Removing low frequency ocean bottom seismometer tilt noise using simple sensor reorientation

Ocean bottom seismometer data are strongly affected by noise from seafloor currents.  Techniques based on the transfer function between noise on the horizontal and vertical channels are commonly used to “clean” this noise from low-frequency (< 0.1 Hz) vertical channel data, but questions remain about the efficiency of this technique and its effect on seismological signals.  We present a method to “pre-clean” the vertical data through simple rotation of the seismometer to minimize the noise on the vertical channel.  The rotation is nearly identical to that indicated by the transfer function method, but has the advantage of losing no information.  Once this pre-cleaning is performed, transfer-function based cleaning can still be performed, generally resulting in lower noise levels than those obtained using the transfer function method alone and the remaining transfer function may provide information beyond that of the instrument’s mis-alignment with the gravitational field.  We will present examples from datasets around the world and discuss new information revealed.