New evidence of wavefield polarization on fault zone in the lower NE slope of Mt. Etna

Fault zones are generally characterized by a damage zone, formed by highly fractured materials, that is seismically characteri -zed by low velocity and rigidity compared to the host rock. Suchgeometrical setting, coupled with impedance contrast, lead to thedevelopment of local amplification of the ground motion and directionaleffects. In the present study, the results of measurements performedin the lower north-eastern area of Mt. Etna are shown and discussed. Ambient noise data were recorded and processed through the horizontal to vertical spectral ratio technique, setting into evidencedirectional effects and providing a direct estimate of thepolarization angle as well. The data were recorded along and acrossthe Piedimonte-Fiumefreddo fault system, a set of NE-SW trendingextensional segmented faults, that is flanked by small conjugate segmentsand is accompanied by several WNW-ESE oriented minor faults and fractures of the Pernicana fault system. Results point out that in most of the investigated sites the pola -rization effects are nearly perpendicular with respect to the minorfaults, striking WNW-ESE. This highlight that the local extensionaldeformation field, related to the shear zone of the Pernicana faultsystem, plays an important role and it appears as the predominant one in the seismic response that characterize this tectonically complicatedarea.