Fibre-Optic Monitoring of Volcanic Processes at Stromboli volcano,

 

Volcanic activity encompasses a wide range of seismogenic phenomena occurring from the deep magmatic conduit to the surface of volcanic flanks. Volcanic tremor, long period (LP), and very long period (VLP) seismic signals are commonly associated with magma and fluid movement within the conduit, whereas sliding mass and density currents along the flanks typically produce minute-long, cigar-shaped seismic traces.

Characterising these phenomena through seismic analysis requires high measurement accuracy over a broad frequency range, together with high spatial and temporal resolution. Meeting these requirements in complex volcanic environments can be particularly challenging because the deployment and the maintenance of dense seismic networks involves considerable logistical effort. Distributed Acoustic Sensing (DAS) offers the opportunity to bridge the gap between sparse seismic networks and denser arrays, enabling continuous strain measurements along fibre-optic cables at comparatively low operational costs.

Here, we investigate several different volcanic processes at Stromboli volcano (Italy) through DAS observations acquired along a 6 km fibre-optic cable integrated within a permanent multiparameter monitoring network comprising broadband seismometers, thermal and visible cameras, and infrasonic pressure sensors. The fibre was deployed on the volcanic flanks between 2020 and 2023 and interrogated during several month-long campaigns using a Febus A1-R. The dataset includes signals generated by ordinary Strombolian explosions, major explosions, lava flows, partial crater collapses and pyroclastic density currents (PDCs), which were analysed using  different analytical approaches.

Array-processing techniques in the 1–5 Hz frequency range were used to track the source of volcanic tremor, explosions, and PDCs with DAS strain-rate signals. Tremor and explosion signals are consistently located near the crater area, whereas PDCs propagate along the volcanic flanks. Moreover, by combining visible imagery with seismic energy recorded by DAS and inertial seismometers, we estimate the flow velocities and volumes of the PDCs and derive empirical, volume-dependent friction angles that provide insight into flow dynamics.

Additionally, we exploit the distributed nature of DAS measurements to reconstruct the axisymmetric principal strain axes of VLP strain signals (between 0.04–0.2 Hz) associated with each explosion. The VLP strain signals recorded along the fibre nicely fit a deformation point-source (Mogi) located beneath the active craters, with an estimated volumetric change of ~30 m³.

Our results demonstrate the capability of DAS measurements to characterise the dynamics of volcanic processes and to resolve the VLP strain distribution with enhanced spatial resolution. Overall, these findings highlight the significant potential of DAS as an innovative tool for analysing and monitoring a wide range of volcanic phenomena across different spatial and temporal scales.