Water-Wave-Induced OBS Noise: Theories, Observations, and Potential Applications

The horizontal records of ocean-bottom seismometers (OBS) are usually highly noisy, generally due to ocean-bottom currents tilting the instrument, which greatly limits their practical usage in ocean-bottom seismology. In shallow water, water waves with energy concentration around 0.07 Hz induce additional noise on OBSs. Such noise is not well understood. In this article, we propose a noise model to explain the horizontal noise around 0.07 Hz. The noise model consists of three types of noise, that is, water-wave-induced noise, current noise with a relatively constant orientation, and background random noise. The wave-induced horizontal acceleration is theoretically shown to be proportional to the time derivative of ocean-bottom pressure. We validate the noise model and related theories using realistic observations. Results are potentially applicable to determine the propagation direction of water waves nearshore, and also provide constraints on the underlying Earth structure. The results can also be applied to the removal of wave-induced noise, achieving a typical maximum improvement in the signal-to-noise ratio of 10–20 dB for time periods with strong wave noise.