This document summarizes a study on environmental monitoring of soil radon in a seismically active area of South West Greece. Researchers set up a radon monitoring station to investigate links between soil radon anomalies and earthquakes. Notable radon disorders were detected in 2008, 2-3 months before a magnitude 6.5 earthquake. Spectral analysis found fractal behavior and low frequency enhancement in radon levels prior to the quake. While radon changes did not correlate with environmental parameters, the anomalies may be explained by an asperity model of heterogeneous medium fracture. Further multivariate analysis of radon anomalies could strengthen understanding of earthquake precursors.

1. Environmental monitoring of
soil radon in a very tectonic
area in South West Greece
A. A. Fotopoulosb, E. Petrakia, E. M. Vlamakisb, X. A. Argyrioub,
N. N. Chatzisavvasb, T. J. Sevvosb, A. Zisosc, C. Nomicosd,
A. Louizie, J. Stonhama, P. H. Yannakopoulosb, D. Nikolopoulosc
aBrunel University, Dept. of Engineering and Design, UK
b Department of Computer Systems Engineering, Technological Educational Institute (TEI) of Piraeus, Greece
c Department of Physics, Chemistry and Material Science, Technological Educational Institute (TEI) of Piraeus, Greece
d Department of Electronics, Technological Educational Institution of Athens, Greece
e Medical Physics Department, Medical School, University of Athens, Greece
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2. Objectives
 Investigation of the usefulness of measuring soil
radon gas anomalies in a very active tectonic area in
South West Greece and possible linkage to
earthquakes
 Set up of radon monitoring station
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3. Introduction
 Radon (222Rn) is a naturally occurring
radioactive noble gas. The presence of radon in
the environment is in rocks, soil, building
materials, underground and surface waters
(UNSCEAR 2000). Radon Measurement
Earth Crust
 The stress–strain developed within the earth's
crust before an earthquake opens up various
pathways and leads to changes in gas
transportation from deep earth to surface
(Thomas, 1988).
 Anomalies of radon concentrations impending
pre-earthquakes periods have been observed
in groundwater, thermal waters and soil gas
(Erees et al., 2007; Choubey et al., 2009;
Cicerone et al., 2009; Ghosh et al., 2009).
 The above issues clearly indicate that radon
monitoring in soil could be very important
from geological point of view. Schematic cross section of the in groundwater basin
(Ulomov and Mavashev, 1971).
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4. Seismicity in South West Greece 1/2
 The study area of Ilia is
located in South West Greece
and is dominated by
extensional seismicity
structures.
 These structures evoked
more than 600 earthquakes
of ML>4.0 in the last century
(http://labtect.geol.uoa.gr/pa
ges/fountoulis/esismol.htm).
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5. Seismicity in South West Greece 2/2
 Ilia is a part of a broad neotectonic
depression structure which is very close to
the convergent boundary between the
African and the European tectonic plates
and it’s close to the western part of the
Hellenic Trench.
 A station for the surveillance of soil radon
has been installed in Kardamas
(Peloponnese, Ilia Prefecture, South West
Greece).
Prior research has shown that both active(Alpha Guard Unit) &
passive techniques (Solid State Nuclear Track Detectors) can be used
for the measurement of Soil Radon gas, with active techniques to be
more precise and quick (Nikolopoulos et. al., 2009).
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6. Materials & Methods
Instrumentation (Active Technique)
• Soil gas is pumped at the
maximum available rate of 1 L/min
to maximize the quantity of the
pumped gas and to enhance the
detection efficiency.
• Radon was measured at the rate
of 1 measurement per 1
min(Nikolopoulos et al., 2012).
• Atmospheric pressure (AP),
relative humidity (RH) and
DATA temperature (T) are continuously
LOGGER monitored as well.
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7. Materials & methods
spectral fractal analysis
 During the complex process of earthquake preparation, linkages
between space and time produce characteristic fractal structures
(Smirnova and Hayakawa, 2007; Hayakawa and Hobara, 2010;
Eftaxias, 2010; Kapiris et. al., 2002; Contoyiannis et. al.,2005)
 Power spectrum directly reflects the physical scales of the
processes that affect structure formation (Kapiris et al., 2003)
 If the recorded time-series A(ti) is a temporal fractal then a power
law spectrum is expected, 𝑺 (𝒇 ) = 𝒂 ⋅ 𝒇−𝒃 where f is the
frequency of the transform, 𝑆 𝑓 the power spectral density and
b the linear spectral slope.
 Spectral scaling exponent is a measure of the strength of time
correlations.
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8. Background noise presents
Scalogram of the DWT 0<b(t)<1, moving from the the first
of the 2008 radon signal stage of general disorder to the
final stage of the earthquake
presenting stability and low self-
organisement.
For the power law spectrum
𝑺 (𝒇 )=𝒂⋅𝒇−𝒃
• The area between the two radon
spikes is very critical and presents
Time evolution of the fractal behaviour (b values above 1,5)
power-law-beta values • This low frequency enhancement
reveals the predominance of the
larger fracture events which is
considered as a footprint of the
preparation of earthquakes
(Eftaxias et al.,2009)
Anomalies detected in radon
concentrations in 2008 3 & 2
Levels of soil radon months before 6,5 Earthquake of
concentration in 2008 6/8/2008
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9. Application of the Discrete Wavelet Transform
Radon concentration
during the five-day
disturbance of the first
radon spike in 2008
Log-log diagram of
S(f)=af-b versus frequency.
The enhancement of low
frequencies (low negative
logarithms) are
superimposed on the
Power Spectrum Density,
the log-log slope is
reduced and,
subsequently, the
calculated power-law b-
value and the Spearman
correlation coefficient.
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10. Material & Methods
Environmental Parameters
 It has been shown that the anomalies
of soil radon concentration
presented non-significant
cross-correlation
with the measured environmental
parameters: i) temperature ii) air-
pressure iii) relative humidity &
iv) precipitation.
(Nikolopoulos et. al., 2012)
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11. Material & Methods
Asperity Model
 From the various theoretical explanations of
the Radon anomalies the asperity model STAGE 1
(Eftaxias et al.,2008) tend to be the
predominant method (Petraki et. al., 2012)
The fracture of the When the
STAGE 2
heterogeneous electromagnetic
system in the focal anomalies are
area obstructs the emitted the “siege”
backbone of of the strong
asperities. asperities begins.
Cracking will occur in strong asperities IF local stress exceeds
their fracture stress
At this stage, critical The anomalous radon emissions of the 2008 signal, could be
anti-persistent MHz attributed to the first stage of the model, i.e., the phase in
electromagnetic which the fracture of the strongly heterogeneous medium
anomalies occur. obstructs the asperities backbone (Petraki et. al., 2012)
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12. Conclusions
 The radon anomalies can give evidence about tectonic
disturbances in the Earth’s crust, though the radon changes
 The study area in South West Greece presented in radon time-
series very peculiar disorders in 2008 (Nikolopoulos et al., 2012)
 The radon geophysical monitoring station revealed particuraly
interesting data in a significant period before the catastrofic
event
 The cross-correlation of radon anomalies as an earthquake
precursor have to be further analyzed with multivariate statistics
in order to strengthened the theory of close interconnection.
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13. References
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