Outlining complicated subsurface geological conditions by elaborating 1-D electrical soundings for hydrogeological purposes

Subsurface investigations for hydrogeological purposes using geophysical (mainly geoelectrical) methods are widely used today. For geoelectrical methods, the array type and the way the electrodes are expanded, are highly depended on the nature of the hydrogeological target, the depth of investigation and the strike of the geological setting. For deep investigations (ABI2=1000 m), the Schlumberger array is more suitable and is mostly used, although the dipole-dipole array gives similar results. In addition, the inherent difficulty of interpreting 1D Schlumberger soundings, arising from non horizontal layering and lateral variations, has recently been faced by proposing several methods, for recognizing lateral resistivity inhomogeneities (Renning and Tennensen 1990) and detecting them by combining the Schlumberger sounding array with two dipole-dipole soundings (Morris et.al. 1997). During the last two decades emphasis has also been given among the geophysicists, to develop 2D interpretation algorithms for a reliable earth structure simulation (Dewand Morrison 1979, Barker 1981, Dahlin 1993, Loke and Barker 1994). Furthermore, it has been pointed out that in some cases the 1D approximation of Schlumberger curve interpretation is adequate (Beard and Morgan 1991, Morris et. al. 1997). In contrast, less attention has been paid among the geophysicists on the role of the in situ electrical measurements, mainly because of the diversity of the measured values, and dealing with detailed surface geology observations. Bath investigations can contribute to the construction of a reliable 2D structure.