Submarine fibre-optic sensing potential for regional seismicity monitoring near Santorini and Kolumbo Volcano

Submarine volcanoes and faults pose hazards to nearby populated islands while their inaccessibility limits monitoring efforts. The Christiana-Santorini-Kolumbo volcanic field is capable of generating devastating eruptions, earthquakes and tsunamis. The recent earthquake swarm near Kolumbo, causing the evacuation of thousands from their homes, underlines the need for accurate and precise monitoring. The high spatiotemporal resolution of fibre-optic networks can complement existing seismic monitoring networks by locally lowering the detection threshold. We investigate a 45 km long dark fibre that extended from Santorini past the submarine volcano Kolumbo for two months in 2021, comparing the performance of the fibre with the existing monitoring network in Greece for earthquake detection and location. The detected quakes originated all over Greece, coming from any azimuth. We can reliably identify events given their epicentral distance and magnitude, and we double the number of detections in the vicinity of the fibre and Kolumbo. For event location, the azimuthal coverage of the existing seismometer network outperforms the spatially dense but approximately linear fibre, emphasising the importance of a nonlinear fibre layout. Our findings suggest that nonlinear fibre-optic networks can complement existing networks for targeted monitoring, but they need careful integration to optimise performance.