Mount Etna is one of the most active and powerful basaltic volcanoes in the world, with an historical record of documented eruptions going back over 2000 years. It is located in eastern Sicily in a complex geodynamic framework, where major regional structural lineaments play a key role in the dynamic processes of the volcano [e.g., Bonaccorso et al., 1996]. Several years of structural and geophysical observations have revealed how the majority of the eruptive fracture systems activated in the last 30 years correspond to those of historical eruptions [e.g., Azzaro and Neri, 1992]. The orientation of the fractures coincides mostly with two structural trends, NNW-SSE and NE-SW, observed both in the volcanic area and in the regional context. These alignments are hypothesized to be the main volcano-genetic structures [e.g., Bonaccorso et al., 1996; Gresta et al., 1998] controlling the evolution of Mt. Etna, as their interference establishes a weak zone along which magma can rise from depth [Rasà et al., 1995]. In the second half of the last century, after nearly 20 years without any major flank eruption, a series of effusive eruptions started in 1971. In the following 15 years, fourteen main sub-terminal and/or flank eruptions affected different eruptive systems [e.g., Azzaro and Neri, 1992]. Afterwards, about two years withouth eruptive activity separated the October 1986-March 1987 eruption from that of 1989, which was one of the most important in terms of effusion rate. This eruption was probably preceded by a major intrusive episode [Ferrucci et al., 1993; Rymer et al., 1993] which also fed the 1991-1993 flank eruption. The latter was the most important lateral eruption at Mt. Etna in the last three centuries, both in terms of duration (476 days) and volume of lava erupted (ca. 250 x 106 m3). After the end of this eruption, volcanic activity was confined to the summit area until the July-August 2001 flank eruption.

Seismological observations have provided information on both the dynamics and structure of the volcano, in addition to their interaction with the regional tectonic structures. Today it appears clear that volcanism and tectonics in the Etnean area interact closely [e.g., Bonaccorso et al., 1996; Cocina et al., 1998; Bonaccorso, 2001; Bonaccorso and Patanè, 2001; Patanè and Privitera, 2001], although the problem of the driving mechanisms of magma upwelling remains an open question. Unfortunately, the local, permanent seismic network had a low density of stations prior to 1990 which severely affected hypocentral location constraints and our knowledge on magma dynamics in the shallower crust. Only from the early 1990's has seismic data been available in digital format for a significant number of stations as well as for three-component sensors [e.g., Patanè et al., 1999; Barberi et al., 2000; Patanè and Privitera, 2001; Patanè et al., 2003]. These improvements have allowed to put high-quality constraints on seismic activity occurring at almost all depths in recent years, and to perform studies which tackle the link between seismicity and eruptive activity.

In this paper we present an overview of seismic activity affecting the volcano in the period 1978-2001. In particular, we focus our attention on the years between 1988 and 2001. We discuss the interaction between the regional and local stress field in this time span, and define seismic constraints on the magma source which yielded eruptive activity.