Some Pictures


fig1
Fig. 1. Mt. Etna Volcano. Waveform (detail) obtainined resampling 200 times the original digitalized waveform (linear interpolation)
fig2
Fig. 2. Mt. Etna Volcano. Spectrum (DFT) of the waveform in fig. 1, as calculated by the Java program


As it is possible to observe in fig. 5 and fig. 6, the resampled signals taken by the seismograph close to an eruption event, shows a clear variation in the time evolution of both the spectrum and the waveform profile. A strong increase of the amplitude and an enrichment of the spectrum thanks to the very low-frequency components (made visible and audible bythe resampling procedure) is clearly observable in the two figures and clearly recognizable if listened to.

fig3
Fig. 3. Mt. Etna Volcano. Waveform obtainined resampling 10 times the original digitalized waveform, using Sample and Hold method for interpolation

fig4
Fig. 4. Mt. Etna Volcano. Waveform obtained using a linear interpolation
among digital samples


fig5
Fig. 5. Mt. Etna Volcano. Detail of a waveform (after a pitch shift 200x) showing the beginning of an eruption phenomenon


fig6
Fig. 6. Mt. Etna Volcano. Sonogram of the waveform reported in fig. 5 the resampling procedure) is clearly observable in the two figures and clearly recognizable if listened to.