Recent seismicity of Mount Etna: implications for flank instability

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Abstract
This study considers seismic activity recorded beneath the low eastern flank of Etna during the period between April 1989 and December 1991 with the aim of placing some seismological constraints on the investigation of slope instability related to the gravitational sliding of this unsupported side of the volcano. The seismicity essentially consists of rather superficial ( z < 10 km for more than 90% of cases), low-magnitude (usually M < 3) earthquakes. Foci of earthquakes are clustered on the main fault systems crossing the region, such as the Santa Tecla fault and the San Leonardello fault system, that have in recent times produced earthquakes of unusually high intensity covering the whole of the Etnean area. The broad picture of seismicity may be partially attributed to the accumulation of stress related to the seaward displacement of moving blocks in the vicinity of the Valle del Bove and adjacent regions in response to the storage and release of elastic energy associated with frequent episodes of magma intrusion. We propose that eastward sliding probably involves a complicated ensemble of moving blocks, resting on shallow independent décollements rather than on a single, widespread decoupling surface.