Observations and interpretations of high-frequency volcanic tremor produced under varying seismic-acoustic amplitude ratios on Mt. Etna

Maurice Weber, Christopher J. Bean, Ivan Lokmer, Silvio De Angelis, Luciano Zuccarello

We present a comprehensive, high-resolution seismic-acoustic dataset from Mt. Etna acquired
through a large, unprecedented deployment of seismometers and microphones in the summit
region, highlighting rarely reported high-frequency (12–15Hz), short-duration volcanic tremor
episodes. These events exhibit variable seismic-acoustic amplitude ratios, implying multiple
triggering mechanisms. Our analysis suggests that while some tremor occurrences are indirectly
associated with degassing processes — evidenced by coincident acoustic signals at different
distinct frequencies — others lack any acoustic counterpart, indicating that degassing and
thus fluid migration are not a necessary condition for tremor generation. We propose that in
addition to traditional models requiring fluid movement for tremor generation, quasi-brittle,
mesoscale failure within weak edifice material may act as a direct source mechanism radiating
high-frequency tremor. This interpretation aligns with prior studies and helps explain shallow
seismic tremor episodes in the absence of acoustic signals.