Volumetric activity of radon within fault zones of Kirov-Kazhim and Pechora-Kolvin aulacogens

The article is devoted to radiometric studies within the Kirov-Kazhim (KKA) and the Pechora-Kolva aulakogenes (PKA). KKA is the first-order structure of the Volga-Ural anticline, which is located within the ancient East European Platform. The PKA is located in the central part of the Timan-Pechora Epibaykal plate. The aim of the research was to develop a technique for express emanation survey of aulacogenes, to reveal the patterns of spatial variations in the volume radon activity (VRA) in soil air and to estimate of the fault zones activity. Studies were carried out on the western and eastern sides of the central and northern parts of the KKA and the central part of the PKA western side. The fault zones were identified according to the seismic methods data, where large amplitudes of vertical displacements were clearly expressed in the seismic sections. The investigations were conducted during three field seasons within the KKA. In the first year, measurements of the VRA were made from the ground surface. In the following years, a borehole with a depth of 50 cm was drilled for each measurement. A borehole was necessary to reduce the influence of meteorological conditions and soil layer. Summarizing the results obtained in different years allowed concludes that within the fault zone the values of the VRA from the borehole were in the range from 200 to 2000 Bq/m3. The values of the VRA obtained from the ground surface was not higher, than 300 Bq/m3. In 2015-2016 years, express radon survey was carried out according to a previous method in the western side of the PKA. The results showed that the fault zones were clearly reflected in the radon field by elevated values of the VRA in the range 400-1555 Bq/m3. The highest values of the VRA was recorded within the faults which most closely approached to the ground surface. The results of the express emanation survey on the territory of two aulacogenes show that all the fault zones clearly appear in the radon field by increased values of the VRA. The maximum values of the radon activity correspond to tectonic dislocation, which most closely approached to the ground surface. Along the fault line values of the VRA can change. At different times within a single fault site, the VRA values can also fluctuate. The width of the increased values the VRA zone is always greater than the own width of fault. Thus, the spatial distribution of radon over the faults is estimated as quite complex, but using this method for complex study of fault tectonics is promising