Volcanic tremor and long period events at Mt. Etna: Same mechanism at different rates or not?

Abstract

Volcanic tremor and long period (LP) events are typical seismic signals recorded on active volcanoes and are characterized by different durations, longer than minutes and a few seconds - tens of seconds for the former and latter, respectively. As they share the same frequency content, they are often grouped together in the literature and referred to by the unique name of LP seismicity. The common spectral features, together with observations in some volcanoes of individual LP events merging to form volcanic tremor, led to hypotheses that LP events and volcanic tremor share the same source mechanism. However, it is still open to debate whether volcanic tremor can be considered a simple coalescence of LP events or not. In this work, to help answer such a question, we analysed volcanic tremor and LP events recorded at Mt. Etna during the period February 2019–June 2020, characterized by minor eruptive activity, varying from weak ash emission to explosive and effusive eruptions at all the summit craters. Results from spectral, amplitude and location analyses, as well as the different scaling laws explaining the distributions of the duration/number of events versus size, led us to infer that LP events and volcanic tremor at Mt. Etna are not due to a common source mechanism.