Multi-disciplinary Approach to the Study of the Pernicana Fault System, Mt. Etna, Sicily: Integration of Structural, Geodetic and Seismological Data

This contribution investigates the Pernicana Fault System (PFS), a seismogenic structure that dissects Mt. Etna (Sicily). The study was carried out through a multidisciplinary approach based on integration of structural, geodetic and seismological data, with the aim to produce a consistent model for this complex sector of the volcano edifice. The PFS is a W-E trending fault array, organized into segments arranged en-échelon, and displays a dominantly left lateral component of strike-slip. From West to East it joins the NE-Rift (1900 m a.s.l.), crossing Piano Provenzana and Piano Pernicana, and reaches Rocca Pignatello (1050 m a.s.l.) and Rocca Campana (900 m a.s.l.) where the fault branches out SE-wards into two fault segments. The former shows a roughly N105°E orientation from Rocca Pignatello to Rocca Campana, where the fault rotates to N090°E and terminates without morphological evidence; the latter propagates downhill from Rocca Campana with a roughly N120°E orientation. During the 2002-03 Mt. Etna eruption, an intense ground-fracturing phenomenon affected the entire NE flank, allowing to identify the development of the N120°E fault segment and to trace it down to the Ionian coast. The work has been carried out with different approaches: structural analysis, to identify the kinematics and geometry of the fault system through the study of well-recognized structural marker; seismology, based on the analysis of focal mechanisms in order to unravel the dynamics of the system, and space geodesy, in order to infer the recent ground motions due to slip along the PFS. Three main segments are recognised within the PFS: a western, a central and an eastern segment. The western and eastern segments indicate dominantly transtensional kinematics, with both important normal and strike-slip displacements, whereas the central segment best illustrates the effects of the strike-slip component. This segment was monitored with local networks based on GPS techniques since early 1997. GPS data indicate daily displacement vectors up to 50 cm as recorded during the first days of the 2002-03 eruptive event of the Mt. Etna volcano. These data collectively indicate a sliding towards SE of the southern block identified by the PFS. The analysis of focal mechanisms is in general agreement with data inferred from structural analysis and GPS techniques, indicating a good kinematic and dynamic consistency. The eastern segment of the PFS is characterised by a low seismic activity and by the lack of recent earthquakes, therefore outlining that this part of the PFS is dominated by aseismic creep.