Environmental monitoring of radon in soil during a very seismically active period occurred in South West Greece

Abstract

This paper focuses on the environmental monitoring of radon in soil as a potential trace gas in the search of earthquake precursors. The paper reports the following: (a) Pre-monitoring experiments. (b) Set-up of methods and devices. (c) Active and passive monitoring results concentrating on two extremely-strong radon anomalies (~ 500 kBq m(-3)). (e) Discussion regarding the employed ± 2σ technique for identifying radon disturbances. (f) Application of wavelet-power-spectrum fractal analysis for detecting power-law behaviour. The strong anomalies exhibited anti-persistent power-law-beta-values (b = (1.8 ± 0.2), b = (1.8 ± 0.3)) significantly higher than those of the baseline. Persistent b-values were also detected. The findings comply with a self-organised-critical pre-earthquake state. (h) Discussion on models that interpret the radon anomalies focusing on the recently-proposed asperity-model. (i) Application of a recent technique which showed that the two strong disturbances were proportional to the strain change. It was concluded that the strong radon disturbances may be linked to the strong earthquake of 8/6/2008, M = 6.5, occurred 29 km away from the installed instrumentation.

Fractal Analysis of Pre-Seismic Electromagnetic and Radon Precursors: A Systematic Approach

“…In comparison, this paper includes nine great earthquakes with M L ≥ 6.0 and the remaining twenty seven events with 5.0 ≤ M L < 6.0 . It should be noted though, that this paper includes also the re-analysis of some earthquake raw data published in other papers of the reporting team [16,27,43,44,[55][56][57][58], however, under a different view and with new approach. It can be, thus, supported, that either from the view of great earthquakes ( M L ≥ 6.0 ) or the perspective of the number of the analysed events (37), this research includes a significant amount of seismic data.…”

“…It is significant to recognise areas in the signals with distinct changes of the scaling exponent b, since such changes are reported to emerge [10,11,16,17,27,43,44] before or during anomalies in the EM radiation either in the water aquifers or air [27,28]. Noteworthy variations of the concentration of radon and progeny have been observed in geothermal fields [29], thermal spas [30], active faults [31][32][33][34][35], soil experiments [36], volcanic processes [37,38] and seismotectonic environments [16,21,25,27,36,[39][40][41][42][43][44][45][46]. Due to its importance, radon monitoring is also a significant study area in the search of premonitory signals prior to earthquakes [25].…”

“…Note, that the fBm class has been linked to pre-earthquake activity of noteworthy precursory value and, especially, in the high b segments. For the analysis, all the studied EM and radon signals were investigated through fractal analysis [10,11,16,17,27,43,44] based on a waveletderived PSD. To calculate the PSD of this study, the continuous wavelet transform (CWT) was used with the Morlet wavelet as a base function.…”

“…These linkages produce characteristic fractal structures which affect electromagnetic and soil-radon disorders emitted from the lithosphere during seismic activity [3,4,10,11,16,27,43,51]. The power spectral density, S(f), is likely the most often utilised method to give helpful information about the inherent memory and the critical behaviour of the system [3,4,10,11,16,27,43,51]. Furthermore, the power spectrum reflects directly the physical scales of the processes that affect the structure formation [10].…”

“…Especially regarding signals recorded prior to earthquakes and according to [3,4,10,11,16,27,43,51], a series of steps in the lithosphere linked in time and space, constitute the complex process of earthquake preparation. These linkages produce characteristic fractal structures which affect electromagnetic and soil-radon disorders emitted from the lithosphere during seismic activity [3,4,10,11,16,27,43,51].…”