The ²²²Rn and CO₂ soil gas distribution at Lembang Fault Zone, West Java - Indonesia

Series of ²²² Rn measurements had been employed around the Lembang Fault Zone, West Java - Indonesia to investigate its relationship with the fault zone. Furthermore, the mechanism of ²²²Rn transport is also investigated by performing soil gas CO₂ and its δ¹³C measurements. The evaluation of ²²²Rn concentration shows that 34% data are within threshold values with an average of 14,117 Bq/m³, with anomalous concentration greater than 20,000 Bq/m³. The concentration of CO₂ in soil gas is varied from 72 ppm to 13,241 ppm and consisted of three populations, with 40% of the data above 655 ppm. The spatial distribution pattern shows that most of Lembang Fault Zone segment coincides with high ²²²Rn concentration indicating high permeability zone. Furthermore, the average ²²²Rn concentration in western part of the fault is higher than the eastern part and this may be correlated with higher seismic activities. In contrast to ²²²Rn, CO₂ concentration shows less correlation to the fault structure. Based on δ¹³C values, the source of soil CO₂ is dominated by atmospheric CO₂, with minor mixing of biogenic origin. Although Lembang Fault Zone is located in the south of an active volcano, there is no indication of magmatic CO₂ origin. The lack of correlation between ²²²Rn and CO₂ suggests that there is no indication of ²²²Rn transport by CO₂ as carrier gas.