GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.1 GNGTS 2024 Following Sebastani & Malagnini (2020), who provided a forecast for the next Parkfeld mainshock via the analysis of the variability of the variance of the daily center of the seismic actvity along the transitonal segment of the SAF in the tme window between 1973 and late 2019, we look at the variability of the variance of the atenuaton anomalies as a functon of tme. Variances are computed over subsequent subsets of atenuaton anomalies, and the later are obtained as follows: afer a number of samples is chosen (e.g. 40) , we look at the longest tme window needed to gather 40 subsequent data points, then we apply that length to all the tme windows that we analyze.  In each tme window we randomly choose a subset of 40 data points to be used to compute the variance. We randomly choose 10% of data points to be eliminated from each subset and do multple estmates of variance by looping through this bootstrap step of the analysis a number of tmes (10). We fnally average all variance determinatons. Time windows are moved, one data point at a tme, toward more recent tmes. The analysis done without applying the bootstrapping/ averaging technique yields very similar results. In Figure 5 we plot the average variances, normalized by the length of the tme window. We also point out that a single estmate of variance does not difer much from what we present here. Finally, Figure 6 shows the average atenuaton parameter calculated for the North American side (black) and for the Pacifc side of the SAF (red), in the indicated tme windows (2001-2004 and 2005-2019). ( Q −1 S ( f ) )