Investigating Volcanic tremor, Explosions and Pyroclastic Flows with Fibre-Optic Sensing at Stromboli Volcano (Italy)

Continuous seismic monitoring of volcanoes is challenging due to harsh environments and associated hazards. However, investigating volcanic phenomena near their sources is essential for eruption forecasting. In seismo-volcanic applications, Distributed Acoustic Sensing (DAS) offers new possibilities for long-duration surveys.  We analyse DAS strain rate signals generated by volcanic tremor, explosions and pyroclastic flows at Stromboli volcano (Italy) recorded along 4 km of a dedicated fibre-optic cable installed between 2020 and 2022. We buried the fibre-optic cable at a depth of 30 cm and designed the layout geometry to provide broad coverage on the active craters. We compared DAS recordings with the data provided by the monitoring network of the University of Firenze (Italy) comprising broadband seismic stations, tiltmeters, infrasonic sensors, tsunami gauges and visible and thermal cameras. We also installed nodal seismometers along the fibre to calibrate the recordings together with an innovative optical strainmeter. The inversion of time delays between DAS strain rate waveforms provides back-azimuths indicating a dominant and persistent seismic source in the proximity of active craters during tremor and explosions. We analysed two pyroclastic flows of varying intensity that occurred in October and December 2022. The two flows propagated from the craters to the shore, generating centimetre-scale tsunami waves. The back-azimuths estimated with the DAS array enabled us to track the downslope movement of the seismic source with a timing consistent with what is observed with monitoring cameras and with seismic and infrasonic observations. These results demonstrate the potential of DAS in monitoring volcanic areas.