GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 - POSTER GNGTS 2023 During the seismic sequence, an investigation was conducted to understand how b -value varies over time with respect to the reference value calculated for all the seismicity of the study area. The importance of the b -value has grown over the last decade. In fact, it assumes various meanings based on the context of application, for example precursor of seismic sequence (Lombardi, 2021), research of magma storage (Murru et al., 2007) or to find a correlation with dynamics of the tectonics structures (Schorlemmer et al., 2005, Petrucelli et al., 2019). During a seismic sequence, as Gulia et al., 2019 defines, it can be seen that the b -value tends to drop immediately after a mainshock, and then it gradually rises again until it stabilizes at the background value of the study area. Calculating the b -value during a seismic sequence is not simple, especially when it occurs at sea. The coverage of the seismic network tends to be insufficient, and therefore a margin of error must be considered. Another aspect to consider when calculating the temporal variation of the b -value is the completeness of the catalogue, the coherence, and accuracy of the location of the earthquakes. In this scenario, we calculated the background b -value and completeness magnitude covering the range time from 2005 to 2022 in order to compare the values of this time range with those shown during the seismic sequence . In fact, seismic sequence data from the day of the mainshock was downloaded every three to four days. Then we calculated the frequency magnitude distribution (FMD). To calculate these values, we made use of the MAXimum Curvature (MAXC) technique (Wiemer and Wyss, 2000) using the ZMAP software, developed in the Matlab environment. Data Analysis The technique that has been chosen for the calculation of the completeness magnitude is the MAXC. This technique consists of evaluating the maximum curvature by computing the maximum value of the first derivative of the frequency-magnitude curve. This method is fast and simple. The maximum curvature estimated for the whole Istituto Nazionale di Geofisica e Vulcanologia (INGV) catalogue, period 2005-2022, is shown in fig 1b. The completeness magnitude was found to be 1.7, with a correction factor of 0.2. The b-value is 1.05 +/- 0.07 and a-value is 4.021. After calculating the reference b-value, it was calculated progressively starting from the day of the mainshock. The first calculation was made in the first five days, the second in the first nine days, the third in the thirteen days, the four in the nineteen days and the last in thirtieth days.