Detection of Earthquake Infragravity and Tsunami Waves With Underwater Distributed Acoustic Sensing

Abstract

Underwater Distributed Acoustic Sensing (DAS) utilizes optical fiber as a continuous sensor array. It enables high‐resolution data collection over long distances and holds promise to enhance tsunami early warning capabilities. This research focuses on detecting infragravity and tsunami waves associated with earthquakes and understanding their origin and dispersion characteristics through frequency‐wavenumber domain transformations and beamforming techniques. We propose a velocity correction method based on adjusting the apparent channel spacing according to water depth to overcome the challenge of detecting long‐wavelength and long‐period tsunami signals. Experimental results demonstrate the successful retrieval of infragravity and tsunami waves using a subsea optical fiber in offshore Oregon. These findings underscore the potential of DAS technology to complement existing infragravity waves detection systems, enhance preparedness, and improve response efforts in coastal communities. Further research and development in this field are crucial to fully utilize the capabilities of DAS for enhanced tsunami monitoring and warning systems.

Towards tsunami early-warning with Distributed Acoustic Sensing: Expected seafloor strains induced by tsunamis

“…The current values of single-channel strain noise ASD of conventional DAS equipment operating at kHz sampling frequencies suggest that these water column changes will not be easily resolved without using the information from the full array. However, beamforming methods allowing fairly large processing gains, may probably lead to enough sensitivity, as shown in recent related efforts (Xiao et al, 2024). The strain noise ASD of conventional DAS systems in this frequency range is dominated by 1/f noise caused by reference updates and laser frequency drifts.…”

“…This demonstrated that DAS can record surface gravity waves, although at much shorter periods than tsunami waves. The first, and so far only reported detection of a tsunami with seafloor DAS (Xiao et al, 2024) made use of 60 km of cable off the northwestern US coast to detect a far-field tsunami, which produced a small tsunami wave height of ∼ 6 mm at a DART station, and reaching ∼ 1 cm by the time it reached the end of the monitored fiber. Although the signal-to-noise ratio of the detected tsunami phase was low, even after beamforming, these findings underscore the feasibility of DAS technology to detect tsunami waves.…”

High‐Frequency Tsunamis Excited Near Torishima Island, Japan, Observed by Distributed Acoustic Sensing

“…Ocean DAS records were also uploaded to a repository (Spica et al, 2023) as part of a project that collected DAS data for teleseismic events that occurred in February 2023 (Wuestefeld & Wilks, 2019). Xiao et al (2024) recently detected tsunami singals; however, DAS observations of tsunamis are still limited because they occur infrequently and their observations depend on the dates and locations of DAS experiments.…”