Distributed Acoustic Sensing Beyond Optical Repeaters Offshore Oregon

Abstract

Seafloor fiber-optic cables could close major observational gaps in ocean basins. A new multispan distributed acoustic sensing (DAS) technique permits strain-rate measurements at ∼10 to 100 m spacing across the entirety of these cables, beyond repeaters. We present the first publicly available multispan DAS dataset from a seafloor observatory. From November 2025 to January 2026, multispan DAS data were collected offshore central Oregon on both cables of the Ocean Observatories Initiative Regional Cabled Array (OOI-RCA) simultaneously with conventional (single-span) DAS data while the observatory remained online. Nonlinear interactions with observatory signals distorted data on some cable sections, but usable multispan DAS data were obtained past three repeaters (> 300 km optical distance). We report coherent recordings of depth-dependent ocean wavefields out to 2900 m water depth, including surface gravity, infragravity, and Scholte waves, with behavior consistent with theory and prior OOI-RCA DAS observations. Background noise characteristics are largely consistent between multispan and conventional DAS techniques. At least 12 earthquakes are recorded with clear P and S waves on both multispan DAS and nearby cabled ocean-bottom seismometers. Our analysis shows that this dataset is suitable for various oceanographic, seismic, and potentially tsunami monitoring applications.