Sensitive seismic sensors based on microwave frequency fiber interferometry in commercially deployed cables.

Area of Science:

• Geophysics and Earth Science
• Optical Sensing Technologies
• Seismology and Natural Hazard Monitoring

Background:

• Optical fibers offer a low-cost, widely deployable infrastructure for environmental sensing, particularly valuable for monitoring remote submarine areas where seismic instrumentation is sparse.
• Existing seismic monitoring methods face limitations in spatial coverage and cost-effectiveness, especially for high-resolution subsea natural hazard detection.
• Distributed Acoustic Sensing (DAS) is a leading optical technique for earthquake detection but is limited in range (<100 km).

Purpose of the Study:

• To introduce and validate a novel technique, the Microwave Frequency Fiber Interferometer (MFFI), for deformation sensing using fiber optic infrastructure.
• To demonstrate MFFI's capability to detect deformation caused by moderate-to-large earthquakes.
• To compare MFFI's performance against established seismic monitoring tools like accelerometers and DAS.

Main Methods:

• A stable microwave frequency is disseminated along optical fibers in a closed-loop configuration to create an interferometer sensitive to deformation.
• The MFFI technique was deployed and tested for its sensitivity to seismic events.
• MFFI signals were cross-validated with data from accelerometers and a commercial DAS interrogator.

Main Results:

• The Microwave Frequency Fiber Interferometer (MFFI) demonstrated high sensitivity to deformation induced by local and regional earthquakes.
• MFFI signals showed remarkable agreement with the dynamical behavior and strain rate estimations from accelerometers and DAS.
• The technique successfully leverages existing fiber optic infrastructure for seismic measurements.

Conclusions:

• MFFI is a novel and effective technique for fiber optic-based seismometers, offering significant advantages over existing methods.
• The technique provides critical benefits in terms of implementation cost, operational range, and simplicity.
• MFFI has the potential to significantly enhance the resolution and coverage of seismic monitoring, especially in challenging submarine environments.