This paper presents the results of soil radon gas measurement in three areas, including Thac Ba and Song Tranh 2 hydropower plants, and the planned locations of the nuclear power plants Ninh Thuan 1&2 using solid-state nuclear track detectors (SSNTD) with the aim of clarifying the activity of tectonic faults in these areas. | Vietnam Journal of Earth Sciences, 39(1), 27-46, DOI: Vietnam Academy of Science and Technology Vietnam Journal of Earth Sciences (VAST) Study on active tectonic faults using soil radon gas method in Viet Nam Pham Tich Xuan, Nguyen Van Pho, Vu Van Chinh, Pham Thanh Dang, Nguyen Thi Lien, Doan Thu Tra, Hoang Tuyet Nga, Bui Van Quynh, Nguyen Van Luan, Nguyen Xuan Qua Institute of Geological Sciences, Vietnam Academy of Science and Technology Received 23 December 2015. Accepted 20 January 2017 ABSTRACT This paper presents the results of soil radon gas measurement in three areas, including Thac Ba and Song Tranh 2 hydropower plants, and the planned locations of the nuclear power plants Ninh Thuan 1&2 using solid-state nuclear track detectors (SSNTD) with the aim of clarifying the activity of tectonic faults in these areas. The activity of tectonic faults was assessed through radon activity index KRn (the ratio between anomaly and threshold), which was divided into 5 levels as follows ultra-high (KRn> 10), high (10≥KRn> 5), high (5≥KRn> 3), medium (3≥KRn> 2) and low (KRn≤2). Soil radon gas measurement results showed that in the radon gas concentrations in the Thac Ba hydropower plant area ranged from 72 Bq/m3 to Bq/m3 and maximum radon activity index KRn reached (high level). High KRn indexes show Chay River fault active in recent time and the sub-meridian distribution of Rn anomalies suggested a right-slip motion of the fault. Rn concentrations in the Ninh Thuan 1&2 areas ranged from 6 Bq/m3 to Bq/m3, however, the KRn indexes were mostly low (KRn≤3) and the highest value was only , suggesting that expression of activity of the tectonic faults in this region is not clear, even no expression of fault activity. In the Song Tranh 2 hydropower plant and adjacent areas, radon concentrations ranged from 29 Bq/m3 to Bq/m3 and maximum KRn index was (ultra-high level). The .
