Long-distance distributed acoustic sensing for seismic acquisition: Technologies and applications

Distributed Acoustic Sensing (DAS) has emerged in recent years as a novel technology for seismic monitoring and subsurface structure investigation. However, applications of long-distance, high-performance DAS for seismic wave data acquisition remain limited. Here we introduce the fiber-optic Raman amplifier (FRA), based on stimulated Raman scattering in optical fibers, into a DAS system. This achieved consistent signal-to-noise ratio (SNR) along the entire 62.10 km fiber length and accurately reproduced a sinusoidal vibration signal near the fiber end (62.04 km). The complex waveform fidelity of the new system was validated by comparison with a seismometer. To validate reliability of this long-distance DAS system for subsurface structure imaging, the study utilized 43.10 km of communication cable along a highway to collect 5 hours of ambient noise data. Subsurface structures at depths down to 50 meters were resolved along the terminal segment of the fiber optic cable using ambient noise imaging methodology. This system applied to a 50 km submarine optical cable across the Bohai Strait successfully recorded a M4.4 earthquake along with its aftershocks in the Bohai Sea area on July 27, 2025. It also captured 0.05−0.25 Hz ocean surface gravity waves and 1−4.5 Hz Scholte waves. Frequency-wavenumber(F-K) analysis of the submarine optical cable data yielded a dispersion curve with a velocity of 1500 m/s, demonstrating the system’s response to high-velocity waves. These results demonstrate that our long-distance DAS system is capable of long-distance seismic acquisition and has potential to facilitate a broad range of seismological research.