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The block model in a homogenous environment can generally serve for presentation of some geological models: changes of facies, changes of rock compactness-fragmentation, underground cavities, bauxite deposits, etc. Therefore, on the block model of increased resistivities in a homogenous environment of low resistivity, the potentials of the electrical tomography method were tested for the purpose of their detection. Regarding potentials of block detection, resolution methods depend on: depth of block location, ratio between block resistivity and the environment in which it is located as well as applied survey geometry, i.e. electrode array. Thus the analyses carried out for the most frequently used electrode arrays in the investigations are the following: the Wenner, Wenner-Schlumberger, dipole-dipole and pole-pole arrays. For each array, maximum depths at which a block can be detected relative to the ratio between block resistivity and parent rock environment were analyzed. The results are shown in the two-dimensional graphs, where the ratio between the block resistivity and the environment is shown on the X-axis, and the resolution depth on the Y-axis, after which the curves defining the resolution limits were drawn. These graphs have a practical use, since they enable a fast, simple determination of potentials of the method application on a specific geological model.

exploration area and for building of a detailed hydrogeological model, especially with complex geological models and 3-D structure shapes. Electrical sounding is based on a theoretical assumption of a horizontally stratified earth model, and electrical profiling maps only lateral resistivity changes at the same depth. Two-dimensional (2-D) electrical imaging (or 2-D electrical tomography), that has been introduced recently, can map the both vertical and lateral resistivity changes and provides for building three-dimensional (3-D) resistivity model of the underground. Exploration has been carried out in the area of the Seona spring to investigate the possibility for pumping more water during dry season, from the well located near the spring. The water of the Seona spring emerges from Badenian carbonate aquifer, which shows irregular 3-D shape and heterogeneous lithologic composition. A network consisting of four electrical profiles has been established to acquire a 3-D resistivity model, which can be transformed in a 3-D hydrogeological model. Inverse resistivity model sections revealed high resistivity zone which has been correlated with Badenian limestone by means of existing outcrops. Low resistivity zones point to the marly layers. Exploratory borehole located on the basis of electrical data has confirmed derived hydrogeological model from the electrical imaging data. Heterogeneous limestone aquifer has been uncovered at depth 8.2 – 55 m. The aquifer is weathered and karstificated with two main cavern intervals. Hydraulic connections between the caverns and the spring have been established during drilling, but also in a pump test by means of the airlift method. The presented case demonstrates great possibilities of the electrical imaging method in mapping of irregularly shaped aquifers and building of a precise 3-D hydrogeological model.

The problem of ambiguity in the interpretation of gravity in platform areas is analised. A theoretical example is given, presenting ambiguity in the determination of depth and position of faults, even when the form of structures is known. It has been concluded, that the best method of gravity interpretation is the construction of the map and profiles showing the depths of horizon where there is the strongest density contrast. An example is given from the Sultana area in Jordan, where the gravity map is converted into the maps of »quantitative regional« and »true residual«, by means of drilling data. Interpretation of the residual by the method of gravity modelling resulted in the construction of the map of structures and depths of the density contrast horizon, with the positions and throws of the main faults.

Gravimetric anomalies were converted into depth contours by using the depth and density data from bore holes. Gravity modelling was performed in two- and threedimensions. The forms of the structures were obtained using the computation methods described. The work performed represent a contribution towards a better use of the gravity data (the paper is published in Croatian).

Water exploration at several localities of the Adriatic karst sea-shore band was carried out by the dual gradient mapping of apparent electrical resistivity. By this method controlling the resistivity relation with depth by constant electric stream fields of different depth actions, the anomalies were obtained with apparent resistivity which can be related to deep karst fault zones, used as communication of water from coast background with off-shore springs and submarine springs. The advantage of this method in comparison with the usual geoelectric exploration methods of water in karst is, that electric fields are kept constant by lateral control of the apparent resistivity at some depth interval, which decreases the impact of surface inhomogenuities and electrically visible infrastructural constructions in urban environment on the correct interpretation of measured anomalies. The sea water as a big mass with low resistivity represents a disadvantage for geoelectrical exploration on the sea shore, which masks the explored anomalies at depth. Although, this anomalies can be recognised by this method. The report discusses the case of a successful exploration on the coastal area upwards of Opatija, where efforts have been made for many years to trap water flowing out of many off-shore and submarine springs (the paper is published in Croatian).

Some characteristic examples are given of the magnetic prospecting for the rocks used as building materials. Conclusions are drawn about the applicability of the magnetic method for this purpose. Method proved to be very speedy and inexpensive, it gives important informations on the extension, position and depth of the magnetic rock. The quality of the rock is better determined by other methods (the paper is published in Croatian).