A multidisciplinary study of an active fault crossing urban areas: The Trecastagni Fault at Mt. Etna (Italy)

The Trecastagni Fault is a NNW–SSE tectonic structure in the densely inhabited southern flank of Mt. Etna, characterised by evident morphological scarps and movements of normal and right-lateral type that directly affect roads and buildings. The fault is affected by continuous dynamics with intermittent accelerations accompanied with shallow seismicity. It has an important role in the instability affecting Mt. Etna's south-eastern flank and represents part of the southern boundary of the unstable sector. The motion of the fault between 2005 and 2011 has been analysed by using a multi-disciplinary approach involving terrestrial and satellite ground deformation data. Active monitoring systems able to investigate the fault in detail are extensometers, a levelling network and InSAR. Two episodes of acceleration were recorded at the end of 2009 and during 2010. Data evidences that the acceleration episodes affected only portions of the fault and that stress may accumulate and be periodically released. Although both magmatic processes (inflation or intrusive episodes) and flank dynamics influence the occurrence of the TF acceleration episodes, the dragging effect of the overall seaward sliding of the south-eastern flank is evident and it causes the subsidence of the hangingwall, accumulating stress on the fault that is periodically seismically released.

► We detected episodic accelerations of the fault, accompanied by seismicity.
► These acceleration episodes may also affect only short portions of the fault.
► The dynamics of the TF appears to involve a thin crust.
► Activity of TF has to be related to the dragging effect of the sliding flank.
► The fault shows a main aseismic displacement, but there are some locked sectors.