Radon as seismic precursor in the framework of the S3 Project A. Riggio 1, M. Santulin 1, A. Tamaro 2 1

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1 Radon as seismic precursor in the framework of the S3 Project A. Riggio 1, M. Santulin 1, A. Tamaro 2 1 Istituto Nazionale di Oceagrafia e Geofisica Sperimentale (OGS), Trieste 2 PhD student of Udine University at OGS, Trieste, Italy Introduction. Natural disasters either on a global scale or on a local region, with a great influence on both national ecomy and social development as well, have become conspicuous problems. The precursors and prediction words, inevitably, bring the mind to distant times, when people tried to relate various previous observable phemena to an earthquake. In particular, since the life was preponderantly in the countryside, the observations were about everything 123

2 related to water and land: for example, changes of the water level in wells, different springs flow, burning and cracking of the land. Today, living in towns, it may be difficult to daily catch these observable phemena; however, they may be quantized, and also other parameters, which cant be detected without instruments, are monitored. (Riggio and Santulin, 2012). All kinds of seismic precursors are a unified reaction of the earthquake preparation process, although the observed physical quantity of precursor is different from each other. The process of occurrence and preparation of large earthquake influences the characteristic of the amaly, including the trend amalies observed that last one year or several years in the phase of long-medium term before a large earthquake occurs, and the abrupt amalis observed in the short term and impending phase. (Zhang et al., 1996). In some works of Chinese researchers of the 90 is already reported the influence of the type of mechanism of the earthquake on the characteristics of the amaly. Between the various precursors observed, a group is constituted by variations of the physical-chemical characteristics of the fluids circulating in the Earth s crust. Changes in the fluids chemical composition, which occur as transient phemena, can indeed provide information about the status of crustal deformation. The relationship between the tectonic structures, the crustal deformation and physic-chemical characteristics of the circulating fluid is in many cases supported by studies and measures that allow correlations between causes and variations of these parameter. This paper describes the activities carried out in the framework of the project DPC INGV: Short term earthquake forecasting - Research Unit 1 (U.R.1): Monitoring of deep seated underground fluids. The U.R.1 had the task of studying the state of the art of observable parameters related to underground fluids taking into account their history and the studies done over the years. Inside the U.R.1, a separate chapter was created for the Radon as it is one of the most monitored parameters with different methods and with different types of instruments. Activities performed. The first task was to make a detailed and well-documented analysis of the existing literature on the subject. The material available was very consistent since the radon was identified as a possible earthquake precursor back in the 1920s. The aim of this collection was also to establish in which cases of failed predictions, the observed radon had been considered. In fact, for disastrous earthquakes of the past, an evaluation of the individual observable was t made, but only a general Forecast evaluation, made according to numerous parameters. The aim of the study was to gather all the information concerning the role of radon in the earthquake prediction, distinguishing between the various acquisition methods. The Kobe earthquake that is considered as a Forecast Failure was actually preceded by radon amalies in the water, but since it was t accompanied by an activity of foreshocks, the signal was t taken into account. The Haicheng earthquake in China was the real earthquake predicted because all protocols were satisfied (abrmal fluid and foreschoks). Instead, the Tangshan earthquake, which occurred in China a year and half after that of Haicheng is reported as a failure of the prediction. In fact, even if variations in the content of radon in the water of 27 wells, distant as 300 km, were recorded before and after the earthquake, the absence of foreshocks did t allow to combine all the parameters required to issue an evacuation order (Santulin and Riggio, 2013). The review was concluded with the identification of all the scientific and amatorial institutions on the national territory that hold possible time series related to radon measurements in soil, in water and in air, and other additional parameters (chemical ones, for water and weather). The second product of the project was a database with all the existing data received, after that an official letter of request was send to insert the same data in the database. The statistical data related to the requests made, the data received and their spatial distribution are shown in Tab. 1 and Fig

3 Tab. 1 List of the contacted institutions, of the received data and of the type of data: radon in soil, in water and in the air, numerical data or bibliographical data. Institution Reply Received Data Type of Data Period INOGS Trieste yes yes Rn in water and in soil (continuous) INGV RoccadiPapa yes yes Rn in soil (continuous) INGV Catania yes yes Rn in soil (continuous) INFN Catania yes yes Rn in soil (continuous) FOND. Prato Ricer.-CAIPrato yes yes Rn in soil (continuous) UNIV. Trieste yes yes Rn in soil (continuous) Provincia Ragusa yes yes Rn in soil (continuous) Oss.Geof.Novara A. yes yes Rn in soil (continuous) Università Roma 3 yes Rn and U in water (continuous) Univ. Roma 3 Fis. e Geolog. yes Rn in water 1980 ISPRA Roma (ANPA) yes Bibl.refer. Rn indoor, in water and in soil (punctual) 2000 Politecnico di Bari INGV Roma yes Rn in water (continuous) Univ. L Aquila Univ. Perugia Uni. Mila yes t existing Casa De Liso -Tori A. yes yes Rn in soil (continuous) 2012 ARPA Abruzzo ARPA Basilicata ARPA Bellu yes yes Rn in water (sampled) ARPA Bolza ARPA Calabria yes Text Publ. Rn in water ARPA Campania ARPA Emilia Romagna yes yes Rn in water (continuous and sampled), Rn indoor , 2007 ARPA FVG ARPA IVREA yes ARPA Val D Aosta ARPA Lazio yes Bibl.refer. ARPA Liguria yes Rn indoor, Rn in soil into the cave ARPA Lombardia yes Bibl.refer. ARPA Marche ARPA Molise ARPA Padova yes yes Rn in thermal water (sampled), georeferenced ARPA Puglia yes yes Rn indoor, georeferenced 1990 ARPA Sardegna ARPA Sicilia ARPA Trento yes yes Rn in water (sampled), Rn indoor , ARPA Umbria yes Text Publ. Rn in water (sampled), Rn indoor , ARPA Valle D Aosta ARPA Veneto yes yes Rn indoor ARPA Venezia yes Text Publ. Rn in water

4 GNGTS 2013 Sessione 2.1 Tab. 1 describes the type of data received: radon in soil, in water or in the air, and if it is a numerical data or only a bibliographical data. Every ARPA of the national territory were contacted even if their data acquired are mainly constituted by indoor radon measurements. In some cases, single institution was related to data from several sites. The institutions contacted were 41, only 27 responded, and of these, 15 sent numerical data, 6 sent references, and the remainder said they did t have useful data for the purposes of the project, or t to be available to their inclusion in the database Following the directives, given by the Information Techlogy Group, the Metadata Form has been compiled and according to this, all data received have been reformatted. A georeferenced database was built and, so far, consists of 3961 sites and more than one million records of radon data. Fig. 2 shows the structure of the database. Fig. 1 Map of the spatial distribution of sites with radon measurements. Fig. 2 Block Diagram of the geodatabase. 126

5 Analysis of the data. The third product of this project is the identification of the Real Amalies and the definition of Theoretical Amalies type. The longer time series were analyzed with the aim of identifying amalies a posteriori. Real Amaly means the Amaly, characterized by amplitude, duration, and precursor time with respect to the earthquake associated. We will call Theoretical Amaly that obtained for a hypothetical earthquake of a given magnitude and epicenter at a given distance from the monitored site. This is the deliverable required for an objective evaluation of the amalies themselves. The data can be grouped into two main categories: 1. measurements of radon in soil and in water (continuous and sampled) 2. measurements of indoor radon Unfortunately, the second task of the project took a long time living only a little time to the last phase, which is the most challenging in terms of interpretation and conclusion. Comparing the tight time to the amount of data, priority was given to the analysis of those relating to measures of radon in continuous and, among these, those consisting of longer time series and with overlapping periods between them. Tab. 2 Real Amalies. Amaly Data Duration Amplitude Real Magnitude > 3,0 Precursor Time Distance Comments / dd 78,43% 3,3 + (3,3+3,7) 4 months < 20 Since January 2003, data have several breaks / dd 42,94% 3,7 61 dd < / months +8dd 755,50% 5,1 + 5,1 6,5 months +10dd / 11 months / d 25,90% 3,3 + 3,8 5 dd < / months 195% 3,3 1 month + 19dd < / dd 64,72% 3,4 5 months + 10dd < 35 < / year + 7 months 328,39% 5,9 2 years + 7months + 26 dd < 500 Amaly long period / dd 201,46% 3,9 + 3,7 9 dd < / dd 129,03% 3,7 13 dd < 25 Amaly within that long period Amaly within that long period / dd 167% 5,5 5 months+8 dd < 350 Amaly within that long period / dd 299% 3,1 + 5,0 4 months+ 6 dd < 350 recalculated / dd 182% 4,4 1 month+22 dd < / dd 167,55% 5,9 5 dd < / dd 493% 4,8 11dd < / dd 684% 3,8 1g (cosismica) < / dd 321%?? / dd 40%?? missing data before 15 May 127

6 Any value greater than the limit of +/- 2-Sigma was considered Amaly, compared to the average value. Only in rare cases recorded values below the - 2sigma line have been. The reference earthquakes were selected according to the relation of Hauksson and Goddard (1981), (OGS, ; ISIDE, ). Tab. 2 shows the characteristics of the amalies found by analysing radon data in soil recorded in Friuli by OGS in the period A first analysis of all the earthquakes selected according Hauksson and Goddard (1981), highlighted that we can see that each Amaly is followed by an earthquake, but the timing precursors can also vary for similar magnitude, depending on the local conditions of stress. The analysis was restricted to earthquakes of magnitude greater than 3.0. The strongest earthquakes were preceded by long-term amalies, although within them there are many small amalies sometimes previous earthquakes of medium magnitude. The required product was obtained, for the moment, with only a small part of the data. Based on the real amalies that occurred during the period in question, theoretical amalies that should occur for certain magnitudes and distances have been obtained. The values of the duration, the distance and the amplitude of the Real Amalies were increased by 30% compared to the real values, the time precursor was decreased by 30% and the magnitude of 10%. Tab. 3 - Theoretical Amalies. Amaly Duration Amplltude Precursor Time Magnitude expected Radius Alarm period 1 5 dd < 102% > 83,3 dd > 3,0 < dd 2 10 dd < 56% > 43 dd > 3,3 < dd dd < 982% > 140 dd > 4,6 < dd 4 1 d < 33,67% > 3,5 dd > 3,4 < 39 5 dd 5 29 dd < 246% > 33 dd > 3,0 < dd 6 11 dd < 84% > 112 dd > 3,1 < 45,5 198 dd 7A 2 dd < 261% > 6 dd > 3,5 < dd 7B 3 dd < 168% > 9 dd > 3,3 < 32,5 17 dd 7C 2 dd < 217% > 110 dd > 5,0 < dd 7 2 years + 7 months < 427% > 676 dd > 5,3 < dd 8 7 dd < 389% > 88 dd > 4,5 < dd 9 1 d < 237% > 36 dd > 4,0 < dd 10 2 dd < 218% > 3,5 dd > 5,3 < 325 6,5 dd 11 6 dd < 641 % > 8 dd > 4,3 < dd 12 3 dd < 889 % > 0,7 d > 3,4 < 52 1,5 dd In addition to the direct comparison with individual earthquakes, the data collected in Friuli were correlated with the seismicity considered in its complexity and expressed by the b-value of the Gutenberg-Richter law (GR) (Riggio and Santulin, 2012). Ather priority was given to the magnitude of the earthquakes. A first analysis was done on the 2 strongest earthquakes occurred during the periods in which long radon time series were available: the L Aquila earthquake and the earthquake in Emilia. A first analysis showed that for both the events, amalies were present on the recorded data of three monitored sites in Italy. Fig. 3a shows an example of amaly by OGS data of radon in the soil in the period prior to the L Aquila earthquake. The amaly reported, is part of a long-term amaly that begins, in fact, already in August The duration was 2 years and 7 months and the 128

7 maximum amplitude over the 2-sigma has reached 328%. The Amaly ends 26 days before the event and the values of radon are reduced by almost 100%. The analysis of the concentration of radon with the seismicity considered in its complexity and expressed by the b-value of the GR was always done on the radon in soil data recorded in Friuli. As matter of fact, some previous studies concerning this region (Riggio and Sancin, 1986; Riggio et al., 2003) have indicated a possible relation between long period Rn variations and the b-value (Gutenberg and Richter, 1944) behaviour in time and space, suggesting thus that Rn degassing could be modulated by stress accumulation. In Fig. 3b it is possible to see how the b value is very low before earthquakes and that it is in phase opposition with the concentration of radon, in agreement with the theory of dilatancy. A similar conclusion was reached in previous work, by the analysis of radon sampled in water springs, in the same area (Petrini et al., 2012). The research was carried out in the framework of the activities of the previous seismological projects DPC-INGV S2 ( ) and S1 ( ). Contributions to the Department of Civil Protection (DPC). The aim of the project was to give an idea on the possibility of using seismic precursors studied as a tool for earthquake prediction. The establishment of the database required a considerable effort that has resulted in a very substantial time spent. Nevertheless, we can highlight the following results: 1. A quantitative and qualitative overview on radon data existing. 2. The references of institutions that operate in this field and the processing and evaluation of the data obtained. 3. Evaluations about the size of the area to be investigated for strong earthquakes. 4. The state of art of the existing sites, recording time series, that could be organized into a network that would give more informations simultaneously. Future prospects. The analyses carried out so far have yielded good results, and suggest that there may be good prospects for use radon as a seismic precursor. The data of indoor radon and the sampled data in water and in soil, can be of support to the continuous measurements of radon in soil and can give you information on new areas where, eventually, create detection sites. Analysis of the data showed that the area to be monitored for major earthquakes can be much larger than those usually considered. We would welcome the use of the sites already monitored for possible enhancement and coding of a monitoring network. Fig. 3 a) Radon in soil recorded in Friuli during the period b) Radon in soil at Cazzaso (black line), b-value (blue line), coefficient correlation (red line) between them and the earthquakes with M > 3.5 (green line), selected according Hauksson and Goddard (1981). 129

8 Simultaneous analysis of all data in the database, and an integrated interpretation of all the precursors studied within the project. Conclusions. All earthquakes of magnitude > 3.0 were preceded by amalies. It can be said that the success rate is 100%, but, for low magnitude, the duration and the time precursor does t seem to have a strictly constant trend with respect to the magnitude. The duration of the Amaly and the Time Precursor seem to be proportional to the high magnitude. High magnitude earthquakes seems to have amalies with order of years. With this type of analysis is difficult, however, to discriminate the false positives, because, each amaly precedes an earthquake although of low magnitude (<3.0) selected according Hauksson and Goddard (1981). From the data analysed above only one amaly t relatable to any seismic event was found. Conversely, all significant long period amalies were followed by earthquakes of magnitude > 5.0. Of course all Amalies have been identified in retrospect. Analysis will be done with ather method of calculation, which will also be applied to other data that are part of the database. The results obtained in previous works, suggest that the variations of radon are indicative of the state of stress of the preparation area of the earthquake and then the deformation. The presence of Amalies in the same periods and in different sites, gives hope in the fact that increasing the number of monitoring sites, located throughout the country, could make a great contribution.the comparison with other observable, last but t least, should lead to identifying areas involved in the processes of deformation. Ackwledgements. The research was carried out in the framework of the activities of the seismological projects S3 ( ) financed by the Italian Department of Civil Protection and the National Institute of Geophysics and Volcalogy. References Gutenberg B. and Richter C.F.; 1944: Frequency of earthquakes in California Bull. Seism. Soc. Am., 34, Hauksson E. and Goddard J.G.; 1981: Radon Earthquake Precursor studies Iceland. J.Geophys.Res. 86, ISIDE; : Lista degli eventi sismici registrati dalla Rete Sismica Nazionale. OGS; : Bolletti della Rete Sismometrica del Friuli Venezia Giulia. OGS, Trieste. Petrini R., Italia F., Riggio A., Slejko F.F., Santulin M., Buccianti A., Bonfanti P. and Slejko D.; 2012: Coupling geochemical and geophysical signatures to constrain strain changes along thrust faults, Bolletti di Geofisica Teorica ed Applicata. Vol. 53, n. 1, pp ; March Riggio A. and Sancin S.; 1986: Variazione nel tempo del parametro b quale precursore. In: Atti del 5 Conveg GNGTS, Esagrafica, Roma, pp A.Riggio, M.Santulin ; 2013: Radon as seismic precursor. Relazione I semester Progetto S3, Riggio A., Sancin S., Santulin M., Popit A., Vaupotic J. and Zmazek B.; 2003: Radon e sismicità in Italia rd-orientale. In: Atti del 22 Conveg Nazionale GNGTS, file /06.26, Prospero, Trieste, CD-Rom A. Riggio, M. Santulin; 2012: Potential seismic precursors: analysis of the recent earthquakes previous periods and problems related to interpretation. 31 Conveg Nazionale GNGTS, Potenza A. Riggio, M. Santulin; 2013: Radon as seismic precursor. Relazione I semestre Progetto S3, Zhang Guomin, LI Xuanhu, LI Li;1996: Research on Earthquake Prediction in China Since the 1980s, in The Selected Papers of Earthquake Prediction in China. State Seismological Bureau. Seismological Press. Editor in Chief, GE Zhizhou, Beijing, pp ISBN /P.836 (1768). 130