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

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a Brunel 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

http://env-hum-comp-res.teipir.gr

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

Objectives

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Introduction

Schematic cross section of the in groundwater basin (Ulomov and Mavashev, 1971).

Earth Crust Radon Measurement

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).

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.

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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/pages/fountoulis/esismol.htm).

Seismicity in South West Greece 1/2

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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).

Seismicity in South West Greece 2/2

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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Materials & Methods Instrumentation (Active Technique)

DATA LOGGER

• 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 temperature (T) are continuously monitored as well.

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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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Anomalies detected in radon concentrations in 2008 3 & 2

months before 6,5 Earthquake of 6/8/2008

For the power law spectrum 𝑺 (𝒇 )=𝒂⋅𝒇−𝒃 • The area between the two radon

spikes is very critical and presents fractal behaviour (b values above 1,5)

• 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)

Background noise presents 0<b(t)<1, moving from the the first stage of general disorder to the final stage of the earthquake presenting stability and low self-organisement.

Scalogram of the DWT of the 2008 radon signal

Time evolution of the power-law-beta values

Levels of soil radon concentration in 2008

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Radon concentration during the five-day disturbance of the first radon spike in 2008

Application of the Discrete Wavelet Transform

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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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)

Material & Methods Environmental Parameters

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From the various theoretical explanations of the Radon anomalies the asperity model (Eftaxias et al.,2008) tend to be the predominant method (Petraki et. al., 2012)

Material & Methods Asperity Model

The fracture of the heterogeneous

system in the focal area obstructs the

backbone of asperities.

At this stage, critical anti-persistent MHz

electromagnetic anomalies occur.

When the electromagnetic

anomalies are emitted the “siege”

of the strong asperities begins.

Cracking will occur in strong asperities IF local stress exceeds their fracture stress

The anomalous radon emissions of the 2008 signal, could be attributed to the first stage of the model, i.e., the phase in which the fracture of the strongly heterogeneous medium obstructs the asperities backbone (Petraki et. al., 2012)

STAGE 1

STAGE 2

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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.

Conclusions

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UNSCEAR, United Nations Scientific Committee on the Effects of Atomic Radiation, 2000. Sources and Effects of Ionizing Radiation. UNSCEAR 2000 Report to the General Assembly with Scientific Annexes, United Nations, New York.

Nazaroff, W.W, Nero A.V., 1988. Radon and its Decay Products in Indoor Air. John Wiley & Sons, Inc., USA. ISBN 0-471-62810-7, 518 pp. Planinic´ J. , Radolic´ V. , Lazanin Z ., Temporal variations of radon in soil related to earthquakes, App Rad Isotop (2001) 55, 267-272 Nikolopoulos, D., Petraki, E., Marousaki, A., Potirakis, S.M., Koulouras, G., Nomicos ,C., Panagiotaras, D., Stonham, J., Louizi, A., 2012.

Environmental monitoring of radon in soil during a very seismically active period occurred in South West Greece. J. Environ. Monit.14, 564-578 Rikitake, T., 1987. Earthquake precursors in Japan: precursor time and detectability. Tectonophysics 136(3–4), 265–282 Cicerone, R.D., Ebel, J.E., Britton, J., 2009. A systematic compilation of earthquake precursors. Tectonophysics. 476, 371-396. D. Mazur, M. Janik, P. Loskiewicz, P. Olko and J. Swankon, Measurements of radon concentration in soil gas by CR-39 detectors, Radiat.

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Nomicos, C., 2010. Unfolding the procedure of characterizing recorded ultra low frequency, kHZ and MHz electromagnetic anomalies prior to the L’Aquila earthquake as pre-seismic ones – Part 2. Nat. Hazard. Earth Sys. 10, 275–94.

Eftaxias, K., Balasis, G., Contoyiannis, Y., Papadimitriou, C., Kalimeri, M., Athanasopoulou, L., Nikolopoulos, S., Kopanas, J. , Antonopoulos, G., Nomicos, C., 2009. Unfolding the procedure of characterizing recorded ultra low frequency, kHZ and MHz electromagnetic anomalies prior to the L’Aquila earthquake as pre-seismic ones – Part 1, Nat. Hazard. Earth Sys. 9, 1953–1971.

Hayakawa, M., Hobara, Y., 2010. Current status of seismo-electromagnetics for short-term earthquake prediction. Geomatics, Natural Hazards and Risk 1(2), 115-155.

R. L. Fleischer and A. Mogro-Campero, Association of subsurface radon changes in Alaska and the northeastern United States with earthquakes, Geochim. Cosmochim. Ac., 1985, 49, 1061–71.

Z. Roumelioti, C. Benetatos and A. Kiratzi, The 14 February 2008 earthquake (M6.7) sequence offshore south Peloponnese (Greece): Source models of the three strongest events, Tectonophysics, 2009, 471 (3-4), 272-84.

References

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http://env-hum-comp-res.teipir.gr/