GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 - POSTER GNGTS 2023 Having a quantity of major events after the first nineteen days of the seismic sequence, we proceeded with the spatial analysis of the b -value. Figure 3a shows a part of the offshore affected by values ranging from 0.9 up to 0.6 and another part with values ranging from 1.2 and above. Discussion The aim of this work is to understand if during the seismic sequence, the b -value can be a precursor of future seismic sequences. As explained in Gulia et al., 2019, the b -value tends to decrease drastically when a mainshock occurs and then gradually increase in value. Subsequently, the value could stabilize to the background value or about one or decrease again if a subsequent mainshock occurs. The calculation of the b -value during seismic sequences is very complicated due to various factors, including that of obtaining a complete, accurate catalogue. Another factor that complicates the calculation is the coverage of the seismic network, in this case study being offshore the seismic sequence is more difficult, one must be careful to consider the exact location of the earthquakes. Considering the case study, the background b -value obtained is equal to 1.05. From the seismic sequence onwards, the b -value went through a decrease of the value of 0.10, remaining constant during these first nineteen days after the event. The possible scenarios can be: a) the value will tend to stabilize returning to a value equal to one, b) it will tend to increase and then decrease and have the second mainshock. In addition to calculating the b -value temporally, it was calculated spatially. In most of the map, we see a coverage of the value of b below the value one. Taking into account the calculation of the focal mechanism carried out by INGV, it can be said that there is a certain correlation between the dynamic movement of the fault concerned and the value of the b -value. When it assumes values lower than one, it indicates an inverse movement (Schorlemmer et al., 2005). References Gulia, L., Wiemer, S., 2019. Real-time discrimination of earthquake foreshocks and aftershocks . Nature 574, 193–199. https://doi.org/10.1038/s41586-019-1606-4 Lombardi, A.M., 2021. A Normalized Distance Test for Co-Determining the Completeness Magnitude and b-Value of Earthquake Catalogs . J. Geophys. Res. Solid Earth 126, 1–14. https://doi.org/10.1029/2020JB021242 Maesano F E., Toscani G., Burrato P., Mirabella F., D'Ambrogi C., Basili R.,2013. Deriving thrust fault slip rates from geological modeling: Examples from the Marche coastal and offshore contraction belt, Northern Apennines, Italy, Marine and Petroleum Geology, Volume 42,Pages 122-134,ISSN 0264-8172, https://doi.org/10.1016/j.marpetgeo.2012.10.008. Murru, M., Console, R., Falcone, G., Montuori, C., Sgroi, T., 2007. Spatial mapping of the b value at