GNGTS 2013 - Atti del 32° Convegno Nazionale

New data on the Pollino and Castrovillari faults: filling the gap between paleoseismology and historical seismicity L. Alfonsi 3 , A. Berlusconi 1 , F. R. Cinti 2 , R. Civico 2 , P.M. De Martini 2 , M.F. Ferrario 1 , R. Gambillara 1 , F. Livio 1 , A.M. Michetti 1 , D. Pantosti 2 , S. Pinzi 2 1 Università dell’Insubria, Como, Italy 2 Istituto Nazionale di Geofisica e Vulcanologia (INGV) - Roma 1, Italy 3 Istituto Nazionale di Geofisica e Vulcanologia (INGV) - Roma 2, Italy Introduction. The Pollino Range is the southernmost segment of the Southern Apennines at the boundary with the Calabrian Arc. Crustal extension characterized this region during the Quaternary creating a system of tectonic basins and is still active today as shown by geological and seismological data (e.g., Cinti et al. , 1997, 2002; Michetti et al. , 1997, 2000a; Fig. 1). Be- tween June 2010 and 2012 the northern part of the Pollino foothills experienced a seismic swarm, culminating in a M = 5.0 event on night of the the October 25 th , 2012 (ISIDe, 2012; Fig. 1a). Several strong, Io = X MCS, earthquakes (e.g., Rovida et al. 2011) occurred to the N (e.g., 1857 Val D’Agri) and to the S (e.g., 1638 Valle del Crati) nevertheless no known historical seismic events of intensity greater than Io =VIII MCS originated in the Pollino area. The seismic catalogue only includes a seismic sequence interesting the region in the 1693; thus making this area one of the most obvious seismic gaps along the central and southern Apennines. This apparent lack of historical seismicity can be caused by the long recurrence interval characterizing the seismogenic sources of this area and/or may be due to the loss of historical sources recording those events. For these reasons during the ‘90s two different research groups took the first steps in investigating the paleoseismology of two of the main faults of the area: the Pollino and the Castrovillari faults, respectively bordering to the south the Pollino Range and crosscutting the Castrovillari basin (Cinti et al. , 1997, 2002; Michetti et al. , 1997). Both the research projects testified Middle Pleistocene to Holocene faulting along these structures and, for both, recognized the occurrence of paleoearthquakes during historical times. Even if there was a general agreement about the occurrence and timing of the faults activity, coming from dating of the paleoearthquakes on both the structures, still exist some open questions about i.e. the possible linkage of the two structures, their deep geometry and recurrence interval.In order to solve some of these issues, in the framework of the of Project S1, DPC-INGV 2012-2013, we studied the Pollino and Castrovillari faults integrating on-fault field survey, paleoseismological analysis and geophysical data acquisition (GPR and ERT). In particular, in recent years, the electrical imaging techniques have been largely applied in near-surface geophysics giving significant results to solve a wide range of geological problems, including the imaging and characterization of active faults (e.g., Caputo et al. , 2003). The geophysical survey was acquired using a PASI® instrument, composed of a PC resistimeter, charged by a 12V–45A battery, 32 steel pikes for voltage measurement divided into two sets of 16 pikes each one and connected by two isolated cables and through two link- boxes to a booster. The sections were acquired using Wenner, Wenner-Schlumberger or dipole-dipole arrays and spacing ranges between 2 and 5 according to the geometry and the estimated depth of the target. Sections were georeferenced through a GPS (horizontal accuracy: 4–6 m) and electrodes position was surveyed, for vertical topographic correction, with a Total Station (sub- cm accuracy). Signal has been processed using the Res2DinV software. The Castrovillari fault. The Castrovillari fault (Fig. 1b) is located in the Castrovillari basin, at the foothills of the Pollino Range, and is composed of three main WSW-dipping normal-fault scarps. The scarps run for ca. 10 km across the Castrovillari basin. Previous paleoseismological studies (Cinti et al. 1997, 2002) indicate that the most recent reactivation of this fault lies between 530 A.D. and 1100 A.D. We selected two investigation sites along the Castrovillari fault: Cozzo S. Elia and Castrovillari site. 109 GNGTS 2013 S essione 1.1