GNGTS 2019 - Atti del 38° Convegno Nazionale

70 GNGTS 2019 S essione 1.1 in two different Italian seismogenic domains: the extensional intra-Apennine belt of Central Italy and the compressional domain of the Marche-Adriatic region, in order to find common points and differences in the characteristic of the TES activity. The Central Apennines are an upper crust high seismic risk zone, that experienced destructive earthquakes both in historical and in instrumental time. In particular, we focus on the axial zone extending between the Irpinia 1980 (Mw 6.9) and the Accumoli-Visso-Norcia 2016 (Mw 6.5) epicentral areas, that was struck by eleven events among the largest historical- early instrumental earthquakes (Mw ≥ 6.5) of the Italian territory since 1349. On the contrary, in instrumental times, if we exclude the Barrea 1984 seismic sequence (Mw 5.9), this area is predominantly characterized by a low level of seismicity, relatively stable in the size and time domains, and by low energy seismic clustering. The eastern Marche-Adriatic region represents a typical active fold-and-thrust belt system; the active structures are mainly buried and their geometric complexity makes the region one of the most intriguing areas of the central Mediterranean. The compressional domain shows three major layers of seismogenic activity (upper crust, middle crust, upper mantle) controlled by the presence of lithospheric shear zones reaching maximum depths of about 70 km (Lavecchia et al. , 2003). To identify TES in the two study areas, we applied the declustering method and the cluster analysis, starting from the ISIDe instrumental databases in the time interval 2005- 2018 (ISIDe, working group 2016) for the extensional area and from the ReSIICO high-quality dataset recorded from 2009 to 2017, for the compressional area. The identified TES were analysed in terms of temporal and spatial evolution, at the light of their location with respect to known active individual seismogenic structures. Extensional TES are mainly located at the tip of the principal individual structures, with recurrence in the same place by the time. Compressional TES appear to be controlled in their specific features by the depth of the seismogenic layer. A principal difference between the extensional and compressional areas consists in the characteristic TES duration, which is shorter in the compressional area than in the extensional one, with a duration of few days in the first case and up to few weeks in the second case. The study is in progress. References Brozzetti F., Cirillo D., de Nardis R., Cardinali M., Lavecchia G., Orecchio B., Presti D. and Totaro C.; 2017: Newly identified active faults in the Pollino seismic gap, southern Italy, and their seismotectonic significance. J. Struct. Geol., 94, 13-31. Hainzl, S., 2004. Seismicity patterns of earthquake swarms due to fluid intrusion and stress triggering, Geophys. J. Int., 159, 1090–1096. ISIDe working group (2016) version 1.0, DOI: 10.13127/ISIDe.4 Lavecchia G., Boncio P. and Creati N. (2003)Alithospheric-scale seismogenic thrust in central Italy. J. of Geodynamics, vol. 36, 79–94. Marzorati, S., M. Massa, M. Cattaneo, G. Monachesi, and M. Frapiccini (2014), Very detailed seismic pattern and migration inferred from the April 2010 Pietralunga (northern Italian Apennines) micro-earthquake sequence, Tectonophysics, 610, 91–109. Passarelli, L., S. Hainzl, S. Cesca, F. Maccaferri, M. Mucciarelli, D. Roessler, F. Corbi, T. Dahm, and E.Rivalta (2015). Aseismic transient driving the swarm-like seismic sequence in the Pollino range, Southern Italy. Geophysical Journal International, 201(3), 1553-1567. Stein, R.S., 1999. The role of stress transfer in earthquake occurrence, Nature,402, 605–609.