Probing subsurface heterogeneity through the spatial variability of spectral peaks in DAS data at Mount Etna

Distributed Acoustic Sensing (DAS) offers unprecedented spatial resolution relative to conventional seismic networks. This provides new opportunities to investigate the composition of the recorded seismic wavefield in volcanic environments, which are often highly heterogeneous. At Mt Etna, recent work (Yates et al. 2026) has highlighted the presence of stable spectral peaks that emerge during broadband volcanic tremor. Using seismic stations from the permanent monitoring network, these were found to vary significantly between stations and to respond to seismic velocity changes through proportional frequency shifts. Combined, these observations support the interpretation that they originate from persistent scattering structures that cause resonance-like effects in heterogeneous environments. 

In this study, we present a preliminary analysis of DAS data acquired between Zafferana and Linera on the eastern flank of Mt Etna in 2019 (~15 km length). Anthropogenic noise is found to dominate the recorded wavefield during a significant proportion of the day. However, stable spectral peaks are clearly visible during periods of reduced activity (late evening / early morning). We  quantify the spatial variability of these peaks, taking advantage of the high spatial resolution offered by DAS. Our work provides the opportunity to (1) better constrain the relative roles of source, path, and site effects in generating stable spectral peaks, and (2) assess subsurface heterogeneity through quantification of the characteristic length scales over which spectral peaks vary. Together, this approach demonstrates the potential of DAS to provide insights into the subsurface at spatial scales not resolvable with conventional seismic networks. 

This work has been performed in the frame of USCV-DAS, 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.

References

Yates, A. S., Heuninck, S., Barajas, A., Bektas, H., Caudron, C., De Angelis, S., & Zuccarello, L. (2026). Tracking subsurface changes via frequency shifts in volcanic tremor spectral lines: observations from Mt Etna. Geophysical Research Letters, 53(2), e2025GL117819.