GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.1 GNGTS 2024 In this study, we generated high resoluton catalogues for seismic sequences in the complex normal fault system of Southern Apennines (Italy) by comparing and integratng advanced state of the art detectors (deep learning models and similarity-based detectors, Yoon et al. 2015, Chamberlain et al. 2018, Mousavi et al. 2020). We found that the integraton of the machine learning and template matching detectors, the former providing templates for the cross- correlaton, largely outperforms techniques based on autocorrelaton and machine learning alone, featuring an enrichment of the existng automatc and manual catalogues of factors 21 and 7, respectvely (Scoto di Uccio et al., 2023). Using deep catalogues of microseismic sequences, we performed accurate double-diference locaton, source parameter estmaton and stress release modelling, that allows for addressing the spatotemporal evoluton and generaton of the sequences. Relocated seismicity clearly identfes local patches on kilometric-scale structures, featuring an orientaton coherent with the main faults of the area. When mapping the seismic sequences at depth, their locaton is generally not compatble with the faults that hosted the 1980, M 6.9 Irpinia event, looking at the fault traces on the Earth surface (Westaway & Jackson 1987), the event dip and the estmated geometry from inversion of seismic and levelling data (Bernard and Zollo, 1989). This indicates that seismic sequences ruptured small patches of secondary segments. When mapping the stress change on the fault plane, the inter-event distance compared to the size of the events suggests that the dominant triggering mechanism within the sequences is the (statc) stress transfer, that allows the nucleaton of individual events. The distributon of the events is not isotropic around the main events of the sequences, but small events tend to align dominantly along the dip directon, which also corresponds to the slip directon for normal faults. They can be interpreted as the boundary between locked and creeping domains (Rubin et al. 1999, Rubinstein and Beroza, 2007). The occurrence of an aseismic event appears to be more likely in the case of the 3-7 July 2020 Rocca San Felice sequence featuring the actvaton of two parallel clusters oriented along the dip directon but distant 5 km from each other. Although evident aseismic transients were not detected during the sequence, we evaluated the maximum average slip allowed on a deep dislocaton whose displacement on the surface does not emerge within uncertaintes from the noise level. We inferred that an aseismic event of Mw ~5.0 could have occurred during the sequence, transferring stress across the two asperites without producing a signal emerging at the GPS statons at the surface References Bernard, P., & Zollo, A. (1989). The Irpinia (Italy) 1980 earthquake: detailed analysis of a complex normal faultng. Journal of Geophysical Research: Solid Earth, 94(B2), 1631-1647. Chamberlain, C. J., Hopp, C. J., Boese, C. M., Warren‐Smith, E., Chambers, D., Chu, S. X., Kostantnos, M. & Townend, J. (2018). EQcorrscan: Repeatng and near‐repeatng earthquake detecton and analysis in Python. Seismological Research Leters, 89(1), 173-181. Gualandi, A., Nichele, C., Serpelloni, E., Chiaraluce, L., Anderlini, L., Latorre, D., Belardinelli, M.E. & Avouac, J. P. (2017). Aseismic deformaton associated with an earthquake swarm in the northern Apennines (Italy). Geophysical Research Leters, 44(15), 7706-7714.