Preprints
https://doi.org/10.5194/egusphere-2025-4412
https://doi.org/10.5194/egusphere-2025-4412
24 Sep 2025
 | 24 Sep 2025
Status: this preprint is open for discussion and under review for Solid Earth (SE).

Constraining the wavefield of volcano-seismic events on Mt. Etna, Italy through rotational sensor and array observations

Nele Inken Käte Vesely, Eva Patrica Silke Eibl, Gilda Currenti, Mariangela Sciotto, Giuseppe Di Grazia, Matthias Ohrnberger, and Philippe Jousset

Abstract. Long-period (LP) events and tremor are characteristic seismic signals of active volcanoes, offering insight into underlying fluid-driven processes. Their emergent wavefield is complex and challenging to characterise. Seismic arrays as well as a rotational sensor with a co-located seismometer (6C station) can decipher LP event and tremor wave field composition. This study aims to analyse and compare directional and phase velocity estimates by processing a 25-day long dataset from a rotational sensor and an array of seven broadband stations deployed at Mt. Etna, Italy, in August–September 2019. We derive the back azimuths (BAz) of LP events and tremor from both the seismometer array and the 6C station, and we compare these estimates with a reference BAz obtained from the network locations from the Istituto Nazionale di Geofisica e Vulcanologia-Osservatorio Etneo (INGV-OE) on Mt. Etna.

Volcanic tremor occurs in distinct phases with varying seismic and surface activity. Depending on the phase, either the array or 6C method provides reliable BAz estimates, agreeing well with the INGV-OE reference. We find that BAz estimates of both methods are shifted southward relative to the reference location for the LP events. We attribute the larger southward deviation observed in the 6C results to local heterogeneities which exert a stronger influence on the 6C station than on the array.

Based on the array derived slownesses we infer that the tremor and LP events mainly consist of surface waves. Further, the rotational sensor recordings suggest a wavefield dominated by SH-type waves. In combination with the observed temporal evolution of the 6C phase velocity in narrow frequency bands, we infer Love-wave dominance. This study highlights the value of a rotational sensor to constrain the wavefield in a deterministic way in a complex volcanic environment.

Competing interests: One of the co-authors, Gilda Currenti, is an associate editor for the journal.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Nele Inken Käte Vesely, Eva Patrica Silke Eibl, Gilda Currenti, Mariangela Sciotto, Giuseppe Di Grazia, Matthias Ohrnberger, and Philippe Jousset

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Nele Inken Käte Vesely, Eva Patrica Silke Eibl, Gilda Currenti, Mariangela Sciotto, Giuseppe Di Grazia, Matthias Ohrnberger, and Philippe Jousset
Nele Inken Käte Vesely, Eva Patrica Silke Eibl, Gilda Currenti, Mariangela Sciotto, Giuseppe Di Grazia, Matthias Ohrnberger, and Philippe Jousset

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Short summary
We compare seismometers with the 6C method, which combines rotational and seismometer data, determining signal directions and wave velocities for short and continuous low-frequency volcanic signals at Mt. Etna. Either the cluster or the rotational sensor reliably detect continuous signal directions, aligning with the observatory data. For short signals, 6C directions deviate more, likely due to a complex underground. Combining both methods' velocity results improves understanding volcanic waves.
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