GNGTS 2013 - Atti del 32° Convegno Nazionale

maximum amplitude over the 2-sigma has reached 328%. The Anomaly 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 (2004-2006) and S1 (2007-2009). 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 2008-2009. 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 GNGTS 2013 S essione 2.1