Search

Abstract: 222Rn activity in soil gas was measured across fault segments of the seismic active Ventaniella Fault and the seismic inactive Sabero-Gordón Fault in the Cantabrian Mountains, NW Spain, in order to investigate the variability of the 222Rn concentration. The sampling took place in summer and autumn 2010. During the autumn measurement program, an additional 222Rn soil gas mapping was carried out in the Sabero-Gordón research area. Zones of elevated 222Rn activity in the soil gas were identified by background 222Rn values of the geological formations used for mapping and local background values from 222Rn values outside the elevated 222Rn activity zones. Unexpectedly, the Sabero-Gordón Fault showed higher 222Rn activity, up to 441kBqm−3, compared to the 222Rn activity of the Ventaniella Fault which had a maximum of 106kBqm−3. Comparison of the results shows that the values measured in summer are about 5 times higher than the autumn values. This difference is not reflected in petrophysical soil parameters or meteorological conditions documented during the field measurements. Based on the results of our work we conclude that the magnitude of 222Rn concentration in soil gas is not an indicator of local seismic activity of the investigated faults. For the studied segment of the aseismic Sabero-Gordón Fault we suggest active genesis of pathways for gas migration driven by aseismic fault slip causing the elevated 222Rn activity in soil gas. [Copyright &y& Elsevier]