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Continuous seismic monitoring of volcanoes is challenging due to harsh environments and associated hazards. However, the investigation of volcanic phenomena 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 explosions and tremor at Stromboli volcano (Italy) recorded along 1 km of dedicated fibre-optic cable. We validate DAS recordings with colocated nodal seismometers. Converting node measurements to strain rate, we observe a perfect match in phase between DAS and node waveforms. However, DAS amplitudes appear to be around 2.7 times smaller than those of node records, which we explain as due to the inefficient ground-to-fibre strain transfer in the loose cable. We invert time delays between strain rate waveforms and confirm that the DAS enables us to retrieve a dominant and persistent seismic source in the proximity of active craters. This stable source location is confirmed by node array analyses. Despite an observed high noise level of strain rate signals outside a range of 2–15 Hz, our results demonstrate the potential of this new technology in monitoring volcanic areas. [ABSTRACT FROM AUTHOR]

Over a period of less than a decade, distributed acoustic sensing (DAS) has become a well-established technology in seismology. For historical and practical reasons, DAS manufacturers usually provide instruments that natively record strain (rate) as the principal measurement. While at first glance strain recordings seem related to ground motion waveforms (displacement, velocity and acceleration), not all the seismological tools developed over the past century (e.g. magnitude estimation, seismic beamforming, etc.) can be readily applied to strain data. Notably, the directional sensitivity of DAS is more limited than conventional particle motion sensors, and DAS experiences an increased sensitivity to slow waves, often highly scattered by the subsurface structure and challenging to analyse. To address these issues, several strategies have been already proposed to convert strain rate measurements to particle motion. In this study, we focus on strategies based on a quantity we refer to as 'deformation'. Deformation is defined as the change in length of the cable and is closely related to displacement, yet both quantities differ from one another: deformation is a relative displacement measurement along a curvilinear path. We show that if the geometry of the DAS deployment is made of sufficiently long rectilinear sections, deformation can be used to recover the displacement without the need of additional instruments. We validate this theoretical result using full-waveform simulations and by comparing, on a real data set, the seismic velocity recovered from DAS with that recorded by collocated seismometers. The limitations of this approach are discussed, and two applications are shown: enhancing direct P -wave arrivals and simplifying the magnitude estimation of seismic events. Converted displacement provides better sensitivity to high velocity phases, improves broadside response and permits the direct application of conventional seismological tools that are less effective when applied to strain (rate) data. [ABSTRACT FROM AUTHOR]