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.

The use of underground thermal gradients as technique for soil radon mitigation

Diffusion coefficients of radon through minerals and rocks are characterised by Arrhenius linear plots, i.e., increasing with temperature. It has been observed, for example, that rocks with a mild heating (<100°C) translate into a radon release that can be enhanced 100–1,000 times than the normal release at STP (Standard Temperature Pressure (STP). Therefore, it is reasonable to think that if the soil is deliberately heated creating a thermal gradient, it could be possible, at least from a theoretical point of view, to thermally pump radon from soil because the radon atoms will escape preferentially from cold regions (low diffusion coefficient) towards hot regions (high diffusion coefficients) if a radon sink is located. In this short note, this approach for soil radon removal is investigated.

Surface identification of undermined spaces with the use of soil radon emanometry

Several surface geophysical methods were used to study the displays of undermined spaces in their physical fields and to try to distinguish undermined from non-undermined parts of underground mining area. The studied area of the Čáry lignite mine in the Western Slovakia represents an actively subsided place with high risk to the population. Despite very low radioactivity and relatively high gas permeability of building geological formations, the results of soil radon emanometry show the possibility of radon gas accumulation inside the undermined spaces, but their permanent subsidence causes loosing of overlying material and escape of radon gas. The boundaries (edges) of undermined and sunken areas were identified as the only places with increased values of 222Rn activity, probably due to the presence of vertical supporting mine walls allowing radon gas accumulation and upward movement. Thus, the soil radon emanometry clearly indicates the borders between undermined or sunken and non-undermined parts.

Thermal Soil Radon Mitigation

In this work consideration is given to the possibility for thermal soil radon mitigation. It is known that the diffusion coefficient of radon through minerals and rocks have are characterized by Arrhenius linear plots increasing inasmuch that temperature increases. For the case of rocks, for example, it was observed that a mild heating -less than 100$^o$C, translates into a radon release which can be enhanced by 100 to 1000 times than the normal release at STP. Therefore, it is reasonable to think that if soil is deliberately heated -for example, harnessing solar thermal energy, it is reasonable to think that it could be possible to pump radon from soil because the radon atoms will escape preferentially from cold regions (low diffusion coefficient) toward hot regions (high diffusion coefficients) where a radon sink is located. Utilizing a simplified two-group thermal one-dimensional model an expression was derived which allows a first assessment on this new mitigation technique