Abstract Tsunamis have been detected as strain variations in optical fibers of submarine cables through distributed acoustic sensing (DAS). However, the usefulness of strain variations during tsunamis for early warning remains unclear. Here, we compare fiber strains and sea‐level changes for both infragravity waves in ambient noise and tsunamis triggered by the Torishima (October 2023) and Kamchatka (July 2025) events, and demonstrate their empirical relations at frequencies >5 mHz. For this comparison, we interrogated a submarine cable at Muroto, southwestern Japan, with DAS and implemented absolute pressure gauges near the cable. At <5 mHz, DAS signals of the Kamchatka tsunamis are observed at water depths of 1,000–2,000 m and may be attributed to temperature variations due to internal waves excited by the tsunamis. Our results suggest that high‐frequency strains of tsunamis are potentially useful for estimating tsunami wave heights, whereas low‐frequency DAS signals can be used for early tsunami detection.
Tonegawa et al. (Sat,) studied this question.
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