Variation of soil gas 222Rn/220Rn concentration ratios along the Balçova–Narlıdere segment of the Izmir Fault

Abstract The Balçova–Narlıdere segment of the İzmir Fault is an active tectonic region with high geodynamic significance. Soil gas radon ( 222 Rn) and thoron ( 220 Rn) concentration ratios were studied along this segment to evaluate their potential as geochemical indicators of fault activity. 222 Rn concentrations ranged from 440 to 32,233 Bq/m 3 and 220 Rn from 328 to 29,367 Bq/m 3 . A special focus was on the 222 Rn/ 220 Rn ratio as a geodynamic precursor. 222 Rn/ 220 Rn ratios were analyzed specifically at locations where single gas anomalies were detected, allowing them to distinguish among different depths of the gas source and hence different fault processes.