GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 - POSTER GNGTS 2023 Recent experiences of projects which integrated several geological and geophysical approaches in the neighbor area affected by the 2016-17 seismic sequence (e.g., The RETRACE-3D project, www.retrace3d.it ; Buttinelli et al., 2021) show that the principal structures activated during the last sequence could be associated with inherited thrusts and normal faults reactivated within the current extensional regime. The comparison with independent data such as high-resolution seismic catalogs (e.g., Michele et al., 2020) contributed to validating such a view. Besides the relevant results in the 2016-2017 areas, the Colfiorito area lies right to the NW, where the 1997 sequence spread in a relatively smaller area. In this work, we present a preliminary study of a reappraisal 1997 Colfiorito seismic sequence. Using a combined dataset of seismic reflection profiles and deep boreholes, as well as detailed data from geological surveys, We show the construction of a new 3D geological and velocity model of the area, working independently from the earthquake information. In addition, the passive seismic data recorded by both the temporary and permanent seismic networks are also re-analyzed in order to compute a new 1-D relocation, using based support of the 3-D geological and new geophysical imaging of the shallow portion of the crust underneath the target area. The geological model mainly shows a substantially vertical and horizontal compartmentation of the shallow crust due to the action of the thrusts. The seismicity arranges by mimicking this organization of crustal volumes, and it seems to always localize at the same structural levels, both on pre-existing thrusts and normal faults structures, possibly reactivated during the sequences. The new 3D geological model could definitely help to shed light on the open question related to the seismogenic faults that generated the 1997 seismic sequence and on the mutual relationship between Quaternary normal faults and Tertiary thrusts. References Amato, A., R. Azzara, C. Chiarabba, G. B. Cimini, M. Cocco, M. Di Bona, L. Margheriti, S. Mazza, F. Mele, G. Selvaggi, A. Basili, E. Boschi, F. Courboulex, A. Deschamps, S. Gaffet, G. Bittarelli, L. Chiaraluce, D. Piccinini, and M. Ripepe (1998). The 1997 Umbria–Marche, Italy, earthquake sequence: a first look at the main shocks and aftershocks, Geophys. Res. Lett. 25, no. 15, 2861–2864 Antonioli, A., D. Piccinini, L. Chiaraluce, and M. Cocco (2005), Fluid flow and seismicity pattern: Evidence from the 1997 Umbria-Marche (central Italy) seismic sequence, Geophys. Res. Lett.,32, L10311, doi:10.1029/2004GL022256 Bally, A. W., L. Burbi, C. Cooper, and R. Ghelardoni (1986). Balanced sections and seismic reflection profiles across the central Apennines, Mem. Soc. Geol. Ital. 35, 257–310. Barchi, M., A. De Feyter, B. Magnani, G. Minelli, G. Pialli, and B. M. Sotera (1998). The structural style of the Umbria–Marche fold and thrust belt, Mem. Soc. Geol. It. 52, 557–578.