Seismological features of the Pernicana–Provenzana Fault System (Mt. Etna, Italy) and implications for the dynamics of northeastern flank of the volcano S. Alparone, O. Cocina, S. Gambino, A. Mostaccio, S. Spampinato, T. Tuvè, A. Ursino ⁎ Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo-Sezione di Catania, Piazza Roma, 2, 95125 Catania, Italy abstract article info Article history: Received 12 June 2011 Accepted 24 March 2012 Available online 1 April 2012 Keywords: Etna volcano Pernicana–Provenzana Fault System Earthquakes Precise location Fault plane solutions Seismic strain release The Pernicana–Provenzana Fault System is one of the most active tectonic systems of Mt. Etna and it plays an important role in the dynamic of the eastern flank of the volcano. Earthquakes occurring close to this structural trend have reached magnitudes up to 4.2, sometimes with coseismic surface faulting, and have caused severe damages to tourist resorts and villages in the vicinity of this structure. In the last decade, a large number of shocks, sometimes in the form of swarms, linked to Pernicana–Provenzana Fault System movements have been detected by the permanent local seismic network operating in eastern Sicily. In this paper, we report on the detailed study of the seismic activity occurring during the 2000–2009 time span in the Pernicana–Provenzana Fault System area. Firstly, we located 407 earthquakes using a standard location code and a 1D crustal velocity model. We then applied two different approaches to calculate precise hypocenter locations of the events. In particular, a non-linear code was adopted to obtain an estimate of the a posteriori Probability Density Function in 3D space for the hypocenter location. Moreover, a relative location of correlated event pairs was performed, using the double-difference method. These two different location approaches allowed defining with good accuracy, the most active and hazarding sectors of the structure. The results of these precise locations showed a tighter clustering in the epicenters and in focal depths, in comparison with standard locations. Earthquakes are located along the Pernicana–Provenzana Fault System, and are mainly clustered in two zones, separated by an area with very low rate of earthquakes occurrence, but characterized by the highest energy release. Depths of the foci are very shallow, ranging between the surface and about 3 km b.s.l. Kinematics of the Pernicana–Provenzana Fault System, revealed by the fault plane solutions computed for the most energetic earthquakes, highlights a predominant dip–slip and left strike movements along E–W oriented fault planes, in agreement with field observations. © 2012 Elsevier B.V. All rights reserved. 1. Introduction The Pernicana–Provenzana Fault System (PPFS, hereafter) is located in the northeastern sector of Etna, a basaltic composite strato-volcano, located in eastern Sicily along the Ionian coast. Two main structural systems, NNW–SSE and NE–SW oriented, are recognizable in the Etna area (Bonaccorso et al., 1996; Patanè et al., 2005). The NNW–SSE structural trend is mainly represented in the southeastern flank of the volcano and, according to Bousquet and Lanzafame (2004), it represents the northernmost prolongation of the Malta Escarpment, a morphological expression of a lithospheric system (Fig. 1). The NE–SW structural trend is recognizable in the northern part of the volcanic edifice, even if the detection of hidden segments in the southwestern and western sectors of the edifice allows to suppose that it involves the whole Etna area (Azzaro, 1999; Bonaccorso et al., 2004). Mount Etna is characterized by a complex geodynamic setting determined by a compressive N–S stress regime related to the Africa– Europe collision (Cocina et al., 1997; Bousquet and Lanzafame, 2004), and an ESE–WNW extensional one, clearly recognizable in the eastern coast of Sicily (Monaco et al., 2005). Moreover, an important role is played by the local stress field induced by volcano-related processes which interacts with the regional tectonics of the area (Cocina et al., 1998). The eastern and southern flanks of the volcano are affected by a continuous ESE seaward sliding, involving an area of about 700 km 2 , due to the interrelationship between gravity instability and magma intrusion (e.g. Borgia et al., 1992; Lo Giudice and Rasà, 1992; Rust and Neri, 1996; Acocella et al., 2003; Walter et al., 2005; Solaro et al., 2010). The PPFS appears to have an important role in the dynamic of the eastern flank of the volcano, and it is considered to represent the northern boundary of this unstable sector (Fig. 1). The PPFS is made up of several seismotectonic structures with a prevalent E–W orientation, which greatly contrast with the orientation of the main structural trends recognizable in the Etna region (Rasà et al., 1982; Azzaro et al., 1988). The morphological evidence of the PPFS can be followed on the surface for about 11 km (Bonforte et al., 2007). From West to East, it intersects the NE Rift (1900 m a.s.l.), one of the main magma intrusion zones of the Journal of Volcanology and Geothermal Research 251 (2013) 16–26 ⁎ Corresponding author. Tel.: + 39 095 7165800; fax: + 39 095 7165826. E-mail address: andrea.ursino@ct.ingv.it (A. Ursino). 0377-0273/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.jvolgeores.2012.03.010 Contents lists available at SciVerse ScienceDirect Journal of Volcanology and Geothermal Research journal homepage: www.elsevier.com/locate/jvolgeores