GNGTS 2013 - Atti del 32° Convegno Nazionale

Any value greater than the limit of +/- 2-Sigma was considered “Anomaly”, 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, 2002-2013; ISIDE, 2002-2013). Tab. 2 shows the characteristics of the anomalies found by analysing radon data in soil recorded in Friuli by OGS in the period 2002-2013. Afirst analysis of all the earthquakes selected according Hauksson and Goddard (1981), highlighted that we can see that each Anomaly 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 anomalies, although within them there are many small anomalies 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 anomalies that occurred during the period in question, theoretical anomalies that should occur for certain magnitudes and distances have been obtained. The values of the duration, the distance and the amplitude of the Real Anomalies were increased by 30% compared to the real values, the time precursor was decreased by 30% and the magnitude of 10%. Tab. 3 - Theoretical Anomalies. Anomaly Duration Amplltude Precursor Time Magnitude expected Radius Alarm period 1 5 dd < 102% > 83,3 dd > 3,0 < 26 155 dd 2 10 dd < 56% > 43 dd > 3,3 < 39 79 dd 3 190 dd < 982% > 140 dd > 4,6 < 325 273 dd 4 1 d < 33,67% > 3,5 dd > 3,4 < 39 5 dd 5 29 dd < 246% > 33 dd > 3,0 < 52 61 dd 6 11 dd < 84% > 112 dd > 3,1 < 45,5 198 dd 7A 2 dd < 261% > 6 dd > 3,5 < 65 12 dd 7B 3 dd < 168% > 9 dd > 3,3 < 32,5 17 dd 7C 2 dd < 217% > 110 dd > 5,0 < 30 455 dd 7 2 years + 7 months < 427% > 676 dd > 5,3 < 650 1256 dd 8 7 dd < 389% > 88 dd > 4,5 < 455 166 dd 9 1 d < 237% > 36 dd > 4,0 < 455 68 dd 10 2 dd < 218% > 3,5 dd > 5,3 < 325 6,5 dd 11 6 dd < 641 % > 8 dd > 4,3 < 520 14 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). Another 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, anomalies were present on the recorded data of three monitored sites in Italy. Fig. 3a shows an example of “anomaly” by OGS data of radon in the soil in the period prior to the L’Aquila earthquake. The anomaly reported, is part of a ‘long-term anomaly that begins, in fact, already in August 2006. The duration was 2 years and 7 months and the 128 GNGTS 2013 S essione 2.1