Periodic and transient radon variations at the Tiberias hot spring, Israel during 2000^|^ndash;2005

Abstract

Radon has continuously been monitored at the Roman spring of Tiberias, Israel since 2000 in the frame of an earthquake research project. However, there was no apparent earthquake related radon anomaly in 5 years of monitoring. Physical mechanisms behind periodic as well as transient radon variations were investigated. The radon signal contained periodic daily and non-periodic multi-day variations as well as seasonal patterns with maxima during winter. Spectral analysis showed diurnal and semidiurnal periodic constituents while tidal effects were absent. In 2003 the long-term average radon concentration dropped by 35%. Coevally, the diurnal and semi-diurnal radon variability considerably decreased. In contrast, the intensity of large-scale signals, corresponding to multi-day radon variability, increased. At this stage the level of the Kinneret Lake is suspected to be the driving force for the radon drop. Until 2003 the lake level hovered around -214 m below sea-level. In spring 2003 the lake level had risen by 4 m. The distance between the monitoring station and the lake shore is about 50 m. The radon concentration inversely followed the lake level with a time delay of about 3 months. Radon measured at a natural hot spring should depend on the flow rate of the hot water rising on the border faults of the pull-apart basin. Increased flow means less time for radon to decay and thus a positive correlation between the flow rate and the radon concentration is expected. Flow velocity is controlled by (i) the pressure at depth, and (ii) the fracture width. Both are affected by the loading forces of the graben filling to which the water column of the lake contributes. Due to the lack of data about the mass flow rates from the spring, a direct link between the flow rate and the radon concentrations cannot be proven. In fact, the hot water discharge seemed to be very stable in time. So, either minor changes of the flow rate affect the radon concentration or another mechanism is needed to explain the observations, e.g., the pressure-dependent gas solubility or the pressure-dependent mixing of different groundwater components. Nevertheless, this does not explain the appearance of long-periodic, intra-seasonal radon signals (with periods in the order of 1 month) which were practically absent before 2003. Such long-periodic radon signals were not reported till today.

Tide-factor anomalies from observations of well level in the Sichuan Province prior to the great Wenchuan earthquake of 2008

“…We have chosen well water level data from the 2 years prior to and post the Wenchuan event, i.e., from 0:00 h on 1 May 2006 to 23:00 h on 31 December 2008. Before conducting the tidal analysis (Woith et al, 2011), we first imputed the missing data using the triple spline interpolation method and then removed the influence of barometric pressure from the raw data using a regression analysis (Nathanial and Todd, 2007;Quilty and Roeloffs, 1991). We used the hourly water level data of each well to conduct harmonic analyses in order to calculate one tide-factor from a dataset of 30 days.…”

“…Such anomalies are, however, usually very complicated because of the effects of rainfall, atmosphere, solid tide and artificial interference (Kümpel, 1991;Matsumoto et al, 2003;Woith et al, 2011). Some researchers regard solid tide as contributing to noise in water level data and make corrections to it (Cutillo and Ge, 2006;Reoloffs et al, 2003).…”

A possible link between radon anomaly and earthquake

“…The stress centers form strain fields and stress gradients of diminishing magnitude towards the periphery. These pre-earthquake stress gradients move underground fluids, carrying some dissolved gases such as radon, helium, methane, carbon dioxide, nitrogen etc., to the subsurface region, mainly through faults, lineaments and thermal areas, which are highly permeable pathways for soil-gas (Yang et al, 2003(Yang et al, , 2006Chyi et al, 2005Chyi et al, , 2010Chyi et al, , 2011Fu et al, , 2008Walia et al, 2005aWalia et al, , 2005bWalia et al, , 2008Walia et al, , 2009Walia et al, , 2010Choubey et al, 2007;Yang, 2008;Montazeri et al, 2011;Woith et al, 2011). So subsoil radon anomaly is observed in the soil-gas measurements at or near a fault and/or a lineament before and after an earthquake.…”

Natural radioactive isotopes in glacier meltwater studies

“…Soluble in water, radon can be carried over longer distances during its mean life time of 5.5 days (period T 1/2 = 3.8 d). Radon is used as a suitable tracer for studying short-lived natural processes (e.g., Chyi et al, 2011;Laskar et al, 2011;Montazeri et al, 2011;Solecki and Tchorz-Trzeciakiewicz, 2011;Tchorz-Trzeciakiewicz and Solecki, 2011;Woith et al, 2011;Wysocka, 2011;Yang et al, 2011).…”