GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 - POSTER GNGTS 2023 Figure 1. a) Epicenters of the initial selection of the earthquakes occurred recently in the Mesima valley area. b) Modified Wadati diagram computed to evaluate the quality of the picking and the Vp/Vs ratio. ​ Data and methods The analysis of the seismic catalog allowed to select some swarms consisting of hundreds of earthquakes located in epicentral areas of few km 2 which occurred within a few weeks or a few months. All available data, i.e., seismograms recorded by the regional seismic network of the University of Calabria (www.sismocal.org ) and by the national seismic network ( www.ingv.it , www.eida.ingv.it ), were used to analyze the selected events. The most important seismic swarms in terms of the number of events include Catanzaro (2022), Umbriatico (2022), Aspromonte (2020), Amantea (offshore, 2020), Cirò (2020), Albi (2020), Gulf of Policastro (2019), Mesima valley (2019), Bagnara Calabra (offshore, 2018), and others. The epicentral area of the various swarms did not allow analysis with the same resolution, mainly because in some cases (e.g., offshore sequences) the configuration of the seismic network is not appropriate and the location is affected by high azimuthal gap. To accurately locate the earthquakes of each swarm, the manual P- and S-wave picking has been performed for all selected events, and the location has been computed using the software Hyposat (Schweitzer, 2001) and a 1D velocity model. Furthermore, the focal mechanism has been computed for as many events as possible using one or more of the following software: FocMec (Snoke, 1989), HybridMT (Kwiatek, 2016), and gCAP (Zhu & Ben-Zion, 2013). FocMec is based on P-wave and (possibly) S-wave polarity, while HybridMT is based on polarity and amplitude of the first P-wave pulse, so these two methods are the most suitable for small magnitude earthquakes (M<3). On the other hand, gCAP is better for medium to high magnitude earthquakes because it is based on the comparison of observed and theoretical seismograms. Using different software gives a strong constraint about the result and increases its reliability. Relative location was also performed for the analyzed swarms following the method proposed by Got et al. (1994). This analysis allows for a more accurate location of the events of a swarm respect to a reference event and it is based on the differences in arrival times observed at the various stations considered. Furthermore, the relative location result allows to compute an approximate but realistic estimation of the seismogenetic volume that generated the swarm, and in the most

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