High-frequency volcano seismic tremor at Mt. Etna, Italy: Insights from varying seismic-acoustic amplitude ratios

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

We present a comprehensive, high-resolution seismic and acoustic datasets from Mt. Etna, Italy acquired
through a large, unprecedented deployment of seismometers and microphones in the summit region during
summer 2022, highlighting about 50 rarely reported high-frequency (12–15 Hz), short-duration, minute- to
half an hour-long volcanic seismic tremor episodes. These events exhibit variable seismic-acoustic amplitude
ratios, implying multiple triggering mechanisms. Evidenced by coincident acoustic signals at different distinct
frequencies our analysis suggests that while some tremor occurrences are indirectly associated with degassing
processes other examples of high-frequency tremor lack any acoustic counterpart, indicating that vigorous
degassing and thus fluid migration might not be a primary driver 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 on numerical simulations of seismic event generation in typical
low-stiffness volcanic materials as well as laboratory experiments with volcanic samples under stress and helps
explain shallow seismic tremor episodes in the absence of acoustic signals.