Spectral analysis of volcanic tremor associated with the 1993 paroxysmal events at Stromboli

1993 was characterized by three paroxysmal phases at Stromboli: two (February and October) consisted of a series of violent explosions, the third (May) of strong Strombolian activity, accompanied by a small lava flow. This paper investigates the characteristics of the tremor before, during and after these paroxysmal phases. The three phases analysed mark a considerable change in the dynamics of the volcano. The energy content drops to very low values after the periods of intense activity. A continuous monitoring of the spectral content of volcanic tremor on Stromboli can be a useful tool to identify the beginning of an instability which may lead to a paroxysmal phase.