© 2007 European Association of Geoscientists & Engineers 263 Non-destructive DC resistivity surveying using flat-base electrodes E.N. Athanasiou * , P.I. Tsourlos, G.N. Vargemezis, C.B. Papazachos and G.N. Tsokas Department of Geophysics, School of Geology, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece Received March 2006, revision accepted February 2007 ABSTRACT The application of flat-base electrodes to geoelectrical measurements is examined. This study is motivated by the inability to apply geoelectrical techniques in environments where conventional spike electrodes cannot be inserted into the ground. The performance of flat-base electrodes is examined in various environments, using different measuring modes. It is shown that flat-base electrodes can be satisfactorily used in most cases, producing data that are almost identical to the measurements obtained using standard electrodes. Several case studies in various urban locations in Greece, where flat-base electrodes have been successfully employed, are also presented. The results indicate that flat-base electrodes provide the advantage of a fully non-destructive application and, therefore, the extension of geoelectrical methods to environments that, otherwise, would not have been considered suitable. archaeological sites and engineered structures) since drilling holes will damage the inspected site. As a result, there is a particular interest in studying techniques which allow resistivity measurements to be performed in a non- destructive manner, such as using flat-base electrodes (Moussa et al. 1977), and therefore extend the application of ERT to other environments (e.g. urban, indoor, etc.). Carrara et al. (2001) demonstrated the application of geoelectrical measurements using copper flat-base electrodes, similar to those presented in this work, on a mosaic floor of a Roman residence. The applica- tion of a non-destructive geoelectrical grid to access wall struc- INTRODUCTION Over the last decade, electrical resistivity tomography (ERT) has been extensively used in geophysical investigations (Dahlin 2001). The most common applications of ERT are geological mapping (Caglar and Duvarci 2001), geothermal field explora- tion (Wright et al. 1985), hydrogeological studies (Flathe 1955; Dahlin and Owen 1998), engineering geology studies (Dahlin et al. 1994), environmental research (Rogers and Kean 1980; Van et al. 1991; Daily et al. 2004) and archaeological prospection (Papadopoulos et al. 2006). The rapid development of urban infrastructures and various constructions resulted in the need to use geophysical techniques in urban environments (indoors, paved surfaces, roads, etc.). Among the existing geophysical techniques, the method of ground-penetrating radar (GPR) is highly popular (Daniels 2004), due to its fully non-destructive nature and survey speed. Furthermore, the introduction of the newly developed technique of capacitive resistivity (Kuras 2002) holds the promise of effi- cient electrical imaging in areas where no (or poor) galvanic contact is possible, but its use is mainly restricted to mapping the shallow subsurface. Applying standard geoelectrical methods in such environ- ments is understandably not popular since, in these cases, the installation of conventional stainless-steel spike electrodes involves drilling holes through the material, which is very labori- ous and costly. Moreover, in most cases it is prohibited (e.g. in * athanael@geo.auth.gr FIGURE 1 Flat-base electrode used in the field applications. Near Surface Geophysics, 2007, 263-272