engleski

The Potentials of Geoelectrical and Seismic Methods in Karstic Water Explorations

Geoelectrical and seismic methods are probably the best choice in a water exploration in karst areas, which are very difficult environments for any geophysical exploration because of very high surface inhomogeneities. Dual gradient mapping (measurements performed at two depth levels), 2D (two-dimensional) resistivity surveying, refraction method and high resolution reflection method have been applied on the characteristic karst case in Croatia. Low resistivity zone with the general extension SW-NE discovered by the gradient mapping point to the fractured rock filled with water. On the map of relative changes of apparent resistivities with depth (calculated as the ratio of resistivity values at two measured depth levels expressed in percentage) two different zones can be detected: increasing resistivity with depth in the eastern part and decreasing resistivity with depth in the western part. Accurate geological model can be established on the basis of the inverse resistivity model derivative from a measured apparent resistivity 2D section. Poor reflections are seen on the reflection profile placed along with the 2D resistivity imaging profile, which are probably caused by differently fractured carbonate rocks. Combining refraction and reflection data faulted and fractured zones can be determined as at surface so at greater depths, which will enable precise definition of their extensions. Geoelectrical methods can be used very efficiently in karstic water explorations at shallow targets, but at deeper targets the seismic methods can be very useful because of poor resolution of the geoelectrical methods.

geoelectrical methods; seismic methods; water exploration; karst

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