G. Vargemezis

A large scale geophysical survey in the archaeological site of Europos (northern Greece)

Abstract The results of a large scale exploration of an archaeological site by geophysical means are presented and discussed. The operation took place in the site where the ruins of the ancient city of Europos are buried. This site is in northern Greece. Resistivity prospecting was employed to detect the remnants of wall foundations in the place where the main urban complex of the ancient city once stood. The data were transformed in an image form depicting, thus, the spatial variation of resistivity in a manner that resembles the plane view of the ruins that could have been drawn if an excavation had taken place. This image revealed the urban plan of the latest times of the life of the city. Trial excavations verified the geophysical result. Magnetic prospecting in the same area complemented the resistivity data. The exact location of the fire hearths, kilns and remnants of collapsed roofs were spotted. Magnetic gradient measurements were taken in an area out of the main complex of the ancient city and revealed the location of several kilns. One of these locations was excavated and a pottery kiln was discovered. The resistivity prospecting in one of the graveyards of the ancient city showed anomalies which were expected and corresponded to monumental tombs. The locations of a few of them were excavated and large burial structures were revealed. Ground probing radar profiles were measured over the tombs which showed pronounced resistivity anomalies, so far unearthed. The relatively high resolving ability of the method assisted the interpretation in the sense that a few attributes were added. In the presented case, it was concluded that a particular tomb consists of two rooms and that it is roofless.

The detection of monumental tombs buried in tumuli by seismic refraction

A tumulus is a construction erected to cover a tomb. Some tumuli are impressively massive and may conceal architectural masterpieces. Seismic refraction is employed to locate the tomb and to allow selective excavation without destroying the tumulus. The detectors are spread along a circular profile on the periphery of the tumulus, and acoustic waves are generated on its top. Time delays observed in the arrivals of the headwaves reveal the position of the monument. The delays are not caused by the monument itself, but are an effect caused by the presence of a ramp that was dug in the undisturbed soil to help in the construction of the tomb. Three case histories in Northern Greece establish the efficiency of the technique. In the first example, an experiment was conducted at a previously excavated tumulus, and time delays attributed to the revealed ramp are observed. The second case study led to the discovery of an impressive monument; 3-D modeling by finite difference verifies the interpretation. A third s...

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 nsample of ancient Greek engineering surviving almost intact. The main construction is a tunnel n1036 m long and almost 1.8 m wide excavated from both ends into mainly the massif limestone. In nsome parts of the overall length of about 240 m, the tunnel is dressed by lining of archaic and nRoman age. This is of remarkable quality, and presumably, it protected the parts of the tunnel that nwere affected by subsidence and cave-ins. At some particular locations, it suffers deformations and nother failures. nThus, prior to its restoration and protection measures design, an integrated geophysical survey nwas carried out on the faces of the supporting walls, consisting in ground-penetrating radar and nelectrical resistivity tomography works. The survey aimed to investigate the structure at the unseen narea behind the lining. nThe thickness of the lining walls was accurately assessed by the ground-penetrating radar nmethod and proved to be about 0.3 m–0.5 m on average. On the other hand, the width of the excavation nbehind the walls was predicted and checked at some particular locations with the electrical nresistivity tomography works.

3D inversion of irregular gridded 2D electrical resistivity tomography lines: Application to sinkhole mapping at the Island of Corfu (West Greece)

We study the case of the combined interpretation of irregularly gridded 2D electrical resistivity tomography nlines. A 3D inversion algorithm was specially modified to accommodate the full 3D processing nof such lines. The chosen approach uses a dense structured mesh and a flexible parameter design nscheme. Tests with synthetic data show that full 3D inversion results are significantly improved when ncompared with the equivalent quasi-3D imaging of the 2D inversion results. It is also shown that 3D ninversion results can provide correct location and shape information about targets that are not directly nlocated under the measured lines. The scheme was tested with real data from a site in the northern part nof the Corfu Island (West Greece) where a large number of irregular gridded 2D electrical resistivity ntomography lines were collected in order to map sinkholes related to gypsum. The 3D inverted nimages provide important information about the structure of the existing sinkholes and the potential nsinkhole generation mechanism. Overall, the possibility of 3D interpretation of irregularly gridded nlines is not only important for obtaining better subsurface images but also allows a more flexible and npractical design of electrical resistivity tomography field surveys.

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.

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.