Tsunami Waves Detected by a Seafloor Fiber Optic Strainmeter

The Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has started continuous observations of crustal deformation using a fiber optic interferometry-based strainmeter in the Nankai Trough since 2019. In this study, we present the detection of tsunami waves caused by earthquakes that occurred off Torishima Island in 2023 and 2024 using optical fiber strainmeters. The amplitude of the strain associated with the 2023 tsunami was <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.003 \mathbf{\mu}\mathbf{\varepsilon}$</tex> ‘ On the other hand, the amplitude of the strain associated with the 2024 tsunami was <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.03 \mathbf{\mu}\mathbf{\varepsilon}$</tex>. This suggests that tsunami observations using fiber optic strainmeters can contribute to the early detection of non-seismogenic tsunamis offshore where there are few tsunami surveillance facilities.