Detection of faults using the profile measurements of radon concentration and gamma dose rate (Bohemian Massif, Czech Republic)

The measurements of radon concentration and gamma dose rate across the detected, mylonitized and assumed faults were performed on 79 profiles situated in metamorphic, magmatic and sedimentary rocks of the Bohemian Massif. At each profile, 10 points (3 m apart) were measured. The position of medians of both measured quantities differs according to the lithological type of rocks. In the clayey weathering rocks, the fault core is mostly characterized by the radon concentration decrease and gamma dose rate increase (paragneisses, granitoids, claystones) whilst in the coarse grained weathering rocks (migmatites, sandstones) the trend is opposite. However, the variations of radon and gamma dose rate were clearly observed even in a detailed scale of meters. The radon and gamma dose rate relationship was found to be close to linear regression except of the sedimentary formations of Carboniferous and Permian age which are characterized by a wide-range of host rocks porosity. Confirming the radon release from bedrock at the fault cores and their damage zones will improve the radon prognostic maps of the Czech Republic and other EU countries. For practical use, the results will help to precise the correctness of the building site assessment in a detailed scale.