The ground displacement in the near-field of the seismo-volcanic source on Stromboli is characterised by a wide frequency content ranging from 30Hz to 0.002Hz. In order to interpret the recorded signals in terms of physical source processes, the seismic instrument response must be removed as completely as possible.

We demonstrate that frequency components as low as  0.001Hz must be taken into account to recover the full waveform of the ground displacement. Furthermore, the horizontal components of the seismic recordings in the near-field of the source are contaminated by the superposition of surface tilt. The fact that the vertical seismic component is not affected by tilt allows us to remove this tilt effect. Finally, the resulting signal can be analysed in terms of volcanic source processes.

We employ a frequency-wavenumber method and model several types of possible volcanic source processes. Stromboli's seismo-volcanic source is located at sea level (600m below the craters) and has the characteristics of a point source exhibiting a very slow inflation and deflation that last for several tens of seconds,  to which the actual Strombolian eruption is superimposed.


Fig : Restitution process with indicated lowest frequency content; energy at 500s and 1000s period contributes to the waveform and must  be taken into account.