435 Early Pleistocene to late Holocene activity of the Magnola fault (Fucino fault system, central Italy) P. GALLI 1,2 , P. MESSINA 2 , B. GIACCIO 2 , E. PERONACE 2 , and B. QUADRIO 2 1 Dipartimento Protezione Civile Nazionale, Rome, Italy 2 Ist. Geologia Ambientale e Geoingegneria, C. N. R., Montelibretti (Monterotondo), Italy (Received: July 4, 2011; accepted: December 16, 2011) ABSTRACT. The Magnola Mounts (the Abruzzi, central Italy) are bound towards the Fucino Plain by a steep fault slope that is marked at its base by a continuous rock fault scarp (a “nastro”, in Italian). In the Apennines, this particular feature is often interpreted a priori as evidence of Holocene tectonic activity, although sometimes climate-related exhumation processes or gravity-driven phenomena can generate such geomorphic markers. To unravel this possibility, we searched for field geological indications, and here report on our findings of both long-term and short-term evidence concerning the activity of the Quaternary Magnola fault. Paleoseismological analysis carried out across the talus resting against the rock fault plane revealed evidence of repeated surface rupture events from, and during, the Holocene, to historic times. Following a comparison of the ages of these events with those already known for the Fucino Basin faults, we argue that the Magnola fault acts as the north-western-most strand of the Fucino fault system, which is, in turn, the structure that was responsible for the devastating 1915, M W 7, earthquake, as for other earthquakes in the past. Key words. Active faults, paleoseismology, earthquakes, fault segmentation, fault interaction, central Italy. 1. introduction After the 2009 L’Aquila earthquake [M W 6.3, the Abruzzi, central Italy; Amato et al. (2011) and reference therein], what we definitely learned is that within the structural, lithological and climatic context of the central Apennines, the geological signature of seismogenic faults that are responsible for such, or larger, crustal events can be reasonably identified on the landscape surface. The morphological and/or tectonic indications can range from displaced Late Pleistocene deposits and forms, to rock-fault scarps carved into the substratum (known as “nastri” in the Italian literature), as with those that characterize the southwestern slopes of many mountain ranges in the Abruzzi (see Bosi, 1975). For instance, in the 2009 epicentral area, as well as faulted Pleistocene deposits and paleosurfaces, the evidence of recent fault activity can be seen in the presence of a discontinuous nastro that affects both the Mesozoic limestone and the Early Quaternary conglomerates [Paganica–San Demetrio fault system; PSDFS; see Fig. 1: Galli et al. (2010c, 2011)]. However, in this case, earthquake geologists have only collected these indications ex post, thus meaning that the seismic hazard related to the PSDFS has never been fully and correctly assessed. On the other hand, if a fault is considered as active (e.g., Bartolini, 2010), in want of robust and integrated field geological constraints (stratigraphical, geomorphological, paleoseismological) Bollettino di Geofisica Teorica ed Applicata Vol. 53, n. 4, pp. 435-458; December 2012 DOI 10.4430/bgta0054 © 2012 – OGS