Seismicity and active tectonics in the Etna Region: Constraints for a seismotectonic model

Abstract

Geodynamic processes at Etna are very fast and result from the interaction of volcano-related movements and regional tectonics. High rates of tectonic activity are indicated by (i) geological and paleoseismological data, with Holocene slip-rates varying from 1.0 to 2.7 mm/yr, (ii) aseismic creep affecting most of the structures of the volcano with short-term slip-rates up to 20 mm/yr, and (iii) frequent seismicity. In particular, the characteristics of shallow earthquakes occurring at Etna may provide effective evidence for the recognition of active faults and the assessment of their kinematics. These events commonly feature shallow foci (H < 5 km), moderate magnitudes (up to 4.9) but high macroseismic intensities reaching the IX-X grade EMS with short recurrence times (tens of years). Destructive effects and damage distributed along narrow areas astride the fault scarp often accompany extensive surface faulting, with end-to-end rupture lengths up to 6.5 km and vertical offsets up to 90 cm. Patterns of coseismic and creeping ground ruptures also reveal the occurrence of hidden faults at Etna, that represent discrete segments of major continuous fault zones previously mapped as distinct. In the present paper a review of long-term seismicity, tectonics and evidence of surface faulting phenomena is presented. The synthesis of previous data has allowed to characterise active faults in the Etna region and to propose a first seismotectonic model which encompasses the following features: i) geometry and kinematics of seismogenic faults; ii) length and behaviour of individual segments; iii) definition of seismic potential.