HIGH-FREQUENCY WAVE-PROPAGATION FROM MANTLE EARTHQUAKES IN THE TYRRHENIAN-SEA - NEW CONSTRAINTS FOR THE GEOMETRY OF THE SOUTH TYRRHENIAN SUBDUCTION ZONE

Propagation of shear waves produced by 25 mantle earthquakes (80-600 k m depth) in the subduction zone of the south Tyrrhenian Sea (southern Italy) has been investigated to infer the geometry and extent of the d escending lithosphere. From all hypocentral depths high-frequency, hig h-amplitude shear waves are recorded at most of the stations in southe rn Italy and easternmost Sicily. This shear-wave energy is interpreted to travel as a guided wave within the descending slab. In contrast, s hear waves are either not recorded at all or they are recorded as low- frequency, low-amplitude signals at stations located in the peninsular part of Italy north of the Calabrian are, in western Sicily and in Sa rdinia. This systematic S-wave attenuation is interpreted in terms of an active and continuous slab correlated with and limited to the Calab rian arc.