Imaging Underwater Faults and Tracking Whales with Optical Fiber Sensing

Abstract

In light of the global shift toward deep-water offshore wind projects, including recent leases off California's central and northern coasts, this study leverages distributed acoustic sensing (DAS) technology on existing dark fiber-optic cables to address environmental and engineering challenges. The primary objective is to identify seafloor geohazards—such as faults, landslides, and turbidites—necessary for the design of floating platform foundations and power cable routes while concurrently monitoring the impact on marine life, specifically whale migrations. To address these two issues simultaneously, we have turned an existing seafloor fiber-optic cable off the central California coast to a DAS array to both image the near-surface conditions of the seafloor and track whale migration through the surrounding area. Passive recordings of ocean waves and ambient seismic noise on DAS were used to image the upper 3000–4000 m of the seafloor sediments, with particularly high resolution on the top sediment layer of geotechnical interest. Fault-scattered seismic waves from local earthquakes also provided fault identification and location within the offshore Los Osos and Hosgri fault zones that the fiber crosses. With the very same recordings, whale calls were used to track the locations of the whales as they passed along and over the fiber. This study shows that DAS can improve both seafloor geophysics and whale monitoring, which are two key issues for emerging energy generation in deep-water locations.

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