The Campania‐Lucania Extensional Fault System, southern Italy: A suggestion for a uniform model of active extension in the Italian Apennines

Abstract

[1] By integrating new field data, seismic lines interpretation and a critical review of the literature, this work highlights a regional array of normal faults in the southern Apennines of Italy, which have been active during the Quaternary and are referred to as the "Campania-Lucania Extensional Fault System" (CLEFS). The CLEFS consists of three main NW-SE striking alignments of normal faults, which for the first time are considered genetically linked and methodically described in their geometry, kinematics and displacement. The CROP04 seismic profile, crossing the central part of the CLEFS, was strictly constrained by detailed geological surveys and reinterpreted to define the downdip trajectory of the major normal faults. These latter have been observed to splay from an east dipping low-angle detachment surface penetrating the upper crust to depths of 12-13 km. The time-space evolution of the faults and the associated basins was defined through a review of the stratigraphic data on the syntectonic deposits. As regards the overall geometry and the associate sense of shear (top-to-east), the CLEFS sensibly differs from the extensional features described previously in this region but shows surprising affinities with the "Etrurian Fault System," an extensional megastructure of the northern Apennines. Remarkable similarities concern the extent, the surface and subsurface geometry, the timing of activity and the amount of the associated deformation. These common characters recognized over a belt nearly 600 km long lead to formulation of a low-angle normal fault-driven extension geometrical-kinematic model, which is sound for the whole active extensional belt of Italy.

The 2013–2018 Matese and Beneventano Seismic Sequences (Central–Southern Apennines): New Constraints on the Hypocentral Depth Determination

“…The extensional structures of the southern Apennines are known mainly at the surface or in their shallow expressions. Brozzetti (2011) [24] investigated the deep geometry of these structures by integrating new field data with seismic lines interpretation.…”

“…As a result, the Tyrrhenian back-arc basin opened and the upper mantle is kinematically required to compensate the slab retreat at depth [20,21]. As a result of previous compression activity, the active NW-SE striking extensional faults are superposed into earlier thrust and transpressional deformation [22][23][24]. Being shallower the mantle in the Tyrrhenian side, the western Apennines have a heat flow of around 60-80 mW/m 2 , whereas it decreases to 30-40 mW/m 2 in the central and eastern side of the Apennines and in the study area [25] above the subduction hinge.…”

Belt-Parallel Shortening in the Northern Apennines and Seismotectonic Implications

“…When a strong shock occurs at the inner extensional decoupling boundary of the MS wedge (Irpinia-Benevento-Matese fault system [8] [27]- [29]) that block accelerates, increasing its belt-parallel push on the eastern part of the LA platform. This indentation induces shear stress at the sinistral transtensional faults (L'Aquila and Fucino [4] [8] [23] [30] [31]), that are located at the boundary between the stressed and non-stressed sectors of LA.…”

A soft linkage between major seismogenic fault systems in the central-southern Apennines (Italy): Evidence from low-magnitude seismicity

“…Based on the seismicity data presented in this work, their distribution, and the general constraints of the transfer model, we favor the soft linkage transfer model. (M w N 5.5) occurs in long (50, 100 or more km) fault systems, regardless of their kinematics (for a summary: Basili et al, 2008;Bigi et al, 1992;DISS Working Group, 2010;Kastelic et al, 2013;Patacca and Scandone, 2004) -a view in part shared also by Brozzetti (2011). After all, fault systems exhibit continuity along strike until adverse constraints occur (Ramsay and Huber, 1987;Wezel, 1986), such as a pre-existing deep-seated ramp, a major structural discontinuity, or a critical shift of topographic and/or tectonic load.…”

“…Brown dots indicate instrumental seismicity from 1981 to 2011 (Castello et al, 2006;ISIDe, 2010). Focal mechanisms of key events (with date; size proportional to M w ) are from: Boncio et al (2004), Frepoli and Amato (2000), Gasparini et al (1985), Herrmann and Malagnini (2011), Pondrelli et al (2006, 2011, and Vannucci and Gasperini (2004). Dates are in yyyy mm dd format.…”