Fault creep and kinematics of the eastern segment of the Pernicana Fault (Mt. Etna, Italy) derived from geodetic observations and their tectonic significance

Abstract

Aseismic fault displacements related to numerous fast-slipping active faults are frequently observed on Mt. Etna, but the characteristics and the rate of displacements, along with the behaviour of individual fault segments, are poorly constrained. To resolve this, we installed two local geodetic networks in 1997 along the eastern segment of the Pernicana Fault, one of the most active structures in the geodynamic framework of the volcano. The networks are based on the electroptical distance measurements (EDM) and global positioning system (GPS) techniques and consist of four and six benchmarks, respectively. Geodetic data confirm that the tectonic activity of the eastern Pernicana Fault is controlled by fault creep, i.e. a near-continuous stable sliding at a mean slip-rate of 2.8 cm/yr punctuated by aseismic displacement episodes. The analysis of the strain tensor calculated from the EDM and GPS data indicates that deformation in the fault zone is related to a clear sinistral strike-slip movement. A more complete picture is obtained from the GPS measurements for the Rocca Campana area, where the main structure branches out eastward into a splay fault. The inversion of 3D displacement vectors suggests a deformation model consisting of two principal sinistral strike-slip faults with an oblique component of movement. The maximum observed displacement, 6.1 cm measured in the period April 1997–February 1999, is accommodated by the splay fault. This finding corroborates the hypothesis that, as proposed by the tectonic models in the literature, the movement of the eastern segment of the Pernicana Fault is transferred easterly towards structures at a lower altitude along the same strike (e.g. the Fiumefreddo Fault). As a consequence, the Pernicana Fault may constitute part of a continuous left-lateral trans-current zone, which displaces the whole north-eastern flank of Mt. Etna.