Offshore DAS Observations from the Marmara Sea: First Insights from a Submarine Fiber-Optic Cable

Distributed Acoustic Sensing (DAS) deployed on submarine telecommunication cables provides continuous and spatially dense measurements in offshore environments where conventional instrumentation is sparse. In this study, we analyze DAS data recorded along a submarine fiber-optic cable in the eastern Marmara Sea (Türkiye), located in close proximity to the North Anatolian Fault.

The dataset consists of continuous strain-rate recordings along a ~34 km-long cable connecting the Istanbul mainland to the Princes’ Islands, which is a component of the integration of fiber-optic sensing into GONAF (Geophysical Observatory of the Northern Anatolian Fault) operated by GFZ in collaboration with the Turkish Disaster and Emergency Management Authority (AFAD). Since May 2024, passive DAS data have been continuously recorded along the marine cable in the Marmara Sea. As an initial step, we focus on understanding the cable geometry and data characteristics, including channel selection, spatial variability, and waveform behavior along the fiber.

Clear and coherent wavefields are observed for multiple events, allowing the tracking of seismic wave propagation along the cable over tens of kilometers. Variations between cable segments indicate differences in coupling conditions and local recording characteristics.

Possible saturation effects are currently being investigated in the analyzed recordings. So far, no obvious signal clipping has been observed within the current data range, although further quantitative analysis and recordings of stronger ground motion are required to better evaluate the dynamic response of the system.

These first observations highlight the potential of submarine DAS for offshore seismic monitoring and provide a basis for future studies focusing on earthquake detection, characterization, and integration with existing seismic networks.