GNGTS 2022 - Atti del 40° Convegno Nazionale

68 GNGTS 2022 Sessione 1.1 For maps the parameters are: • Number of events > Mc node: this parameter allows to define how many events you would like to include in a grid node. • Mc correction: is related to the cumulative curve • Events with constant radius: this parameter allows you to select events with a constant radius of inclusion • Grid size: parameter that allows you to have a large grid or a little grid and to obtain a more or less dense distribution of the parameters Figure 2 presents the Italian seismic distribution in the period from 1 st January 2015 to 28 February 2022. The various points change in size based on the magnitude and in colour based on the depth of the events (fig. 2a). The variation of the completeness magnitude is shown in fig. 2b: this map as well as the maps shown in Figure 3 have been created by providing the input parameters such as: minimum number of events greater than the mc at node 100, the grid size of 20 km , the Mc correction 0.9, constant radius of 60 km. Always using the MAXC as an analysis technique for the estimation of the magnitude of completeness. As regards the variation of the completeness magnitude, in figure 2 b, it could be said that in some areas there is a Mc equal to 1.6-1.8 very low values, certainly because there will be a density relative to the national seismic network. There are other areas that have higher values of Mc (yellow zones) which are probably areas where the national network is less dense. Fig. 2 - a) Seismic distribution from 2015 to today. b) Mc varation about 2015 to today. To estimate the b-value, we can see how it varies from area to area. It is noted that some areas such as the central Apennines has a value of b about 1.2-1.4, the Calabrian arc has a value of about 0.9-0.7, eastern Sicily is presented with values 0.9-1.4, a part of the Tyrrhenian Sea has values about 1.0. For b-values greater than 1.0 there will be a predominantly relaxing dynamics, for values less than 1.0 there will be a compressive dynamic for values around 1.0 there will be a strike-slip dynamics (Petrucelli et al., 2019). Discussion. In this first approach towards the calculation of the completeness magnitude, it was decided to consider all the Italian seismicity, thus considering the whole seismic catalogue