GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 1.1 71 RECENT AND ACTIVE TECTONICS IN THE CAMPANIAN PLAIN BASED ON INTEGRATION OF FAULT KINEMATICS AND SEISMOLOGICAL DATA: PRELIMINARY RESULTS S. Forlano¹, L. Ferranti¹, G. Milano² 1 Dipartimento di Scienze della Terra, delle Risorse e dell’Ambiente, Università Federico II, Napoli, Italy 2 Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Napoli, Italy The Campanian Plain is a sector of Quaternary extension and subsidence on the Tyrrhenian margin of the Southern Apennines characterized by a complex evolutionary framework. From Pleistocene times extension was chiefly accommodated by E-W to NE-SW striking, listric- shaped normal faults, which caused domino-block faulting and growth of up to ~3.5 km deep extensional basins segmented by buried ridges (Milia et al. , 2003). Jointly with this articulated subsurface architecture, the Plain exhibits a low-energy historical and instrumental seismicity. The background seismicity in the Plain, with the exception of the local seismicity of Vesuvio and Campi Flegrei volcanic areas, is characterized prevalently by isolated events with magnitudes generally less than 3.0 even if seismic clusters are located close to the Massico Mountain and along the Avella Mountain (Gaudiosi et al. , 2012). So far, very few fault structural data were available to unravel the kinematic evolution of the plain. Similarly, no complete and detailed assessment of the instrumental seismicity and fault plane solutions outside the Neapolitan volcanic area are at present available. The aim of this study is to understand and reconstruct the structural setting and the kinematics evolution of the Campanian Plain and how active and seismogenic deformation is expressed in it. The choice of a multidisciplinary approach sees integration of geological-structural data and instrumental seismicity to link the long-term kinematics evolution and the present day seismogenic deformation. The study is focused on the tectonic borders of the Plain where the footwall of faults is exposed, and tectonic seismicity is present. We studied the geometry and kinematics of major and minor faults in the footwall of the primary faults buried in the subsurface (Bruno et al. 1998), as indicative of the extensional strain recorded on the latter faults. To characterize these structures at the border between the margin of the Plain and theApennine chain, structural and fault-slip data have been acquired and collected on ~280 fault planes at more than 80 sites along the flanks of the Plain. In particular, the analysis was concentrated along three of the main border ridges (Caserta, Avella and Sarno ridges) which extend along the western flank of the Apennines into the central portion of the plain. The ridges are dissected by faults with orientation from NW-SE to E-W. In each of these sectors, we observed superposition of two sets of slip lineations (S1, S2) on the major and minor fault surfaces. S1 and S2 slip lineations have both a moderate (~40° an average) and high (~80° on average) rake angle that indicate transtensional (left or right depending on fault orientation) or dip-slip motion, respectively. The existence of two sets of differently oriented slip lineations on the fault surfaces reveals two different kinematics regimes and related deformation events. The first set S1 is associated to normal and right-transtensional slip on NE-SW faults and minor left-transtensional slip on NW-SE and E-W striking faults. This lineation set defines an extensional T axis whose trend progressively switch from NNE- SSW (Sarno, Avella and in the southern portion of the Caserta ridge) to NNW-SSE (Caserta ridge) (Fig. 1). Based on morphostructural criteria, this first displacement is regarded as the major episode of slip recorded on the studied faults and it is responsible for the shape of the relief. A second set S2 of lineations developed primarily on NW-SE striking faults that had a normal to right-transtensional slip with a T axis that trends from ~NE-SW (central portion of the Caserta ridge) to ~E-W (Sarno and Avella ridges) (Fig. 1). Although this lineation set is subordinate relative to the first set, it is locally observed as the only kinematics as in the western