Volcanic
infrasound is useful because it is a close representation of material accelerations
at the volcanic vent. A first order
observation, that is not immediately possible with seismology, is
that the duration of an infrasonic transient is directly related
to the source process at the volcanic vent.
A short acoustic waveform, for instance, reflects an
short-duration volcano source, perhaps continued degassing. The duration of a seismic
signal is a function of both the source process and reverberations,
echos, reflections, and different wave speeds inside the volcano.
The
signal on the next page, for instance is an eruption from Erebus, in which the
acoustic pulse (red) represents an explosive bubble burst at the
surface of the lava lake.
The short-period seismic response (blue) is most likely complex
‘ringing’ of the edifice.