The Contribution of DAS to the Routine Monitoring of Seismicity in Oceanic Islands: The Case for Faial (Azores)

Distributed acoustic sensing (DAS) deployed on submarine telecom cables is bound to revolutionize the earthquake monitoring routine currently performed by seismic network operators, particularly in domains where most seismic activity originates offshore. In this work, we analyze one year of DAS data recorded on a submarine telecommunication cable joining the Islands of Faial and Flores in the Azores, an area where seismic crises of volcano-tectonic origin are frequent. We explore whether spatially decimated channels can be added to the operational routine without major changes. During the DAS operation, the land network recorded 368 local and regional earthquakes. The best of these events were jointly analyzed, and earthquake parameters were compared between the original locations and those obtained by adding DAS picks. Despite the larger picking uncertainty on DAS channels, adding P and S or S-wave picks only from DAS data showed a considerable improvement in earthquake parameters, reducing the error ellipse area and the focal depth formal uncertainty. These results demonstrate that in domains where offshore seismicity is a concern and submarine telecom cables are available, integrating DAS channels into the routine operation of seismic networks considerably improves the accuracy of earthquake parameter estimation. A procedure to accomplish these results is presented.