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

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.