ABSTRACT

We report the first ground rotation observations on the seafloor from an experiment we carried out in the North Sea close to the island of Heligoland. A slightly modified commercial fiber optic gyroscope was mounted on an ocean‐bottom seismometer (OBS) platform together with an intermediate‐period seismometer. The system was lowered to the seafloor for 4 days. To investigate a potential tilt contamination of horizontal translational recordings, we calculate the coherence between the corresponding motion components (rotations around x axis and translations along y axis, and vice versa). We find very high correlations in the 5–13 s period interval, in which the correlation coefficient reaches 0.94 over 8.5 hrs. This clearly indicates that horizontal translational components are severely contaminated by rotations. We find that these rotational motions are caused by seafloor currents or deformation of the seafloor rather than by seismic waves. The ground rotation observations allow correcting for the cross‐coupling effect, thereby decreasing the power spectral density up to 11 dB at 10 s period on horizontal OBS components. We discuss general requirements for broadband rotation sensors for OBS applications as well as for possible further applications.

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