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. Plain Language Summary Ocean Bottom Seismometers (OBSs) are important instruments for seafloor seismology. However, OBS recordings are highly noisy, and the noise mechanism is not well understood. Currently, most research focuses on the noise in the vertical channel, and understanding of the horizontal noise has been limited. In this study we investigate one specific type of OBS noise, which is commonly observed in shallow water is associated with water waves. We propose a noise model to explain the noise, and also develop analytical theories for the noise generation. The noise model and related theories are verified by realistic recordings. Based on the theories, we propose potential applications, for example, derivation of the water‐wave propagation direction and subsurface structure inversion using the noise. A method of noise removal is also developed, which highly improves the signal‐to‐noise ratio. Key Points We propose a noise model to explain the horizontal OBS noise around 0.07 Hz in shallow water The noise model and related theories are validated by realistic observations Potential applications to determine water‐wave direction, Earth structure inversion and noise removal are discussed