GNGTS 2022 - Atti del 40° Convegno Nazionale

60 GNGTS 2022 Sessione 1.1 THE ROLE OF COULOMB STRESS TRANSFER IN THE EVOLUTION OF SEISMIC CYCLES: INSIGHTS FROM THE CENTRAL APENNINE FAULT SYSTEM G. Valentini 1,2 ., T. Volatili 1 , P. Galli 3,4 , E. Tondi 1,2 1 School of Science and Technology - Geology Division, University of Camerino, Italy 2 National Institute of Geophysics and Volcanology, Rome, Italy 3 Dipartimento Protezione Civile, Rome, Italy 4 Consiglio Nazionale delle Ricerche, Istituto di Geologia Ambientale e Geoingegneria, Rome, Italy The Central Apennine Fault System (CAFS in Cello et al. , 1997) is composed of several active normal to oblique faults that caused several destructive earthquakes during the last millennium. According to available seismic catalogues (CPTI15 - Rovida et al. , 2022; ISIDe working group, 2007) 18 seismic events with 5.8 ≤ Mw ≤ 7.0 in central Italy (since 1279A.D.) can be associated with CAFS-related structures. Seismicity appears to be concentrated in 3 distinct time-windows: in the 12 th -13 th and 17 th -18 th centuries and from the 1970s to 2017. The most recent seismic events struck the axial zone of the central Apennine fold‐and‐thrust belt between 1979 (Valnerina sequence) and 2016-2017 (Amatrice-Visso-Norcia sequence) also involving the northern area of the CAFS and its southern border (1997 Colfiorito-Sellano and 2009 L’Aquila sequences, respectively) causing severe damages and several casualties, leading to awaken interest in the study of the seismic behavior of these seismogenic structures. In this study we reconstructed the CAFS seismic cycle (Tondi and cello, 2003) considering the 3 time-windows of seismicity over the last millennium and investigated the role of Coulomb stress transfer in promoting or inhibiting ruptures of neighboring faults. We conducted specific analyzes to understand how the permanent static stress change can affect either the individual seismic phases and the entire seismic cycle. Furthermore, considering the importance of fault geometry in influencing the result, we analyzed the effect of three-dimensional elliptical fault geometries in modelling static Coulomb stress transfer. In order to reduce critical simplifications during the workflow, we tested a new detailed and multidisciplinary approach. We first selected 5 earthquakes from the ISIDe (Italian Seismological Instrumental and Parametric Data-Base) catalogue with Mw≥5.8 and 13 historical earthquakes from the CPTI15 (Catalogo Parametrico dei Terremoti Italiani) catalogue with Mw≥6 (Fig.1). Different magnitude thresholds between historical and instrumentals datasets were adopted to overcome the likely overestimation of the estimated magnitude for historical events (Vannucci et al. , 2021 and references therein). A causative fault has been associated to each studied earthquake after a detailed scrutiny of fault-related data present in literature (i.e., paleoseismological, structural, macroseismic). Secondly, the most reliable fault traces, with solid field-based constrains from literature (Tondi, 2000; Galderisi and Galli, 2020; Tondi et al. , 2020; Galli et al. , 2022 and references therein), have been elaborated in a Geographic Information System, GIS (Fig.1). The fault dataset was compiled with the following fields: i) fault name, ii) dip angle, iii) rake (using the Aki and Richards (1980) conventions), iv) dip direction, and v) length. We estimated the seismic moment released by historical earthquakes and compared seismic energy released during the main time-windows of seismicity that clustered in the CAFS area together with the coseismic and cumulative displacements computed by these faults to better constrain the spatiotemporal evolution of the CAFS seismic cycle. To analyze how faults interacted we propose a novel approach to model seismogenic sources for coulomb stress transfer calculation purposes. This approach adopts as a cornerstone the hypothesis that the most reliable approximation of 2D-fault geometry is an ellipse (Barnett et al. , 1987; Walsh and Watterson,1987; Gupta and Scholz, 2000), this concept is strictly related to the variation in displacement that ranges from a maximum at the center of the fault to zero at the elliptical tip-line loop. Furthermore, faults are frequently modelled as planar geometries in coulomb calculations but as demonstrated by