RADON IN SOIL VARIATIONS FOR THE VRANCEA SEISMIC AREA
Maria ZORAN
National Institute of R & D for Optoelectronics, Remote Sensing Department
PO Box MG-5, 76900 Bucharest-Magurele, Romania; mzoran@inoe.inoe.ro
Earthquakes occur as a result of a built up of pressure between colliding
sections of the Earth's crust. These sections, known as continental plates,
meet at "fault lines". According to the classical earthquake theory,
small earthquakes should continue to grow into large earthquakes until they
spread all along the fault line. The Vrancea region fits to such a model. The
mechanical processes of earthquake preparation are always accompanied by deformations;
afterwards complex short- or long-term precursory phenomena may appear. Macro-fracturing
processeses are preceded by micro-fracturing phenomena resulting in radon and
other gas precursors (He, CH4, NO) anomalies in soil-gas and groundwater. Studies
of geochemical and hydrological anomalies preceeding significant earthquakes
have been reported from China, Japan, Uzbekistan, Mexico, Italy, India and
Germany. However, studies of these pre-seismic phenomena have been controversial
for several reasons.
Temporal variations of radon in soil or water, can give evidence that the emanation
of this gas can be correlated with tectonic disturbances.
Were used nuclear track detectors LR-115 and CN-85 for radon concentration
monitoring in soil at 50 cm depth exposed for a period of 30 days in the Vrancea
region, namely the Vrancioaia test area. Time series radon data in soil-gas
during a three year observation period have established that more than 50%
of the radon concentration increases were correlated with microseismic events
of 2-4 magnitude on the Richter Scale. A clear positive correlation for radon
concentration one month prior to the seismic event was associated with registered
events over 5 magnitude on the Richter scale. In order to differentiate the
changes due to tectonic disturbances and that of the meteorological parameters,
the barometric pressure, precipitation and temperature were measured. Negative
correlation between radon concentration in soil and meteorological parameters
was found.
To predict a future earthquake, all precursory phenomena must be investigated
.The interdisciplinary nature of the earthquake prediction and the complexity
of the problems necessitate scientists' integrated cooperation and discussion
in relevant fields such as seismology, geology, and rock physics to infer geomagnetic
and electromagnetic, geodetic, geochemical, and laboratory data .
Key words: Vrancea, earthquake precursors, radon, seismic hazard.