Ricerc@Sapienza

Understanding natural variations of Rn (222Rn) concentrations is the fundamental
prerequisite of using this radioactive gas as a tracer, or even precursor, of natural processes, including
earthquakes. In this work, Rn concentrations in groundwater were continuously measured over
a seven-month period, during 2017, in the Giardino Spring, Italy, together with groundwater levels
in a nearby well installed into a fractured regional aquifer. Data were processed to reduce noise,
and then analyzed to produce the Fourier spectra of Rn concentrations and groundwater levels.
These spectra were compared with the spectrum of tidal forces. Results showed that diurnal and
semidiurnal cycles of Rn concentrations, and filtered oscillations of groundwater levels, in the nearby
well, are correlated with solar and luni-solar components of tidal forces, and suggested no correlation
with the principal lunar components. Therefore, influencing factors linked to solar cycles, such as
daily oscillations of temperature and atmospheric pressure, and related rock deformations, may have
played a role in Rn concentrations and groundwater levels. An open question remains regarding the
correlation, which is documented elsewhere, of Rn concentrations and groundwater levels with the
lunar components of the solid Earth tides.