Noise Reduction from Vertical-Component Seismograms Recorded by Broadband Ocean-Bottom Seismometers Deployed at the Western Pacific

ABSTRACT We modified existing methods of noise reduction to data recorded by Japanese broadband ocean-bottom seismometers (BBOBSs) deployed on the western Pacific seafloor conducted as the Oldest-1 Array observation. We removed the tilt and compliance noise that are dominant in low-frequency seismograms. We estimated the noise transfer function from the horizontal- to vertical-component seismograms to remove tilt noise from the vertical component. Throughout the observation period of about one year, the tilt noise transfer function was time-invariant and in phase at low frequencies (<0.06 Hz), which, in contrast to previous studies, enabled us to apply a constant transfer function and to estimate the tilt of the sensor. We estimated the noise transfer function from the pressure- to the vertical-component records and removed the compliance noise in the frequency range of 0.002–0.02 Hz. As a result of tilt and compliance noise removal, noise levels were reduced by up to 20 dB at frequencies below 0.03 Hz. We show that tilt noise reduction using the constant transfer function is appropriate for Japanese BBOBSs equipped with the CMG-3T sensor. Tilt angles of Oldest-1 Array are estimated as 0.3°–1.1° and maximum tilt directions are along the H1 component of the sensor, which are attributed to the architecture of the CMG-3T sensor.