by Philip M Benson, Sergio Vinciguerra, Philip G Meredith, and R Paul Young

Physical processes generating seismicity within volcanic edifices are highly complex and
remain not fully understood. We report results from a laboratory experiment in which basalt from
Mount Etna volcano (Italy) was deformed and fractured. The experiment was monitored using an
array of transducers around the sample to permit full-waveform capture, location and analysis of
microseismic events. Rapid, post-failure decompression of the water-filled pore volume and
damage zone triggered many low frequency events, analogous to volcanic long period seismicity.
The low-frequencies were associated with pore fluid decompression and were located in the
damage zone in the fractured sample; these events exhibited a weak component of shear
(double-couple) slip, consistent with fluid-driven events occurring beneath active volcanoes.

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