| Summary: | Optical interferometry can be used to measure the propagation time of the light along fibre optic cables, enabling the detection of environmental perturbations such as earthquake waves as they interact with the fibre [Marra et al., 2018]. However, at any point in time, the measured signal is an integration of the optical path length changes along the entire fibre. This can result in a high measurement noise floor since the ambient noise along the entire length of the seafloor cable is integrated. Over the lengths of thousands of kilometres of transoceanic seafloor cables, this can prevent the detection of smaller magnitude events.We present a novel technique that allows many discrete spans along a single fibre optic cable to be used as individual ocean bottom seismometers. These spans are tens of kilometres long and this reduction in length of each line-receiver allows us to monitor specific locations along the cable path. From an observation window of four months, we show that earthquakes, tides, wave heights and ocean microseisms can all be recorded on individual spans between repeaters on a 5,860 km-long transatlantic cable, in addition to monitoring along the whole cable length.On the continental shelf we observe strong correlations between periodic signals at different frequencies with tides, wave heights and microseisms. In the comparatively quieter deep ocean we have detected two teleseismic earthquakes greater than M w 7. Other enigmatic signals related to ocean tides and the solid Earth’s microseisms are also evident.
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