Fault Pattern and Seismotectonic Style of the Campania – Lucania 1980 Earthquake (Mw 6.9, Southern Italy): New Multidisciplinary Constraints

Abstract

New fault trace mapping and structural survey of the active faults outcropping within the epicentral area of the Campania-Lucania 1980 normal fault earthquake (Mw 6.9) are integrated with a revision of pre-existing earthquake data and with an updated interpretation of the CROP-04 near-vertical seismic profile to reconstruct the surface and depth geometry, the kinematics and stress tensor of the seismogenic fault pattern. Three main fault alignments, organized in high-angle en-echelon segments of several kilometers in length, are identified and characterized. The inner and intermediate ones, i.e. Inner Irpinia (InIF) and Irpinia Faults (IF), dip eastward; the outer Antithetic Fault (AFA) dips westward. Both the InIF and the IF strike NW-SE along the northern and central segments and rotate to W-E along the southern segments for at least 16 km. We provide evidence of surface coseismic faulting (up to 1 m) not recognized before along the E-W segments and document coseismic ruptures with maximum vertical displacement up to ∼1 m where already surveyed from other investigators 40 years ago. Fault/slip data from surface data and a new compilation of focal mechanisms (1980 – 2018) were used for strain and stress analyses to show a coherent NNE-directed least principal stress over time and at different crustal depths, with a crustal-scale deviation from the classic SW-NE tensional direction across the Apennines of Italy. The continuation at depth of the outcropping faults is analyzed along the trace of the CROP-04 profile and with available hypocentral distributions. Integrating all information, a 3D seismotectonic model, extrapolated to the base of the seismogenic layer, is built. It outlines a graben-like structure with a southern E-W bend developed at depth shallower than 10–12 km, at the hanging wall of an extensional NE- to E-dipping extensional basal detachment. In our interpretation, such a configuration implies a control in the stress transfer during the 1980 earthquake ruptures and provides a new interpretation of the second sub-event, occurred at 20 s. Our reconstruction suggests that the latter ruptured a hanging wall NNE-dipping splay of the E-W striking main fault segment and possibly also an antithetic SSW-dipping splay, in two in-sequence episodes.

GPR signature of Quaternary faulting: a study from the Mt. Pollino region, southern Apennines, Italy

“…This set of conjugate SW-and NE-dipping normal faults represents the local expression of the Quaternary extensional belt that develops all along the Italian peninsula, nearly parallel to the axial zone of the Apennines, from northern Tuscany to the Calabrian Arc (Brozzetti 2011). North of Campotenese, (Lucania and southern Campania) the Apennine extensional belt includes several continental basins and their boundary faults, as the Irpinia, Vallo di Diano, Tanagro, Melandro-Pergola and Val d'Agri (Ascione et al 1992;Maschio et al 2005;Amicucci et al 2008;Villani and Pierdominici 2010;Brozzetti 2011;Seeber 2019 andBello et al 2021). To the south, it continues with the Crati graben that dissects the northern sector of the Calabrian Arc (Tortorici et al 1995;Brozzetti et al 2017b).…”

Structural complexities and tectonic barriers controlling recent seismic activity of the Pollino area (Calabria-Lucania, Southern Italy) – constraints from stress inversion and 3D fault model building

“…1a). From north to south they are: i) northern alignment: including the Irpinia fault and the Melandro-Pergola and Agri basins; ii) intermediate alignment: developing from the Tanagro-Vallo di Diano basins to the Mercure-Campotenese and Morano Calabro basins, and iii) southern alignment: from the Castrovillari fault to the southern Crati basin Valensise, 1990, 1993;Ascione et al, 2013;Galli and Peronace, 2014;Vezzani, 1982, 1983;Barchi et al, 1999Barchi et al, , 2007Blumetti et al, 2002;Amicucci et al, 2008;Maschio et al, 2005;Villani and Pierdominici, 2010;Brozzetti, 2011, Faure Walker et al, 2012Brozzetti et al, 2009Brozzetti et al, , 2017aBrozzetti et al, , 2017bRobustelli et al, 2014;Sgambato et al, 2020;Bello et al, 2021a).…”

“…We applied the methodology defined by the Community Fault Model of Southern California (Nicholson et al, 2014;Nicholson et al, 2015;Plesch et al, 2014) which was also used, in previous works, to depict the subsurface geometry of the faults reactivated during recent Italian earthquakes (Lavecchia et al, 2017;Castaldo et al, 2018;Bello et al, 2021a).…”

“…Following the approach adopted and described in literature for the 3D fault model building (Lavecchia et al, 2017;Castaldo et al, 2018;Bello et al, 2021a), we created several sets of closely spaced transects (half-width=2 km) to cross and sample the seismogenic fault zones in different directions (Fig. 6).…”

Joint Interpretation of Geophysical Results and Geological Observations for Detecting Buried Active Faults: The Case of the “Il Lago” Plain (Pettoranello del Molise, Italy)

“…In particular, active normal faults typically trigger rapid feedback response of surface processes, such as gravitational instability and erosional dismantling of the uplifted footwall blocks, coupled with enhanced sedimentation in the downthrown hanging wall counterpart (e.g., [1][2][3][4]). In the Southern Apennines of Italy, tectonically active extensional structures are characterized by low strain-rates and a tectonic architecture (e.g., [5][6][7] and reference therein) inherited from previous phases of shortening. Here, the identification and characterization of active faults is not always straightforward.…”