Fault delineation study using soil–gas method in the Dharamsala area, NW Himalayas, India

Assessment of radon transportation and uranium content in the tectonically active zone of Himalaya, India

The study shows how geology and tectonic activity affect the soil gas 222Rn concentration. The tectonically active zone, namely the Ghuttu region, which is located within the Himalayan seismic belt, was studied to decipher its impact on soil gas 222Rn concentrations. A soil gas 222Rn study was performed in the soil at a depth of 30 cm, and it varied from 426 ± 156 Bq m-3 to 24,057 ± 1110 Bq m-3 with an average of 5356.5 ± 1634.6 Bq m-3, and at 60 cm below the soil surface, the concentration varied from 1130 ± 416 Bq m-3 to 30,236 ± 1350 Bq m-3 with an average of 8928.5 ± 2039.5 Bq m-3. These concentrations vary in soil from -3.4 % to 437.3 % as the depth moves from 30 cm to 60 cm. The variation in uranium content also shows anomalies, and higher values of uranium content in the soil affect the radon concentration in the study area. The average soil gas 222Rn concentration in the Ghuttu window was found to be higher than that in its surrounding region. This is likely due to transportation from daughter products of uranium. 222Rn mass exhalation rate measurements were also carried out, and a weak correlation with the soil gas 222Rn concentration was observed. A significant variation in the mass exhalation rate was noticed in tectonically active areas. This study is vital to understanding the behavior of radon and uranium in tectonic regions.

Spatial-temporal evolution of soil gas Rn before two Ms ≥ 5.0 earthquakes in the mid-eastern of the Qilian fault zone (QLF)

The mid-eastern segment of the Qilianshan fault zone (QLF) on the northeastern margin of the Qinghai-Tibet Plateau is considered one of the key seismic hazard areas. The Zhangye Ms5.0 earthquake and Menyuan Ms6.9 earthquake are the two Ms ≥ 5.0 earthquakes in recent years. The spatio-temporal evolution of Rn across the fault before the two Ms ≥ 5.0 earthquakes were explored by combining a solid seismogenic model and numerical simulation results in this study. The results demonstrates the spatial distribution of Rn concentration intensity varies over time, indicating the evolving characteristics of fracture zone activity. The time-series variation characteristics are closely related the Zhangye Ms5.0 earthquake and Menyuan Ms6.9 earthquake. Overall, in the seismic source area and surrounding medium area of Zhangye Ms5.0 earthquake, the soil gas Rn anomaly across faults characterized by a turning upward trend after continuous decline. The closer to the source area, the more obvious the upward trend. For Menyuan Ms6.9 earthquake, the survey line (HT1) located in the main fracture zone of the earthquake and the survey line (HT7,30km from the epicenter) closer to the epicenter also showed a similar trend, while the other measurement lines in far-field exhibit declining trend before the Menyuan Ms6.9 earthquake. Therefore, the continuous decline trend of soil gas may be crucial information for medium-term earthquake preparation in the seismogenic zone, and the trend of turning upward after continuous decline is a significant signal of short-term seismogenic event in far-field. This research could improve the understanding of the anomalous features of soil gas precursors and tracking the active sections of the fault. According to the model, the earthquake area canseismic source area, the surrounding medium area be divided into three sections: the seismic source area, the surrounding medium area, and the fracture fragmentation area.

SOIL GAS RADON MEASUREMENT AROUND FAULT LINES ON THE WESTERN SECTION OF THE NORTH ANATOLIAN FAULT ZONE IN TURKEY

Soil gas radon activity measurements were made around the western section of the North Anatolian Fault Zone. In the study, the variation of radon concentration at 12 different locations along the fault line was monitored by using LR-115 (solid-state nuclear track detectors) detectors for 12-monthly periods. Twelve radon stations were determined in the study region, and in each station, LR-115 films were installed in the borehole of ∼50 cm. The recorded radon concentration varies from 29 to 7059 Bqm-3 with an average value of 1930 Bqm-3. The influence of meteorological parameters such as temperature, pressure, total rainfall and humidity on soil radon concentrations in the study area was also investigated. The positive and poor correlation was observed between average value of 222Rn concentration and temperature. There is a reverse proportion between radon level with other meteorological factors (humidity, pressure and rainfall). The results show that the measured soil gas radon activity concentration shows seasonal variation in a highly permeable sandy-gravelly soil with definite seasons without obvious long transitional periods. The summer (from June 2013 to September 2013) is characterised by 1.8 times higher average soil gas radon activity concentration (median is 2.372 kBqm-3) than the winter (from December 2012 to March 2013) (median is 1.298 kBqm-3).

Effective radium-226 concentration in rocks, soils, plants and bones

Effective radium-226 concentration, ECRa, is the product of radium activity concentration, CRa, multiplied by the emanation coefficient, E, which is probability of producing a radon-222 atom in the pore spaces. It is measured by accumulation experiments in the laboratory, achieved routinely for a sample mass >50 g using scintillation flasks to measure the radon concentration. We report on 3370 ECRa values obtained from more than 11 800 such experiments. Rocks (n=1351) have a mean ECRa value of 1.9±0.1 Bq kg−1 (90% of data in the range 0.11–35 Bq kg−1), while soils (n=1524) have a mean ECRa value of 7.5±0.2 Bq kg−1 (90% of data between 1.4 and 28 Bq kg−1). Using this large dataset, we establish that the spatial structure of ECRa is meaningful in geology or sedimentology. For plants (n=85), ECRa is generally <1 Bq kg−1, but values of larger than 10 Bq kg−1 are also observed. Dedicated experiments were performed to measure emanation, E, in plants, and we obtained values of 0.86±0.04 compared with 0.24±0.04 for sands, which leads to estimates of the radium-226 soil-to-plant transfer ratio. For most measured animal bones (n=26), ECRa is >1 Bq kg−1. Therefore, ECRa appears essential for radon modelling, health hazard assessment and also in evaluating the transfer of radium-226 to the biosphere.

SOIL 222Rn CONCENTRATION, CO2 AND CH4 FLUX MEASUREMENTS AROUND THE JWALAMUKHI AREA OF NORTH-WEST HIMALAYAS, INDIA

Soil ²²²Rn concentration, CO₂ and CH₄ flux measurements were conducted around the Jwalamukhi area of North-West Himalayas, India. During this study, around 37 soil gas points and flux measurements were taken with the aim to assure the suitability of this method in the study of fault zones. For this purpose, RAD 7 (Durridge, USA) was used to monitor radon concentrations, whereas portable diffuse flux meter (West Systems, Italy) was used for the CO₂ and CH₄ flux measurements. The recorded radon concentration varies from 6.1 to 34.5 kBq m^-3 with an average value of 16.5 kBq m^-3 The anomalous value of radon concentrations was recorded between Jwalamukhi thrust and Barsar thrust. The recorded average of CO₂ and CH₄ flux were 11.8 and 2.7 g m^-2 day^-1, respectively. The good correlation between anomalous CO₂ flux and radon concentrations has been observed along the fault zone in the study area, suggesting that radon migration is dependent on CO₂.

Effective radium concentration in agricultural versus forest topsoils

Effective radium-226 activity concentration (ECRa), the radon-222 source term, was measured in the laboratory with 724 topsoil samples collected over a ∼110 km(2) area located ∼20 km south of Paris, France. More than 2100 radon accumulation experiments were performed, with radon concentration measured using scintillation flasks, leading to relative uncertainties on ECRa varying from 10% for ECRa = 2 Bq⋅kg(-1) to less than 6% for ECRa > 5 Bq⋅kg(-1). Small-scale dispersion, studied at one location with 12 samples, and systematically at 100 locations with three topsoils separated by 1 m, was of the order of 7%, demonstrating that a single soil sample is reasonably representative. Agricultural topsoils (n = 540) had an average (arithmetic) ECRa of 8.09 ± 0.11 Bq⋅kg(-1), and a range from 2.80 ± 0.22 to 19.5 ± 1.1 Bq⋅kg(-1), while forest topsoils (n = 184), with an average of 3.21 ± 0.14 Bq⋅kg(-1) and a range from 0.45 ± 0.12 to 9.09 ± 0.55 Bq⋅kg(-1), showed a clear systematic reduction of ECRa when compared with the closest agricultural soil sample. Large-scale organization of ECRa was impressive for agricultural topsoils, with homogeneous domains of several kilometers size, characterized by smooth variations smaller than 10%. These patches emerged despite heavy human remodeling; they are controlled by the main geographical units, but do not necessarily coincide with them. Valleys were characterized by larger dispersion and less organization. This study illustrates how biosphere and anthroposphere modify the soil distribution inherited from geological processes, an important baseline needed for the study of contaminated sites. Furthermore, the observed depletion of forest topsoils suggests an atmospheric radon signature of deforestation.

Investigation of some factors affecting on release of radon-222 from phosphogypsum waste associated with phosphate ore processing

The aim of this study is oriented to investigate the influence of some physicochemical factors such as radium distribution, grain size, moisture content and chemical constituents on releases of radon-222 from the accumulated phosphogypsum (PG) waste. The emanation fraction, activity concentration in the pore and the surface exhalation rate of radon-222 in the bulk PG waste are 34.5 ± 0.3%, 238.6 ± 7.8 kBq m(-3) and 213 ± 6.9 mBq m(-2) s(-1), respectively. These values were varied and enhanced slightly in the fine grain sizes (F1 < 0.125 mm) by a factor of 1.05 folds compared to the bulk residue. It was also found that release of radon from residue PG waste was controlled positively by radium (Ra-226), calcium (CaSO4) and strontium (SrO). About 67% of radon release attributed to the grain size below 0.5 mm, while 33% due to the large grain size above 0.5 mm. The emanation fraction of Rn-222 is increased with moisture content and the maximum emanation is ∼43% of moisture of 3-8%. It reduced slowly with the continuous increase in moisture till 20%. Due to PG waste in situ can be enhancing the background to the surround workers and/or public. Therefore, the environmental negative impacts due to release of Rn-222 can be minimized by legislation to restrict its civil uses, or increasing its moisture to ∼10%, or by the particle size separation of the fine fraction containing the high levels of Ra-226 followed by a suitable chemical treatment or disposal; whereas the low release amount can be diluted and used in cement industry, roads or dam construction.

In situ measurements of radon levels in water and soil and exhalation rate in areas of Malwa belt of Punjab (India)

Radon concentration levels in water and soil gas from 36 locations pertaining to some areas of Malwa region of Punjab have been measured on an in situ basis using a continuous active radon detector (AlphaGuard, Model - PQ 2000 PRO, Genitron instruments, Germany). Exhalation rate measurements have also been carried out at these places, using a closed-circuit technique. The radon concentrations in soil and water varied from 1.9 to 16.4 kBq m(-3) and 5.01 to 11.6 kBq m(-3), respectively. The exhalation rate (E (Rn)) ranged between 7.48 and 35.88 mBq m(-2) s(-1) with an average value of 18.17 mBq m(-2) s(-1). Annual dose rates have been calculated for water radon concentrations. The minimum to maximum values of dose rates were found to be 13.42-31.08 μSv y(-1). The recorded values of radon concentration in water are within the safe limit of 11 Bq l(-1) recommended by the US Environment Protection Agency [National Research Council, Risk Assessment of Radon in Drinking Water (Academy Press, Washington, DC, USA, 1999)]. All measurements were made in similar climatic and environmental conditions to ensure minimal variations in meteorological parameters. An intermediate correlation coefficient (0.5) was observed between radon exhalation rates and soil gas values.

Geochemical variation of soil-gas composition for fault trace and earthquake precursory studies along the Hsincheng fault in NW Taiwan

The present study is proposed to investigate geochemical variations of soil-gas composition in the vicinity of the geologic fault zone of Hsincheng in the Hsinchu area of Taiwan. Soil-gas surveys have been conducted across the Hsincheng fault, to look for the degassing pattern of this fault system. During the surveys, soil-gas samples were collected along traverses crossing the observed structures. The collected soil-gas samples were analysed for He, Rn, CO(2), CH(4), Ar, O(2) and N(2). The data analysis clearly reveals anomalous values along the fault. Before selecting a monitoring site, the occurrence of deeper gas emanation was investigated by the soil-gas surveys and followed by continuous monitoring of some selected sites with respect to tectonic activity to check the sensitivity of the sites. A site was selected for long term monitoring on the basis of coexistence of high concentration of helium, radon and carrier gases and sensitivity towards the tectonic activity in the region. A continuous monitoring station was established at Hsinchu National Industrial Science Park (HNISP) in October 2005. Preliminary results of the monitoring station have shown possible precursory signals for some earthquake events.