GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 1.2 161 STRUCTURAL STYLE OF SEISMOGENIC EXTENSION IN CENTRAL ITALY – A 3D INSIGHT FROM L’AQUILA 2009 AND CENTRAL ITALY 2016-17 SEISMIC SEQUENCES G. Lavecchia, R. de Nardis, F. Ferrarini, D. Cirillo, F. Brozzetti CRUST-DiSPUTer, Università G. d’Annunzio, Chieti, Italy Fundamental aspects to be addressed in the understanding of seismogenic fault systems regards, on one side, the recognition of the long-term structural style of the active deformation field at a regional-scale and, on the other, the recognition of the locally active fault system and stress field and the reconstruction of the process of progressive fault development. The latter, in turn, contributes to control the nucleation, development and arrest of earthquakes and seismic sequences. A 3D approach to reconstruct the active fault geometry and to build a database of detailed, non-planar, seismogenic and potentially active fault segments is an essential tool for seismic hazard evaluations. To reach this goal and to fully constrain the fault geometry, high-quality geological and seismological data are both necessary, together with a deep knowledge of the regional seismotectonics of the area. An excellent laboratory for such purpose is represented by the sector of the Intra-Apennine extensional belt struck by the L’Aquila 2009 Seismic Sequence (AQSS) and by the 2016-2017 Central Italy Seismic Sequence (CISS) (Fig.1). Within a lapse of three days (6 to 9 April 2009), AQSS released three events with magnitude decreasing from M w 6.3 to 5.5, which activated two independent en-echelon west-dipping fault segments (Paganica and southern Gorzano faults) and the underlying common east-dipping detachment (Lavecchia et al. , 2012). Coseismic surface fractures for a total length of 13 km were surveyed along the trace of the Paganica fault (Boncio et al. , 2010). Fig. 1 - From Lavecchia et al. (2016): a) location map of the L’Aquila 2009 Seismic Sequence (AQSS) and of the Central Italy Seismic sequence (CISS); V, G and P = Vettore, Gorzano, Paganica master faults; b) schematic view of the East-dipping Extensional Fault System (EFS) and of the outer front of the Umbria-Marche-Abruzzi (UMA) SW- dipping Quaternary extensional belt; c) sketch model of the spatial relationships between the east-dipping extensional detachment and the antithetic SW-dipping high-angle normal faults responsible for most of the energetic intra-Apennine extensional earthquakes.