A method for measuring horizontal strain at the seafloor using optical fiber interferometry has been in development for some time and has now come to maturity. Zumberge et al.  report on field testing of an optical fiber cable stretched between two seafloor anchors off the Oregon coast on the Cascadia subduction zone. This technique includes interesting features such as auto-temperature compensation/calibration. The authors describe further improvements that can increase the capabilities of the system. This type of sensor is likely to make important contributions to long-term seafloor geodesy in future.
Citation: Zumberge, M. A., Hatfield, W., & Wyatt, F. K. . Measuring seafloor strain with an optical fiber interferometer. Earth and Space Science, 5. https://doi.org/10.1029/2018EA000418
—Benoît Pirenne, Editor, Earth and Space Science