000/1900 BC. The research focuses on the palaeogeographical evolution of the city valley, the coastal zone, and the nearshore seabed. On land, the study area is the lower part of the river valley located between the archaeological site and the foothills of the Agia Triada coastal hill. Data were acquired by geomorphological and geophysical research, drillings (up to 14.5 m depth) stratigraphical and paleontological analysis, and high accuracy topography using GNSS receivers and Unmanned Aerial Vehicles (UAVs). The marine survey extends to the entire Voroskopos (Poliochni) Bay including satellite image analysis, single-beam echo soundings, side-scan sonar seafloor detection and imaging, and visualization of special seabed features. Ancient Poliochni was founded on a coastal terrace shaped by the erosive action of the waves on the hard formations of the Limnos Island geological basement. The seabed morphology and geology of the Poliochni Bay shows that it was part of the coast, during the city habitation, in a progressively flooded by the rising sea level coastal environment.