Current-Induced Noise in Ocean Bottom Seismic Data: Insights From a Laboratory Water Flume Experiment

The ocean-bottom currents are believed to be largely responsible for the high noise level in ocean bottom seismograph (OBS) data, in particular on the horizontal components. Due to the lack of in-situ experiments and measurements, the generation mechanism and characteristics of the current-induced noise are still poorly understood. In this paper, we designed an experiment to explore the features of current-induced noise. A sensor module from a typical passive-source OBS was installed in a water flume that can produce controllable steady water flows. We measured and analyzed the recorded noise with changing current velocities, with and without shielding. With other noise sources, such as infragravity waves precluded, this experiment demonstrates that the currents can generate low-frequency noise, particularly <0.1 Hz. The noise level depends on the current velocity as well as the frequency. While the current-induced noise affects the horizontal components significantly, its impacts on the vertical component appear negligible. The experiment shows that current-induced noise has a dominant direction approximately perpendicular to the currents, a pattern consistent with an actual OBS on the flank of Mariana Trench, where the current direction is supposed to be along the trench. Shielding the sensor module with a plastic casing can substantially suppress the noise, indicating that shielding is a practical, low-cost scheme to reduce the current-induced noise.