GNGTS 2022 - Atti del 40° Convegno Nazionale

GNGTS 2022 Sessione 1.1 69 from 1985 to the present day. This choice was made to understand how the parameters of the mc vary after the upgrade of the national seismic network in 2005. In fact, a difference in magnitude of completeness was obtained between the catalogue before 2005 and the one after. Before 2005 we have a Mc of 2.8, while after 2005 we have 2.0. The b-value before 2005 is 1.21 while after 2005 it is 0.97. These differences can lead to attention in several respects. The first thing is is the decrease of the Mc after 2005, which however could be caused by the updating of the national network. The change in the b-value before 2005 and after 2005 may be due to a change in the tectonic activity of some areas. The variation of b-value is very significant in fact if we calculate a 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 (Petruccelli et al. , 2019). If we note the values obtained in this first approach and associate with the geodynamicists of Italy, the parameters are in line with the seismic and tectonic activity of the areas that greatest interest. Among the purposes there is that of going to calculate the differences between the maps before 2005 and those after 2005, in order to understand if there are actually significant differences in estimated b-values. The variation in tectonics could be deduced from these calculations and clearly also from a bibliographic study. Another aspect that we would like to bring forward is to use other analyses already mentioned in the introduction in order to carry out and highlight the relative pros and cons in the use of a specific technique, up to the point of experimenting with the latest technique developed by Taroni et al., 2021. Having made a choice that is to be able to use the entire national catalogue, the estimates of the magnitude of completeness and of the b-value can have various applications such as those in volcanic areas to understand if the variation of the b-value can be influenced by material in ascent and therefore by heat or also be influenced by mini cracks always due to material rising. Another important aspect for the purposes of this type of study is to better analyse a given seismic sequence where all the geophysical and geodynamic aspects are known and calculate the b-value, in order to understand if in future this variation of the b-value can be used as a possible precursor of a seismic sequence and an earthquake. Therefore, analysing the pre, during and post event would be an additional element to enrich the research of the calculation of b. Fig. 3 - a) estimation of b-value varation from 2015 to today b) estimation of standar deviation for b-value stimation.