Recent deep earthquake occurrence at Mt. Etna (Sicily, Italy)

Abstract

The seismic activity of Mt. Etna from April 1988 until the December 1991 eruption was monitored by means of permanent and temporary seismic networks. Volcanic activity that occurred during this period (tremor increase with lava fountains at the Summit Craters and eruptions) was preceded and accompanied by the occurrence of deep ( Z ≥ 15 km) seismicity. This deep seismic activity, occurring a few days up to some weeks before the volcanic phases, was characterized by typical mainshock-aftershocks sequences. Focal mechanisms of the more energetic events which preceded the eruptions show that the compression axis was nearly north-south, parallel to the direction of the compressive stress field acting in the area at regional scale. Both the observation of deep seismicity occurrence also before or during previous eruptions and the role played by tectonics as controller of the magma uprise suggest the hypothesis of a relation between the seismic energy released in the volcanic basement and the recharge mechanisms of the volcanic system. In this hypothesis the deep seismicity located in the Etnean area could be considered as a possible ‘forerunner’ of volcanic activity.