Highlights from a seismic broadband array on Stromboli

An array of nine three-component broadband seismometers was deployed in two different configurations on Stromboli volcano. The analysis of the seismic wavefield related to volcanic explosions revealed some observations which offer a completely new insight into the internal dynamics of a volcano. These new observations are restricted to the low-frequency range below 1 Hz and underline, therefore, the superiority of broadband recordings over conventional short-period observations. Surprisingly simple wavelets indicate an initially contracting source mechanism. Gas-jets that could not be seen in a short-period seismic record at all, generate a clear dilatational wavelet in a broadband recording suggesting the same contracting source mechanism. The analysis of particle motion and seismic array techniques permits a location of the seismic source. We find low-frequency signals of 3s and 6s period that are not related to eruptions and do not share a common source with the eruption-related events. A video recording of visible volcanic activity at the crater region allows one to correlate precisely eruptive features with seismic signals.