GNGTS 2015 - Atti del 34° Convegno Nazionale

36 GNGTS 2015 S essione 2.1 before a strong earthquake occurs, and from one day to months, usually in the short term and impending phase (Zhang et al. , 1996). In this paper, we show the methods used to identify the effects of meteorological phenomena on the radon values recorded in various time series, and the subsequent removal of these effects. Data analysis . The aim of the project was to verify if the observables multiparametric monitoring could represent a tool to improve the knowledge about the seismic hazard (Albarello, 2015). The priority areas, object of study, are the Po Plain and the southern Apennines. The data provided by the various institutions were homogenized according to previously defined metadata sheet. Among all the data contained in the database, those with the longest period of acquisition and the smallest sampling intervals were taken into consideration. Are at least six institutions have provided data acquired continuously for a time period greater than or equal to a year, in one or more sites, for a total of fifteen time series. Ten of these are located within a maximum radius of 300 km from the Project S3 priority area of the Po Valley (Italiano et al. , 2012). The series here considered were acquired in the soil, but with different instruments and sampling intervals. The characteristics of the sites which have produced the longest time series are reported In Tab. 1. The Cazzaso survey site, managed by the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), is equipped with a continuous radon recording, Lucas scintillation cell type. The operating modalities are both continuous and grab sampling. The air is inhaled by pumping, from a 40.5 m deep well with a 9 cm diameter, at a 7 m depth. The groundwater level is about 17 m deep from the top of the well. The well is closed by a gully-hole (Riggio and Sancin, 2005). The site is located between the Alpine and Dinaric structures. The sites in the Novara zone, managed by the Geophysical Observatory of Novara, are located on both sides of the Cremosina fault. The sensors are placed in wells, that in the case of Pogno and Gozzano were placed in basements well closed and automated. Torre Pellice site, managed by Seismic Precursor Study Center (SPSC), and Rocca di Papa site, managed by the Istituto Nazionale di Geofisica e Vulcanologia (INGV), are located in basements whereas Prato site, managed by Prato Research and CAI - Section of Prato, is located in a cave. In the first phase of the project, the longest time series with the most continuous acquisition time were analysed, each with their time sampling (between ten minutes to twelve hours), identifying as anomalies those values that exceed the limit of 2-sigma (Wakita, 1980). In Tab. 2, an example related to the site of Cazzaso is shown. Earthquakes in the table have been recorded Tab. 1 - Characteristics of continuous monitoring Radon sites, in central-northern Italy. SITE NAME MEASUR.UNIT ACQUIS.MOD. SITE TYPE INSTRUM. BORGOLAVEZ. (NO) counts/h soil well Prototype CASALINO (NO) counts/h soil well Prototype CAVAGLIA (NO) counts/h soil well Prototype GOZZANO (NO) counts/h soil well Prototype NOVARA counts/h soil well Prototype POGNO (NO) counts/h soil well Prototype CAZZASO (UD) Bq/m3 soil well PrassiSilena TORRE PELICE (TO) Bq/m3 air basement Geoex 1027 ROCCA DI PAPA (RM) Kbq/m3 soil soil AlphaGuard PRATO Bq/m3 air cave AlphaGuard