A mechanism for radon decline prior to the 1978 Izu-Oshima-Kinkai earthquake in Japan

Precursory changes in the radon concentration of groundwater were observed by Wakita et al. (1980) prior to the 1978 Izu-Oshima-Kinkai earthquake of magnitude 7.0. Mechanisms for interpreting the anomalous radon decrease are examined in this paper. The SKE-1 well is situated in a volcanic-rock fractured aquifer of limited recharge. Given these geological conditions, the dilation of brittle rock mass occurred at a rate faster than the recharge of groundwater and gas saturation developed in newly created cracks preceding the earthquake. Radon volatilization into the gas phase can explain the anomalous decrease of radon precursory to the 1978 earthquake. To support the hypothesis, vapor–liquid two-phase radon-partitioning experiments were conducted at formation temperature (14 °C) using formation water from the SKE-1 well. Experimental data indicated that the decrease in radon concentration from 483 ± 3 count/min to 439 ± 7 count/min required a gas saturation of 2.35% developed in rock cracks through the dilatancy process.     

Concurrent concentration declines in groundwater-dissolved radon,methane and ethane precursory to 2011 MW 5.0 Chimei earthquake

Radon volatilization mechanism into the gas phase was hypothesized to explain the anomalous declines in groundwater radon precursory to three major earthquakes – (1) 2003 M_W = 6.8 Chengkung, (2) 2006 M_W = 6.1 Taitung, and (3) 2008 M_W = 5.4 Antung in Taiwan. The epicenters were located 24 km, 52 km, and 13 km from the Antung radon-monitoring well D1, respectively. To verify the mechanism of in situ volatilization, we monitored groundwater-dissolved ethane in addition to radon and methane at well D1 in the Antung hot spring since November 30, 2010. The mechanism of in situ radon volatilization has been corroborated by the simultaneous concentration declines in groundwater-dissolved radon, methane, and ethane precursory to the 2011 M_W 5.0 Chimei earthquake. The epicenter was located 32 km from the Antung radon-monitoring well D1. Observations at the Antung hot spring also suggest that radon is the best-choice tracer among the groundwater-dissolved gases for strain changes in the crust preceding an earthquake. On the southern segment of the Chihshang fault, the observed radon minima decrease as the earthquake magnitude increases.     

Measurements of soil radon in South Russia for seismological application: Some results

Results of soil radon concentration measurements at the surface in Northern Caucasus (Krasnodar territory) in different geological features are shown. Measurements were made in mud volcanoes, faults, mineral deposits and landslips. The data were compared to seismicity. Before earthquakes, the changes in the concentration of radon appear as “humps” or “splashes” of various durations. Monthly, daily and hourly changes of the concentration of soil radon during the earthquakes are shown for each zone of researches. The simultaneous measurement of radon in the big area has shown the movement of the increased concentration of radon to the epicenter several days prior to the earthquake.     

Radon anomalies precursory to the 2003 Mw = 6.8 Chengkung and 2006 Mw = 6.1 Taitung earthquakes in Taiwan

Contrary to the normally observed increase in groundwater radon that occurs prior to earthquakes, we have measured anomalous decreases in radon concentration prior to the 2003 M_W = 6.8 Chengkung and 2006 M_W = 6.1 Taitung earthquakes that occurred within a 55 km radius from the Antung D1 monitoring well in eastern Taiwan. The v-shaped pattern of radon anomalies recognized at Antung is valuable for detecting the aseismic strain precursory to potentially disastrous earthquakes in a fractured aquifer surrounded by ductile aquitard in seismotectonic environments in this area.     

Variation of radon flux along active fault zones in association with earthquake occurrence

Radon flux measurements were carried out at three radon stations along an active fault zone in the Langadas basin, Northern Greece by various techniques for earthquake prediction studies. Specially made devices with alpha track-etch detectors (ATDs) were installed by using LR-115, type II, non-strippable cellulose nitrate films (integrating method of measurements). Continuous monitoring of radon gas exhaling from the ground was also performed by using silicon diode detectors, Barasol and Clipperton type, in association with various probes and sensors including simultaneously registration of the meteorological parameters, such as precipitation height (rainfall events), temperature and barometric pressure. The obtained radon data were studied in parallel with the data of seismic events, such as the magnitude, M_L of earthquakes, the epicentral distance, the hypocentral distance and the energy released during the earthquake event occurred at the fault zone during the period of measurements to find out any association between the rad on flux and the meteorological and seismological parameters. Seismic events with magnitude M_L ≥ 4.0 appeared to be preceded by large precursory signals produced a well-defined “anomaly” (peak) of radon flux prior to the event. In the results, the radon peaks in the obtained spectra appeared to be sharp and narrow. The rise time of a radon peak, that is the time period from the onset of a radon peak until the time of radon flux maximum is about a week, while the after time, that is the time interval between the time of radon flux maximum and the time of a seismic event ranges from about 3 weeks or more.     

A preliminary study of post-seismic effects of radon following the Ms 8.0 Wenchuan earthquake

The observation data for radon from national geochemical observation points have been collected and analyzed following the Ms 8.0 Wenchuan earthquake on 12th May, 2008 and a post-seismic effect of radon was observed. It has provided the most abundant record since the radon observation network had been set up in china. In this paper, the behaviour of the post-seismic effects of radon gas and water radon is reported. The results were obtained that observation points recording post-seismic effects of radon release were distributed mainly along the extended line of Longmenshan faults, and located on the boundary faults of regional tectonic blocks (Category II) and inside some tectonic blocks (Category II). The pattern of variation in radon emission observed was largely in the form of rising steps. A comparison was made with the variation of water level and flow observed simultaneously with radon measurement, to investigate a dynamic link with post-seismic radon with underground water conditions. This study confirmed a response of radon concentration to the seismic wave, and also raised other scientific issues, such as the dynamic association between geochemical composition of underground water and medium parameter variation of aquifers under dynamic loading, which may support the study of the mechanism of earthquake precursors of radon.     

Variations of soil radon and thoron concentrations in a fault zone and prospective earthquakes in SW Taiwan

An automatic station for soil gas monitoring was set up on an active fault zone of SW Taiwan. After more than one year of continuous measurements, some spike-like anomalous high radon and thoron concentrations could be observed. A similar soil radon spectrum was also obtained from an independent monitoring station, which was only 100 m away. These anomalous peaks usually occurred a few days or weeks before the earthquakes (M_L4.5). This indicates that variations of both soil radon and thoron can serve as useful tools for earthquake surveillance, esp. at fault zones.     

Indoor radon survey in dwellings of some regions in Yemen

Indoor radon survey in a total of 241 dwellings, distributed in some regions of Yemen was performed, using CR-39 based radon monitors. The objective of this radon survey is to get representative indoor radon data of three regions, namely Dhamar, Taiz and Hodeidah, situated at different altitudes above sea level. The radon concentrations varied from 3 to 270 Bqm⁻³ with an average of 42 Bqm⁻³. It was found that the average radon concentration in the surveyed areas increases with altitudes. The highest average radon concentration of 59 Bqm⁻³ was found in Dhamar city while the lowest average concentration of 8 Bqm⁻³ was found in Hodeidah city.     

Radon anomalies along faults in North of Jordan

Radon emanation was sampled in five locations in a limestone quarry area using SSNTDs CR-39. Radon levels in the soil air at four different well-known traceable fault planes were measured along a traverse line perpendicular to each of these faults. Radon levels at the fault were higher by a factor of 3–10 than away from the faults. However, some sites have broader shoulders than the others. The method was applied along a fifth inferred fault zone. The results show anomalous radon level in the sampled station near the fault zone, which gave a radon value higher by three times than background. This study draws its importance from the fact that in Jordan many cities and villages have been established over an intensive faulted land. Also, our study has considerable implications for the future radon mapping. Moreover, radon gas is proved to be a good tool for fault zones detection.     

温度及围护通风对独头巷道氡浓度分布的影响

根据计算流体力学以及氡的物理性质,建立具有硐室的独头巷道内氡的三维稳态传输模型,采用Fluent软件求解控制方程,使用UDF实现巷道内壁氡的析出和氡的衰变,得到独头巷道内的风场结构及氡的浓度分布。研究发现：通风量一定时,温度对氡的浓度影响显著,巷道内温度越高,巷道各处氡浓度越高。整个巷道硐室氡浓度最大,相比于修建防氡围护,对硐室采用局部通风,降氡效果更好。采用压入式通风时,巷道内氡浓度由内向外递增,提高巷道的通风率能够有效地降低巷道入口的氡浓度,但对硐室内氡浓度影响不大。     

Soil gas radon as an earthquake precursor: some considerations on data improvement

A data processing technique based on impulse responses from multivariable time series was applied to radon data. It was found that soil gas radon at 50 cm depth was affected more by meteorological parameters than at 100 cm depth. This fact together with the fact that the radon change at the latter depth was larger when an earthquake occurred, radon measurement at 100 cm depth was tested as an earthquake precursor. The result showed correlation between radon anomalies and earthquake events.     

In situ measurements of gamma-ray intensity from radon progeny in rainwater

The radon progeny concentration in raindrops as well as in cloud droplets has been determined based on a simplified rainout model from the in situ measurement of gamma-ray intensity using an HPGe detector. The radon concentration in cloud air was deduced from the radon progeny concentration in cloud droplets by applying the Junge's equation. From the measured radon progeny concentration in raindrops the additional exposure rate due to rainfall has been evaluated and compared with the HPIC monitoring data.     

Emanation power of radon and its concentration in soil and rocks

Experiments were carried out to determine emanation power and radon levels in different kinds of soil and bedrocks. Seven stations were selected in the investigated district, which covers an area of about 2300 km² in the northern and western part of Jordan. Five holes were dug in each station at different depths. Two to three passive dosimeters using plastic detectors (CR-39) were put in each hole. Two weeks later, the dosimeters were collected and chemically etched. Some soil and rock samples from the study area were collected and analyzed for radioactive nuclides using γ-ray spectroscopy. The correspondence between radon levels in the soil gas and its precursor concentrations is not clear. However, the study confirms the exponential increase in radon level with depth. In general, Al-Hisa phosphate limestone showed the highest radon concentration while Amman silicified limestone showed the lowest concentration.     

北京一次小震级地震前异常声-重力波产生机理的研究

观测到北京一次小震级地震(ML=3.0)前的异常声-重力波,并同时记录到异常地表倾斜信号。二者相关系数比较高,在接近震中的地区相关系数达到最大值0.5,相关系数随着远离震中的距离增大而减小。经过研究表明,异常声-重力波的产生与震前的地表缓慢活动引发的山体缓慢晃动导致的气流风速波动变化有关。基于350 m高的气象铁塔观测的风速数据,对两层大气模型传播的声-重力波进行了数值计算,得到的相对山体非平稳气流引起的声-重力波与观测信号在特征周期、幅度和速度三个参数上近似。以地表倾斜为例的模型与观测数据的一致性表明该震前声-重力波与地震存在关联性。      

Study on generation mechanism of anomalous acoustic-gravity waves before the 2011 Beijing earthquake(M_L=3.0)

Observation results of abnormal acoustic-gravity waves before a Beijing earthquake(M_L=3.0) are presented.During this period,abnormalities of earth surface tilt variations were also recorded.The cross-correlations between the both values are high,which reach maximal values of 0.5 in the area close to the epicenter.The correlations decrease with increasing distances from the epicenter.It was proposed that generation of the anomalous waves may be associated with the pressure and wind perturbations in the air flow caused by slowly shaking mountains during slow surface motion preceding the earthquake in Beijing.Based on the wind velocity data taken from a 350 m meteorological tower in Beijing,the propagation of ducted acoustic-gravity waves in a two-layer model of the atmosphere was numerically simulated.It is shown that characteristic periods,amplitudes and velocities of the simulated phases which were assumed from non-stationary air flow relative to mountains are approximate to the observed phases.A consistency between the simulated results and observation data indicates that a slow surface motion may be a possible source of the anomalous acoustic-gravity waves observed prior to the earthquake.     

Indoor radon measurement via Nuclear Track Methodology: A comparative study

Indoor radon concentration represents an important public health challenge, for simple and inexpensive measurement devices and methods, suitable for large-scale indoors radon measurements, are required. Nuclear Track Methodology, by using a closed-end cup device as a radon chamber is an attractive option for such large-scale indoor radon measurements. A comparative analysis of the detection efficiency of four different (one commercial and 3 specially designed) passive closed-end cup devices for the measurement of indoor radon concentrations is presented. CR-39 (Lantrack®) polycarbonate was the detector material. The four devices were simultaneously exposed to a mean radon concentration of 860 ± 60 Bq m⁻³ inside a closed room for periods of one, two and three months. An AlphaGUARD^® radon monitoring system was used to continuously monitor the radon concentration within the room. The chemical etching and reading procedures were carried out following a well-established protocol for indoor radon surveys. The detection efficiency and the exposure-time-response relationship of each of the devices were determined.     

Experimental and theoretical study of radon levels and entry mechanisms in a mediterranean climate house

An experimental study has been carried out in an inhabited single-family house. Radon concentration in the different rooms of the house and in its garden soil has been measured with Nuclear Track Detectors. No high differences of radon concentration have been observed between the different rooms of the house, so that the proximity of the room level to the soil seems not to affect the radon concentration. The annual radon concentration obtained indoors and in the soil has been respectively 35 Bq m⁻³ and 24 kBq m⁻³. Since radon generation in the source, entry into indoor air and accumulation indoors depend on several parameters, the effect of a specific parameter on indoor radon concentration is difficult to explain from the radon measurements only. The RAGENA (RAdon Generation, ENtry and Accumulation indoors) model has been adapted to the room in the basement of the house. The mean radon concentration values obtained with the model are compared to experimental results derived from measurements using Nuclear Track Detectors. The use of the model, together with the experimental study, has allowed characterising radon sources, levels and entry mechanisms in the house. The concrete walls have been found to be the most relevant radon source, while the contribution of the soil is negligible in this case. The indoor radon level is given by the balance of the permanent exhalation from concrete and the removal due to ventilation. The indoor radon levels are close to the average value for the Barcelona area which, in turn, is close to the world averaged value.     

Helium/radon precursory signals of Chamoli Earthquake, India

The Bhagirthi and Alaknanda valleys of Garhwal Himalaya, were rocked, respectively, by two major earthquakes: the Uttarkashi earthquake of magnitude m_b=6.5, M_s=7.0 on October 20, 1991 and the Chamoli earthquake of m_b=6.8, M_s=6.5 on March 29, 1999, during this decade. Both these seismic events are associated with ongoing deformation along the main central thrust of the Himalayas. Helium and radon anomalies on March 24 and March 27, 1999, respectively, were recorded at Palampur which is about 393 km from the Chamoli earthquake epicentre. A He/Rn ratio anomaly was recorded on March 20, 9 days before the Chamoli earthquake. The precursory nature of radon and helium anomalies is a strong indicator of the physical basis of earthquake prediction and a preliminary test for the proposed conceptual He/Rn ratio model.     

Seasonal variation on radon emission from soil and water

Radon is being measured continuously in spring water and soil-gas at Badshahi Thaul Campus, Tehri Garhwal in Himalayan region by using radon Emanometer since December 2002. An effort was made to correlate the variance of radon concentrations in spring water and soil-gas with meteorological parameters at the same location. The main meteorological parameters that affect the radon emanation from host material is surrounding temperature, barometric pressure, wind velocity, rain fall and water level of the spring. The correlation coefficient between radon concentration in spring water and different atmospheric parameters was computed. The correlation coefficient between radon concentration in spring water and the maximum atmospheric temperature was 0.3, while it was 0.4 for minimum atmospheric temperature at the monitoring site. The correlation coefficient for radon concentration in spring water with minimum and maximum relative humidity was 0.4. Spring water radon concentration was found positively correlated (0.6) with water discharge rate of the spring. A weak correlation (0.09) was observed between the radon concentration in spring water and rain fall during the measurement period. As temperature of near surface soil increases, the radon emanation coefficient from the soil surface also increases. The possible effects due to global warming and other climatic changes on environment radiation level were also discussed in detail.      

Spatial variations of radon and helium concentrations in soil-gas across the Shan-Chiao fault, Northern Taiwan

Spatial variability of gases like radon and helium in soil-gas can be used for seismic surveillance and for finding fault system. The present study is aimed at determining a possible connection between eventual radon/helium anomalies and active fault. Radon and helium concentrations in subsurface soil-gas have been monitored along the Shan-Chiao fault, Northern Taiwan. Twenty transverse profile surveys have been conducted across the fault, where 235 and 125 samples were collected for helium and radon analyses, respectively. The data analysis clearly reveals anomalous values of both radon and helium along the fault. To find the fault system, where the migration of gases is governed by advection, it is essential to identify the anomalies in both radon and helium together. The consistency of this pattern confirms that radon and helium together can act as a powerful tool for the detection and mapping of active fault zones.