Assessing the Seismic Sensitivity on a Submarine Optical Fiber Link between Malta and Catania (Sicily, Italy)

Submarine regions remain sparsely instrumented, limiting the spatial coverage of seismic monitoring in offshore environments. Recent studies have shown that optical fibers, including those actively used for telecommunications, can detect ground motion through laser interferometry. We present an ongoing evaluation of the seismic sensitivity of a 260 km optical fiber link between Malta and Catania, predominantly submerged in the Ionian Sea and continuously carrying internet traffic.

The optical-fiber recordings were analysed for signals corresponding to the arrival times of ~1500 earthquakes listed in the INGV catalogue between January 2023 and March 2025. The waveforms were manually inspected for seismic arrivals and compared to seismic data recorded on nearby land stations on Malta and Sicily. Earthquakes ranging from magnitude 1.4 to 7.9 originating from distance of 3 to 16,000 km were successfully observed. Each event was assigned a category according to signal clarity and confidence, ranging from clearly visible arrivals (category A) to non-detectable signals (category E). Preliminary results indicate that <10% of events fall into category A, 10-15% in category B, 20-25% in category C, 20-25% in category D, and >30% in category E, providing an initial characterisation of the optical-fiber cable’s sensitivity. While a majority of observations fall within lower quality categories (D-E), at least 35% of the analysed events remain robustly identifiable, highlighting the contribution of the submarine fiber to existing land-based seismic networks and extending observational coverage in submarine regions. The sensitivity of the fiber strongly depends on the earthquake magnitude-distance relationship, as expected. We compare our results with previously reported measurements on terrestrial fibers (Donadello, et al., 2024), and show that the Malta-Catania submarine cable can be a reliable new seismic tool for a submarine environment, although recording fewer high-confidence events than onshore systems.

Noise in the fiber exhibits correlations with wind and with daytime anthropogenic activity. This reduces the signal-to-noise ratio and limits the detectability of earthquakes with M<2. Ongoing data acquisition will further refine sensitivity estimates and improve the characterisation of the fiber’s seismic performance.

This study is part of the Horizon Europe–funded SENSEI project, which aims to transform fibre-optic communication networks into distributed sensors for detecting environmental and geophysical signals, improving monitoring and early warning across Europe (Project ID 101189545).