Radon Anomalies Research Articles

Patterns of manifestation of faults of the Pechora-Kolvinsky aulacogen in the radon field

The article presents results of an express radon survey on the territory of the Pechora-Kozhvinsky and Kolvinsky megswells, which are part of the Pechora-Kolvinsky aulacogen. Radon studies were carried out along profiles across the large structure-forming faults, identified on the basis of seismic data. The results show that faults in the radon field correspond to areas with increased values of the radon volumetric activity. In the course of radon studies, main patterns of the manifestation of faults in the radon field were established. The faults may correspond to the maxima of volume activity of radon against the background of low values or to zones with a minimum concentration of radon. In addition, areas with abnormal radon concentrations not associated with known fractures were identified. The systems faults are characterized by wider radon anomalies or alternation of maxima and minima of radon volumetric activity along the profile. The maximum radon concentration is recorded in the fault zones that are closest to the surface, as well as in faults along which large amplitudes of vertical displacements are noted. Similar levels of radon concentration are observed within the normal faults and thrust faults, covered by sedimentary rocks. Most of the studied faults, according to the relative indicator of radon activity, belong to the group of high radon activity. The concentration of radon in the soil air within the faults varies both in the transverse and longitudinal directions. In some areas, the radon volumetric activity of at the same level at different times. This proves the existence of a constant radon flux. The main factors affecting the formation, transport to the surface, and accumulation of radon in the soil are the composition and depth of the basement, the internal structure of fault zones, the degree of porosity and fracturing of rocks and modern geodynamics of the region. Thus, radon survey as an additional method to other geophysical methods can be used to map faults and identify various blocks that differ in fluid-geochemical features.

ВЗАИМОСВЯЗЬ ЭМАНАЦИИ РАДОНА С УРОВНЕМ ВНЕШНЕГО ВОЗДЕЙСТВИЯ НА ОСНОВЕ МОНИТОРИНГА КРУПНЫХ ОПОЛЗНЕЙ В ГОРНЫХ РАЙОНАХ

The paper investigates the phenomenon of radon emanation in various geological conditions – rocks, thick boulderpebble strata and a powerful landslide. Instrumental measurements of micro-seismic vibrations, radon volumetric activity (RAR) were carried out, and long-term values of the gravitational movement of the soil strata were determined on the largest Loire landslide in North Ossetia. A low OAR level was obtained, which did not exceed during the experiment (0.6 Bq/m3). It has been established that the concentration of radon can reflect the degree of enrichment in underground cracks and, therefore, information about geological cracks and the stress state of a landslide body. It has been determined that the analysis of radon anomalies can be used as an independent method for assessing the state of landslide and providing an objective scientific basis for assessing the stability of mountain slopes. The purpose of this work was to study the relationship between radon emanation and the level of external impact on the basis of monitoring large landslides in mountainous areas. Research results. As a result of the research, a low OAR level was obtained, not exceeding 0.6 Bq/m3 during the experiment. It has been established that the concentration of radon can reflect the degree of enrichment in underground cracks and, therefore, information on geological fracturing, the stress-strain state of a dispersed landslide body. This phenomenon was expressed in the fact that an increase in the amplitudes of the micro-seismic background manifests itself with a delay in an increase in the RAR or the “aftereffect time tp of radon”, after which a targeted effect on the environment or pulse-vibration processes in the environment itself, characterized by intense fluctuations, cause an increase in the intensity of radon emanation on surface. It has been established that the analysis of radon anomalies can be used as an independent method for assessing the stress-strain state of a landslide by analyzing the statistical characteristics of microscale events and, thus, providing an objective scientific basis for operational assessments of the stability of mountain slopes.

Occurrence of anomalies in soil radon volume activity before tectonic earthquakes

Research subject. Earthquakes are a global problem for the entire world population. Therefore, a search for ways to predict and prevent tectonic events is a highly relevant task. Despite the existence of controversial opinions on the possibility of predicting tectonic earthquakes, research in this direction continues. Among numerous possible precursors of earthquakes, anomalies in the volume radon activity (VRA) are the most physically justifed ones. The aim of this research was to compare the observed anomalies of soil radon with the recorded seismic events in order to fnd common patterns. The research area was the Kuril Islands. VRA monitoring was conducted at the South Kuril Geophysical Station of the Institute of Marine Geology and Geophysics of the Far Eastern Branch of the Russian Academy of Sciences.Methods and materials. Measurements were carried out in the advective mode: soil air from a depth of 70 cm was forcibly delivered to the detector using a pump. For a retrospective analysis, we took registered seismic events with a magnitude greater than 4 that occurred within a radius of 500 km from the monitoring station in Yuzhno-Kurilsk during 2011–2018. Statistical data were processed using Microsoft Excel, Statistica software. Results. A method for comparing radon anomalies and earthquakes was developed. Using the developed methodology, it was found that the geodynamic criterion of ≥2 (the ratio of earthquake magnitude to logarithm of distance from event epicenter to the monitoring station in km) can be used when comparing VRA anomalies with tectonic earthquakes. Out of the 166 considered tectonic earthquakes meeting the geodynamic criterion of ≥2.148, the events were preceded by VRA anomalies. The position of the earthquakes was determined relative to the extremum of previous anomalous radon values in the time interval. Eac of the considered earthquakes meeting the geodynamic criterion ≥2, which had been preceded by a radon anomaly, occurred either after its extremum or coincided with it in time. Conclusions. The manifestation of tectonic earthquakes in VRA anomalies after passing the extremum can be considered as a short-term prognostic criterion and be used for distinguishing between “near” and “far” events.

Long Short Term Memory networks (LSTM)-Monte-Carlo simulation of soil ionization using radon

Earthquake events are usually associated with atmospheric processes variations. Some of the important events in seismic periods include the atmospheric electricity/conductivity modification, which mostly depends on the ion population in the vicinity of earthquake preparation area. Radon, together with cosmic radiation are the major ionization sources in the lower troposphere. The radon induced soil ion-pair production rate was estimated for Erzincan, a city along the North Anatolian Fault Zone, Turkey. The Long Short-Term Memory networks (LSTM's) and Monte Carlo method are proposed to account for uncertainty in estimating the ion production rate. The advantage of the LSTM model is taken to study radon anomalies during the M = 5 Girlevik earthquake, Erzincan. Radon concentration is found to increase prior to the 5.0 Girlevik earthquake. According to estimations, 23 × 109 ion-pairs m−3s−1 were generated at 1 m depth from the Earth's surface during this earthquake. The soil-ion production estimation rate due to radon and its progeny in Erzincan is at the order of 109 ion-pairs m−3s−1. When these generated ions and charged aerosols reach the surface and were added to other ionization sources, parameters such as the near surface conductivity and electric field would be modified. In addition, under pronounced conditions could favor ionospheric perturbations.

Incorporating Persistent Scatterer Interferometry and Radon Anomaly to Understand the Anar Fault Mechanism and Observing New Evidence of Intensified Activity

Interferometric Synthetic Aperture Radar (InSAR) monitors surface change and displacement over a large area with millimeter-level precision and meter-level resolution. Anar fault, with a length of ~200 km, is located in central Iran. Recent seismological studies on the fault indicated that it is approaching the end of its seismic cycle. Although a large earthquake is imminent, the mechanism of the fault is not well understood. Therefore, understanding and discovering the mechanism of Anar fault remains a challenge. Here, we present an approach of displacement fault analysis utilizing a combination of InSAR data obtained from the persistent scatterer interferometry (PSI) method and 178 Sentinel-1 images (ascending and descending) (2017–2020). We incorporated groundwater samples from 40 wells, radon concentration anomaly mapping, Global Positioning System (GPS), and 3D displacement measurement acquired over four years (2016–2020). We investigated and monitored the deformation of the fault plate’s behavior over the last three years (2017–2020) to explore new evidence and signature of displacement. The results show that the time series analysis in the fault range has an increasing displacement rate in all dimensions. We observed that the line-of-sight (LOS) displacement rate varied from −15 mm to 5 mm per year. Our calculations show that the E–W, N–S, and vertical displacement rates of the fault blocks are 2 mm to −2 mm, 6 mm to −6 mm, and 2 mm to −4 mm per year, respectively. An anomaly map of the radon concentration shows that the complete alignment of the high concentration ranges with the fault strike and the radon concentration increased on average from 23.85 Bq/L to 25.30 Bq/L over these three years. Therefore, we predict rising the radon concentration is due to the increase in activity which resulted in a deformation. Finally, our findings show that the Anar fault is an oblique and right-lateral strike-slip with a normal component mechanism. We validated the proposed method and our results by comparing the GPS field data and PSI measurements. The root mean square error (RMSE) of the PSI measurement is estimated to be 0.142 mm. Based on the supporting evidence and signature, we conclude that the Anar fault activity increased between 2017 and 2020.

Study of Abnormal Seasonal Variations in the Radon Exhalation Rate in a Fault Zone

Strong seasonal variations in the radon exhalation rate from the soil surface were revealed during a two-year monitoring cycle in a fault zone on a slope of Mount Beshtau in the Caucasus Mineral Water Resort area, Russia. The variations are characterized by very high radon levels in summer and low levels in winter. In the warm season (from late April to early October), the radon exhalation rate values ranged from 4.5 to 23.8 Bq m–2 s–1. During the cold period (from November to March), the radon levels decreased to 0.04–0.17 Bq m–2 s–1. A strong correlation was found between the radon exhalation and atmospheric air temperature (the Pearson correlation coefficient is 0.8). The simulation results show that seasonal fluctuations in the radon exhalation rate are caused by an inversion of the convective radon transport direction in the fractured zones of the rock massif. In summer, the convective flow of radon is directed from the rock massif to atmosphere, whereas this flow in winter comes from the atmosphere to rock massif. The rate of convective transport varies from 5 to 28 m day–1 during the warm season and from –2 to –4 m day–1 during the cold one. Seasonal radon anomalies in fault zones are most probably caused by thermally induced convective air flows in the highly permeable rock zone due to the temperature difference between the rock air and atmospheric air. Seasonal radon anomalies should be taken into account both when mapping radon risk and when using radon as a tracer of gas transport in geochemical and geophysical research.

Radon and magnetic anomalies in the territory of the city Kyiv: environmental aspect

Magnetic and radon anomalous fields are essential geophysical entities of environment which determine to a considerable degree its ecological state. Revelation of magnetic and radon anomalous zones is an urgent task for the studies of geo-environmental state of the territory and appraisal of its ecological safety. The greatest danger is produced by the areas where the faults are localized with radon anomalies related in the upper part of the Earth crust. For the territory of Kyiv geological characteristics of the studied area has been reviewd, schemes of regional and accompanying faults have been adjusted and completed, maps of module and anomalies of module of geomagnetic field induction as well as a scheme of radon anomalies in water and subsoil air have been elaborated. Connection between radon anomalies with faults and natural magnetic fields has been shown which consisted in correlation of radon anomalies with negative and small positive values of anomalous magnetic field and related to thick zones of fracturing with active fluidal-dynamic activity and the faults of diagonal and orthogonal systems being the zones of radon emanation into atmosphere. Radon anomalies in subsoil air are mainly controlled by Irpin-Borshchagivka, Pushcha-Vodytsya, Kyiv and Darnytsya faults of northwestern-northern strike and Petrivka-Pukhivka and Glevakha-Brovary faults of northwestern strike. For some stations of Kyiv metro the excess of environmental norms of magnetic field and radon anomalies has been determined which can be explained by constructive features of metro compartments and their location in fault zones. It has been shown that radon anomalies are spatially and temporally stabile and magnetic anomalies, especially in metro, are characterized by considerable changes of magnetic field in both low-frequency and high-frequency spectra of their variation. Combined analysis of the fault tectonic scheme, magnetic and radon anomalies will permit to find out environmentally hazardous zones in the territory of Kyiv and out of it more reasonably.

Three-dimensional distribution and oxidation degree analysis of coal gangue dump fire area: A case study

Spontaneous combustion of coal gangue dumps poses a significant threat to the health and safety of nearby residents and has adverse effects on the environment. The establishment of measures to extinguish these fires requires information on the three-dimensional characteristics and oxidation degree of the dumps. An acquisition method for the index data was proposed. The temperature and the radon concentration were used as the principal indicators, and the gas concentration was a secondary index for verifying the results. Kriging interpolation was applied to predict the value of the unsampled points. Additionally, the three-dimensional characteristics of the temperature and radon anomalies were determined, thresholds were set, and the changes in the temperature and radon migration were considered to estimate the extent and depth of the fire in the coal gangue dumps. The oxidation degree of the anomalous area was identified according to the critical value of the temperature and radon anomalies. The application of this method in the gangue dump of the Tashan coal mine showed the existence of 17 oxidation areas, covering an area of 31,433 m2, including 4 shallow oxidation areas, 4 deep oxidation areas in coal waste dumps, and 9 medium-deep oxidation areas. According to the decision criterion, 4 areas with relatively high oxidation degree were identified, whereas the remaining sites were low-oxidation areas. Additionally, surface fires and internal fires can be transformed into each other, posing a significant threat. The results obtained from the various data sources were consistent and in agreement with the ground survey results, indicating that the proposed method is effective for the detection of fires in coal gangue dumps.

Identification of radon anomalies induced by earthquake activity using intelligent systems

The temporal variability of soil radon concentration of tectonically active origin is considered a potential earthquake precursor. However, the reliable identification of radon anomilies possibly induced by earthquake activity is still enigmatic. The present study applies intelligent algorithms such as artificial neural networks (ANN), multiple linear regressions (MLR) and decision trees (DT) for an improved and more reliable identification of radon anomalies of the tectonically active origin in northern Pakistan. The dataset utilized in the present investigation includes the soil radon concentration and associated meteorological parameters recorded at a seismically active location in northern Pakistan. The recorded dataset is subdivided into seismically active (SA) and stable (NSA) periods using a time window of ±7 days around the time of earthquake. The NSA dataset is utilized for the training/cross-validation of intelligent algorithms using three input (meteorological factors) and one output parameter (radon). The trained intelligent models are then used to simulate the expected radon level during the SA periods based on the measured environmental parameter. The discrepancy (Q) between the simulated and measured radon is utilized to identify statistically significant (x¯±2σ) radon anomalies. Our results reveal that all the employed intelligent algorithms show a significant deviation in Q values around the time of earthquake occurrence. Furthermore, comparative analysis suggests that ANN performs better than the other techniques. In conclusion, our study paves the way for the possible use of radon in designing an optimized strategy for earthquake forecasting.

Stress-Related Pre-Seismic Water Radon Concentration Variations in the Panjin Observation Well, China (1994–2020)

Continuous observation data from a period of 26 years show that water radon concentrations in the Panjin observation well document pre-seismic anomalies prior to earthquakes of 4.8 ≤ M ≤ 7 within a radius of 300 km. Among these earthquakes, two distinct groups with different water radon concentration anomalies and anomaly mechanisms are apparent. The abnormal characteristics of water radon concentrations clearly reflect the processes of stress change, while Cl− concentration, Ca2+ concentration, Mg2+ concentration, and escaping gas flow only document part of these processes. According to Global Positioning System main strain rate fields and area strain rate fields, the change in anomalous behavior coincides with the 2011 Great Tohoku M 9.1 earthquake. This event caused the stress state of the study area, located in eastern China, to change from a relative compressive stress state to a tensile state, and may be the main reason for the change in the precursory characteristics of water radon concentrations (from increasing to decreasing prior to earthquakes). Regardless, water radon concentration in the well remains a good pre-seismic indicator for earthquakes of M ≥ 4.8. In the near future (∼50–100 years), water radon anomalies in the Panjin observation well prior to earthquakes of M ≥ 4.8 will most likely manifest as a V-shaped concentration change. Helium and neon isotopic compositions of gas samples from the Panjin observation well show that the present relatively high levels of water radon concentrations are normal and not an earthquake precursor.

Allocation of active morphostructures of the Northern Ladoga using a complex of geological and geomorphological data

Based on the analysis and generalization of geological and geomorphological information, including new data obtained by the authors, we developed a scheme of activated Precambrian morphostructures of the Northern Ladoga area. When we compiled it, the severity of the ancient structures in the relief, the confinement of the epicenters of earthquakes, paleoseismic dislocations, helium and radon anomalies to them, as well as the results of the analysis of the movement of GPS points, computer and physical modeling on equivalent materials were taken into account.

Groundwater radon precursor anomalies identification by decision tree method

Radon in groundwater has long been recognized as a sensitive indicator of crustal stress. Significant changes in groundwater radon concentration before earthquakes have been documented in many studies. However, the radon concentration in groundwater may be affected by many interference factors. The anomalies before seismic activities may not be large enough to be clearly identified by the conventional statistical method. Therefore, new methods are needed to identify the possible pre-seismic anomalies. In this study, we investigated 38 years’ worth of radon time series data (1977–2015) in a hot spring to identify the possible precursor anomalies. We first identify the factors that may affect the radon fluctuations by wavelet coherence analysis, spring discharge, water temperature, rainfall and barometric pressure. All are found to be closely related to the radon fluctuation. The time series (1980–2008) were used for further decision tree analysis as a high correlation in the duration. Following this, we constructed the decision tree models based on these factors to model the “background” radon fluctuation and identify the anomalies by comparing the difference between the observed radon changes and the “background” fluctuations. The modeled “background” fluctuation is closely related to the observed data during the non-seismic activity period, with the correlation coefficient of 0.8. Following this, we compared the modeled “background” fluctuation of the radon time series with the observed one during the seismic activities period. The decision tree could identify 15 possible radon anomalies among the 24 chosen earthquakes. The identified anomalies are also supported by the anomaly changes in water temperature and spring discharge. Therefore, we believe that the decision tree method could be an efficient way to identify the possible precursor anomalies in future studies. Additionally, we explore the mechanism of radon anomalies. The plausible mechanism for the anomalous increase is that radon is continuously supplied from newly formed internal surfaces of the crack to the aquifer system. For the anomalous decrease, it might be related to radon partitioning into the gas phase and the change of mixing ratio of shallow and depth water.

Радон як можливий індикатор сейсмічності регіону Західної Антарктиди

The measurements of near-surface radon concentration have been carried out at the Ukrainian Antarctic Akademik Vernadsky station (Akademik Vernadsky station) since 2003. Abnormal concentrations of radon could serve as a possible valuable indicator of tectonic activity, along with other evidence, potential signs of an expected earthquake. The aim of the work is to find the relationship between the abnormal values of the surface radon concentration, which correlate with tectonic activity. During the measurements, dosimetric methods for detecting the decay of isotopes and daughter products were used. When analyzing the data, statistical analysis methods were used. The sequence of earthquakes that occurred during instrumental observations of radon concentration, has been analyzed. The potential seismic regions affecting the location of the Akademik Vernadsky station were determined. The distances were determined at which geophysical anomalies are likely to occur within the framework of the proposed model and the expected effect of seismicity on the radon yield at the observation site is estimated. The result of the studies shows low correlation between the concentration of radon at the observation point and tectonic activity in the region at distances up to 1100 km with a magnitude of M > 7. At shorter distances to an earthquake, radon anomalies can be expected at M > 6. In some cases, the increase in radon concentration in day–two before the earthquake has been observed. That can be used as a potential predictor, however, no stable recurrence of such events was measured. It is noted that for the correct interpretation of the radon concentration measurements, the analysis of meteorological parameters can be necessary.

О генезисе радоновых аномалий в зонах тектонических разломов

As a result of almost three-year observations conducted in the fault zone in the Beshtau magmatic massif area (Caucasian Mineral Waters), anomalous seasonal fluctuations in radon exhalation rate were registered. Seasonal fluctuations are characterized by highs in summer and lows in winter. Summer values reached 23800 mBq/(m2s), while in winter the radon exhalation rate decreased to 40 mBq/(m2s). Radon exhalation rate in the fault zone shows a clear direct correlation with air temperature. The rise of radon levels in spring and fall in autumn are timed to the moments when the temperature of the atmospheric air becomes, respectively, above and below the temperature of the rock massif. It is established that seasonal fluctuations of radon levels are caused by changes in the direction of convective radon transport in the fractured zones. The obtained data suggest that the formation of seasonal radon anomalies in the fault zones is due to the circulation of atmospheric air in permeable zones of the rock massif, which occurs due to the temperature difference between the massif and the atmosphere.

Detecting time series anomalies using hybrid methods applied to Radon signals recorded in caves for possible correlation with earthquakes

Anomalies in the Radon activity concentration time series recorded in five European caves (Czech Republic, Slovakia, Slovenia) are detected using three hybrid methods: (1) multiple linear regression and autoregressive integrated moving average statistical methods, (2) Empirical Mode Decomposition with Support Vector Regression techniques and (3) the Singular Spectrum Analysis composed with a predicting methodology. Results coming from the three methods are compared and the best hybrid method is selected based on statistical evaluation criteria of the uncertainty. Radon anomalies occur ± 30 days from earthquake occurrence, selected according to the Dobrovolsky’s earthquake preparation zone formula and to seismic events (with magnitude ≥ 4) occurred in the neighboring European Countries to the monitoring caves. The anomalies detection furnishes results consistent across the used methodologies, as proven by the calculation of a statistical parameter that search the presence of anomalies coming from the hybrid methods within ± 30 days from earthquake event.

High seasonal variations of the radon exhalation from soil surface in the fault zones (Baikal and North Caucasus regions)

The seasonal variations of radon exhalation rate from soil surface were studied in two seismically active regions of the Russian Federation - the Baikal rift and the North Caucasus. In each region, monthly measurements of the radon exhalation have been carried out at two relatively proximal sites, one of which was located within the active fault zone and the other outside of the fault zone. The Open Charcoal Chamber Method was used. Very high radon exhalation rate values were found in the fault zones at both regions. At the Baikal rift, the radon exhalation reached 1.4 Bq m−2 s−1, and at the Caucasian region in some periods it even achieved 24 Bq m−2 s−1, which is an extremely high value. The same pattern of seasonal variations of radon levels with abnormal high radon exhalation rate values in summer and extremely low in winter were observed in both the Baikal and Caucasus regions. Clear correlation between radon exhalation and air temperature were also revealed. The obtained data and simulation results indicate that seasonal fluctuations in the radon exhalation rate are caused by the inversion of the direction of convective air flow in the fractured zones of the rock massif. In summer, the convective air flow is directed from the rock massif to the atmosphere and in winter, vice versa, from the atmosphere to the rock massif. This phenomenon is similar to the well-known “chimney effect”, i. e. in winter there is a direct draft in the system of fractures, and in summer — the reverse one. Thus, the detected radon anomalies are due to near-surface convective air circulation in permeable zones of the mountain ranges and most probably are not associated with deep crustal or mantle degassing. Seasonal thermally induced radon anomalies should be taken into account both in the radon risk mapping and in the application of radon as a tracer of natural processes in various fields of geology and geophysics.

In soil radon anomalies and volcanic activity on Mt. Etna (Italy)

We present here the first attempt to understand the fast dynamics of an active basaltic volcano, namely Mt. Etna using soil gas radon measured in some sites located in strategic places around the volcano. Data were measured continuously from July 2015 to February 2017 and the raw signals were treated in order to filter out all possible periodic components that are normally due to non-volcanic factors, applying a method that does not require acquisition of other parameters, which are not always available. The residual signals highlighted seven anomalous changes, with radon values reaching levels from 2 to 5 times higher than the normal background. In six out of seven cases, anomalies were almost contemporaneous in all or almost all of the sites, indicating a common source for the observed radon variations. The pattern of anomalies suggests a transient wave-like propagation in the space/time domain, compatible with pressure-induced displacement of the gas. The observed patterns are most probably caused by the rapid upward motion of gas-rich magma into the volcano conduits, as almost all anomalies precede or accompany major volcanic events. In some cases, an alternative explanation could be the strong and sudden strain releases through earthquakes swarms, with consequent variations in the permeability of rocks at a large scale, given the apparent correlation between those anomalies and intense seismicity.

Analysis of geophysical and meteorological parameters influencing 222Rn activity concentration in Mladeč caves (Czech Republic) and in soils of Phlegrean Fields caldera (Italy)

The present work concerns a detailed analysis of Radon time series to differentiate endogenous from exogenous phenomena which provide anomalous signals. Two-year data from two sites in Czech Republic and in Italy are analyzed in order to contribute to the prevention of natural hazards. A new hybrid forecasting method is implemented and tuned for the identification of Radon anomalies in the time series. It is based on the combination of Multiple Linear Regressions, Empirical Mode Decomposition and Support Vector Regression methods that decompose the signal and analyze the components to distinguish the variations due to Radon originated in depths from those due to environmental parameters. The possible correlations with fumarolic tremors in the Italian site and the faults microdisplacements in the Czech site have been studied, as well as with the earthquakes that have influence on two studied areas. Results show that: (i) the used method is very effective considering the calculated statistical uncertainties; (ii) the outer temperature is the main influencing Radon driving force; (iii) the extracted Radon anomalies due to endogenous phenomena are well correlated with fault displacements, fumarolic tremors, and with earthquakes under a characteristic delay time for each area; (iv) significant correlations among earthquake magnitude and depth with fault displacement and fumarolic tremor are found.

Implication of Radon Monitoring for Earthquake Surveillance Using Statistical Techniques: A Case Study of Wenchuan Earthquake

The seismotectonically induced changes in groundwater radon (Rn) are considered to be strong imputes for the surveillance of imminent major earthquakes. Groundwater facilitates the migration of soil gases as a result of tectonic stresses. In this regard, a radon time series is statistically analysed to identify the radon anomalies possibly induced by Wenchuan earthquake. The statistical analysis mainly involves the deterministic analysis of the Rn data and residual Rn analysis using a criterion x¯±2σ of anomaly selection having a confidence interval of 95%. The deterministic analysis reveals that the Rn time series follows a persistent trend 0.5≤H≤1 which confirms the absence of a chaotic regime. On the other hand, the residual Rn shows a notable upsurge straddling the time of the Wenchuan earthquake in the form of pre- and post earthquake changes at monitoring stations having RE/RD≤0.3. The residual Rn level passes the anomaly selection criterion x¯±2σ and is declared as a tectonically induced Rn anomaly. Contrary to this, the response of distant monitoring stations (RE/RD>0.3) to this particular earthquake further validates the link between Rn and earthquake activity. In a nutshell, the present study highlights the potential implications of earthquake-induced radon anomalies for earthquake prediction research.

ANALYSIS OF RADON TIME SERIES RECORDED IN SLOVAK AND CZECH CAVES FOR THE DETECTION OF ANOMALIES DUE TO SEISMIC PHENOMENA.

Anomalies in the radon (222Rn) releases in underground environments are one of the phenomena that can be observed before earthquake occurrence. Continuous measurements of radon activity concentration, and of meteorological parameters that influence the gas emission, were performed in three Slovak and Czech caves during 1-y period (1 July 2016-30 June 2017). The radon activity concentration in caves shows seasonal variations, with maxima reached during summer months. The anomalies in the radon time series are identified using a combination of three mathematical methods: multiple linear regression, empirical mode decomposition and support vector regression. The radon anomaly periods were compared with earthquake occurrences in Europe. Coincidences between both phenomena were found, since all monitored caves reflect contemporaneous local tectonic changes. The results indicate that radon continuous monitoring could assist a better understanding of radon emissions, along active tectonic structures, during seismic events.