Volcanic hazard monitoring using Distributed Acoustic Sensing at Stromboli volcano

This thesis project aims at testing Distributed Acoustic Sensing (DAS) technology to conduct a higher-resolution analysis of the source and wave-field propagation of Strombolian explosions at the Stromboli volcano, Italy. The study will utilize a dedicated fiber-optic cable, with a focus on its implications for volcanic monitoring.

Stromboli is an open-conduit volcano known for its mild and intermittent explosive eruptions, typically producing jets of gas and incandescent blocks at a rate of around 10 events/hour. Due to its reliable and persistent activity, and the broad frequency range of associated seismic signals, several instrumental deployments have been carried out on the volcano. However, these previous experiments have only relied on a few tens of sensors, allowing limited and local spatial access to the wave fields.

In this sense, DAS technology offers the possibility to estimate the strain field at a high spatial and temporal resolution, providing a more realistic view of the physical processes associated with Strombolian explosions. Between 2020 and 2022, we installed 4 km of optical fibre on the flank of the volcano at a depth of 30 cm. DAS data were collected using a Febus A1-R interrogator. The data acquisition period increased from one week in 2020 to over four months in 2022, while the total number of sensing points distributed along the cable from over 480 in 2020 up to 3250 in 2022.

The Laboratory of Experimental Geophysics at the University of Firenze, Italy, is operating the monitoring of Stromboli activity with a geophysical and geochemical multi-parameter network (infrasonic acoustic, seismic, deformation, optic and thermal images, gas volume and composition) with the goals of a better understanding and interpretation of the dynamics of Stromboli and the definition of possible risk scenarios.

This study will address several issues by using data recorded during the thesis, including the ground/fiber coupling in ashes, the resolution of the measurement according to external conditions and distance to the source, the strain component recorded as a function of the fiber orientation with respect to the source position, the stability of the measurement over time, the repeatability, robustness, and durability of the technique. With the high spatial sampling of DAS measurements, we expect to be able to better image the superficial structure and more accurately describe the physical processes generated by Strombolian activity.