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Optical fibers, stretched between anchors attached to the Earth, offer an inexpensive and robust means to observe Earth strain. Interferometrically recording the optical path through the fiber can reveal strain with sensitivity well below 1 nanostrain (delta L / L ~ 1e-9). We have deployed optical fibers in boreholes, buried them in shallow trenches, and stretched them across the seafloor. The method offers solutions for problems in offshore slow-slip detection, land subsidence monitoring, deformation from fluid injection or withdrawal, and possibly in earthquake early warning.