Resolving seismic wavefield components using combined distributed strain and rotational measurements

Distributed dynamic strain sensing (DDSS) enables dense observations of seismic wavefields in complex environments such as active volcanoes, but records only axial strain along the fibre and therefore captures a limited projection of the full wavefield. Co-located rotational ground-motion measurements provide complementary constraints on wavefield geometry, propagation direction, and wave type.
We investigate the December 2025–January 2026 eruptive activity of Mount Etna using a combined dataset of distributed acoustic sensing and broadband rotational measurements at the Serra La Nave observatory. The work has been performed in the frame of ROTATIONAL-NIGHT project, a Transnational Access to the Eastern Sicily testbed supported by the EU project Geo-INQUIRE. Geo-INQUIRE is funded by the European Commission under project number 101058518 within the HORIZON-INFRA-2021-SERV-01 call.
The DDSS system comprises a ~300 m fibre-optic cable (10 m gauge length, 2 m channel spacing, 500 Hz sampling), complemented by a BlueSeis-3A rotational sensor. The dataset spans multiple eruptive phases, including pre-activation, escalating unrest, and the 27 December paroxysmal episode.
We track the evolving seismic wavefield by integrating spatially distributed strain observations with rotational constraints. Frequency–wavenumber (FK) analysis along the fibre resolves tremor propagation and apparent phase velocities, while rotational polarization analysis constrains dominant propagation directions and wavefield composition. Together, these measurements enable robust characterization of temporal changes in the wavefield during eruptive activity.
In addition, we analyze local volcano-tectonic (VT) events to investigate attenuation processes. By combining spatially distributed strain amplitudes with rotational constraints on propagation geometry, we explore the separation of intrinsic and scattering attenuation through frequency-dependent energy decay and wavefield characteristics.
Preliminarily results demonstrate that combining distributed strain sensing with rotational ground motion extends the observable seismic wavefield beyond the limitations of individual techniques, providing a pathway toward resolving source, path, and site effects within a unified framework.