GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.1 GNGTS 2023 The possible correlation between regional seismic events and CO 2 anomalies in the Gallicano spring has been recently investigated over the period April 2017 - March 2021 (Pierotti et al., 2022) by applying a statistical approach similar to that successfully applied to satellites data (Fidani, 2021). In this framework, correlations have been used to estimate the conditional probabilities of seismic events, allowing for a sort of “earthquake forecasting experiment” based on continuous geochemical signals. Here, we focus on CO 2 time series acquired during the 2010 – 2013 period. Raw data were processed with appropriate moving median smoothing procedures (Box and Jenkins, 1976; Velleman and Hoaglin, 1981) to filter out a number of outliers recorded during monthly maintenance operations. Unrepresentative data recorded during the interruption of the water inflow into the cells, generally due to pump failures and/or short electrical blackouts, were eliminated from the dataset before any statistical/numerical processing. For ease of use, the dataset was further reduced by substituting punctual data with daily average values. CO 2 time series have been decomposed according to Census I method (Makridakis et al., 1998) to detrend the CO 2 signal for external influences. In particular, according to Census technique, original CO 2 time series were polished for seasonal and cyclical components (combined with the additive model) to separate a residual component called “irregular component”. The decomposition was performed following a step-by-step procedure that considered a reference frame of 12 months (Makridakis et al., 1998). Fig. 1. Earthquake dataset displayed by z-map 1° around Gallicano, completeness magnitude is 1.3. The epicentre distribution by black squares is shown in a); the brown line is the Tyrrhenian coastline, the blue lines are the main local faults, and the red diamond marks the position of the Gallicano station. Square symbols dimensions are proportional to earthquakes magnitude. The yellow star marks the epicentre of the most energetic seismic event occurred in the area during the observation period of this study. The cumulative number of seismic events versus magnitude is shown in b). The cumulative rate with the main shock are shown in c).