JOURNAL OF THE BALKAN GEOPHYSICAL SOCIETY, Vol. 13, No. 1, February 2010, p. 1-8, 6 figs, 1 table. 1 Integrated geophysical methods for imaging saline karst aquifers. A case study of Stylos, Chania, Greece Hamdan Hamdan * , George Kritikakis, Nikos Andronikidis, Nikos Economou, Emmanouil Manoutsoglou and Antonis Vafidis Technical University of Crete, Department of Mineral Recourses Engineering, Chania, 73100, Greece ( * hamdan@mred.tuc.gr ) (Received 03 October 2009; accepted 12 January 2010) Abstract: Geophysical methods are useful for mapping the boundary between fresh and saline water in coastal areas. However, the existence of karstic formations increases the uncertainty on geophysical sections and complicates the interpretation of geophysical data. In this paper, a systematic geophysical methodology for imaging saline water intrusion, in complex geological structure is being presented. We applied three methods for the inversion of resistivity data, as well as multi array data joint inversion and time lapse tomography. For the interpretation of the geophysical data we combined seismic velocity and resistivity sections. This integrated geophysical survey revealed saline water zones in the investigated area and verified that a major normal NE-SW fault zone is mainly responsible for the groundwater salinization in the Stylos area. Key words: Electrical and seismic tomography, Saline karst aquifers, resistivity inversion, Stylos-Chania. INTRODUCTION Geophysical methods have been used by many researchers to monitor salt water intrusion in coastal areas (Singh et al., 2004, Abdul Nassir et al., 2000, Lashkaripour, 2003, Gnanasundar and Elango, 1999, Imhof et al., 2001, Haxhiu and Uci, 1994, Prakash et al., 1980). The presence of dissolved chlorine ions in aquifers reduces dramatically their resistivity and thus electrical resistivity methods are very effective in locating salinization zones. Although the seismic methods are unable to delineate directly the salinization, they can provide valuable information about the geological causes that favor the contamination of fresh water (Balia et al., 2003, Mela, 1997, Jarvis and Knight, 2002, Haeni, 1986). The saline water in karstic formations contaminates the aquifers through a complex system of karstic or fractured carbonate rocks. The strong lateral inhomogeneity of such complex structures complicates the imaging and interpretation of geophysical data. In this paper, we present the preliminary results of an integrated geophysical survey, for imaging saline karstic aquifers of Stylos (Chania, Crete, Greece) area. This survey combines VLF, electrical sounding, electrical tomography, seismic refraction and Multichannel Analysis of Surface Waves (MASW) methods in order to map the complex geology of the area. SURVEY REGION The springs of Stylos village, Crete, Greece (Fig. 1) play an important role in Chania irrigation water supply. In a water well near a polje located approximately 1300 m N-NW of Stylos village, saline (brackish) water was drilled in 1981-2. The absence of gypsum, anhydrite, or mineral salt in the area and the presence of faulted carbonate formations, indicates that the groundwater salinizaton is caused by seawater intrusion. The seashore is located north of the polje, at a distance of 2900 m (Fig. 1) (Hamdan et al., 2007). A detailed hydrogeological survey was carried out in the region, combining information from boreholes, hydrogeological data (Zervogiannis and Xatziagorakis, 1969) and recent geological mapping (scale 1:5,000, Michalakis et al., 2006). The western part of the area, covered by carbonates, consists of two major tectonic units: the lowermost Plattenkalk group and the brecciated carbonates of theTrypali unit. Poljes are observed on this later unit (Fig. 1). A major normal NE-SW fault is observed near the Aptera horst. Neogene marls and marly limestones are in contact with the Trypali carbonates along this fault and cover the eastern part of the investigated area (Fig. 1).