Mathematical and geophysical methods for searching anomalies of the Radon signal related to earthquakes

A detailed analysis of a time-series of the Radon (Rn-222) specific activity is carried out to identify anomalies that can be correlated with earthquakes occurrence in the monitored area. New hybrid methods are developed for this purpose and the advantages of each single component method are exploited. These methods are applied to two-years data series recorded continuously in the soils of a site within the seismo-volcanic area of Phlegrean Fields (NaplesItaly). Since the measurement system distinguishes and separately measures the Rn- 222 and Rn- 220, an alternative estimation of the remote fraction of the gas and its anomalies has been also performed using the( 220)Rn trend. The results of different methods are compared to recognize and to highlight Radon anomalies. Clear relationships have been found between anomalies and earthquakes of local origin and selected according to a specific formula of the earthquake preparation zone. The effectiveness of the methods and the goodness of the results are established by the high values of the cross correlation factors between the anomalies and the occurrence of the earthquakes.