Real-Time Earthquake Detection with a Submarine DAS Array in the Marmara Sea

Distributed Acoustic Sensing (DAS) applied to existing fiber optic telecommunication cables provide dense spatial measurements and enables seismic monitoring in regions where conventional instrumentation is limited. In this study, we evaluate the performance of a submarine DAS system deployed along a ~60 km fiber-optic telecommunication cable for earthquake detection and monitoring in the Marmara Sea, Türkiye.

The DAS interrogator, installed at Tavşantepe Metro Station in İstanbul, continuously records strain-rate data with 10 m channel spacing and a sampling rate of 1500 Hz. The cable extends between the Istanbul mainland and the Princes’ Islands, crossing the Marmara Sea in close proximity to the North Anatolian Fault, thereby enabling continuous offshore seismic observations in one of the most seismically critical regions of Türkiye.

Since early 2023, the system has recorded more than 1,500 seismic events with magnitudes ranging from Mw 1.7 to 7.8, as well as teleseismic events up to Mw 8.8. In addition to cataloged earthquakes, the DAS data reveal smaller local events that are not clearly detected by traditional seismic networks. This highlights the high sensitivity of the system, enabled by its dense spatial sampling.

We implement a simple real-time detection approach based on characteristic functions applied to selected DAS channels, showing that earthquake signals can be detected reliably under operational conditions. The continuous spatial sampling along the cable also allows following the wavefield propagation over tens of kilometers.

The dataset also reveals several important limitations of the current system. During the April 23, 2025 Silivri, İstanbul earthquake (Mw 6.2), the DAS recordings exhibit clear signal saturation, indicating that the current interrogator dynamic range is insufficient for strong ground motion. The distance of the nearest channel to the source zone of the Silivri earthquakes was less than 40 km.  Magnitude estimates derived from DAS data agree well with national catalogs for moderate events, but show increasing deviations for larger magnitudes (approximately Mw ≥ 5.0), likely due to this saturation effect. In addition, the linear geometry of a single cable limits the accuracy of standalone event location.

Overall, the study demonstrates the operational feasibility and long-term stability of submarine DAS systems for real-time earthquake monitoring in the Marmara region, while also highlighting current instrumental and geometrical limitations that must be addressed for future earthquake early warning and rapid response applications.