Radon (222Rn) concentration in water of several thermal springs was measured with the aim of obtaining a correlation with the seismic activity of the region. Though a qualitative correlation was found for a spring with deep water circulation, we are far from being able to predict either the time or the place of an earthquake. An additional study with more relevant sampling sites and more frequent water analyses would be necessary to achieve this.Mjerili smo količinu radona (222Rn) u vodi iz više izvora radi utvrđivanja moguće korelacije sa seizmičkom aktivnosti u Sloveniji. Iako smo našli kvalitativnu korelaciju za jedan izvor s dubokim kruženjem vode, nismo još u mogućnosti predvidjeti mjesto ili vrijeme potresa. Za to su potrebna proširena mjerenja na više mjesta i sa češćim uzorkovanjem vode

Kobal, I.

Premru, U.

Vaupotič, J.

Zmazek, B.

Živčić, M.

English

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ISSN1330–0016CODEN FIZBE7RADON MONITORING FOR EARTHQUAKE PREDICTION IN SLOVENIAB. ZMAZEKa, J. VAUPOTIČa, M. ŽIVČIĆb, U. PREMRUc and I. KOBALa,1aJ. Stefan Institute, Jamova 39, 1000 Ljubljana, SloveniabGeological Survey of Slovenia, Dimičeva 16, 1000 Ljubljana, SloveniacGeophysical Survey of Slovenia, Kersnikova 3, 1000 Ljubljana, SloveniaReceived 22 December 1999; Accepted 4 May 2000Radon (222Rn) concentration in water of several thermal springs was measured withthe aim of obtaining a correlation with the seismic activity of the region. Thougha qualitative correlation was found for a spring with deep water circulation, weare far from being able to predict either the time or the place of an earthquake.An additional study with more relevant sampling sites and more frequent wateranalyses would be necessary to achieve this.PACS numbers: 87.52.-g UDC 539.164Keywords: 222Rn concentration in water, monitoring in Slovenia, earthquake prediction1. IntroductionAnomalous changes in radon concentration of ground water have been observedprior to certain large earthquakes, first in Russia [1] and then in China [2]. Sincethen, in addition to hydrological studies, numerous radon concentration determi-nations in ground waters and in soil gas have been performed in many seismicallyactive areas in several countries [3,4] in order to elaborate a methodology to pre-dict earthquakes. Thus in many countries extensive radon studies have been carriedout [5-45]. For earthquake prediction, radon is determined either in grab samplesof air and water or it is measured continuously [26,28,29,32,33]. Radon itself orits decay products are detected by ionization chambers [6,12], alpha scintillationcells [2,15,32,35], alpha track detectors [9,16,23,28,30,46], silicon solid state detec-tors [36], gamma spectroscopy [8,25,33] or by liquid scintillation counting [13,29].In addition to radon, seismic data and meteorological parameters, sometimes alsothoron (220Rn) [26,31], gases like Ar, N2, CH4, CO2 [32,34,47], or other chemicalconstituents and physico-chemical parameters of water are systematically measured[18,22,30,33,48,49]. For the selection of reliable sampling sites and frequency of sam-1Contact person, Tel: +00386 1 177 3580; Fax: +00386 1 177 3811; e-mail: ivan.kobal@ijs.siFIZIKA B (Zagreb) 9 (2000) 3, 111–118 111zmazek et al.: radon monitoring for earthquake prediction in sloveniapling and analysis, a thorough knowledge of the geology, hydrology and tectonicsof the area under consideration is needed [25,28,31,45]. As known from the liter-ature, radon monitoring in soil gas and waters has been shown to be a successfulmethod for predicting earthquakes. Radon levels are correlated with meteorologicaland hydrological data as well as with seismic activity, and often abrupt changesin radon levels appear as precursors of earthquakes [4,33-35,45,46,50]. Since in theneighbouring regions of Friuli (Italy) and Carinthia (Austria), radon monitoring asan earthquake prediction tool is already applied [7,51], we carried out a researchprogramme with the aim of implementing and checking this methodology in ourown seismically active region. The analysis of radon concentrations in waters fromthe uranium ore deposit area at Žirovski vrh [52,53] led to no reliable correlationbetween radon concentration and earthquakes in this region. Since these analyseswere carried out monthly, we decided to increase the frequency of measurementsand extended sampling to tectonically relevant sites in Slovenia.2. Seismotectonics of the Slovenian territorySeismic phenomena in Slovenia are manifested in the active fault zones, whichare several tens of kilometres long and several kilometres wide. The active faultzone represents a netlike pattern of active faults and fractures [54,55]. On the ba-sis of geological and geomorphological studies, as well as neotectonic studies, theirseismic activity in the Würm Glacial, i.e. 10,000 to 20,000 years ago, was deter-mined [55,56]. Superficially active fault zones resulted from the earthquakes whichoccurred in shallow depths [55]. Geomorphological signs and a netlike pattern offaults and fractures are relevant for the dip-slip, reverse and strike-slip movementsof tectonic blocks. In active fault zones, epicentres of earthquakes have been regis-tered in the last 1200 years [56]. The seismotectonics of Slovenia is most probablyinfluenced by three kinds of deep lithospheric mass: the Adriatic mass in the west,the Pannonian mass in the south-east, and the Central Alps mass in the north.The most mobile is the Adriatic mass, exerting pressure towards the NW withits frontal part (in Friuli) causing reverse faulting and underthrusting under theSouthern Alps [57]. In western Slovenia, reverse fault zones arose with simulta-neous left and right horizontal side movements. North of the Friuli reverse zones,which extend to the Julian Alps, there are rightward and leftward strike-slip faultzones with tectonic block movements because of the blocking effect of the CentralAlps mass to the north. The latter mass also affected the formation of strike-slipfault zones in north-eastern Slovenia. Here, in addition, it meets the WNW directedpressure of the Pannonian mass.3. ExperimentalFor this preliminary study, four sites for sampling water in the vicinity of Ljubl-jana, the capital of Slovenia, were selected (Fig. 1): Skaručna (S), a spring in alluvialdeposit, Pirniče (P), a thermal spring located in a contact zone of alluvial deposit112 FIZIKA B (Zagreb) 9 (2000) 3, 111–118zmazek et al.: radon monitoring for earthquake prediction in sloveniaFig. 1. Map of Slovenia, with sampling sites: S-Skaručna, P-Pirniče, Pp-Podpeč,F.T.-Furlanove Toplice. Epicentres of earthquakes in 1981-82 are presented by cir-cles: radius is proportional to magnitude, colour presents depth.with dolomite, Podpeč (Pp) and Furlanove Toplice (F.T.) - both thermal springswith deep water circulation in karstified limestone at the border between alluvialdeposit and the karst region. Measurements and sampling at each spring wereperformed every Monday from January 1981 to December 1982 at Podpeč, andfrom January 1981 to December 1981 at other locations. The temperature of the airand water was recorded and samples were taken to be analysed in the laboratory.Radon was measured weekly and Cl−, SO2−4 , water hardness and pH monthly.Average weekly barometric pressures and 5-day rainfall were obtained from theHydrometeorological Survey of Slovenia. For radon determination, a water samplewas enclosed in a 0.6 dm3 glass flask and transported to the laboratory, whereradon was isolated in a trap cooled with liquid nitrogen [58] and transferred into ascintillation cell [59]. Alpha activity was counted after three hours. Cell constants(efficiency) were about 2 s−1 Bq−1 (radon in equilibrium with its short-lived decayproducts), background from 0.5 to 1.0 min−1 and counting times from 30 to 60min. The lower limit of detection [60] was around 200 Bqm−3.FIZIKA B (Zagreb) 9 (2000) 3, 111–118 113zmazek et al.: radon monitoring for earthquake prediction in slovenia4. Results and discussionResults of monitoring radon in the selected waters are presented in Fig. 2,together with seismic activity (recorded and provided by the Geophysical Surveyof Slovenia), water temperature, barometric pressure and rainfall (the latter twoobtained from the Hydrometeorological Survey of Slovenia). The highest radonconcentrations were found in Furlanove Toplice water, while in Skaručna and Pirničevalues are about five times lower. Podpeč lies in between. There is no correlationbetween earthquake activity and radon concentration in Furlanove Toplice. Thus,for instance, the earthquake in the middle of March 1982 was followed by an increasein radon concentration, while a series of smaller earthquakes in the middle of June1982 were preceded by a decrease of radon concentration. Further falling of radonconcentration in this period may be assigned to heavy rains in June, which is alsosupported by an abrupt decrease of water temperature. On the other hand, therainfall in May was too low to decrease the water temperature, thus the decrease inradon concentration in this period might be assigned to earthquake activity and notto dilution by rainfall waters. All other decreases of radon concentration in waterfrom Furlanove Toplice seem to be related to rainfall and not to seismic activity.Variations in radon concentration in Skaručna and Pirniče waters are very small,with an exception in the summer 1981. A steady increase in radon concentrationin both waters from the mid of June to the mid of August might be attributedto a number of small earthquakes in this period. But, on the other hand, theconcentration in both waters fell off substantially after that time even though theseismic activity did not alter. At this stage, we are not able to interpret theseobservations. Podpeč water seems to be promising for earthquake prediction. Thegreat majority of radon concentration maxima coincide well with the occurrence ofearthquakes. Unfortunately, radon data from the beginning of 1982 are missing, andthe relation to the earthquake in March was not recorded. One of the exceptionsis June 1982 when, in spite of several small earthquakes, radon concentration fellsignificantly. As in the Furlanove Toplice case, this decrease could be attributedto a heavy rainfall in this period. No correlation between radon concentrationand barometric pressure was observed. We consider the obtained results as verypreliminary and, therefore, we have not done a theoretical analysis of the data.5. ConclusionsFrom all sampling sites selected, only the water from Podpeč was found to bepromising for predicting earthquakes on the basis of a correlation between radon-in-water concentration and seismic activity [4,61]. With only a few exceptions,occurrence of earthquakes is preceded by a peak in radon concentration. At thisstage, a correction due to rainfall dilution of water has not been taken into account.The oscillations of radon emanation are also considerable in the Furlanove Toplicespring. Some characteristic peaks and falls are in an evident relation to earthquakes,but others, which could be even more intense, do not show any relation to earth-quakes. At this preliminary stage, it was obvious that weekly or even daily radon114 FIZIKA B (Zagreb) 9 (2000) 3, 111–118zmazek et al.: radon monitoring for earthquake prediction in slovenia02040222 Rn/(kBqm- 3)024E- quakes/ML101520Water temp/o C970980990Air pressure/(hPa)050100150Rainfall/mmPodpecPodpecFurlanove topliceSkarucnaPirnicePirnicePodpecFurlanove toplicePodpecMonthYear1   2   3   4    5   6    7   8   9   10  11 12 1   2   3   4    5   6    7   8   9  10  11 121981 1982Fig. 2. Radon concentrations in selected spring waters together with seismic ac-tivity (earthquakes with epicentre distances up to 150 km), water temperature,barometric pressure, and rainfall.FIZIKA B (Zagreb) 9 (2000) 3, 111–118 115zmazek et al.: radon monitoring for earthquake prediction in sloveniaanalyses are not frequent enough to follow the seismic events adequately. Recently,reliable instruments for continuous radon in water determination have become com-mercially available [8,40,62]. We shall continue our research at two locations: (i)along the Soča (Isonzo) river several thermal waters were selected to continuouslymeasure radon concentration (every 15 minutes) [63], electric conductivity and tem-perature (once an hour), with periodic chemical and isotopic analyses of water andcarbon dioxide [64]; (ii) at the Krško polje, in the vicinity of a 635 MW nuclearpower plant, radon in soil gas in five boreholes above a fault will be continuouslymeasured [63]. 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Sci. (Paris) 321 (1995) 473.MJERENJE RADONA U VODI RADI PREDVID– ANJA POTRESA USLOVENIJIMjerili smo količinu radona (222Rn) u vodi iz vǐse izvora radi utvrdivanja mogućekorelacije sa seizmičkom aktivnosti u Sloveniji. Iako smo našli kvalitativnu ko-relaciju za jedan izvor s dubokim kruženjem vode, nismo još u mogućnosti predvid-jeti mjesto ili vrijeme potresa. Za to su potrebna proširena mjerenja na vǐse mjestai sa češćim uzorkovanjem vode.118 FIZIKA B (Zagreb) 9 (2000) 3, 111–118

Mjerenje radona u vodi radi predviđanja potresa u Sloveniji

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