Bedrock topography in a buried karstic area by applying multielectrode measurements completed with "pricking probe"

HR: 0803h
AN: NS11D-0788 [Abstracts]
TI: Bedrock topography in a buried karstic area by applying multielectrode measurements completed with "pricking probe"
AU: Szalai, S
EM: szalai@ggki.hu
AF: GGRI HAS, Csatkai u. 6-8, Sopron, H-9400, Hungary
AU: Veress, M
EM: vmarton@bdf.hu
AF: BDF, Karolyi Gaspar ter 4, Szombathely, H/9400, Hungary
AU: Novak, A
EM: novak@ggki.hu
AF: GGRI HAS, Csatkai u. 6-8, Sopron, H-9400, Hungary
AU: * Szarka, L
EM: szarka@ggki.hu
AF: GGRI HAS, Csatkai u. 6-8, Sopron, H-9400, Hungary
AB: Formation of surface depressions is a significant geological hazard. Prediction of future sinkholes in buried karstic areas needs a knowledge about the subsurface. In order to determine the varying topography of the karstifiable bedrock (in Bakony Mts, Hungary), we carried out multielectrode measurements, but among the hard field conditions the bedrock depth could not be reached. The resistivity anomalies in some places had a seasonal variation (low-resistivity in springtime, high-resistivity in the end of summer), therefore we interpreted the resistivity lows as indicators of locations with high water content. At the same time, when pushing the current- and potential electrodes into the ground, we discovered a regularity in the areal distribution of the soil's rock debris content. Therefore we carried out a systematic electrode-pricking experiment, and categorised the soil's "toughness" as 0, 0.5 or 1 (corresponding to soft penetration, scratching or blockage within the upper 30 cm). We have found a relationship between the locations of resistivity- and the soil's toughness extrema. From some epikarstic features we think that high "pricking probe" values indicate smaller depths of the intact bedrock. The corresponding resistivity minima may indicate originally intact horsts of the carbonate rock, either already collapsed or going to be collapsed.
DE: 0925 Magnetic and electrical methods (5109)
DE: 5109 Magnetic and electrical properties (0925)
DE: 5114 Permeability and porosity
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting