Exploration of Deep Carbonate Aquifers by Magnetotellurics

Electrical tomography is often considered as the main geophysical method in groundwater investigations, especially in complex geological models, but in case of deep exploration it cannot achieve deeper aquifers and the electrical sounding cannot ensure complete and dense space coverage. In such a case the use of the magnetotelluric method can ensure determination of deep targets, as well as a good space sampling. The capabilities of the MT method are shown in a common hydrogeological model in Croatia which can be found in both regions, in the Pannonian basin and Dinarides. The carbonate aquifer is underlying at depths greater than 100 m below impermeable package of clastic deposits. Two filed examples of groundwater investigations are presented, Gotalovec (north-western Croatia) and Baška (karstic Adriatic island Krk) areas. A main conclusion can be drawn that the MT method provides the most complete data on lithological and structural relationships in the considered model, but it is very sensitive to surface and urban noises. The results of the other geophysical methods can improve the resolution (seismic reflection) and reduce the interpretation ambiguity (electrical tomography).